Yokogawa In-Situ Gas Analyzer TDLS200 - Manual (Page 89)

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IM 11Y01B01-01E-A 6th Edition :Feb 13, 2013-00
<6. BASIC OPERATION>
Normal Operation – TDLS200 TruePeak Software Main
Menu
The analyzer is configured to measure not only H
2
O ppm
but it will also indicate the CH
4
% concentration value, as
shown on the Main Menu display below: Note that the flow
cell gas temperature is also shown as Active (based on flow
cell sensor active input) and pressure is input as a Fixed
value (shown in psiA units, based on the external sample
system regulator fixed setting).
Note, during normal process operation with 90-
100% methane gas flowing in the cell, the laser
temperature set point (LTSP) is configured to control
the methane peak position at data point 220 (as
shown red in absorption spectrum, right):
The actual measurement of H
2
O ppm absorption
peak is made in the data point region of 160 – note
that H
2
Oppm is not visible to the eye within this
absorption spectrum when <100 ppm (as shown
blue in absorption spectrum, right):
6.8 Introduction to Gas Temperature Predictions with High Temperature Oxygen Measurements
For some high temperature oxygen measurements operating at the correct conditions, the analyzer can predict
the gas temperature as well as the oxygen concentration. The TruePeak TDL analyzer scans a tunable diode
laser over a small wavelength range across measurement gas absorption line profile. The measurement gas
concentration can be predicted from the absorption peak with combustion parameters of optical path length, gas
temperature and gas pressure. The gas temperature has significant effect on the absorption line intensity, typically
weaker absorption at higher temperature for oxygen. However, there are several oxygen lines whose absorption
intensity has different temperature response. By simultaneously comparing two oxygen lines with different
temperature effect on absorption intensity, we can calculate the gas temperature.