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GASMET FAQ: FREQUENTLY ASKED QUESTIONS PAGE

QUESTIONS REGARDING THE INFRARED PRINCIPLE 2Q: WHAT IS IR? HOW DOES FT-IR WORK? 2Q: WHAT IS AN INFRARED SPECTRUM? 2Q: WHAT IS THE REFERENCE SPECTRUM? 2Q: HOW IS IT POSSIBLE TO MAKE THE QUANTIFICATION? WHAT IS BEER'S LAW? 2QUESTIONS REGARDING GASMET APPLICATIONS AND DETECTION LIMITS 3Q: WHICH GASES CAN BE MEASURED BY THE GASMET? 3Q: WHICH ARE GOOD GASMET APPLICATIONS? 3Q: WHAT IS CEM? 3Q: WHAT IS THE TYPICAL GASMET PERFORMANCE IN CEM APPLICATIONS? 4Q: WHAT ARE THE DETECTION LIMITS FOR COMMONLY MEASURED GASES? 4Q: WHAT IS THE MEASUREMENT ACCURACY? 5Q: WHAT ARE THE MAXIMUM ERRORS IN THE MEASUREMENT FOR EACH OF THE FOLLOWING DX-4000 RANGES? 5Q: WHAT IS THE FACTORY SPECIFIC CALIBRATION? 5Q: WHAT CALIBRATION TECHNIQUES DOES TEMET USE IN THE FACTORY LABORATORY? 6Q: WHICH CALIBRATIONS MUST BE PERFORMED AFTER THE INSTALLATION? 6Q: WHY IS H2O CALIBRATION SO IMPORTANT? 6Q: WHAT IS THE TEMET REFERENCE LIBRARY COLLECTION? 6Q: WHAT IS THE ACCURACY IF ONE USES A REFERENCE SPECTRUM MEASURED BY A 7 DIFFERENT ANALYZER?Q: WHAT IS THE BEST WAY TO ADD NEW GASES TO THE LIBRARY? 7Q: SHOULD THE GASMET BE RECALIBRATED? 8Q: IS IT POSSIBLE TO RECALIBRATE ANY COMPONENT AT THE FACTORY IF THE 8 CUSTOMER REQUESTS IT?Q: HOW STABLE IS THE CALIBRATION? WHY IS IT SO STABLE? 8Q: HOW CAN NO2 BE MEASURED IN THE PRESENCE OF UP TO 45% WATER VAPOUR? 9Q: WHY IS THE LOW RESOLUTION GASMET BETTER FOR QUANTITATIVE GAS ANALYSIS? 10Q: IS IT POSSIBLE TO SHOW IN FIGURES HOW MUCH BETTER IS THE SIGNAL-TO-NOISE RATIO 11 IF RESOLUTION 8 CM-1 IS USED INSTEAD OF RESOLUTION 0.5 CM-1?QUESTIONS REGARDING THE GASMET HARDWARE, LIFE TIME, SPARE PARTS 11Q: HOW IS IT POSSIBLE THAT THE TEMET ANALYZERS ARE SO GOOD AND RUGGED? 11Q: WHAT IS SO SPECIAL IN THE TEMET INTERFEROMETER? 11Q: CAN WE COMPARE THE TEMET INTERFEROMETER TO COMPETITIVE SOLUTIONS? 12Q: WHAT IS SO SPECIAL IN THE TEMET SAMPLE CELL? 12Q: IS IT POSSIBLE TO CHANGE THE SAMPLE CELL OR THE ABSORPTION PATH LENGTH? 13Q: WILL HCL, HF OR SIMILAR COMPONENTS CORRODE THE COATING OF THE 14 “GOLD-PLATED” CELL?Q: WILL CL2 OR BR2 REACT WITH THE GOLD COATING OF THE CELL? 14Q: SHOULD RHODIUM PROTECTION ALWAYS BE RECOMMENDED? 14Q: WHAT HAPPENS IF THE SAMPLE GAS CONDENSES IN THE CELL? 14Q: WILL THE GASMET OPERATE UNDER VACUUM (I.E., REPLACING THE HEATED SAMPLE 14 PUMP WITH EDUCTOR AFTER THE CELL) CONDITIONS?Q: MUST THE SAMPLE CELL ALWAYS BE HEATED AT 180ºC? 14Q: HOW SHOULD THE GASMET BE MAINTAINED? 15Q: HOW IS IT POSSIBLE THAT THE IR SOURCE HAS SO LONG A LIFETIME? 15Q: WHAT IS PRICE FOR THE SPARE PART FOR THE IR SOURCE? 16Q: IS AIR CONDITIONING NEEDED? 16Q: DOES THE GASMET MEASURE THE PRESSURE? 16Q: HOW IS PRESSURE COMPENSATION DONE? 16Q: HOW IS OXYGEN COMPENSATION DONE? WHAT PERCENTAGE? 16Q: HOW MUCH TIME IS REQUIRED FOR THE USUAL TRAINING OF THE DX-4000? 17SOFTWARE QUESTIONS 17Q: WHAT ARE THE SPECIAL FEATURES OF THE TEMET SOFTWARE (CALCMET)? 17

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GASMET FAQ: Frequently Asked Questions

Questions Regarding the Infrared Principle

Q: What is IR? How does FT-IR work?

In infrared spectroscopy, IR radiation is passed through a sample of gaseousmolecules. Some of this radiation is transmitted through while the rest is absorbedby the sample, producing an infrared spectrum, or “molecular fingerprint”. Becauseeach molecular structure has a unique combination of atoms, each produces aunique infrared spectrum. From this, identification (Qualitative analysis) and analysis(Quantitative measurement) of the gas is possible, the two major applications of FT-IR spectrometry.

FT-IR stands for Fourier Transform Infrared, the preferred method of infraredspectroscopy. Since chemical functional groups absorb light at specific frequencies,one can identify the make-up of the sample. As well, through calibration of thespectrometer, one can determine the intensity of the absorption (relates to thecomponent concentration). Knowing the make-up and the concentration of thesample gas is important in many applications.

Q: What is an Infrared Spectrum?

The infrared spectrum is a plot of the sample transmission of infrared radiation as afunction of wavelength. The infrared spectrum results from the interaction of infraredradiation with sample molecules. The wavenumber scale (x-axis) is used to presentthe spectrum, to achieve constant distances between the data points. As there existno two chemicals that would have the same IR spectrum, the infrared spectrum isoften referred to as a "fingerprint" of a molecule. This also explains why the FT-IRanalyzer is so specific when the application is set up correctly.

Q: What is the Reference Spectrum?

The reference spectrum is an infrared spectrum of a known concentration of thetarget substance. During the analysis, all sample spectra are compared to thereference spectra available. The reference spectra form the basis for the calibration.The CALCMET analysis software uses the reference spectra to identify and quantifythe target components.

Q: How is it possible to make the quantification? What is Beer's law?

Measuring the concentration of an absorbing species in a sample is accomplished byapplying the Beer-Lambert law. The Beer-Lambert law is the linear relationshipbetween the absorbancy and concentration of absorbing species. The general Beer-Lambert law is usually written as,

A=a(λλ)*b*cwhere A is the measured absorbance, a(λλ) is a wavelength-dependent absorptivitycoefficient, b is the path length, and c is the analyte concentration. Using this

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formula, the concentration of the component in the sample can be calculated. Theapplicability of the Beer-Lambert law is limited by chemical and instrumental factors.

Questions Regarding the GASMET Applications and Detection Limits

Q: Which gases can be measured by the GASMET?

The GASMET FT-IR gas analyzer can measure any gas, with the exception of thefollowing:

• Noble (or Inert) gases• Homonuclear diatomic gases (e.g., N2, Cl2, H2, F2, etc)• H2S (detection limit too high)

Q: Which are good GASMET applications?

Any measurement of an infrared active gas in concentrations well above thedetection limit are good. Typical measurements include the measurement of processgas or contaminated air.

The majority of analyzers are sold for:- Process control measurements- Exhaust air measurements- Emissions monitoring- Work place monitoring/ industrial hygiene- Various research applications

The GASMET offers its greatest benefits when the customer needs to:1) Analyze several components, or2) Analyze the gas hot/wet (e.g., hot humid applications for HCN, NH3 or HCl etc)3) Analyze any gas in complicated gas mixtures (limited cross interference effects)

Q: What is CEM?

CEM stands for: Continuous Emissions Monitoring

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Q: What is the typical GASMET performance in CEM applications?

The typical performance of GASMET in CEM applications can be seen in the chartbelow. The ranges depend on 1) customer needs, 2) analyzer configuration (i.e. pathlength, detector) and 3) H2O concentration

Compound Typical range Lowest concentration rangeavailable for CEM in wet gas

Highest concentrationranges seen in realcustomer applications

Nitric oxide NO 0-600 mg/m3 0-150 mg/m3 10 000 mg/m3

Nitrogen dioxide NO2 0-600 mg/m3 Depends on H2O level 5 000 mg/m3

Nitrous oxide N2O 0-150 mg/m3 Not specified 5 000 mg/m3

Sulfur dioxide SO2 0-300 mg/m3 0-75 mg/m3 5 000 mg/m3

Ammonia NH3 0-100 mg/m3 0-15 mg/m3 2 000 mg/m3

Hydrogen chloride HCl 0-90 mg/m3 0-15 mg/m3 2 000 mg/m3

Hydrogen fluoride HF 0-90 mg/m3 0-20 mg/m3 1 000 mg/m3

Methane CH4 0-200 mg/m3 0-75 mg/m3 5 000 mg/m3

Carbon monoxide CO 0-300 mg/m3 0-75 mg/m3 10 000 mg/m3

Carbon dioxide CO2 0-20 vol-% Not specified 0-50 vol-%Water H2O up to 0-45 vol-% Tested up to 0-25 vol-% H2O 0-60 vol-%

Detection limit < 2% of the rangeLinearity deviation < 2% of the rangeDrifts < 2% of the rangeSum of the cross interferences < 4% of the range

Q: What are the detection limits for commonly measured gases?

The detection limit is a parameter that is often asked as a first question concerningthe analyzer performance. The GASMET provides very good detection limits.Various institutes have tested detection limits in various applications. The tablebelow presents some detection limits defined by TÜV Rheinland, Germany:

Compound Tested Detection LimitNO < 1.3 mg/m3

NH3 < 0.3 mg/m3

CO < 0.3 mg/m3

SO2 < 0.9 mg/m3

HCl < 0.3 mg/m3

HF < 0.3 mg/m3

TABLE: Tested detection limits, TÜV, Germany 1999. GASMET Dx-3000, 180°C,60 s measurement time; analyzer configured for CEM up to 25% of H2O

Usually, the detection limit for most components is well below 1 ppm. TemetInstruments is planning to experimentally generate a table of detection limits in air.This will be available in the near future.

The difficulty in defining the detection limits is that: even if the detection limits aregood, it is very important to define the application in more detail. A specifiedmeasuring range is a better way of estimating the detection limit. We have specifiedthe overall performance criteria for the measuring range, for example, detection limit< 2% of the scale, cross interference effects < 4% of the scale, etc. Sometimes, it isthe detection limit and other times, the cross interference effects, which limit thesmallest possible measuring range.

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Q: What is the measurement accuracy?

The measurement accuracy depends on the application. We do not know anypossibility to prove the real accuracy in all the situations.

However, there are some parameters that can be defined when the application iswell known (CEM or an application where the customer has the information of all thecomponents). Based on a desktop study, an application engineer is able to definethe analytical areas and optimum path length. From this information, it is possible toestimate the possible measuring ranges. In this situation, the analytical accuracy isdefined as follows:

Detection limit < 2% of the rangeLinearity deviation < 2% of the rangeSum of the cross interferences < 4% of the range

The above specification is valid only if the calibration is instrument specific andTemet Instruments has made both the factory calibration and the application.

Q: What are the maximum errors in the measurement for each of the following DX-4000 ranges?

NOx 0-300ppm SOx 0-100ppm CO2 0-20% CxHy 0-100ppm

We specify the measurement ranges for each component. The most importantparameters defining the accuracy are:

• sum of the cross interference effects < 4% of the smallest range promisedto the customer

• linearity deviation < 2% of the range

The possible measurement ranges will depend on the gas matrix (in emissionmonitoring applications, it depends mainly on the H2O concentration). If the H2Oconcentration is < 25%, then the ranges listed above are quite possible. However,CxHy measurement is special and is not comparable to the FID analyzer.

Q: What is the factory specific calibration?

The factory specific calibration is performed in our laboratory, after themanufacturing and final testing have been completed. Each calibration gas isintroduced to the instrument in known concentrations in pure nitrogen. Referencespectra are generated in different concentrations to cover the complete measuringrange. Linearity is proofed. If needed, gas mixtures are generated and crossinterferences tested.

The instrument specific calibration ensures the best possible performance of ananalyzer. As calibration involves much work and material costs, it is charged as a

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separate cost. If the reference spectrum library is used instead of the instrumentspecific calibration, the accuracy will not be the same.

Q: What calibration techniques does Temet use in the factory laboratory?

Most gases (NO, SO2, CO, CO2, CH4, C2H4, C3H6, C3H8, HCl, NH3, HF etc) arecontained in cylinders. Typically, the accuracy of the calibration gas concentration is2% or 3%, depending on the gas and on the manufacturer. The calibration gases areusually taken directly from these gas cylinders. If needed, additional concentrationsare produced with two identical Brooks mass flow controllers (N2 is mixed with thecalibration gas to get the concentration). The mass flow controller linearity is betterthan 2%.

Liquids (H2O, methanol, etc) are calibrated with a special calibration device (TemetCalibrator). The Temet calibrator incorporates a syringe pump, a manual needlevalve and a stainless steel injection chamber. A known nitrogen flow is directed tothe calibrator by using the Brooks mass flow controllers. The syringe pump injects aknown and very precise flow of the liquid into a nitrogen flow in a heated injectionchamber, producing a continual flow of a known concentration calibration gas.

In each case, a spectrum of a known mixture of the target gas and N2 is measured.There is no need to measure any complicated gas mixtures, unless we want to makeadditional testing of the performance. This makes the calibration procedure verysimple in comparison to some of our competitors. In addition, we gain more costsavings.

Q: Which calibrations must be performed after the installation?

Zero point calibration (background) is required once a day. Water vapor calibrationmust be performed after every major maintenance operation (minimum once a year).

In typical situations, there is no need to repeat the other calibrations.

Q: Why is H2O calibration so important?

Water has absorption lines all over the infrared spectrum. In many applications, theH2O concentration can even be thousands of times higher than the concentrations ofthe target components. In order to separate the H2O absorption lines from the othercomponents, we have to have as good a "fingerprint" of H2O as possible. By re-measuring the H2O calibration, we compensate for any effects from maintenanceoperations to this spectrum.

In other words, proper H2O calibration guarantees accurate analysis of othercomponents, which are usually present in the sample gas in ppm concentrations.

Q: What is the Temet Reference Library Collection?

The GASMET library consists of our reference files of gas spectra measured to datewith different GASMET gas analyzers. The absorptivity is a physical constant

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specific to each gas, and the reference spectra (or calibrations) can be transferredfrom analyzer to analyzer. The library contains hundreds of spectra and eachreference spectrum contains both quantitative and qualitative information about thecomponent. In principle, an application can be generated without the instrumentspecific calibration.

All GASMET analyzers are similar in the optical structure. If used correctly, thespectra of the reference library can be used for the analysis with relatively goodaccuracy. However, each analyzer has minor differences. These differences mayaffect the measured spectrum and cause some error to the analysis results. It mustalso be kept in mind that the reference library is generated by different laboratorieswith different instrument parameters and environmental conditions (path length,pressure, temperature). The temperature and pressure may affect the spectrum lineshape and cause some deviation in the results. These library references areexcellent if used for semi-quantitative analysis or to help identify unknowns. TheReference Library Collection does not provide as good accuracy as real instrumentspecific calibration, which is always recommended for obtaining the best accuracy.

Even if the Reference Library is used for the analysis, some components shouldalways be calibrated specifically for each instrument. These components include theones having very sharp absorption lines, for example H2O, HCl, NH3, and CH4.

Effective use of the GASMET library requires a good laptop computer, Windows 98operating system and MS Excel, and the Temet CALCMET for Windows software.The library is delivered on a CD-ROM as reference spectra and ADS software. Thelicense for the Reference Library Collection is free of charge if ordered together withany Dx-series analyzer. The Library Reference Collection is delivered upon requestonly.

Q: What is the accuracy if one uses a reference spectrum measured by adifferent analyzer?

The accuracy will depend on the component. Water vapor references should neverbe transferred.

If the two analyzers have the same path length and the same sample celltemperature, most references can be transferred (not the components with sharpabsorption lines) with good accuracy. However, Temet Instrument gives nocertification for the analytical performance unless the analyzer is factory calibrated.

Q: What is the best way to add new gases to the library?

The best way is to make the instrument specific calibration. The second best way isto use the Temet Reference Library.

The procedure to add new components to the CALCMET is very easy. The usermust specify the correct reference spectra and the spectral area and interferencesfor analysis. The procedure is described in detail in the manual.

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Q: Should the GASMET be recalibrated?

Background measurement is required daily. Due to the constant absorptivitycoefficients of gases, the calibrations will remain constant and no recalibration isrequired, if the absoption path length is not changed. The software collects for thechanges in temperature and pressure, if set active.

H2O is the only exception in normal operation. The H2O calibration must be valid inorder to make reliable measurements for other components. We calibrate H2O eachtime we service an instrument. The water vapor calibration gas is generated with ourTemet Calibrator.

Q: Is it possible to recalibrate any component at the factory if the customerrequests it?

Yes, but there is no need. The calibration is a relatively easy procedure and a trainedcustomer can do it him/herself. It is possible to program the computer to performcalibrations automatically, if absolutely necessary.

Q: How stable is the calibration? Why is it so stable?

The answer has 2 dimensions:

1) The wavenumber scale is very precise because:

The GASMET has a built-in He-Ne laser. The laser signal is used to measurethe exact position of the moving mirrors in the interferometer. The measuredinterferogram presents the detector signal strength as a function of the mirrorposition. Now, when we make the FFT (Fast Fourier Transformation) to themeasured interferogram, the result is the infrared spectrum. The mirrorposition scale is transformed to the wavenumber (wavelength) scale, which isthus measured with laser precision.

As such, the instrument is continuously calibrated with a He-Ne laser, whichprovides a stable wavenumber scale. High spectral signal to noise ratio andhigh wavenumber precision are characteristic of the FT-IR method. Thisyields high analytical sensitivity, accuracy and precision.

2) No span calibrations are needed because:

It is necessary to make the 0-calibration (background) measurement once aday. The 0-calibration compensates for all changes in the signal level or inthe instrument. Background spectrum is measured by filling the gas cell withan infrared-inactive gas (for example, dry nitrogen, dry oxygen, or even dryinstrument air). As seen in the following figure, the background spectrumshows the total radiation detected by the detector as a function ofwavenumber.

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CO2 absorption peak

H2O

H2O

FIGURE: A background spectrum containing CO2 and H2O as impurity.

The transmittance of this gas is the ratio between the sample spectrum and thebackground spectrum. 100 % transmittance shows that all the radiation ispassing the sample gas without any attenuation. Less than 100 % transmittancemeans that part of the radiation is absorbed by the sample molecules.

The above spectrum contains a small CO2 and H2O absorption peak. In thiscase, about 25% of the total radiation is absorbed by the CO2. If the abovespectrum is divided by a clean background spectrum, the result is atransmittance spectrum with the CO2 absorption of 25%, or transmittance of 75%at CO2.

Transmittance spectrum

FIGURE: A transmittance spectrum with CO2 absorption.

It is evident that the transmittance spectrum will depend only on the absorption -the shape or strength of the background spectrum does not effect theabsorption. The span calibration is not needed - it is actually replaced by the 0-calibration which ratios out instrument's own inherent response from samplespectra.

Q: How can NO2 be measured in the presence of up to 45% water vapor?

If the sample gas is dry, FT-IR is probably one of the best methods to measure NO2.As seen in the figure below, NO2 has a very strong absorption peak at 1550-1650cm-1. If the analysis is made using this spectral range, the detection limit for NO2

can be as low as 0.02 ppm in dry gas.

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However, the strong NO2 absorption is located right under the strong H2Oabsorption. Consequently, if the H2O concentration is high, the analysis accuracy ofNO2 will be affected relatively soon. The strong absorption peak can be used for H2Olevels of up to 10-20% vol (depending on absorption path length). If the H2Oconcentration is above 20%, the spectral range 2800-2950 cm-1 must be used forthe analysis. The absorption of this small peak is about 20 times weaker than themain absorption. Therefore, the smallest possible range is about 0-250 ppm (5m-path length) if the weaker peak is used for the quantification.

1000120014001600180020002200240026002800300032003400360038004000

Wavenumbers (cm -1)

Absorbance

NO2

FIGURE: a NO2 absorption spectrum

Q: Why is the low resolution GASMET better for quantitative gas analysis?

• The most important parameter in quantitative gas analysis should be overallanalytical accuracy. A low-resolution enables better signal-to-noise ratiobecause of: 1) High optical throughput (large IR source) of a low-resolutionspectrometer, and 2) Short interferograms (less noise is transformed to thespectrum). Overall analytical accuracy is the most important parameter of FT-IRgas analyzers for quantitative measurements.

• Typically, a high-resolution spectrometer needs a liquid nitrogen detector in mostapplications, which is inconvenient and expensive. In contrast, the low resolutionGASMET is equipped with a Peltier cooled MCT type detector, which is fast andoffers the benefits of a liquid nitrogen cooled detector in the wavenumber area of900-4200 cm –1.

• Using a DTGS detector with a high-resolution spectrometer requires a lengthyscan time. As well, the danger exists that the gas mixture composition willchange during the measurement, which may result in unstable results. The scantime of the GASMET is short, resulting in a more reliable measurement.

• The risk of altering the measured sample spectrum (due to changing the samplegas pressure and temperature) is generally avoided when using a low-resolutionspectrum. On the other hand, high-resolution calibration spectra may become

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obsolete in some applications due to these effects (especially if any inorganic gaslike H2O is present in high concentrations).

• A low-resolution spectrometer can be built to be more rugged; for example, theGASMET provides excellent stability over vibrations, shocks and swings intemperature.

• Due to a more complicated design, high-resolution spectrometers tend to bemuch more complex and expensive to maintain and service than low resolutionspectrometers.

Q: Is it possible to show in figures how much better the signal-to-noise ratiois, if resolution 8 cm-1 is used instead of resolution 0.5 cm-1?

Yes. The GASMET operates in most applications with 8 cm-1 resolution. The tablebelow shows relative signal-to-noise ratios between different resolutions.Theoretically, resolution 8 should provide 716 times better baseline than resolution0.1! The values are valid if the instrument remains otherwise the same, but apertureis changed according to the resolution and the measurement is kept constant.

Resolution Noise level compared to resolution 8 cm-18 14 2.82 81 230.5 640.1 716

Questions Regarding the GASMET Hardware, Life Time, Spare Parts

Q: How is it possible that the Temet Analyzers are so good and rugged?

The Interferometer, the sample cell, and the CALCMET analysis software are (muchmore) superior in design…

Q: What is so special about the Temet Interferometer?

The Temet Carousel interferometer of the GASMET provides excellent thermalstability and vibration insensitivity. It is designed for long term stability in changingenvironmental conditions. Simple and rugged mechanical structures are essential towithstand the challenges of demanding field use. Temet invested 10 years todevelop the Temet Interferometer.

The interferometer consists of a beamsplitter and five plane mirrors. Four of themirrors are mounted on a carousel, which swings back and forth. The only part thatrequires any alignments is the beamsplitter. After the factory settings, there is noneed for our customers to touch the beamsplitter alignment.

During the manufacturing process, each interferometer must pass extensive shockand temperature tests without practically any modulation decreases. This excellent

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stability leads to great analytical performance and reliability. As a result, the TemetInterferometer is the most reliable interferometer in the marketplace.

Q: Can we compare the Temet Interferometer to competitive solutions?

A common interferometer is such where both the corner-cube pair swings back andforth on a common wishbone mount, around the center of beamsplitter, creating acircular interference pattern. This is simply the Michelson interferometer with thecube-corner mirrors replacing the plane mirrors (Michelson 100, patented by BomemInc). The tilt problem in the driving system is avoided by the swinging movement ofthe mirrors. The drawbacks of this solution are the huge distances between themirrors and the two-dimensional design. This solution is prone to modulationfluctuations caused by vibration and ambient temperature changes. Thesemodulation fluctuations cause errors and instability in the measured spectrum, whichin turn reduces the analytical sensitivity, accuracy and precision.

Another competitor has designed a relatively good refractively scannedinterferometer (Orbital fx-6200 or fx-6250). This interferometer uses fixed cube-corner retroreflectors, and the scanning takes place by moving one half of thebeamsplitter, which consists of two wedges. The optical path difference x isincreased by increasing the distance the IR-beam travels through the beamsplitter.However, one of the most expensive and sensitive components of any interferometeris the beamsplitter. The above solution will require a specially shaped beamsplitterthat will be very expensive and mechanically sensitive. Furthermore, such a structurecan be reasonably constructed only from KBr, which is a very hygroscopic material.Consequently, even a small amount of humidity inside the interferometer wouldcause malfunctioning.

The Temet Interferometer has a symmetric design, minimum optical distances andno hygroscopic or fragile materials. In addition to this, the Temet Interferometer isthe only interferometer that provides stability in all three dimensions. It producesoptical path difference of more than 8 times the geometrical movement of the movingmirrors.

Q: What is so special in the Temet Sample Cell?

The structure of our sample cell and the interferometer is astonishing simple. This isknow-how. The sample cell consists of only three parts: 2 mirrors and the samplecell body. All the parts have special coating.

Due to its superior design, two major product properties can be achieved:1) The sample cell is resistant against corrosive chemicals: the optical mirrors are

coated with several thick “non porosity” gold layers.2) The sample cell has no optical alignments; the mirrors are made of solid metal!

Any competitive solution with alignments has one major drawback: opticalalignments tend to change with high temperatures and pressure changes.

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Aluminum

Protective Metal 1

Protective Metal 2

Gold layer 1, non-porous

Gold layer 2

FIGURE: During the unique coating process the aluminum mirror is plated withseveral different metal layers to achieve chemically resistant, high quality, non-porous protection and high mirror reflectivity.

FIGURE: The Gold coated one-piece cell mirror is precision machined with diamondcutting to provide excellent long-term calibration stability and high reproducibility.

Q: Is it possible to change the sample cell or the absorption path length?

The gas cell is located in an oven. The GASMET oven construction is very simple.The sample cell can be replaced in about 10 minutes time with another same volumecell. If the customer has different sample cells, he/she can have different pathlengths as well. However, the sample cell volume and the dimensions will remain thesame.

Note: the H2O must be recalibrated every time the sample cell is changed. Accordingto the application, the H2O calibration can take from 30 minutes time up to 3 hours(depending on experience & equipment).

Q: Will HCl, HF or similar components corrode the coating of the “gold-plated”cell?

The gold coating is a non-porous protective layer. The corrosion resistance is almostas is for solid gold.

There is no problem, for HF or HCl do not damage the cell. There are applicationswhere we measure in hot incineration process HCl in continuous concentrations >>1000 ppm. There are installations where the instrument has been running in thisapplication for years without any corrosion or signal drop. We have also tested liquidHCl and HF without any corrosion.

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Q: Will CL2 or Br2 react with the gold coating of the cell?

Yes, we have learned that even the highest quality gold coating does not survive inan environment where CL2 or Br2 are present in high concentrations in hot wet gas. Ifthe gas contains high concentrations of these gases, rhodium protection isrecommended for longer cell lifetime. Rhodium will not react with any known gas.The rhodium is very expensive and the rhodium protection will increase theinstrument price remarkably.

Q: Should rhodium protection always be recommended?

Absolutely not. The rhodium has two drawbacks:

1) The price (about 2000 USD/ 10 g) and,2) Weak infrared reflectivity. As gold reflects infrared radiation much better thanrhodium, the gold coating should always be used unless rhodium is absolutelyneeded (Cl2 or Br2). When one does not have Cl2 or Br2 in the sample gas, thegold mirrors will definitely provide superior performance, due to better infraredreflectivity.

The benefit exists only if the Cl2 is high, otherwise the coating is just more expensive(we charge an additional 2000 Euro / mirror -> 4000 Euro /instrument) for thecustomer (while weakening the signal throughput).

Q: What happens if the sample gas condenses in the cell?

A: The sample cell can quite possibly be destroyed. The most important rule is thatcondense or any liquid should never enter the sample cell. If the system has beenbuilt correctly, this situation will never occur. However, the most fatal mistake in thesystem construction is one that leads to condense formation in the cell.

Q: Will the GASMET operate under vacuum (i.e., replacing the heated samplepump with eductor after the cell) conditions?

It is strongly recommended that the pump is located before the sample cell. Inprinciple, it would work if the pump were located after the sample cell. However, inthis case, the sample cell would have underpressure and the situation would be verydifficult to control. If the filters are blocked, the pressure will decrease accordingly.The calibration task would be more complicated. Temet guarantees no analyticalaccuracy if the external pump or an eductor is located after the sample cell. Thesample cell outlet flow should be exhausted to ambient pressure if possible.

Q: Must the sample cell always be heated at 180ºC?

In hot /wet applications it is important that the sample does not condense in the cell.Consequently, the cell and system temperature are kept continuously at 180°C. TheGASMET should never be used in such an application in a lower temperature.

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A lower temperature is possible, depending on the application. For example, werecommend a temperature of 40ºC for ambient air applications. Still, it is veryimportant that the gas does not condense in the cell.

The instrument specific calibration is valid for one temperature only. If the user hasapplications at different temperatures, he/she will need separate calibrations for alltemperature settings, if highest performance is required.

Q: How should the GASMET be maintained?

The customer should provide zero gas for daily zero gas calibration. The filtersshould be replaced and kept clean inside the probe and the system. Othermaintenance includes:

Once a week:A quick visual inspection by the plant operators (a few minutes), to check that Zerogas is available, sample gas flow is correct, gas lines, pumps and filters are correct,etc.

1-2 times a year :General inspection by a qualified GASMET service technician (1 hour). If there isneed for any maintenance operation, a new water vapor calibration must beperformed (3-4 hours) after the maintenance. Even if no other maintenance isperformed, the H2O calibration is recommended at least once a year.

Every 1-2 years in continuous operation:Replace light source. After the light source replacement, the new H2O calibrationmust be performed.

Every 2-3 years in continuous operation:Replace laser tube and power supply. After the laser tube replacement, the new H2Ocalibration must be performed.

Special remarks for the system construction:In operation, the most sensitive part of the GASMET is the sample cell. If the gas ishot and filtrated, there is no reason to clean or service the cell. However, if the cellbecomes contaminated with dust, the mirrors can be easily cleaned. After H2Ocalibration, normal usage can proceed.

The situation becomes dangerous if the sample gas forms condense in the samplecell. If the corrosive gas condenses in the cell, there is a high probability that the cellmirrors will get damaged. The mirrors are very expensive parts. Therefore, thecondense must not enter the sample cell under any conditions. This can be avoidedby having a good system design.

Q: How is it possible that the IR source has such a long lifetime?

Even if Temet Instruments recommends that the IR source be replaced every 1-2years, the average lifetime is in most cases several years longer.

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The optical throughput of the GASMET is so high that we can operate the lightsource with relatively low voltage (about 9 V). As such, the light source will operatevery reliably. We know that some of our competitors use similar light sources with12V voltage, resulting in lifetimes of a few months only in continuous applications.Even if the price of the light source spare part is relatively low, the long lifetime is aclear advantage in process control and in CEM applications.

Q: What is the price of the spare part for the IR Source?

We sell the IR Source element for €120. This price is very low in comparison withany of our competitors.

Q: Is air conditioning needed?

In continuous operation, the GASMET must be kept at/below room temperature.Therefore, the cabin holding the GASMET must be air-conditioned. The GASMETFX-model is an exception. This model has built-in cooling.

Q: Does the GASMET measure the pressure?

Yes, every new GASMET Gas Analyzer (except the DX-3000) has a built-in pressuresensor in the electronics. The sensor measures the ambient pressure for thepressure compensation.

Q: How is the pressure compensation done?

The GASMET measures the number of molecules in the sample cell. If the pressurein the sample cell changes, the analyzed concentration will change accordingly. Allcurrent GASMET gas analyzers (except the DX-3000) have a built-in pressuresensor in its electronics. If the sample cell outlet is into ambient atmosphere, the cellpressure will correspond to the ambient pressure, which is measured with the built-insensor. Consequently, ambient pressure changes are automatically corrected.

An optional pressure sensor can be applied if the customer wants to measure thesample cell pressure directly. However, in most applications the ambient pressurecorrection is sufficient.

Q: How is oxygen compensation done? What percentage?

The default percentage is 11% if the compensation is activated but the parametervalues not changed. The calculation is made based on the following formula:

M

ROMOR O

OCC

−−

∗=21

21....

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Where, CR.O. = Concentration at reference O2

CM.O. = Concentration at measured O2

CR = % of Oxygen as referenceCM = % of Oxygen measured

In order to make the oxygen compensation, the O2 concentration must be measured.Oxygen does not absorb infrared radiation and thus cannot be measured with theGASMET. However, the GASMET can be equipped with an oxygen analyzer or theoxygen signal can be transported to the GASMET from any O2 analyzer as ananalog signal.

Q: How much time is required for the usual training of the DX-4000? What does this training consist of?

Two days training is usually enough to begin normal usage. The training is hands-on– using the analyzer for the task it is made for. A basic knowledge in computers andin sample gas handling is required. The training also involves a short introduction tothe technology.

If the customer uses the analyzer in a variety of application, or if he is making theapplications himself, the learning curve will be much longer. Additional training isrecommended after a few weeks. All later training is focused on customer questionsand possible problems or application specialties.

Software Questions

Q: What are the special features of the Temet software (CALCMET)?

The Calcmet Analysis Algorithm is the only patented analysis algorithm in IRspectroscopy.

The advanced, easy to use CALCMET™ software provides outstanding analyticalperformance. The software analyzes the sample spectrum, operates the GASMETand controls automated sampling system units. For superior and analyticalaccuracy, the software utilizes patented multicomponent algorithms to enhanceanalysis specificity. The software enables simultaneous detection, identification andquantification of up to 50 different gas components.

The GASMET measures both organic and inorganic gases in concentrations fromìg/m3 to several percentages. Cross interference effects are compensated for andanalysis accuracy is maintained when analyzing complex gas mixtures with spectraloverlapping. Accurate results are available within seconds. Stored spectra can beeasily re-analyzed for identification of previously unknown components.

The CALCMET automatically carries out spectral identification for accurate analysisto be performed without detailed stream composition information. The software isalso designed for easy and efficient processing of results. Since water content of thesample gas is measured, the results can be reported on either a “wet” or “dry” basis.

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The CALCMET software supports continuous multipoint on-line applications. Whenthe GASMET is equipped with a suitable sampling system, it has full capability forautomatic and remote control operation. The software processes the results into therequired format and offers advanced possibilities for multipoint sampling withadjustable alarm settings.