Network Analyzer

Principle - Flame Ionisation detection method (FID) with selective combustion

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The flame ionisation detection method (FID) --- used in combination with the selective-combustion system--- utilises the ionisation that occurs as the result of the high-temperature energy from combustion at the tip of the burner jet when organic carbon com-pounds are introduced into the hydrogen flame. The hydrogen flame is located between two electrodes. When an electrical voltage is applied across these electrodes a minute ion current proportional to the hydrocarbon concentration is produced. This current is monitored by a low leakage amplifier, giving a voltage readout for THC. To measure CH4 the sample gas is passed through the selective catalytic combustion unit (the NMHC cutter), which oxidises NMHC without oxidising CH4. This is shown as A below. B represents the THC concentration measured without passing the gas through the NMHC cutter. Thus B - A will give the concentration of

NMHC. The final concentration value is calculated using a relative sensitivity correction coefficient, k, as shown below.

CH4 Concentration A

NMHC Concentration k (B - A)

THC Concentration A + k (B - A)

The highly sensitive, highly accurate, and minimal-maintenance APHA-360 provides precise atmospheric pollution monitoring data.

The APHA-360 has TA-Luft approval.

Ambient HC Monitor

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APHA-360

Features

The APHA-360 uses a combination of the flame ionisation detection method and selective-combustion. This gives it the advantages of the single- detector method plus the ability to do continuous, zero-drift free measurements of THC, NMHC, and CH4. The design gives great stability and high sensitivity (F.S. 5 ppm). The APHA-360 has a relative-sensitivity correction function for CH4 and NMHC.

A catalytic unit for generating reference gas and auxiliary combustion air is standard equipment in the APHA-360.

All the necessary features are built into a single rack sized instrument, including a catalytic unit for selective combustion (i.e., an NMHC cutter); a catalytic unit for generating reference gas and auxiliary combustion air; and a sampling pump.

The only supplemental gas required is hydrogen.

General Purpose Gas Analyzers

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510 Series

Outline
General purpose gas analyzers are used to measure a wide variety of gases, including clean gases and stack gases, in such diverse areas as scientific experimentation, industry, and global environmental preservation. Specifically, general-purpose gas analyzers measure a wide range of gases, including CO, CO2, NOX, SO2, CH4, and O2, as well as THC concentration levels. These general purpose gas analyzers also offer a high degree of operational efficiency and functionality. The VIA-510 general purpose infrared analyzer, the FIA-510 general purpose oxygen analyzer, the CLA-510SS general purpose nitrate oxide analyzer, and four types of FIA-510 Series general purpose hydrocarbon analyzers can be used in conjunction with the ES Series sampling unit for high-grade particle dust and vaporous gases, including stack gases. The analyzers can be used in an extremely wide variety of areas and applications, including monitoring gases affecting the global environment, checking the efficiency of denitrification and desulfurization equipment, monitoring stack gases, testing combustion devices, monitoring gases inside heat-treatment furnaces, testing and regularly measuring exhaust emissions generated by internal combustion engines, and monitoring gases in the area of biotechnology.

Main Features
The analysis device and the sampling device are two separate into components. A desktop design and a 19-inch rack provide a wide-range of layout choices.

Featuring an internal CPU, digital display, one-touch calibration of zero and span, and self diagnosis, the units offer enhanced ease of use.

510 Series units provide dynamic ranging, with 4 range and comparison ranges with a maximum of 10x as standard functions. Comparison ranges with a maximum of 20x can be added as an option.

Measured concentration output is 0V-1V, 0V-10V, and 4mA-20mA (or 0mA-16mA) via parallel insulation output and connection to an external unit simple.

The units achieve repeatability of ±0.5% F.S. (standard range), zero and span drift of ±0.5% per day (standard range) and offers a high degree of selectivity in measured values.

Main Features of X-ray Fluorescence Sulfur Analyzer

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Software
SLFA-2800 and 2100 make analysis a much easier job to perform. They also feature the latest functions and new applications.
Units of measurement: Operators can choose between % and ppm.
Sample ID: Operators can enter up to 10 alphanumeric characters (A through Z, 0 through 9).
Analytical curve: The analyzers' display enlarges an analytical curve chart and automatically chooses the correct one from the seven scales available (0.002/0.01/0.05/.../10%). Two kinds of scales are available for display, % and ppm. Also, operators can choose between linear and quadratic numeric expressions, which can be selected both manually and automatically. Up to five calibration curves can be stored in the analyzers' memory, and operators can specify either manual or automatic selection of which curve to use.

Measurable range
The measurable concentration range has been broadened to cover 0 to 9.999%. This enables the analyzers to correctly measure a broader range of sulfur concentrations contained in more kinds of substances, from low concentration in light oil to high concentration in heavy oil.

External design
The appearances of the new analyzers reflect Horiba's new design philosophy. The function keys are now rearranged into the same order as those of a cellular phone, for easier key operation.

Easy-to-read, larger display screen
The new large, backlit LCDs make measurement results easier to read and thus help operations.

A broad variety of data printed out in large, easy-to-read letters
In addition to measurement values, the time (hour and minute) and date of a measurement, the time length of a measurement, the number of times a measurement was repeated, the sample ID, the average measurement value, the standard deviation, calibration curve charts, the X-ray spectrum, and many other items necessary for data management are printed out on 80 mm-wide sheets of paper in large, easy-to-see letters.

Data output (with RS-232C interface)
The analyzers can also output measurement results to an external computer for storage and statistical processing of many kinds.

Safety mechanism
The analyzers have a double fail safe mechanism to protect operators from X-rays. This mechanism never allows X-ray radiation unless the sample chamber or the shutter is shut. This eliminates the need to set up an off-limit area. Also, the analyzers use no radioisotope.

Turntable (continuous and prioritized measurement)
SLFA-2800 features a turntable to let operators measure up to eight samples continuously. Also available is a function called "interrupt measurement," which allows the measurement of a different sample while measuring multiple samples in a row.

Repeatability of 1.6 ppm, and a lower detection limit of 5 ppm
The analyzers feature a small yet high-power X-ray tube to provide excellent repeatability with no need to purge helium or other gases. Also featured are an automatic pulse height adjustment, which keeps reliable measurement results in case of a violent temperature change or drifting of the analyzer, and a function to compensate for changes in the temperature and atmospheric pressure, which eliminates the need to purge helium. The analyzers boast excellent repeatability performance in measuring low-concentration samples repeatedly, achieving a standard deviation of 1.6 ppm in case of a sample containing 0% sulfur. With heavy oil and other samples containing higher sulfur concentration, the analyzers can complete measurement in a shorter period of time.

Automatic correction of C/H ratio
The analyzers' automatic C/H ratio correction eliminates problems related to measuring errors caused by different kinds of oil. Now, you can obtain highly precise measurement results no matter what kind of oil you handle.

Spectrum measurement
The analyzers can work in a spectrum measurement mode, which enables evaluation of a sample from many different perspectives. This mode is also useful in examining how well the X-ray tube and the analyzer itself are functioning.

X-ray Fluorescence Sulfur Analyzer

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SLFA-2800/2100

Outline
We are facing countless aspects of environmental crisis today. Efforts to prevent hazardous pollution call for higher-precision, higher-sensitivity analysis technologies. In addition, we see many restrictions aimed at reducing the sulfur contents in diesel fuel, light, and heavy fuel oils. Those restrictions are expected to grow even more rigid as the public's awareness of the environmental crisis sharpens. Horiba's SLFA-2800 and 2100 analyzers, featuring the latest innovations in sulfur content analysis, satisfy such demand for advanced analysis.

History of Oscilloscope

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Hand-drawn oscillograms
Illustration of Joubert's step-by-step method of hand-plotting waveform measurements. [4]

The earliest method of creating an image of a waveform was through a laborious and painstaking process of measuring the voltage or current of a spinning rotor at specific points around the axis of the rotor, and noting the measurements taken with a galvanometer. By slowly advancing around the rotor, a general standing wave can be drawn on graphing paper by recording the degrees of rotation and the meter strength at each position.

This process was first partially automated by Jules François Joubert with his step-by-step method of wave form measurement. This consisted of a special single-contact commutator attached to the shaft of a spinning rotor. The contact point could be moved around the rotor following a precise degree indicator scale and the output appearing on a galvanometer, to be hand-graphed by the technician. [5] This process could only produce a very rough waveform approximation since it was formed over a period of several thousand wave cycles, but it was the first step in the science of waveform imaging.

Automatic paper-drawn oscillograph

Schematic and perspective view of the Hospitalier Ondograph, which used a pen on a paper drum to record a waveform image built up over time, using a synchronous motor drive mechanism and a permanent magnet galvanometer. [6][7]

The first automated oscillographs used a galvanometer to move a pen across a scroll or drum of paper, capturing wave patterns onto a continuously moving scroll. Due to the relatively high-frequency speed of the waveforms compared to the slow reaction time of the mechanical components, the waveform image was not drawn directly but instead built up over a period of time by combining small pieces of many different waveforms, to create an averaged shape.

The device known as the Hospitalier Ondograph was based on this method of wave form measurement. It automatically charged a capacitor from each 100th wave, and discharged the stored energy through a recording galvanometer, with each successive charge of the capacitor being taken from a point a little farther along the wave. [8] (Such wave-form measurements were still averaged over many hundreds of wave cycles but were more accurate than hand-drawn oscillograms.)

Photographic Oscillograph

Top-Left: Duddell moving-coil oscillograph with mirror and two supporting moving coils on each side of it, suspended in an oil bath, Top-Middle: Rotating shutter and moving mirror assembly for placing time-index marks next to the waveform pattern. Top-Right: Moving-film camera for recording the waveform. Bottom: Film recording of sparking across switch contacts, as a high-voltage circuit is disconnected.[9][10][11][12]

In order to permit direct measurement of waveforms it was necessary for the recording device to use a very low-mass measurement system that can move with sufficient speed to match the motion of the actual waves being measured. This was done with the development of the moving-coil oscillograph by William Duddell which in modern times is also referred to as a mirror galvanometer. This reduced the measurement device to a small mirror that could move at high speeds to match the waveform.

To perform a waveform measurement, a photographic slide would be dropped past a window where the light beam emerges, or a continuous roll of motion picture film would be scrolled across the aperture to record the waveform over time. Although the measurements were much more precise than the built-up paper recorders, there was still room for improvement due to having to develop the exposed images before they could be examined.

CRT Invention

Cathode ray tubes (CRTs) were developed in the late 19th century. At that time, the tubes were intended primarily to demonstrate and explore the physics of electrons (then known as cathode rays). Karl Ferdinand Braun invented the CRT oscilloscope as a physics curiosity in 1897, by applying an oscillating signal to electrically charged deflector plates in a phosphor-coated CRT. Applying a reference oscillating signal to the horizontal deflector plates and a test signal to the vertical deflector plates produced transient plots of electrical waveforms on the small phosphor screen. The first dual beam oscilloscope was developed in the late 1930s by the British company A.C.Cossor (later acquired by Raytheon). The CRT was not a true double beam type but used a split beam by placing a third plate between the vertical deflection plates. It was widely used during WWII for the development and servicing of radar equipment. Although extremely useful for examining the performance of pulse circuits it was not calibrated so could not be used as a measuring device. It was, however, useful in producing response curves of IF circuits and consequently a great aid in their accurate alignment.

The triggered oscilloscope

Oscilloscopes became a much more useful tool in 1946 when Howard Vollum and Jack Murdock invented the triggered oscilloscope, Tektronix Model 511. The first oscilloscopes used analog technology in which the electron beam traced on the oscilloscope's screen directly traced the input voltage's waveform. It would start a horizontal trace when the input voltage exceeded an adjustable threshold. Triggering allows stationary display of a repeating waveform, as multiple repetitions of the waveform are drawn over the exact same trace on the phosphor screen -- without triggering, multiple copies of the waveform are drawn in different places, giving an incoherent jumble or a moving image on the screen.

As oscilloscopes have become more powerful over time, enhanced triggering options allow capture and display of more complex waveforms. For example, trigger holdoff is a feature in most modern oscilloscopes that can be used to define a certain period following a trigger during which the oscilloscope will not trigger again. This makes it easier to establish a stable view of a waveform with multiple edges which would otherwise cause another trigger.

Tektronix

Vollum and Murdock went on to found Tektronix, the first manufacturer of calibrated oscilloscopes (which included a graticule on the screen and produced plots with calibrated scales on the axes of the screen). Later developments by Tektronix included the development of multiple-trace oscilloscopes for comparing signals either by time-multiplexing (via chopping or trace alternation) or by the presence of multiple electron guns in the tube. In 1963, Tektronix introduced the Direct View Bistable Storage Tube (DVBST), which allowed observing single pulse waveforms rather than (as previously) only repeating wave forms. Using micro-channel plates, the most-advanced analog oscilloscopes (for example, the Tek 7104 mainframe) could display a visible trace (or allow the photography) of a single-shot event even when running at extremely fast sweep speeds.

Digital oscilloscopes

The first Digital Storage Oscilloscopes (DSO) was invented by Walter LeCroy (who founded the LeCroy Corporation, based in New York, USA) after producing high-speed digitizers for the research center CERN in Switzerland. LeCroy remains one of the three largest manufacturers of oscilloscopes in the world.

Starting in the 1980s, digital oscilloscopes became prevalent. Digital storage oscilloscopes use a fast analog-to-digital converter and memory chips to record and show a digital representation of a waveform, yielding much more flexibility for triggering, analysis, and display than is possible with a classic analog oscilloscope. Unlike its analog predecessor, the digital storage oscilloscope can show pre-trigger events, opening another dimension to the recording of rare or intermittent events and troubleshooting of electronic glitches. As of 2006 most new oscilloscopes (aside from education and a few niche markets) are digital.

Digital scopes rely on effective use of the installed memory and trigger functions: not enough memory and the user will miss the events they want to examine; if the scope has a large memory but does not trigger as desired, the user will have difficulty finding the event.

PC-based oscilloscope (PCO)

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Although most people think of an oscilloscope as a self-contained instrument in a box, a new type of "oscilloscope" is emerging that consists of a specialized signal acquisition board (which can be an external USB or Parallel port device, or an internal add-on PCI or ISA card). The hardware itself usually consists of an electrical interface providing insulation and automatic gain controls, several hi-speed analog-to-digital converters and some buffer memory, or even on-board DSPs. Depending on the exact hardware configuration, the hardware could be best described as a digitizer, a data logger or as a part of a specialized automatic control system.

The PC provides the display, control interface, disc storage, networking and often the electrical power for the acquisition hardware. The viability of PC-based oscilloscopes depends on the current widespread use and low cost of standardized PCs. Since prices can range from as little as $100 to as much as $3000 depending on their capabilities, such instruments are particularly suitable for the educational market, where PCs are commonplace but equipment budgets are often low. The acquisition hardware, in certain cases, may only consist of a standard sound card or even a game port, if only audio and low-frequency signals are involved.

The PCO can transfer data to the computer in two main ways - streaming, and block mode. In streaming mode the data is transferred to the PC in a continuous flow without any loss of data. The way in which the PCO is connected to the PC (e.g. USB) will dictate the maximum achievable speed using this method. Block mode utilizes the on-board memory of the PCO to collect a block of data which is then transferred to the PC after the block has been recorded. The PCO hardware then resets and records another block of data. This process happens very quickly, but the time taken will vary according to the size of the block of data and the speed at which it can be transferred. This method enables a much higher sampling speed, but in many cases the hardware will not record data whilst it is transferring the existing block, meaning that some data loss will occur.

The advantages of PC-based oscilloscopes include:

* Lower cost than a stand-alone oscilloscope, assuming the user already owns a PC. Professional-grade PCO hardware (e.g. with bandwidth in the MHz rather than in the kHz range) tends to be more expensive than e.g. a typical PCI sound card, and some can even cost more than a new PC [1].
* Easy exporting of data to standard PC software such as spreadsheets and word processors.
* Ability to control the instrument by running a custom program on the PC.
* Use of the PC's networking and disc storage functions, which cost extra when added to a self-contained oscilloscope.
* PCs typically have large high-resolution color displays which can be easier to read than the smaller displays found on conventional scopes. Color can be utilized to differentiate waveforms. It can also show increased information including more of the waveform or extras like automatic waveform measurements and simultaneous alternative views.
* Portability when used with a laptop PC.

There are also some disadvantages, which include:

* Power-supply and electromagnetic noise from PC circuits, which requires careful and extensive shielding to obtain good low-level signal resolution.
* Data transfer rates to the PC, which are dependent upon the connection method. This affects the maximum sampling speed achievable by the PCO when streaming.
* Need for the owner to install oscilloscope software on the PC, which may not be compatible with the current release of the PC operating system.
* Time for the PC to boot, compared with the almost instant start-up of a self-contained oscilloscope (although, as some modern oscilloscopes are actually PCs or similar machines in disguise, this distinction is narrowing).

As more processing power and data storage is included in oscilloscopes, the distinction is becoming blurred. Mainstream oscilloscope vendors manufacture large-screen, PC-based oscilloscopes, with very fast (multi-GHz) input digitizers and highly-customized user interfaces.

Software for a PC may use the sound card or game port to acquire analog signals, instead of dedicated signal acquisition hardware. However, these devices have very restricted input voltage ranges, limited precision, and very restricted frequency ranges. The ground reference for these inputs is the same as the ground for the PC logic and power supply; this may inject unacceptable amounts of noise into the circuit under test. However, these devices can be useful for demonstration or hobby use.

If a sound card is used, frequency response is usually limited to the audio range, and DC signals cannot be measured. The number of inputs is limited by the number of recording channels and the inputs can handle only audio line-level voltages without the risk of damage.

If the game port is used as the acquisition hardware, the sampling frequency is very low, typically below 1 kHz, and the input voltages can only vary over a range of a couple of volts. In addition, the game port cannot easily be programmed for a specific sampling rate, nor can it be easily assigned a precise quantization step. These limitations only make it suitable for low-precision visualization of low frequency signals.

Mixed signal oscilloscope

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A mixed signal oscilloscope (or MSO) has two kinds of inputs, a small number (typically two or four) of analog channels, and a larger number (typically sixteen) of digital channels. These measurements are acquired with a single time base, they are viewed on a single display, and any combination of these signals can be used to trigger the oscilloscope.

An MSO combines all the measurement capabilities and the use model of a Digital Storage Oscilloscope (DSO) with some of the measurement capabilities of a logic analyzer. MSOs typically lack the advanced digital measurement capabilities and the large number of digital acquisition channels of full-fledged logic analyzers, but they are also much less complex to use. Typical mixed-signal measurement uses include the characterization and debugging of hybrid analog/digital circuits like: embedded systems, Analog-to-digital converters (ADCs), Digital-to-analog converters (DACs), and control systems.

Digital storage oscilloscope

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The digital storage oscilloscope, or DSO for short, is now the preferred type for most industrial applications, although simple analog CROs are still used by hobbyists. It replaces the unreliable storage method used in analog storage scopes with digital memory, which can store data as long as required without degradation. It also allows complex processing of the signal by high-speed digital signal processing circuits.

The vertical input, instead of driving the vertical amplifier, is digitised by an analog to digital converter to create a data set that is stored in the memory of a microprocessor. The data set is processed and then sent to the display, which in early DSOs was a cathode ray tube, but is now more likely to be an LCD flat panel. DSOs with color LCD displays are common. The data set can be sent over a LAN or a WAN for processing or archiving. The screen image can be directly recorded on paper by means of an attached printer or plotter, without the need for an oscilloscope camera. The scope's own signal analysis software can extract many useful time-domain features (e.g. rise time, pulse width, amplitude), frequency spectra, histograms and statistics, persistence maps, and a large number of parameters meaningful to engineers in specialized fields such as telecommunications, disk drive analysis and power electronics.

Digital oscilloscopes are limited principally by the performance of the analog input circuitry and the sampling frequency. In general, the sampling frequency should be at least the Nyquist rate, double the frequency of the highest-frequency component of the observed signal, otherwise aliasing may occur.

Digital storage also makes possible another unique type of oscilloscope, the equivalent-time sample scope. Instead of taking consecutive samples after the trigger event, only one sample is taken. However, the oscilloscope is able to vary its timebase to precisely time its sample, thus building up the picture of the signal over the subsequent repeats of the signal. This requires that either a clock or repeating pattern be provided. This type of scope is frequently used for very high speed communication because it allows for a very high "sample rate" and low amplitude noise compared to traditional real-time scopes.

To sum this up: Advantages over the analog oscilloscope:

* Brighter and bigger display with color to distinguish multiple traces
* Equivalent time sampling and Average across consecutive samples or scans lead to higher resolution down to µV
* Peak detection
* Pre-trigger
* Easy pan and zoom across multiple stored traces allows beginners to work without a trigger
o This needs a fast reaction of the display (some scopes have 1 ms delay)
o The knobs have to be large and turn smoothly
* Also slow traces like the temperature variation across a day can be recorded
* The memory of the oscilloscope can be arranged not only as a one-dimensional list but also as a two-dimensional array to simulate a phosphorus screen. The digital technique allows a quantitative analysis (E.g. Eye diagram)
* Allows for automation, though most models lock the access to their software

A disadvantage of digital oscilloscopes is the limited refresh rate of the screen. On an analog oscilloscope, the user can get an intuitive sense of the trigger rate simply by looking at the steadiness of the CRT trace. For a digital oscilloscope, the screen looks exactly the same for any signal rate which exceeds the screen's refresh rate. Additionally, it is sometimes hard to spot "glitches" or other rare phenomena on the black-and-white screens of standard digital oscilloscopes; the slight persistence of CRT phosphors on analog scopes makes glitches visible even if many subsequent triggers overwrite them. Both of these difficulties have been overcome recently by "digital phosphor oscilloscopes," which store data at a very high refresh rate and display it with variable intensity, to simulate the trace persistence of a CRT scope.

Analog storage oscilloscope

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An extra feature available on some analog scopes is called 'storage'. This feature allows the trace pattern that normally decays in a fraction of a second to remain on the screen for several minutes or longer. An electrical circuit can then be deliberately activated to store and erase the trace on the screen.

The storage is accomplished using the principle of secondary emission. When the ordinary writing electron beam passes a point on the phosphor surface, not only does it momentarily cause the phosphor to illuminate, but the kinetic energy of the electron beam knocks other electrons loose from the phosphor surface. This can leave a net positive charge. Storage oscilloscopes then provide one or more secondary electron guns (called the "flood guns") that provide a steady flood of low-energy electrons traveling towards the phosphor screen. The electrons from the flood guns are more strongly drawn to the areas of the phosphor screen where the writing gun has left a net positive charge; in this way, the electrons from the flood guns re-illuminate the phosphor in these positively-charged areas of the phosphor screen.

If the energy of the flood gun electrons is properly balanced, each impinging flood gun electron knocks out one secondary electron from the phosphor screen, thus preserving the net positive charge in the illuminated areas of the phosphor screen. In this way, the image originally written by the writing gun can be maintained for a long time. Eventually, small imbalances in the secondary emission ratio cause the entire screen to "fade positive" (light up) or cause the originally-written trace to "fade negative" (extinguish). It is these imbalances that limit the ultimate storage time possible.

Some oscilloscopes used a strictly binary (on/off) form of storage known as "bistable storage". Others permitted a constant series of short, incomplete erasure cycles which created the impression of a phosphor with "variable persistence". Certain oscilloscopes also allowed the partial or complete shutdown of the flood guns, allowing the preservation (albeit invisibly) of the latent stored image for later viewing. (Fading positive or fading negative only occurs when the flood guns are "on"; with the flood guns off, only leakage of the charges on the phosphor screen degrades the stored image.)

Dual beam oscilloscope

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A dual beam oscilloscope was a type of oscilloscope once used to compare one signal with another. There were two beams produced in a special type of CRT. Unlike an ordinary "dual-trace" oscilloscope (which time-shared a single electron beam, thus losing about 50% of each signal), a dual beam oscilloscope simultaneously produced two separate electron beams, capturing the entirety of both signals.

Two pairs of vertical plates deflect the beams. Vertical plates for channel A had no effect on channel B beam. Similarly for channel B, separate vertical plates existed which deflected the beam B only.

On some scopes the time base, horizontal plates and horizontal amplifier were common to both beams; on more elaborate scopes like the Tektronix 556 there were two independent time bases and two sets of horizontal plates and horizontal amplifiers. Thus one could look at a very fast signal on one beam and a slow signal on another beam.

Most multichannel 'scopes do not actually have multiple electron beams. Instead, they display only one dot at a time, but switch the dot between one channel and the other either on alternate sweeps (ALT mode) or many times per sweep (CHOP mode). Very few actual dual beam oscilloscopes were built.

With the advent of digital signal capture, true dual beam oscilloscopes became obsolete, as it was then possible to display two truly simultaneous signals from memory using either the ALT or CHOP display technique, or even possibly a raster display mode.

Cathode-ray oscilloscope (CRO)

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The earliest and simplest type of oscilloscope consisted of a cathode ray tube, a vertical amplifier, a timebase, a horizontal amplifier and a power supply. These are now called 'analog' scopes to distinguish them from the 'digital' scopes that became common in the 1990s and 2000s.

Before the introduction of the CRO in its current form, the cathode ray tube had already been in use as a measuring device. The cathode ray tube is an evacuated glass envelope, similar to that in a black-and-white television set, with its flat face covered in a phosphorescent material (the phosphor). The screen is typically less than 20 cm in diameter, much smaller than the one in a television set.

In the neck of the tube is an electron gun, which is a heated metal plate with a wire mesh (the grid) in front of it. A small grid potential is used to block electrons from being accelerated when the electron beam needs to be turned off, as during sweep retrace or when no trigger events occur. A potential difference of at least several hundred volts is applied to make the heated plate (the cathode) negatively charged relative to the deflection plates. For higher bandwidth oscilloscopes where the trace may move more rapidly across the phosphor target, a positive post-deflection acceleration voltage of over 10,000 volts is often used, increasing the energy (speed) of the electrons that strike the phosphor. The kinetic energy of the electrons is converted by the phosphor into visible light at the point of impact. When switched on, a CRT normally displays a single bright dot in the center of the screen, but the dot can be moved about electrostatically or magnetically. The CRT in an oscilloscope uses electrostatic deflection.

Between the electron gun and the screen are two opposed pairs of metal plates called the deflection plates. The vertical amplifier generates a potential difference across one pair of plates, giving rise to a vertical electric field through which the electron beam passes. When the plate potentials are the same, the beam is not deflected.

When the top plate is positive with respect to the bottom plate, the beam is deflected upwards; when the field is reversed, the beam is deflected downwards. The horizontal amplifier does a similar job with the other pair of deflection plates, causing the beam to move left or right. This deflection system is called electrostatic deflection, and is different from the electromagnetic deflection system used in television tubes. In comparison to magnetic deflection, electrostatic deflection can more readily follow random changes in potential, but is limited to small deflection angles.

The timebase is an electronic circuit that generates a ramp voltage. This is a voltage that changes continuously and linearly with time. When it reaches a predefined value the ramp is reset, with the voltage reestablishing its initial value. When a trigger event is recognized the reset is released, allowing the ramp to increase again. The timebase voltage usually drives the horizontal amplifier. Its effect is to sweep the electron beam at constant speed from left to right across the screen, then quickly return the beam to the left in time to begin the next sweep. The timebase can be adjusted to match the sweep time to the period of the signal.

Meanwhile, the vertical amplifier is driven by an external voltage (the vertical input) that is taken from the circuit or experiment that is being measured. The amplifier has a very high input impedance, typically one megohm, so that it draws only a tiny current from the signal source. The amplifier drives the vertical deflection plates with a voltage that is proportional to the vertical input. Because the electrons have already been accelerated by hundreds of volt, this amplifier also has to deliver almost hundred volts, and this with a very high bandwidth. The gain of the vertical amplifier can be adjusted to suit the amplitude of the input voltage. A positive input voltage bends the electron beam upwards, and a negative voltage bends it downwards, so that the vertical deflection of the dot shows the value of the input. [3]

The response of this system is much faster than that of mechanical measuring devices such as the multimeter, where the inertia of the pointer slows down its response to the input.

When all these components work together, the result is a bright trace on the screen that represents a graph of voltage against time. Voltage is on the vertical axis, and time on the horizontal.

Observing high speed signals, especially non-repetitive signals, with a conventional CRO is difficult, due to non-stable or changing triggering threshold which makes it hard to "freeze" the waveform on the screen. This often requires the room to be darkened or a special viewing hood to be placed over the face of the display tube. To aid in viewing such signals, special oscilloscopes have borrowed from night vision technology, employing a microchannel plate in the tube face to amplify faint light signals.
Tektronix Model C-5A Oscilloscope Camera with Polaroid instant film pack back.

Although a CRO allows one to view a signal, in its basic form it has no means of recording that signal on paper for the purpose of documentation. Therefore, special oscilloscope cameras were developed to photograph the screen directly. Early cameras used roll or plate film, while in the 1970s Polaroid instant cameras became popular.

The vertical amplifier and timebase controls are calibrated to show the vertical distance on the screen that corresponds to a given voltage difference, and the horizontal distance that corresponds to a given time interval.

The power supply is an important component of the scope. It provides low voltages to power the cathode heater in the tube, and the vertical and horizontal amplifiers. High voltages are needed to drive the electrostatic deflection plates. These voltages must be very stable. Any variations will cause errors in the position and brightness of the trace.

Later analog oscilloscopes added digital processing to the standard design. The same basic architecture - cathode ray tube, vertical and horizontal amplifiers - was retained, but the electron beam was controlled by digital circuitry that could display graphics and text mixed with the analog waveforms. The extra features that this system provides include:

* on-screen display of amplifier and timebase settings;
* voltage cursors - adjustable horizontal lines with voltage display;
* time cursors - adjustable vertical lines with time display;
* on-screen menus for trigger settings and other functions.

Features and uses

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Description
Exterior

A typical oscilloscope has a display screen, numerous input connectors, and control knobs and buttons on the front panel. Portable instruments are small enough to carry to a work site and may even be battery operated. Laboratory grade 'scopes, especially old instruments using vacuum tubes, are bench-top devices. Special purpose 'scopes may be permanently mounted in a rack. To aid measurement, a grid called the graticule is drawn on the face of the screen. Each square in the graticule is known as a division. On old low-cost CRT 'scopes the graticule was a printed piece of plastic; higher-cost instruments have the graticule printed on the face of the CRT, to eliminate parallax errors. Digital 'scopes generate the graticule markings on the display in the same way as the trace.

Large bench-top oscilloscopes were sometimes mounted on carts to allow sharing one expensive instrument by several work areas. Miniaturized oscilloscopes were of great value for field service equipment repair. Today even a very capable laboratory instrument can be lifted by a single person, and hand-held digital oscilloscopes are made by several manufacturers.

Inputs

The signal to be measured is fed to one of the input connectors, which is usually a coaxial connector such as a BNC or N type. Binding posts or banana plugs may be used for lower frequencies. If the signal source has its own coaxial connector, then a simple coaxial cable is used; otherwise, a specialised cable called a "scope probe", supplied with the oscilloscope, is used. General-purpose oscilloscopes have a standardised input resistance of 1 megohm in parallel with a capacitance of around 20 picofarads. This allows the use of standard oscilloscope probes. Scopes for use with very high frequencies may have 50-ohm inputs, which must be either connected directly to a 50-ohm signal source or used with Z0 or active probes.

The trace

In its simplest mode, the oscilloscope repeatedly draws a horizontal line called the trace across the middle of the screen from left to right. One of the controls, the timebase control, sets the speed at which the line is drawn, and is calibrated in seconds per division. If the input voltage departs from zero, the trace is deflected either upwards or downwards. Another control, the vertical control, sets the scale of the vertical deflection, and is calibrated in volts per division. The resulting trace is a plot of voltage against time, with the more distant past on the left and the more recent past on the right.

If the input signal is periodic, then a nearly stable trace can be obtained just by setting the timebase to match the frequency of the input signal. For example, if the input signal is a 50 Hz sine wave, then its period is 20 ms, so the timebase should be adjusted so that the time between successive horizontal sweeps is 20 ms. This mode is called continual sweep. Since the calibrated oscilloscope timebase may not exactly match the period of the input signal, the trace will drift across the screen making measurements difficult. If the time base is adjusted to stabilize the trace, the time per horizontal division is altered, and usually uncalibrated.

Trigger

To provide a more stable trace, modern oscilloscopes have a function called the trigger. When using triggering, the scope will pause each time the sweep reaches the extreme right side of the screen. The scope then waits for a specified event before drawing the next trace. The trigger event is usually the input waveform reaching some user-specified threshold voltage in the specified direction (going positive or going negative).

The effect is to resynchronize the timebase to the input signal, preventing horiz

ontal drift of the trace. In this way, triggering allows the display of periodic signals such as sine waves and square waves. Trigger circuits also allow the display of nonperiodic signals such as single pulses or pulses that don't recur at a fixed rate.

Types of trigger include:

* external trigger, a pulse from an external source connected to a dedicated input on the scope.
* edge trigger, an edge-detector that generates a pulse when the input signal crosses a specified threshold voltage in a specified direction.
* video trigger, a circuit that extracts synchronizing pulses from video formats such as PAL and NTSC and triggers the timebase on every line, a specified line, every field, or every frame. This circuit is typically found in a waveform monitor device.
* delayed trigger, which waits a specified time after an edge trigger before starting the sweep. No trigger circuit acts instantaneously, so there is always a certain delay, but a trigger delay circuit extends this delay to a known and adjustable interval. In this way, the operator can examine a particular pulse in a long train of pulses.

Bandwidth

Bandwidth is a measure of the range of frequencies that can be displayed. The bandwidth of the 'scope is limited by the vertical amplifiers and CRT (in analog instruments) or by the sampling rate of the analog to digital converter in digital instruments. The bandwidth is defined as the frequency at which the sensitivity is 0.707 of the sensitivity at lower frequency (a drop of 3 dB). The rise time of the fastest pulse that can be resolved by the scope is related to its bandwidth approximately:

Bandwidth in Hz x rise time in seconds = 0.35 [2]

For example, a 'scope intended to resolve pulses with a rise time of 1 nanosecond would have a bandwidth of 350 MHz.

For a digital oscilloscope, a rule of thumb is that the continuous sampling rate should be ten times the highest frequency desired to resolve; for example a 20 megasample/second rate would be applicable for measuring signals up to about 2 megahertz.

X-Y mode

Most modern oscilloscopes have several inputs for voltages, and thus can be used to plot one varying voltage versus another. This is especially useful for graphing I-V curves (current versus voltage characteristics) for components such as diodes, as well as Lissajous patterns. Lissajous figures are an example of how an oscilloscope can be used to track phase differences between multiple input signals. This is very frequently used in broadcast engineering to plot the left and right stereophonic channels, to ensure that the stereo generator is calibrated properly.

Other features

Some oscilloscopes have cursors, which are lines that can be moved about the screen to measure the time interval between two points, or the difference between two voltages.

Oscilloscopes may have two or more input channels, allowing them to display more than one input signal on the screen. Usually the oscilloscope has a separate set of vertical controls for each channel, but only one triggering system and timebase.

Better quality general purpose oscilloscopes include a calibration signal for setting up the compensation of test probes; this is (often) a 1 kHz square-wave signal available at a test terminal on the front panel.

Sometimes the event that the user wants to see may only happen occasionally. To catch these events, some oscilloscopes, known as "storage scopes", preserve the most recent sweep on the screen. This was originally achieved by using a special CRT, a "storage tube", which would retain the image of even a very brief event for a long time.

Some digital oscilloscopes can sweep at speeds as slow as once per hour, emulating a strip chart recorder. That is, the signal scrolls across the screen from right to left. Most oscilloscopes with this facility switch from a sweep to a strip-chart mode at about one sweep per ten seconds. This is because otherwise, the scope looks broken: it's collecting data, but the dot cannot be seen.

Oscilloscopes were originally analog devices. In more recent times digital signal sampling is more often used for all but the simplest models.

Many oscilloscopes have different plug-in modules for different purposes, e.g., high-sensitivity amplifiers of relatively narrow bandwidth, differential amplifiers, amplifiers with 4 or more channels, sampling plugins for repetitive signals of very high frequency, and special-purpose plugins.

Examples of use

One of the most frequent uses of scopes is troubleshooting malfunctioning electronic equipment. One of the advantages of a scope is that it can graphically show signals: where a voltmeter may show a totally unexpected voltage, a scope may reveal that the circuit is oscillating. In other cases the precise shape of a pulse is important. In a piece of electronic equipment, for example, the connections between stages (e.g. electronic mixers, electronic oscillators, amplifiers) may be 'probed' for the expected signal, using the scope as a simple signal tracer. If the expected signal is absent or incorrect, some preceding stage of the electronics is not operating correctly. Since most failures occur because of a single faulty component, each measurement can prove that half of the stages of a complex piece of equipment either work, or probably did not cause the fault.

Once the faulty stage is found, further probing can usually tell a skilled technician exactly which component has failed. Once the component is replaced, the unit can be restored to service, or at least the next fault can be isolated.

Another use is to check newly designed circuitry. Very often a newly designed circuit will misbehave because of design errors, bad voltage levels, electrical noise etc. Digital electronics usually operate from a clock, so a dual-trace scope which shows both the clock signal and a test signal dependent upon the clock is useful. "Storage scopes" are helpful for "capturing" rare electronic events that cause defective operation.

Another use is for software engineers who must program electronics. Often a scope is the only way to see if the software is running the electronics properly.

Pictures of use

Heterodyne

AC hum on sound.

AM signal.

Bad filter on sine.

Dual trace, showing different time bases on each trace.

Selection

Heterodyne	AC hum on sound.	AM signal.	Bad filter on sine.

Oscilloscopes generally have a checklist of some set of the above features. The basic measure of virtue is the bandwidth of its vertical amplifiers. Typical scopes for general purpose use should have a bandwidth of at least 100 MHz, although much lower bandwidths are acceptable for audio-frequency applications. A useful sweep range is from one second to 100 nanoseconds, with triggering and delayed sweep.

The chief benefit of a quality oscilloscope is the quality of the trigger circuit. If the trigger is unstable, the display will always be fuzzy. The quality improves roughly as the frequency response and voltage stability of the trigger increase.

Analog oscilloscopes have been almost totally displaced by digital storage scopes except for the low bandwidth (< 60 MHz) segment of the market. Greatly increased sample rates have eliminated the display of incorrect signals, known as "aliasing", that was sometimes present in the first generation of digital scopes. The used test equipment market, particularly on-line auction venues, typically have a wide selection of older analog scopes available. However it is becoming more difficult to obtain replacement parts for these instruments and repair services are generally unavailable from the original manufacturer.

As of 2007[update], a 350 MHz bandwidth (BW), 2.5 giga-samples per second (GS/s), dual-channel digital storage scope costs about US$7000 new. The current real-time analog bandwidth record, as of February 2007[update], is held by the Tektronix DPO70000 and DSA70000 oscilloscope families with a 20 GHz BW (non-interleaved) and a sample rate of 50 GHz. The current equivalent time sampling bandwidth record for sampling digital storage oscilloscopes, as of June 2006[update], is held by the LeCroy WaveExpert series with a 100 GHz bandwidth.

Software

Many oscilloscopes today provide one or more external interfaces to allow remote instrument control by external software. These interfaces (or buses) include GPIB, Ethernet, serial port, and USB.

Oscilloscope

2009-01-01T21:28:00.000-08:00

An oscilloscope (commonly abbreviated to scope or O-scope) is a type of electronic test equipment that allows signal voltages to be viewed, usually as a two-dimensional graph of one or more electrical potential differences (vertical axis) plotted as a function of time or of some other voltage (horizontal axis). The oscilloscope is one of the most versatile and widely-used electronic instruments. [1]

Oscilloscopes are widely used when it is desired to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can measure the frequency, show distortion, and show the relative timing of two related signals. Oscilloscopes are used in the sciences, medicine, engineering, telecommunications, and industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for such purposes as adjusting an automotive ignition system, or to display the waveform of the heartbeat.

Originally all oscilloscopes used cathode ray tubes as their display element, but modern digital oscilloscopes use high-speed analog-to-digital converters and computer-like display screens and processing of signals. Oscilloscope peripheral modules for general purpose laptop or desktop personal computers can turn them into useful and flexible test instruments.

Uses of Logic Analyzer

2009-01-01T21:26:00.000-08:00

Many digital designs, including those of ICs, are simulated to detect defects before the unit is constructed. The simulation usually provides logic analysis displays. Often, complex discrete logic is verified by simulating inputs and testing outputs using boundary scan. Logic analyzers can uncover hardware defects that are not found in simulation. These problems are typically too difficult to model in simulation, or too time consuming to simulate and often cross multiple clock domains.

Field-programmable gate arrays have become a common measurement point for logic analyzers.

Operation of Logic Analyzer

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A logic analyzer can trigger on a complicated sequence of digital events, and then capture a large amount of digital data from the system under test (SUT). The best logic analyzers behave like software debuggers by showing the flow of the computer program and decoding protocols to show messages and violations.

When logic analyzers first came into use, it was common to attach several hundred "clips" to a digital system. Later, specialized connectors came into use. The evolution of logic analyzer probe has led to a common footprint that multiple vendors support, which provides added freedom to end users. Introduced in April, 2002, connectorless technology (identified by several vendor specific trade names: Compression Probing; Soft Touch; D-Max) has become popular. These probes provide a durable, reliable mechanical and electrical connection between the probe and the circuit board with less than 0.5pF to 0.7 pF loading per signal.

Once the probes are connected, the user programs the analyzer with the names of each signal, and can group several signals into groups for easier manipulation. Next, a capture mode is chosen, either timing mode, where the input signals are sampled at regular intervals based on an internal or external clock source, or state mode, where one or more of the signals are defined as "clocks," and data is taken on the rising or falling edges of these clocks, optionally using other signals to qualify these clocks.

After the mode is chosen, a trigger condition must be set. A trigger condition can range from simple (such as triggering on a rising or falling edge of a single signal), to the very complex (such as configuring the analyzer to decode the higher levels of the TCP/IP stack and triggering on a certain HTTP packet).

At this point, the user sets the analyzer to "run" mode, either triggering once, or repeatedly triggering.

Once the data is captured, it can be displayed several ways, from the simple (showing waveforms or state listings) to the complex (showing decoded Ethernet protocol traffic). The analyzer can also operate in a "compare" mode, where it compares each captured data set to a previously recorded data set, and stopping triggering when this data set is either matched or not. This is useful for long-term empirical testing. Recent analyzers can even be set to email a copy of the test data to the engineer on a successful trigger.

Logic Analyzer

2009-01-01T21:24:00.000-08:00

A logic analyzer is an electronic instrument that displays signals in a digital circuit that are too fast to be observed and presents it to a user so that the user can more easily check correct operation of the digital system. They are typically used for capturing data in systems that have too many channels to be examined with an oscilloscope. Software running on the logic analyzer can convert the captured data into timing diagrams, protocol decodes, state machine traces, assembly language, or correlate assembly with source-level software.

Presently there are three distinct categories of logic analyzers available on the market:

* The first is mainframes, which consist of a chassis containing the display, controls, control computer, and multiple slots into which the actual data capturing hardware is installed.
* The second category is standalone units which integrate everything into a single package, with options installed at the factory.
* The third category is pc based logic analyzers. The hardware connects to a computer through a USB or LPT connection and then relays the captured signals to the software on the computer. These instruments are less expensive than either mainframes or standalone units although they lack the sophisticated functionality.

Residual Gas Analyzer

2008-12-19T02:52:00.001-08:00

A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in the semiconductor industry. Utilizing quadrupole technology, there exists two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to 10 − 14 Torr levels, possessing sub-ppm detectability in the absence of background interferences.

RGAs would also be used as sensitive in-situ, helium leak detectors. With vacuum systems pumped down to lower than 10 - 5Torr—checking of the integrity of the vacuum seals and the quality of the vacuum—air leaks, virtual leaks and other contaminants at low levels may be detected before a process is initiated.

Gas Analyzer

2008-12-19T02:49:00.000-08:00

The Thermal and Evolved Gas Analyzer (TEGA) is a scientific instrument aboard the Phoenix spacecraft. TEGA's design is based on experience gained from the failed Mars Polar Lander. Soil samples taken from the Martian surface by the robot arm are eventually delivered to the TEGA, where they are heated in an oven to about 1,000ºC. This heat causes the volatile compounds to be given off as gases which are sent to a mass spectrometer for analysis. This spectrometer is adjusted to measure particularly the isotope ratios for hydrogen, oxygen, carbon, nitrogen, and heavier gases. Detection values as low as 10 parts per billion. The Phoenix TEGA has 8 ovens, which are enough for 8 samples.

A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in the semiconductor industry. Utilizing quadrupole technology, there exists two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to 10 − 14 Torr levels, possessing sub-ppm detectability in the absence of background interferences.

RGAs would also be used as sensitive in-situ, helium leak detectors. With vacuum systems pumped down to lower than 10 - 5Torr—checking of the integrity of the vacuum seals and the quality of the vacuum—air leaks, virtual leaks and other contaminants at low levels may be detected before a process is initiated.

Absorption of Infrared Radiation

2008-12-10T18:57:00.000-08:00

A large number of materials absorb infrared radiation (wavelengths of 0.7 to 300 µm) due to intramolecular vibrations and for any specific material the strength of absorption varies with the wavelength of the impinging radiation (the absorption spectrum). The absorption spectrum is different for every material.

The figure below shows the absorption spectra for a number of typical materials.

Infrared absorption spectra for gases

Figure 1 - Absorbance of infrared radiation (absorption spectra)

There are certain components that are common to all infrared gas sensors. These include: an infrared source such as a simple incandescent lamp, a detector, generally pyroelectric detectors, a means to select the desired wavelengths (band pass filters) and a sample chamber. Radiation from the source passes through the sample chamber and band-pass filter. The choice of wavelength and "width" of the band-pass filter are basically responsible for the relative selectivity of the sensor. The radiation NOT absorbed by the sample is then detected and the ratio of this radiation to the zero level provides a measure of the concentration of target gas in the sample. A zero level is taken using a gas that does not contain any of the target gas and hence will absorb or pass all wavelengths equally.

A further component needed for good performance of IR gas sensors is a temperature sensor. All these components have temperature dependencies which must be compensated to provide an accurate measure of gas concentration. This temperature sensor should be sited in close proximity to the chamber.

Infrared sensors basically give a measure of the number of target gas molecules in the light path between source and detector. As a result, the output signal not only varies with concentration but also with pressure, they are partial pressure devices. For high measurement accuracy, compensation for pressure is, required. This dependency also infers that sensors with a longer optical path length (the distance travelled by radiation between source and detector) will have increased resolution and tend to have a lower dynamic range.

Using a single target gas, fixed optical path device at constant pressure, the signal output decays with increasing concentration roughly exponentially, so infrared gas sensors are inherently non-linear. The measurement accuracy decreases with increasing concentration.

The components described above form a typical infrared gas sensor. However, some supporting electronics are essential to build a practical system. The common detector technologies provide extremely small analogue signal outputs that require a lot of amplification. Basic analogue filtering of the amplified output signal is generally necessary to improve measurement accuracy.

The source also requires a power driver circuit. It is usual practice to modulate the source output by pulsing. This creates periodic variations in the emitted intensity and so allows the use of synchronous detection techniques.

The temperature and pressure compensations are generally computed using sophisticated algorithms in a microprocessor. This first requires the analogue signals to be converted into digital signals. The compensated data is then made available to the signal display or processing unit.

Permeation dryers

2008-12-10T18:56:00.000-08:00

Flue gas conditioning for moisture removal is commonly performed for criteria pollutant measurements, especially for extractive CEM systems at combustion sources. An implicit assumption is that conditioning systems specifically remove moisture without affecting pollutant and diluent concentrations. Gas conditioning is generally performed by passing the flue gas through a cold trap (Peltier or refrigerant dryer) to remove moisture by condensation, which is subsequently extracted by a peristaltic pump. Many air pollutants are water-soluble and potentially susceptible to removal in a condensation dryer from gas interaction with liquid water.

An alternative technology for gas conditioning is the permeation dryer, where the flue gas passes over a selectively permeable membrane for moisture removal. In this case, water is transferred through the membrane while other pollutants are excluded, and the gas does not come into contact with condensate.

Laboratory experiments were performed to measure the relative removal of a water-soluble pollutant (sulphur dioxide, SO₂) using the two conditioning techniques. A wet gas generator was used to create hot, wet gas streams of known composition (15 % and 30 % moisture, balance nitrogen) and flow rate. Pre-heated SO₂ was injected into the wet stream using mass flow valves to achieve concentrations of 20, 50, and 100 ppm. The mixed gas was directed through a heated sample line to either a peltier or a permeation conditioning system. Two different types of gas analyzer were used to measure the SO₂ concentration after sample conditioning. Both analytic methods demonstrated that SO₂ is removed to a significantly greater extent by the peltier dryer. These results have important implications for monitoring of SO₂and other soluble gases.

Theory:

The selective and continuous removal of water vapour is performed by leading the flue-gas through a tube. Water vapour is absorbed through the tubing walls and moves through it. Dry purge gas is flowing at the outside of the drying-tube in the opposite direction and carries the water vapour away. Virtually all elements of the flue-gas sample remain unchanged, only the water vapour is removed. The drying effect is relative to the difference in vapour pressure between the gas outside the tube and the wet gas inside.

Gas permeation is the term used to describe a membrane separation process using a non-porous semi-permeable membrane. In this type of process, a gaseous stream is separated into permeating and non-permeating streams. The non-permeating stream is generally called the non-permeate in gas separations terminology. Transport occurs by a solution diffusion mechanism, and membrane selectivity is based on the relative permeation rates of the components through the membrane. Each gaseous component transporting through the membrane has a characteristic permeation rate that is a function of the ability to diffuse through the membrane material. The mechanism for transport is based on solubility and diffusion. The two relationships upon which the equations are based are Fick's law for diffusion and Henry's law for solubility.

Diffusive flux through the membrane can be expressed by Fick's Law related to the membrane system as given by:

(I)

Where: J_i : flux of component i (mole/m_²/s)

D_i : diffusivity of component i (m²/s)

L : thickness of the membrane (m)

C_im1: concentration of component i inside membrane on feed side (mole/m3)

C_im2: concentration of component i inside membrane on permeate side (mole/m3 )

From Henry's Law:

C_im = S_i * p_i (II)

Where, S_i : solubility constant for component i in the membrane (mol/m³.Pa)

p_i : partial pressure of component i in the gas phase (Pa)

Permeation through the membrane is a function of solubility and diffusivity:

P_i = D_i * S_i (III)

Separation efficiency aij is based on the different rates of permeation of the gas components, data that is not commonly available:

(IV)

An experimental separation factor a*ij is frequently used to quantify the separation of a binary system of components i (oxygen) and j (nitrogen), where Cp and Cr represent molar concentrations in the permeate and retentate (non-permeate) streams, respectively. The separation factor can also be defined in terms of Cp and Cf, i.e., concentrations in the permeate and feed streams. These relationships can be written in terms of mole fractions xp, xr and xf, which is more convenient.

(Va)

(Vb)

Recovery is defined by the equations below, where Qp, Qr and Qf represent the volumetric flow rates of permeate (or non-permeate) and feed streams, respectively (m³/s).

(VIa)

(VIb)

Stage cut defines the ratio of permeate flow rate to total feed flow rate. This assumes that both concentrations and volumetric flow rates are measured at atmospheric pressure in the permeate and the non-permeate streams.

(VII)

The total flux of a component, J_i may be calculated from the expression below:

(VIII)

Where, Q_ip : volumetric flow rate of species i in the permeate (m³/sec).

ρ : density of permeate (mole/m³).

A : area of membrane (m²)

n : number of modules used.

The permeation dryer is one of the most effective and compact means available to remove water from a system, particularly if feedback of the dried gas is used to improve drying effect.

Infrared Sensors

2008-12-10T18:50:00.000-08:00

Most of us are by now familiar with the applications where an infrared sensor is used. This is just a short article to sum it up for the record.
Carbon dioxide CO2:

For many years we were satisfied with the calculated value of carbon dioxide supplied by the average flue gas analyser. One of the very simple reasons for this was that there was no low cost method of measuring CO2. The direct measurement of CO2 was attempted by some manufacturers of electrochemical sensors, but without significant success. Carbon dioxide proved to be very difficult to measure in this way. The Kyoto Protocol and an increased public interest in carbonTop view of a NDIR infrared sensor for carbon dioxide in flow configuration dioxide as a greenhouse gas generally fuelled research into affordable methods of assessing the concentration of CO2. Of course, there have always been mass spectrometers and other laboratory equipment perfectly capable of carrying out these measurements, but that is not really something you can carry with you into the field! The price is just slightly outside the range of most companies interested in flue gas analysis.

The advent of small, low cost infrared sensors such as those produced by madur electronics has changed all that and the IR sensor used for carbon dioxide fits Component side of the NDIR sensoreasily inside the existing flue gas analyser housing with no mechanical changes. The advantages of directly measuring CO2 are perhaps not instantly apparent: This is essential in cases where the fuel cannot be adequately defined or no information is available. Oil refineries burning process gas are one good example, as are waste incinerators. Biogas plants need the measurement of carbon dioxide for two reasons: To assess the quality of the biogas before combustion, and to measure the products after combustion. Since the biogas contains some CO2 anyway, there is no way of calculating the quantity produced after combustion. The carbon dioxide present in the biogas is not a product of combustion, and should not be included in the combustion gas equation.
Methane CH4:

It is not readily obvious that methane will be present in flue gases from burner systems. It is a highly combustible gas and there is no reason to expect CH4 to survive at high temperatures in the presence of oxygen. The fact is, it does, if only in small quantities. There was earlier no efficient way of measuring the concentration of methane in these gases. The only technology coTop view of a NDIR infrared sensor for methanemmonly available was the Pellistor sensor, which is a highly inaccurate and not particularly reliable method of measuring CH4. The Pellistor sensor operates by catalytically burning all carbon compounds found in the gas and comparing the temperature between the non-catalyst side and the catalyst side of a pair of elements. The catalyst side will have a higher temperature and hence higher resistance than the non-catalyst side. This means that the two elements must be correctly balanced as a Wheatstone bridge measuring circuit before use, since the differences are very small. Whilst the sensor will only catalytically burn carbon compounds such as methane and carbon monoxide, the initiation of combustion will automatically affect all other combustible compounds such as H2S which might be present. The result of this is an unstable cross-sensitivity: In the presence of methane or carbon monoxide there is an cross-sensitivity to other combustibles, without these gases there is no answer from the sensor. This type of cross-sensitivity is impossible to predict and can not be removed by calculation. The Pellistor sensor is highly susceptible to poisoning by sulphur dioxide, SO2. The presence of this gas will cause the sensor to fail in a very short time. Special tubing must also be used since the commonly used silicone tubing will also cause the sensor to lose sensitivity and fail prematurely. Furthermore, the Pellistor sensor consists of two very thin wires exposed to the gas being measured. Vibration will cause fluctuations in the readings and failure is common after slight knocks. The Pellistor sensor is designed for fixed installation for safety measurement, which it does very well. A Pellistor is not a sensor for portable equipment. Methane can only really be effectively measured using a dedicated infrared sensor. Care must be taken to dry the gas efficiently, since the sensor will react slightly to the presence of water vapour as well as CH4. Although it is generally believed that an infrared sensor is completely dedicated to one component, all the alkanes have a wavelength similar to methane and the sensor is so constructed that it will react to their presence as well. Naturally, since it is calibrated for methane, the reaction to the longer chain alkanes will not be as accurate, but the correspondence is still better than that produced by a Pellistor sensor. Methane is now recognised as one of the major contributors to the greenhouse effect, so a measurement of CH4 is now essential.
Sulphur dioxide SO2:

It is possible to measure sulphur dioxide with electrochemical sensors relatively accurately, but there are certain disadvantages. SO2 measurement can also be carried out using infrared or ultraviolet sensors, both types of sulphur dioxide sensor being roughly equal in popularity. One of the major problems with SO2 is its extremely corrosive nature and the affinity for sulphur dioxide for water. The presence of any condensate will quickly remove all traces of SO2 from a measuring system. In addition, there is an absorption line for water very near the line for SO2. This means that the presence of any water vapour will affect the low readings of sulphurSide view of portable infrared flue gas analyser showing three infrared gas sensors dioxide to be expected. The infrared sensor for sulphur dioxide has the advantage of lower cost, but at the expense of greater size. Nevertheless, infrared sensors are one of the preferred methods of measuring SO2 in the field.

Nitric oxide NO:
Roughly the same applies for nitric oxide as for sulphur dioxide. It is quite possible to measure it reasonably accurately with electrochemical sensors, but infrared measurement can also be carried out, or may be required. There is, regrettably, exactly the same problem with interference from water vapour as well. Nitric oxide is usually measured at low concentrations in flue gas, and for this reason it is important to remove practically all the water from the sample stream. The Peltier dryer cannot cope with this level of drying, so the best option for portable equipment is a permeation dryer. Stationary equipment will generally use a refrigeration dryer, but the permeation dryer is here also an option.

As can be seen, these sensors are considerably longer than the sensors for methane or carbon dioxide. This is essential to give the necessary resolution to measure down to single parts per million.
General infrared measurement:

The infrared sensors manufactured by madur work on the NDIR (Non Dispersive InfraRed) principle. Light of a certain wavelength is absorbed by a particular gas, the amount of absorption proportional to the number of molecules of the gas present in the path of the light. By measurement of this infrared absorption the concentration of the gas can be determined with great accuracy.

Sick Building Syndrome and indoor climate control

2008-12-10T18:49:00.000-08:00

The problem of high levels of CO2 in ambient air appears to be a modern one. Yet, this is not one of the new fads that crop up from time to time and then disappear again, never to be mentioned again. It is, indeed, a modern problem, caused by the improvements in building standards and especially window manufacture. These improvements, hailed as a triumph over the age-old problem of draughty buildings, have nevertheless created a new negative effect. Ventilation was never a matter for discussion in most cases, it happened naturally as the wind blew and the air in rooms was replaced on a regular basis. With the new, draught-proof buildings this no longer happened, particularly since central heating made it unnecessary to have an air flow for any reason. This has given birth to the concept of indoor climate control.

The result was stale air. Air that has been used and breathed and not replaced, seen as a rising concentration of carbon dioxide, not to mention humidity. These effects had a detrimental influence on the buildings, promoting the growth of mould and other unwanted plant life. This was not the only effect. Slowly, the level of days off for sickness rose and the quality of work sank in these newer or refurbished buildings, leading to something referred to as Sick Building Syndrome, since it appeared to affect everybody in one building. The causes were not known for a long time, but now it is recognised that this is a result of breathing stale air with a high concentration of carbon dioxide over an extended period. Studies have shown that a level of 1000 ppm carbon dioxide will reduce the ability to concentrate by about 30 %, a significant drop by any means.

The obvious solution to this problem of indoor climate control was ventilation, and ventilation or air-conditioning systems were installed in all of these buildings leading only to the next problem: the heating bills in winter rocketed and staff complained of stiff necks and other maladies. Sick Building Syndrome was still here, but in a different form. How to provide adequate ventilation without simply heating the environment in winter? The only viable solution is control of the ventilation to reduce the exchange of air to the minimum required to keep a healthy atmosphere in the rooms, which is where indoor climate control becomes an active instead of just a passive discipline.

The real problem is the carbon dioxide, which is often difficult to quantify and is best measured with a NDIR infrared sensor. These are available in one or two channel technology for CO2, but the single channel version is quite accurate and stable enough for this purpose today. Older types of sensor used to drift, as do cheaply manufactured ones, but a good-quality single channel sensor today will remain stable over years, only requiring a reference point occasionally to set a relative zero point. Such infrared sensors for CO2 are now available from a number of manufacturers such as Madur Electronics in Austria. These come complete with an appropriate analogue output to allow the CO2 level to control the function of the ventilation system. Industry standard for these control functions is the 0 -10 V output, but there are other varieties in use. These can be readily accommodated in the construction or calibration of the system to ensure a high quality of indoor climate control. Perhaps we have finally seen the end to Sick Building Syndrome and can now enjoy the benefits of a controlled climate indoors, if not outdoors.

What type of sensors are used in madur instruments?

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Most of the sensors used in madur flue-gas analysers are of the electrochemical type.

The major elements of Toxic Gas electrochemical sensors are three coated electrodes (sensing, counter, and reference) and a small volume of an acidic or alkaline solution.

In use, the gases diffuse through an orifice on the sensing face of the sensor onto the electrode surface and cause a small electrical current. This current is amplified and measured by the electronics. The measured value is then displayed and available for printing, storing or downloading to a computer.

In its simplest form, a sensor operating on electrochemical principles requires two electrodes x a sensing and a counter x separated by a thin layer of electrolyte. Gas diffusing to the sensing electrode reacts at the surface of the electrode either by oxidation or reduction. This reaction causes the potential of the electrode to rise or fall with respect to the counter electrode. With a resistor connected across the electrodes, a current is generated which can be detected and used to determine the concentration of gas present.

One of the conditions required for the above sensor to work accurately is that the potential of the counter electrode should remain constant. In reality, however, the surface reactions at each electrode causes them to polarise. This effect may be small initially, but it increases with the level of reactant gas and effectively limits the concentration range the sensor can be used to measure. This effect can be counteracted by the introduction of a reference electrode of stable potential.

The reference electrode is shielded from any reaction, and so maintains a constant potential. Instead of the signal therefore being measured between the counter and sensing electrodes, it can now be more accurately measured between reference and sensing. With this arrangement, the change in potential of the sensing electrode is due solely to the current generated at the electrode by the reactant gas.

As the reference electrode must maintain a constant potential for correct operation, it is important that no current is drawn from this electrode. In order therefore to measure the potential difference between sensing and reference, it is not sufficient just to place a load resistor across them, as this would draw current. For this reason a potentiostatic feedback operating circuit is used.

The oxidation of carbon monoxide, for example, at the sensing electrode can be represented by the equation:

CO + H2O ===> CO2 + 2H+ + 2e-

The counter electrode acts to balance out the reaction at the sensing electrode by reducing oxygen in air to water:

1/2O2 + 2H+ + 2e- ===> H2O

A similar equation can be given for other sensors depending on the reaction of the gas they are designed for on the sensing electrode:

Sulphur dioxide: SO2 + 2H2SO4 ===> CO2 + 2H+ + 2e-

Nitric oxide: NO + 2H2O ===> HNO3 + 3H+ + 3e-

Nitrogen dioxide: NO2 + 2H+ + 2e- ===> NO + H2O

Toxic sensor construction

Oxygen sensors are slightly different. In use, oxygen diffuses through a membrane and the gas contacts the sensing electrode and the base solution and reacts at the wet surface of the electrode, this reaction consumes the counter electrode. The chemical change in the counter electrode allows a circuit in the instrument to measure a potential (voltage) between the electrodes. In reality, the oxygen sensor acts as a current source, so the voltage measurement must be carried out over a load resistor. This should not be large, otherwise the balance ofthe oxygen circuit will be upset.

Oxygen sensor construction

All oxygen sensors used are of the self-powered, diffusion limited, metal-air battery type comprising an anode, electrolyte and an air cathode as shown below.

At the cathode oxygen is reduced to hydroxyl ions according to the equation:

O2 + 2H2O + 4e- ===> 4OH-

The hydroxyl ions in turn oxidise the metal anode as follows:

2Pb + 4OH- ===> 2PbO + 2H2O + 4e-

Overall the cell reaction may be represented as:

2Pb + O2 ===> 2PbO

The oxygen sensors used are current generators, and the current is proportional to the rate of oxygen consumption (Faraday's Law). This current can be measured by connecting a resistor across the output terminals to produce a voltage signal. If the passage of oxygen into the sensor is purely diffusion limited, this signal is a measure of oxygen concentration.

Other types of sensors may also be used, such as infrared sensors.

The Modern Importance of Biogas

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The use of biogas is increasing rapidly rapidly today for a number of reasons:

1. Fuel costs have been rising steadily for a number of years and the taxation burden increases as well, leading to a double load ofr the user to bear.
2. Attempts are now being made to improve the use of renewable energy sources.
3. The gas produced, mainly methane, is one of the major causes of the greenhouse effect.
4. The production is possible in small scale sites, obviating the need to supply energy to outlying areas.
5. Even a very basic construction using mostly used materials will produce gas if a few simple design rules are followed.

This is not meant to be a construction guide for biodigesters or any of the other equipment needed for this purpose, it is rather a discussion of the control systems in use for the landfill schemes that are in use in many countries already.

Nevertheless, a few points are worthy of mention. The links below will give some good information on this topic and hopefully clear up any queries that you might have.

The gas produced and the slurry being fermented are corrosive. This means that some of the fittings must be made of corrosion-proof material. Plastic can be used for many things, but where pressure and sunlight are involved, then stainless steel may be needed. Again, as the gas is corrosive due to the presence of hydrogen sulphide and other impurities, it may have to be collected in a stainless steel tank in some cases. The cost for such materials is high and may be prohibitive, but larger industrial systems will be forced to go in this direction to get a useful working life. Stainless steel is not cheap, but it has properties that make its use essential sometimes.

The gas produced may be used for a number of purposes, but one of the main uses in larger plants is driving engines for production of electricity. To this end it is essential to know the concentration of methane in the gas, allowing the mixture to be adjusted appropriately. The level of carbon dioxide and proportion of methane will give valuable information about the state of the fermentation process as well. Infrared sensors are the best means employed today for this purpose. The need for calibration is minimal or nonexistent and the small size, relatively low cost and minimal power consumption make them ideal for this type of application. Combined heat and power uses are increasingly common. This is probably the most effective use of the biogas produced, although there will be cases where the heat is more difficult to use profitably. In industrial schemes where there is a steady demand for steam or other heat resources, this will present no problem, but areas using the power for residential purposes will find the demand for heat is very much lower in summer than in winter for obvious reason, whilst the demand for electricity will be reduced, but not as greatly.

Infrared sensors may be of the more expensive two channel variety or the more popular single channel sensor. Whilst more prone to drift, single channel sensors are usually more than adequate for this task. Very small, househod schemes will get by without any form of sensor being used, but any scheme that relies on selling the gas will have to ensure and prove a constant quality of service.

Measurements of carbon dioxide and methane in biogas have, nevertheless, shown a marked deviation from the behaviour of an ideal gas, with the sum of the calcualted partial pressures not equalling the total pressure. The result of these measurements must be taken into account in all cases where both sensors are employed.

Measurements in biogas

Biogas calculator

Calculates the number of a type of animal needed to drive a desired size of engine.

CONTINUOUS EMISSIONS MONITORING

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GENERAL

A continuous emissions monitor is basically a flue gas analyser designed for fixed use and to monitor permanently. Having said this, there are many differences in the construction of the instruments to reflect these differing roles. A portable flue gas analyser must be light enough to carry around all day, yet strong enough to cope with the knocks and general ambient conditions of the industrialContinuous emissions monitor - CEMS workplace. A continuous emissions monitor is fixed to the wall, so weight is not really a major consideration. If it is in a sealed cabinet with its own filter system for cooling air and supply of mains power, then it can be built very much more robustly than the portable flue gas analyser. The continuous emissions monitor (after this it will be referred to as CEMS - Continuous Emissions Monitoring System) is, nevertheless, exposed to the heat and dust of the industrial environment on a permanent basis, so the cabinet and filter system must be able to deal with extreme conditions without letting contaminants through or losing the cooling effect needed to keep the CEMS working at optimal efficiency.
CONSTRUCTION OF A CEMS

As stated above, a CEMS will generally be mounted in a cabinet or will be a sealed unit in some way. Since these analysers are often mounted outdoors, there is a need for mounting enclosures. Due to the environmental conditions in many of these areas, such enclosures have to counteract extremes of heat, cold and humidity, without the electronics inside being affected. This will require heating or air conditioning units to be mounted on the enclosures, insulation against heat or cold to reduce the power drain of the utilities and possibly some form of extra shading from extreme sunlight or snowstorms. Connections to the outside will tend to be waterproof and as well sealed as possible.
INSTALLATION OF A CEMS

A CEMS is usually designed for a particular job or to cover a particular set of regulations. All the wiring will be fixed and the unit is left alone except for periodic maintenance. CEMS units will often be complete with an automatic calibration system. A group of various people will be needed to fit a CEMS. The manufacturer will want to ensure that the equipment is installed correctly. Electricians and technicians for the various utilities will need to complete their part of the operation, and then the signal outputs or data processing system for the CEMS will need to be tested for a period of time. This period of testing can often be several weeks, a month is not uncommon. This allows the operator to be certain that data from the continuous emissions monitor will be transferred and stored under all operational conditions.
OPERATION OF A CEMS

A CEMS will mostly operate unattended. Periodic checks for condition of filters and other general maintenance tasks will be carried out on a fixed schedule dependent on the application and experience of the individual operator. Some continuous emissions monitoring systems will have an automatic calibration function that enables the instrument to switch to locally stored standard gas cylinders and perform a span calibration without intervention. Other CEMS installations will require manual calibration at set intervals.

TECHNOLOGY OF A CEMS
Sensor technology

Continuous emissions monitors have been built using most types of sensor technology. There are systems in use using electrochemical, infrared, ultra-violet, chemiluminescent and other measurements for the toxic gases, whilst oxygen measurements are mainly carried out with electrochemical, zirconium or paramagnetic sensors. All these methods have their own advantages and drawbacks, be it technological or financial. In earlier days the only common and affordable technology was electrochemical measurement, which led to a very hard life for the sensors. The electrochemical sensors are not designed for permanent use. They require short pauses with fresh air to regain a zero point and regenerate generally. Failure to adhere to this will lead to a very rapid demise of the sensor and a poor quality of measurement whilst the sensor is operating. There are a number of solutions to this problem, the simplest being to switch the sensors to fresh air for a certain proportion of the time. This may, however, cause difficulties with national regulations that insist on an unbroken measurement of the gas concentrations. It may also be a problem when the output signals from the CEMS are used as part of the control system for the burner system, as is becoming more common. The next variation was to have two or more banks of sensors, that are rotated from fresh air to measurement and then back again. The next advantage is that calibration of the sensors can be carried out when they are not in use, preventing any interruption to operation. This system is still quite common and has proved itself time and time again in practice. The major disadvantage is cost. The extra sensors cost money, as does the technology to switch gas inlets and signals between the banks. Nevertheless, these systems are very popular, despite the additional equipment increasing the maintenance needs of the system. Infrared systems were common in continuous emissions monitors long before they were considered for portable equipment. The higher cost for this technology was not such a disadvantage in the CEMS branch, and the advantage of less maintenance needs was more important. Infrared sensors are inherently more stable, although they also require occasional zeroing for good repeatability. The calibration of infrared sensors is also necessary, although they will remain more stable than their electrochemical counterparts.
Cooling Technology

Since continuous emissions monitors are inherently large installations that will not be moved, most of the cooling systems work on the refrigerant principle. These coolers require much less power than the Peltier coolers used on portable equipment, despite their other disadvantages. Some way of removing the heat will nevertheless be needed, as will an outlet for condensate. Permeation dryers are another alternative method of drying the gas when space and power supply are not a problem. These dryers use the different size of the molecules to remove components selectively from a mixed stream. CEMS installations utilising electrochemical sensors will require a certain level of moisture in the gas, which may not be achieved when using the most effective refrigerant dryers. The time spent purging with fresh air should make up for this deficiency and prevent damage. Infrared sensors do not suffer from this drawback and will work best if the gas is completely dry. There are two basic possibilities for the placement of the cooling unit: near the stack, or with the CEMS. This choice will be dependent on the site and how far from the stack the CEMS must be placed.
Sampling technology

This description is concerned with extractive systems that remove a sample continuously from the stack and transport it to an analysis unit. In-situ and cross-stack methods have their own adherents and advantages. A probe of some sort will have to be installed in the stack to provide an appropriate sampling point. A heated filter will be needed to remove the largest particles that would otherwise block the transport line. This filter must be kept at a consistent high temperature to prevent condensation forming. The place must be chosen to allow regular inspection and changing of the filter elements. A differential pressure sensor can simplify the inspection of the filter elements. The gases must be transported to the cooling unit with a heated hose to ensure that absolutely no condensation can occur in transport. Such heated hoses are generally kept at about 180°C to leave some margin for error. Depending on the relative positioning of sample point and CEMS, the position of the cooling unit and hence the length of the heated hose will be decided. A heated hose requires about 100 Watts of power per metre of length, so long hoses are to be avoided if possible. From the cooling unit to the CEMS a length of standard tubing can be used, saving energy and installation costs.
Data output technology for a CEMS

The data outputs can be analogue, digital, or a combination of both. Digital outputs can be directly fed into a computer programme for data treatment, but do not lend themselves easily to use as control parameters. If the CEMS is to be included in the control system for the burner, then analogue outputs simplify the matter greatly. Current outputs are more appropriate than voltage outputs in most cases, since the distances to be covered are often large. Digital outputs with appropriate software are common with most types of continuous emissions monitoring systems. The data is presented in a form that can be easily understood by laypeople or sent on electronically to the appropriate authorities. One of the great advantages of digital information is that it can be sent by wireless, avoiding the laying of extra data cables. Provided line of sight transmission is given, this can be achieved with very low power levels.

Oxygen Sensors

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There are a number of possible methods to measure the concentration of oxygen in a gas sample. By far the most common is the electrochemical sensor to measure the concentration directly. The methods regularly used to measure oxygen are:

Electrochemical sensor

Partial pressure sensor

Zirconia sensor

Paramagnetic measurement.

These systems all have advantages and disadvantages for use in a flue gas analyzer, as will be discussed below.
Electrochemical Sensor:

The electrochemical sensor is, as stated above, by far the commonest type used in a flue gas analyzer. The basic functioning of an oxygen sensor is similar to a battery. It functions as a current source. The lifetime depends on the amount of electrolyte and material present for the reaction, as well as the exposure to oxygen, but lies generally in the region of one to two years. The link will lead to a more complete explanation. The major disadvantages of the standard electrochemical oxygen sensor are a cross-sensitivity to carbon dioxide and a tendency to form a carbonate layer on the internal lead electrode when high concentrations of carbon dioxide are encountered regularly. Added to the limited lifetime, this is a serious disadvantage. The great advantage is the simplicity of the sensor and measuring circuit, and a relative lack of sensitivity to pressure changes. This last point is particularly important for equipment such as flue gas analyzers that is used in all countries and at all levels.

The lifetime of the electrochemical sensor can be increased by leaving it open circuit when the instrument is switched off, but this has the disadvantage that the sensor takes about 20 minutes to settle down after reconnection. The commonest solution is to short the terminals of the sensor when not in use. This detracts from the lifetime of the sensor, but means that the sensor can be used immediately after switching on. One possible solution is to disconnect the sensor when the instrument will not be used for a longer period of time, but this is a somewhat unsatisfactory answer, and raises questions about warranty conditions.
Partial pressure sensor:

The partial pressure sensor is very similar in construction to the electrochemical sensor in many ways. This sensor is mainly used for medical or diving purposes, where the effect on the human body is the most important aspect of the measurement. Naturally, this sensor can also be used for other purposes, such as flue gas analyzers. It has the major advantage of not being sensitive to carbon dioxide, which is a major point when biogas measurements are considered. Since this sensor measures the partial pressure of oxygen directly, it is essential to compensate for ambient pressure if a concentration is needed as a result, which is the case with a flue gas analyzer, for instance. With an ambient pressure sensor, the partial pressure sensor can be used outside of the normal pressure range for an electrochemical oxygen sensor (typically atmospheric +/-10 %) and still measure accurately.
Zirconia sensor:

This has always been popular for fixed flue gas analyzers, so-called CEMS. It has advantages, in that it is not sensitive to carbon dioxide, and can also be used inside the stack, not requiring extractive technology. The most common use, however, is for installations where only oxygen is to be measured, for control of a burner system or chemical process, such as heat-treatment. It is also used in the medical sector, and produces very accurate results if used correctly. Below is a short description of the operating theory.
Principles of Operation

Pure zirconium oxide is a monoclinic crystalline material that transforms reversibly to a tetragonal form at 1000°C with a large change in volume. If placed in solid solution, however, with 4 % to 12 % MgO, CaO or Y2O3, it is held in the stable isometric (cubic) form which has no transformation in the range of normal flue temperatures. Due to the addition of these stabilizing oxides, oxygen ion vacancies are created in the crystal lattice. The mobility of O2- ions is greatly enhanced, and under specific conditions of temperature and composition, the conductivity is entirely due to oxygen ions. This condition coincides with the existence of the pure cubic crystalline phase, and is responsible for the oxygen sensing capability of stabilized zirconia.

A minimum quantity of the stabilizing oxides will ensure the existence of the pure cubic crystalline phase of zirconia. When this amount is present, the zirconia is said to be fully stabilized. The commercially available zirconia for oxygen sensors will have generally somewhat less than this minimum amount, resulting in a "partially stabilized" electrolyte with a better resistance to thermal fracture. The zirconia in average sensors contains about 6 mole % (10.5 weight %) of Y2O3. The cell construction demonstrates a characteristic typical of electrolytes having unity transference numbers for an ionic species; there is an electromotive force displayed at the terminals that can be precisely related to the corresponding molecular concentration at the two surfaces. In the case of cubic zirconia, the cell voltage is given by a form of the Nernst equation,

UC = -0.01528TK log10(p0/p1) millivolts

where TK is the absolute temperature in Kelvin, p0 and p1 are the oxygen concentrations at the inner and outer electrodes respectively.

The major disadvantages of the zirconia sensor are a strong cross-sensitivity to any combustible gases and a sensitivity to dirt in the gas. Whilst this is not a problem in medical applications, a flue gas analyzer is often required to measure dirty gases where combustibles may be found.
Paramagnetic sensor:

The paramagnetic oxygen sensor is a highly accurate measurement technique for oxygen concentration. The major disadvantage to this method is the price. Below is the theory of this type of measurement:
Magnetic properties of gases

All paramagnetic measuring instruments available on the market today utilize the paramagnetic properties of oxygen. Oxygen is one of very few gases with a strong magnetic susceptibility. The movement of the electrons within a molecule generates magnetic moments. A distinction must be made in this context between:

- orbital magnetic moment: movement of electrons around the nucleus, within the orbitals

- spin magnetic moment: the electron's own rotation

External magnetic fields influence these magnetic moments, causing them to align. The orbital magnetic moment responds diamagnetically, in other words aligns in the opposite direction to the external field, thereby weakening it. In contrast, the spin magnetic moment responds paramagnetically, i.e. aligns parallel to the external field and hence strengthens it. Depending on the structure of a molecule, the orbital and spin magnetic moments will be more or less strongly marked, which in turn results in the different magnetic properties of gases. Oxygen has strong paramagnetic properties, while nitrogen responds diamagnetically.
Principle of measurement

There are various different principles of paramagnetic measurement, though in recent years the magnetomechanical or "dumb-bell" principle has come to be used in most measuring instruments. The principle of measurement is based on a sensor in which a dumb-bell comprising two nitrogen-filled spheres is arranged in rotational symmetry within a magnetic field. The gas to be measured passes through the sensor. If the sample gas contains oxygen, the oxygen is drawn into the magnetic field on account of its paramagnetic properties as described above, thereby strengthening the field. The nitrogen inside the glass spheres has the opposite magnetic polarization and is forced out of the field, causing the dumb-bell to rotate. The degree of rotation is directly proportional to the oxygen concentration. To reduce sensitivity to vibration, the dumb-bell's rotation is no longer measured directly in modern sensors. Instead, a mirror is attached at the dumb-bell's rotational axis and symmetrically reflects a beam of light onto a pair of photocells. When the dumb-bell starts to rotate, a potential difference is generated at the photocells. The resulting current is amplified and conducted around the dumb-bell through windings. The current flow generates an electromagnetic countermoment which causes the dumb-bell to return to its original position. The current needed to maintain the dumb-bell in its null position is directly proportional to the oxygen concentration.
Conclusion:

Despite years of using the standard electrochemical sensor, the partial pressure sensor is now becoming very attractive due to its lack of reaction to CO2. This is a cumulative action, where the lead electrode slowly reacts with carbon dioxide to form lead carbonate, and effectively shield the electrode from further reaction. There are appropriate ambient pressure sensors on the market at a reasonable price, which makes it quite possible to change the type without great difficulty. The Photon may well be fitted with the partial pressure sensor as standard, as will any flue gas analyzer intended for use with biogas or fitted with a CO2 sensor measuring in excess of 25 % carbon dioxide. There will in future be a conversion kit, allowing standard electrochemical oxygen sensors to be converted to the partial pressure sensor in most flue gas analyzers.

The zirconia sensor is well-known in most countries and is required in some of them. Despite its disadvantages and higher cost, it will remain popular for its simplicity of use, particularly where only oxygen is to be measured for control purposes. It will in future at some point be possible to connect a zirconia sensor to the stationary analyzers, to cover this need. Nevertheless, it will never be the mainstay of oxygen measuring technology for portable flue gas analyzers.

The paramagnetic sensor is a wonderfully accurate piece of technology, but both too expensive and too fragile for use in portable equipment. The paramagnetic sensor is used in many CEMS constructions, often as a standard requirement.

For portable use, the partial pressure sensor will possibly become the sensor of choice for many flue gas analyzer applications in the future, not least for its increased lifetime of about five years.

Zirconium Oxide Oxygen Analyzer

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The type of oxygen analyzer that uses this type of oxygen sensor is occasionally referred to as the “high temperature” electrochemical sensor and is based on the Nernst principle [W. H. Nernst (1864-1941)]. Zirconium oxide sensors use a solid state electrolyte typically fabricated from zirconium oxide stabilized with yttrium oxide. The zirconium oxide probe is plated on opposing sides with platinum which serves as the sensor electrodes. For a zirconium oxide sensor to operate properly, it must be heated to approximately 650 degrees Centigrade. At this temperature, on a molecular basis, the zirconium lattice becomes porous, allowing the movement of oxygen ions from a higher concentration of oxygen to a lower one, based on the partial pressure of oxygen. To create this partial pressure differential, one electrode is usually exposed to air (20.9% oxygen) while the other electrode is exposed to the sample gas. The movement of oxygen ions across the zirconium oxide produces a voltage between the two electrodes, the magnitude of which is based on the oxygen partial pressure differential created by the reference gas and sample gas. The zirconium oxide oxygen sensor exhibits excellent response time characteristics. Another virtue is that the same sensor can be used to measure 100% oxygen, as well as parts per billion concentrations. Due to the high temperatures of operation, the life of the sensor can be shortened by on/off operation. The coefficients of expansions associated with the materials of construction are such that the constant heating and cooling often causes “sensor fatigue”. A major limitation of the zirconium oxide oxygen analyzer is their unsuitability for trace oxygen measurements when reducing gases (hydrocarbons of any species, hydrogen, and carbon monoxide) are present in the sample gas. At operating temperatures of 650 degrees Centigrade, the reducing gases will react with the oxygen, consuming it prior to measurement thus producing a lower than actual oxygen reading. The magnitude of the error is proportional to the concentration of reducing gas. The zirconium oxide oxygen analyzer is the “defacto standard” for in-situ combustion control applications.

Other types of oxygen analyzer types under development and in some cases being used for specific applications. They include, but are not limited to, luminescence polarization, opto-chemical sensors, laser gas sensors, et al. As these techniques are further developed and improved, they may represent viable alternatives to the existing technologies used in today's oxygen analyzer.

Polarographic Oxygen Analyzer

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The oxygen analyzer that features a polarographic oxygen sensor is often referred to as a Clark Cell [J. L. Clark (1822- 1898)]. In this type of sensor, both the anode (typically silver) and cathode (typically gold) are immersed in an aqueous electrolyte of potassium chloride. The electrodes are separated from the sample by a semi-permeable membrane that provides the mechanism to diffuse oxygen into the sensor. The silver anode is typically held at a potential of 0.8V (polarizing voltage) with respect to the gold cathode. Molecular oxygen is consumed electrochemically with an accompanying flow of electrical current directly proportional to the oxygen concentration based on Faraday's law. The current output generated from the sensor is measured and amplified electronically to provide a percent oxygen measurement. One of the advantages of the polarographic oxygen sensor is that while inoperative, there is no consumption of the electrode (anode). Storage times are almost indefinite. Similar to the galvanic oxygen sensor, they are not position sensitive. Because of the unique design of the polarographic oxygen sensor, it is the sensor of choice for dissolved oxygen measurements in liquids. For gas phase oxygen measurements, the polarographic oxygen analyzer type is suitable for percent level oxygen measurements only. The relatively high sensor replacement frequency is another potential drawback, as is the issue of maintaining the sensor membrane and electrolyte.

A variant to the polarographic Oxygen Analyzer is what some manufacturers refer to as as oxygen analyzer that uses a non-depleting coulometric sensor where two similar electrodes are immersed in an electrolyte consisting of potassium hydroxide. Typically, an external EMF of 1.3 VDC is applied across both electrodes which acts as the driving mechanism for reduction/oxidation reaction. The electrical current resulting from this reaction is directly proportional to the oxygen concentration in the sample gas. As is the case with other sensor types, the signal derived from the sensor is amplified and conditioned prior to displaying. Unlike the conventional polarographic oxygen sensor, this type of sensor can be used for both percent and trace oxygen measurements. However, unlike the zirconium oxide, one sensor cannot be used to measure both high percentage levels as well as trace concentrations of oxygen. One major advantage of this sensor type is its ability to measure parts per billion levels of oxygen. The sensors are position sensitive and replacement costs are quite expensive, in some cases, paralleling that of an entire oxygen analyzer of another sensor type. They are not recommended for applications where oxygen concentrations exceed 25%.

Paramagnetic Oxygen Analyzer

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Within this category, the magnetodynamic or `dumbbell' type of design is the predominate sensor type. Oxygen has a relatively high magnetic susceptibility as compared to other gases such as nitrogen, helium, argon, etc. and displays a paramagnetic behavior. The paramagnetic oxygen sensor consists of a cylindrical shaped container inside of which is placed a small glass dumbbell. The dumbbell is filled with an inert gas such as nitrogen and suspended on a taut platinum wire within a non-uniform magnetic field. The dumbbell is designed to move freely as it is suspended from the wire. When a sample gas containing oxygen is processed through the sensor, the oxygen molecules are attracted to the stronger of the two magnetic fields. This causes a displacement of the dumbbell which results in the dumbbell rotating. A precision optical system consisting of a light source, photodiode, and amplifier circuit is used to measure the degree of rotation of the dumbbell. In some paramagnetic oxygen sensor designs, an opposing current is applied to restore the dumbbell to its normal position. The current required to maintain the dumbbell in it normal state is directly proportional to the partial pressure of oxygen and is represented electronically in percent oxygen. There are design variations associated with the various manufacturers of magnetodynamic paramagnetic oxygen analyzer types. Also, other types of sensors have been developed that use the susceptibility of oxygen to a magnetic field which include the thermomagnetic or `magnetic wind' type and the magnetopneumatic sensor. In general, paramagnetic oxygen sensors offer very good response time characteristics and use no consumable parts, making sensor life, under normal conditions, quite good. It also offers excellent precision over a range of 1% to 100% oxygen. The magnetodynamic sensor is quite delicate and is sensitive to vibration and/or position. Due to the loss in measurement sensitivity, in general, the paramagnetic oxygen sensor is not recommended for trace oxygen measurements. Other gases that exhibit a magnetic susceptibility can produce sizeable measurement errors. Manufacturers of the paramagnetic oxygen analyzer should provide details on these interfering gases.

Oxygen Analyzer

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Today's oxygen analyzers use one of a several types of oxygen sensors. As industrial process applications call for improved measurement accuracy and repeatability, users of oxygen analyzers are also demanding oxygen analyzers that require a minimum of maintenance and calibration. To this end, users of oxygen analyzers are encouraged to evaluate the merits of a particular oxygen sensor type in context to the application for which it is intended. There is no one universal oxygen analyzer type.

The synoptic review of the various gas phase oxygen sensors provided below should be used in conjunction with information gathered from manufacturers of oxygen analyzers. This combination will help to ensure the selection of the right sensor type for the application under consideration.

Oxygen Analyzer with Ambient Temperature Electrochemical Oxygen Sensors.
Electrochemical-Oxygen Analyzer:

The ambient temperature electrochemical sensor, often referred to as a galvanic sensor, is typically a small, partially sealed, cylindrical device (1-1/4” diameter by 0.75” height) that contains two dissimilar electrodes immersed in an aqueous electrolyte, commonly potassium hydroxide. As oxygen molecules diffuse through a semi-permeable membrane installed on one side of the sensor, the oxygen molecules are reduced at the cathode to form a positively charge hydroxyl ion. The hydroxyl ion migrates to the sensor anode where an oxidation reaction takes place. The resultant reduction/oxidation reaction generates an electrical current proportional to the oxygen concentration in the sample gas. The current generated is both measured and conditioned with external electronics and displayed on a digital panel meter either in percent or parts per million concentrations. With the advance in mechanical designs, refinements in electrode materials, and enhanced electrolyte formulations, the galvanic oxygen sensor provides extended life over earlier versions, and are recognized for their accuracy in both the percent and traces oxygen ranges. Response times have also been improved. A major limitation of ambient temperature electrochemical sensors is their susceptibility to damage when used with samples containing acid gas species such as hydrogen sulfide, hydrogen chloride, sulfur dioxide, etc. Unless the offending gas constituent is scrubbed prior to analysis, their presence will greatly shorten the life of the sensor. The galvanic sensor is also susceptible to over pressurization. For oxygen analyzer applications where the sample pressure is > 5 psig, a pressure regulator or control valve is normally recommended.

Large-Signal Network Analyzer (LSNA)

2008-11-12T17:22:00.000-08:00

Details

The Maury/NMDG Large-Signal Network Analyzer (LSNA) is the latest advancement in large-signal network analysis. It was developed by NMDG Engineering and Maury Microwave, using technology licensed to Maury by Agilent Technologies (patents pending). It combines a unique set of hardware and software tools that calibrate and measure non-linear component characteristics, with mathematical tools for describing and interpreting non-linear behavior. The LSNA is, at present, the only commercially available solution that provides for accurate and complete measurement of two-port DUT characteristics in large-signal environments where non-linear component behavior may occur.

Applications

* Transistor reliability/Repeatability
* Breakdown Current
* Forward Gate Conductance
* Transistor model qualification under realistic large-signal conditions
* Transistor model improvement using realistic large-signal measurements
* Application of PA design theory through waveform engineering
* Resistive Mixer Studies
* System-level studies using simple-to-complex signals with a single connection

Benefits

* Comprehensive understanding of complete large-signal DUT behavior under realistic RF or µwave excitation
* Reduced manufacturing costs by minimizing design cycles
* Optimize model parameters to LSNA measurements
* Benchmark a wide range of device models (e.g., BSIM, MM11, EKV, VBIC, MEXTRAM, HICUM, etc.)
* Higher confidence in your model versus small-signal modeling techniques

System Concept

The LSNA is designed to measure incident and scattered traveling voltage waves (or voltages and currents) in time, frequency domain or time-frequency domain (related to envelope simulation), as they appear at both signal ports of any two-port DUT under-going periodically modulated excitation. This is done while taking into account the possible interactions of what might be less-than-ideal qualities of the instrument in relation to the signal environment. This information represents the complete large-signal (non-linear) behavior of a device. The LSNA is a unique tool that measures the relevant spectral components of a two-port DUT under periodic, realistic RF or microwave excitation, and displays the resulting data as, a) Physical Quantity Sets (i.e., V-I and A, B) and b) Representation Domains (i.e., frequency (ƒ), time(t), and envelope). The measured data can be linked into other tools like ADS and ICCCAP using the supported CITIFile format.

Microwave Transition Analyzer

2008-11-12T17:17:00.000-08:00

The microwave transition analyzer brings time-domain analysis to RF and microwave component engineers. A very wide-bandwidth, dual-channel front end, a precisely uniform sampling interval, and powerful digital signal processing provide unprecedented measurement flexibility, including the ability to measure magnitude and phase transitions as fast as 25 picoseconds.

As signal processing capabilities advance, modern microwave and radio frequency (RF) systems are becoming more and more sophisticated. Pulsed-RF signals, once used only for radar applications, are increasingly being used in communication systems as well. These signals routinely have complex modulation within the pulse, especially frequency and phase variations (see Fig. 1). Operating frequencies and bandwidths continue to increase, placing additional demands on the components of the systems.

Engineers responsible for the design and testing of such components and systems often need to measure them under the same dynamic conditions as those in which they are used. For example, it may be necessary to measure a device's response to phase coding or linear frequency chirp inside an RF pulse.

Measurements with traditional frequency-domain instrumentation are often insufficient to characterize and understand fully the operation of components in dynamic signal environments. Before the microwave transition analyzer introduced in this article, no single instrument could handle the diverse range of measurements required for dynamic testing at microwave frequencies. In addition to the new measurements it makes, this analyzer can perform many of the measurements previously requiring the use of network, spectrum, dynamic signal, and modulation analyzers, as well as oscilloscopes, counters, and power meters.

Importance of the Time Domain

A key benefit of the microwave transition analyzer is that it brings time-domain analysis to RF and microwave component engineers. In addition to its use in pulsed-RF testing, the time domain is essential to characterizing and understanding nonlinear devices because one can clearly and intuitively see the relationship between the input and output signals. As an example, both signals in Fig. 2 would appear identical if displayed on a spectrum analyzer. Even if the phase of the harmonics were known, the differences between the signals would not be immediately obvious. When viewed in the time domain, however, it is clear that signal 1 is clipped (the output of a limiter, say), while signal 2 has crossover distortion (what might be seen at the output of a Class-B amplifier, for example). Without the time domain, engineers have had to guess at the underlying causes of observed frequency-domain behavior. The ability to view microwave signals in the time domain has also proved to be extremely valuable to designers that are using CAE microwave design simulators, such as HP's MDS. Now simulations based on circuit models can be easily compared to actual measurements in both the time domain and the frequency domain.

Historically, most measurements on high-frequency nonlinear devices have been performed in the frequency domain. Often, this has been because of inadequacies in time-domain instrumentation. When frequency-domain information is of prime concern, spectrum analyzers are superb in their ability to display harmoniC, modulation, and spurious signals with a large dynamic range. However, without the phase of the frequency components, the time-domain signal cannot be reconstructed. Network analyzers are excellent for performing linear, small-signal, frequency-domain testing, but they are limited in their ability to characterize nonlinear devices. The addition of harmonic and offset sweep capability in network analyzers has helped, but the time-domain perspective is still missing.

For envelope analysis of pulsed-RF signals, spectrum analyzers offer some limited time-domain capability. Recently, network analyzers have been adapted for pulsed-RF timedomain testing as well. Because of the architecture of these instruments, the intermediate frequency (IF) bandwidth imposes an upper limit on the measurement bandwidth. The result is minimum measurable edge times of greater than 100 ns. The microwave transition analyzer's architecture does not have this restriction. Edge speed is limited only by the RF bandwidth. Consequently, magnitude and phase measurements on pulses with rise times as fast as 25 ps are possible. Fig. 3 shows an example of a microwave transition analyzer measurement.

The ability to measure narrow pulses in the time domain can also be used to determine the impulse response (and therefore magnitude, relative phase, and group delay) of frequency translation components such as mixers and receivers. By stimulating these devices with a narrow 'pulse of RF energy, -time-domain distortion can be directly observed. Often, it is the time-domain distortion that is of interest, even though it may be specified indirectly as magnitude and phase flatness versus frequency. By transforming the input and output pulses to the frequency domain with the built-in fast Fourier transform (FFT) and computing their ratio, the transfer function is obtained. From this, familiar results of magnitude and group delay versus frequency can be displayed. Network analyzers are only able to measure the phase and group delay of frequency translation components relative to a reference or "golden" device.

Automatic Network Analyzer

2008-11-12T17:15:00.000-08:00

BACKGROUND

The present invention relates generally to test equipment, and more
particularly, to an automatic network analyzer that measures continuous
wave radio frequency microwave driven transfer characteristics of
nonlinear devices and simultaneously calculates and displays corresponding
noise driven transfer characteristics and noise power ratio (NPR).

Previously, to obtain CW and noise transfer characteristics, including
noise power ratio (NPR), two separate sets of test equipment were
required, including one for CW measurements and a separate one for noise
measurements. Equipment required for noise measurements includes power
meters, spectrum analyzers and noise spectrum generating equipment.
Simulation of noise parameters may be accomplished with the use of a
separate communication software program on a separate computer.

In order to simplify the testing equipment, it would be advantageous to
have an automatic network analyzer that includes both noise and noise
power ratio measurement capability.

SUMMARY OF THE INVENTION

Tile present invention provides for a piece of test equipment comprising an
automatic network analyzer that measures continuous wave (CW) radio
frequency (RF) microwave driven transfer characteristics of nonlinear
devices and simultaneously calculates and displays corresponding noise
driven transfer characteristics and noise power ratio (NPR). The automatic
network analyzer combines the functionality of a conventional automatic
network analyzer with the ability to calculate noise parameters that
otherwise would have to be measured using separate test equipment.

The automatic network analyzer employs software or firmware that uses
closed form equations to exactly calculate noise parameters. This is done
in real-time as CW measurements are taken. Integrating the ability to make
these noise calculations and display results of the calculations
simultaneously with the CW measurements allows hardware designers the
ability to view results of adjustments to devices under test as they are
made. This is done with one piece of integrated test equipment. No other
known automatic network analyzer can view CW measurements and calculated
noise data simultaneously.

The equations are preferably provided in firmware employed in the test
equipment and use exact closed form equations to obtain predicted noise
data. To obtain noise results using currently available test equipment,
they must be either measured or simulated. Measurement normally requires
separate equipment set-up. Simulation also normally requires separate
equipment and software. Both of these testing endeavors can be expensive
and time consuming. The present automatic network analyzer provides a user
a way to see noise data in real time and allows for decreased test and
troubleshoot time during design and production of nonlinear devices, for
example.

TAPR Vector Network Analyzer

2008-11-12T17:13:00.001-08:00

The TAPR Vector Network Analyzer is a low-cost Vector Network Analyzer (VNA) that operates from 200 kHz to 100 MHz, and connects to a personal computer using a USB 1.1 interface.

The VNA is one of the more useful pieces of test equipment for designers and experimenters. It can measure the forward and reverse gain and phase response of a circuit, and the input and output reflection properties (complex impedance). The VNA is used to measure and adjust filters, coaxial cables, amplifiers, antenna input impedance vs. frequency, just to name a few.

QEX July/August 2004 The July/August 2004 QEX article discusses the design of the measurement hardware, control processor software on the instrument itself, and the software on a personal computer that controls and displays the measurements.

8757D Scalar Network Analyzer

2008-11-12T17:09:00.000-08:00

The Agilent 8757D scalar network analyzer allows you to measure insertion loss, gain, return loss, SWR, and power quickly and accurately . With high-performance detectors and directional bridges, and a companion Agilent source and printer, this analyzer becomes the basis of a complete measurement system with superb performance.

Setup time is reduced by external disk save/recall, and measurement data can be sent directly to a printer while you proceed to the next measurement.

You can configure your system using an Agilent PSG signal generator with ramp sweep capability. The dynamic range can be extended from 75 dB to 83 dB using the PSG's high power option.

* Up to 83 dB dynamic range
* Buffered plotter/printer output
* Built-in limit testing for quick pass/fail decisions
* External disc and internal register save/recall of test setups
* Color display
* Optional internal power meter calibrator and precision detectors provide near power meter accuracy

The Two Main Categories of Network Analyzers

2008-11-12T17:08:00.000-08:00

Special types of network analyzers can also cover lower frequency ranges down to 1 Hz. These network analyzers can be used for example for the stability analysis of open loops or for the measurement of audio and ultra sonic components.[2]

The two main categories of Network Analyzers are

* Scalar Network Analyzer (SNA) - Measures amplitude properties only
* Vector Network Analyzer (VNA) - Measures both amplitude and phase properties

A VNA may also be called a gain-phase meter or an Automatic Network Analyzer. An SNA is functionally identical to a spectrum analyzer in combination with a tracking generator. As of 2007, VNAs are the most common type of network analyzers, and so references to an unqualified 'network analyzer' most often mean a VNA. The three biggest VNA manufacturers are Agilent, Anritsu, and Rohde & Schwarz.

A new category of network analyzer is the Microwave Transition Analyzer (MTA) or Large Signal Network Analyzer (LSNA), which measure both amplitude and phase of the fundamental and harmonics. The MTA was commercialized before the LSNA, but was lacking some of the user-friendly calibration features now available with the LSNA.