Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 205)

Model 9110EH Instruction Manual Theory of Operation
10.4.3. Temperature/Pressure Compensation (TPC)
The software features a compensation of some temperature and pressure changes critical in
the measurement of NO and NO
X
concentration. When the TPC feature is enabled (default
setting), the analyzer divides the value of the PMT output signal (PMTDET) by a value
called TP_FACTOR. TP_FACTOR is calculated according to the following equation.
Where A, B, C, D are gain functions. The four parameters used to compute TP_FACTOR are:
• RCELL TEMP: The temperature of the reaction cell, measured in K.
• RCEL: The pressure of the gas in the vacuum manifold, measured in in-Hg-A.
• BOX TEMP: The temperature inside the analyzer’s case measured in K. This is
typically about 5 K higher than room temperature.
The current value of all four of these measurements are viewable as TEST FUNCTIONS
through the instrument’s front panel display.
Note that, as RCEL TEMP, BOX TEMP and SAMP pressure increase, the value of
TP_FACTOR increases and, hence, the PMTDET value decreases. Conversely, increases in
the reaction cell pressure (RCEL) decrease TP_FACTOR and, hence increase the PMTDET
value. These adjustments are meant to counter-act changes in the concentrations caused
by these parameters.
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=
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_
K 298
K TEMP BOX
D
Hg in 29.92
Hg in SAMP
C
Hg in RCEL
Hg in
B
K 323
K TEMP RCELL
A FACTOR TP
Eq 10-5
• SAMP: The pressure of the sample gas before it reaches the reaction cell, measured
in in-Hg-A. This measurement is ~1 in-Hg-A lower than atmospheric pressure.
Each of the terms in the above equation is attenuated by a gain function with a numerical
value based on a preset gain parameter (shown below in CAPITALIZED ITALICS) normalized
to the current value of the parameter being attenuated. The gain functions A, B, C and D
are defined as:
Eq 10-6 ] _ _ ) 1
) ( 323
) ( _
[( 1 GAIN TPC RCTEMP
K
K temp rcell
A × − + =
Eq 10-7 ] _ _ ) 1
) (" _
) (" 7
[( 1 GAIN TPC RCPRESS
Hg pressure rcell
Hg
B × − + =
Eq 10-8 ] _ _ ) 1
) ( 323
) ( _
[( 1 GAIN TPC SPRESS
K
K temp rcell
C × − + =
Eq 10-9 ] _ _ ) 1
) ( 298
) ( _
[( 1 GAIN TPC BXTEMP
K
K temp box
D × − + =
The preset gain parameters are set at the factory and may vary from analyzer to analyzer.
Section 6.5 describes the method for enabling/disabling the TPC feature.
M9110EH Rev 0 191