Teledyne 7120 - NDIR analyzer - Manual (Page 25)

3 Start-up and Theory of Operation Model 7120
3-2
Teledyne Analytical Instruments
houses the timer and operates the sampling system is called the master. The
other Control Units of the other instruments are called slaves.
Each of the other instruments may be monitoring the concentration of
several different gases of interest in the sample, for example CO, CO2 and/or
Combustibles as CH4 in flue gas.
3.2.2 Operational Calibration
After the instrument has stabilized, let zero gas flow through the
analyzer
Perform a zero of the analyzer.
Perform a span of the analyzer.
Open the span gas tank and set the pressure regulator to 20 psig.
Switch the mode switch to sample. Refer to Section 4 again.
Induce an automatic zero cycle as described in Section 4 also.
After the zero cycle, the analyzer reverts to the sample cycle. The
sample reading is now accurate and the analyzer is placed in continuous
operation. See Sections 4.6-4.8.
NOTE: In case slave analyzers are involved, calibrate them
simultaneously with the master analyzer.
After the instrument is calibrated, when no Auto-Cal option was
selected, shut off the main valve on the span gas tank. This tank is not used
during automatic sampling. Leave the zero tank open.
3.3 Theory of operation
3.3.1 General
T
he 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