FTIR FAQ

Here are some often asked questions related to Fourier Transform Infrared Spectroscopy and its application to gas analysis

  1. When should Gasmet™ FTIR Gas Analyzers be recalibrated?
  2. Must the sample cell always be heated at 180 °C?
  3. Does Gasmet™ FTIR Gas Analyzers also measure the pressure?
  4. What is CEM?
  5. How do you measure in-situ with FTIR?
  6. What certifications does Gasmet have?
  7. Can I measure in explosive or other dangerous areas?

 

If you would like to receive more comprehensive information on FTIR gas analysis, please download our FTIR White Paper.

1. When should Gasmet™ FTIR Gas Analyzers be recalibrated?

FTIR gas analyzers do not require periodic recalibration. A daily background spectrum measurement with zero gas is enough to preserve measurement accuracy. Instead of periodic span calibrations, reference spectra for analyzed gases are measured at the factory when the instrument is made and these do not drift.

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2. Must the sample cell always be heated at 180 °C?

Corrosion of the sample cell can be avoided by preventing condensation inside the cell. The cell temperature should exceed the dew point of the sample gas by a safety margin. For this reason, Gasmet analyzers have different temperature set points as shown in the table below:

Model Temperature Used for
CX4015 and DX4015 50 °C ambient temperature samples
CX4000 and DX4000 180 °C stack emissions monitoring
In-Situ variable, typically 20 °C above process temp stack emissions monitoring

 

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3. Does Gasmet™ FTIR gas analyzers also measure the pressure?

Gasmet FTIR gas analyzers always have a pressure sensor for measuring atmospheric air pressure. In the preferred sampling technique, the outlet of the cell is open to atmosphere, ensuring that the pressure in the cell is equal to the measured air pressure thereby simplifying pressure measurement. Optionally the gas cell can be fitted with a pressure sensor or an analog input signal from external pressure sensor can be used to measure process pressure if the outlet of the gas cell cannot be vented to atmospheric pressure.

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4. What is CEM?

CEM stands for Continuous Emissions Monitoring and refers to a fixed analyzer system on a power plant, waste incinerator plant etc. CEN standards use the abbreviation AMS (Automated Measurement System) instead.

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5. How do you measure in-situ with FTIR?

The In-Situ FTIR analyzer places the interferometer in a rugged waterproof cast aluminum housing cooled with a Peltier cooler. A steel probe tube containing multi-pass sample cell mirrors similar to those explained in question 12 with 6.0-meter optical path length. The sample gas enters and exits the probe through sintered steel filter panels which prevent dust from entering. The entire probe is temperature stabilized with heating elements and the temperature and pressure changes are automatically compensated.

The in-situ probe is cleaned with instrument air as part of the zero calibration cycle every 24 hours and based on installations in biomass boilers, cement kilns, and aluminum plants the in situ FTIR approach withstands a large range of stack conditions. The main limitations are:

  • wet stacks with a gas temperature down to the dew point
  • very hot stacks with a gas temperature above 250 °C
  • ducts with a diameter less than probe length (ca. 700 mm)

In the above cases, an extractive FTIR is recommended.

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6. What certifications does Gasmet have?

TÜV / German Type Approval (includes EN 15267-3): Gasmet CEMS, Gasmet CEMS II
MCERTS product conformity certificate (includes EN 15267-3): Gasmet CEMS, CEMS II, Gasmet CX4000 gas analyzer, Gasmet DX4000 gas analyzer
GOST certificate (Russia): CR2000, CR4000, DX4000, DX4015 gas analyzers

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7. Can I measure in explosive or other dangerous areas?

The Gasmet FTIR gas analyzer is not intrinsically safe as it contains a potential source of ignition (infrared source, laser source). If the analyzer is placed in a sealed cabinet with overpressure purge system it may be installed in explosive hazardous areas.

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