Teledyne 7300A manual Theory of operation General, Analyzer

Infrared Gas Analyzer Start-up and Operation

are not used during automatic sampling.

3.3Theory of operation

3.3.1General

The non-dispersive infrared (NDIR) analyzer is one of the major components of the system. It employs the basic principles of spectroscopic analysis to measure a specific concentration of one gas in a multicomponent gas system. The concentration of a gas is determined by exposing a chamber filled with a gas mixture to infrared radiant energy and measuring how much of the specific (non-dispersive) infrared wavelength is absorbed by the gas being measured.

As an example, the NDIR analyzer is used most in flue gas applications where the amount of carbon monoxide in a flue gas mixture is measured. The specific infrared wavelength at which the carbon monoxide molecule absorbs infrared energy is at 4.65 microns. The more carbon monoxide present in the measurement cell, the more energy its molecules absorb.

The NDIR analyzer needs four basic components to measure the spectral absorbance.

a)A source of emitted infrared radiation to be absorbed by the gas of interest.

b)A chamber opened to accept a flowing sample gas.

c)A detector specifically tuned to measure only the wavelength of infrared energy that will be absorbed by the gas being measured. For example, carbon monoxide requires a detector turned to 4.65 microns, while carbon dioxide needs one tuned to 4.27 microns.

d)An electronics system to process the changes in the electronic resistance of the detector, and to convert these changes into specific electronics signals that deliver a voltage at current linearly proportional to the concentration of the gas measured. The Teledyne NDIR analyzer employs all of the above features.

3.3.2 Analyzer

The emitted IR energy is generated by one specially configured miniature lamps in parabola’s focused and operating at low power of only 0.5 watts.

Teledyne Analytical Instruments 3-3