Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 318)

Model 9110TH NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 298
8.8.3. 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.
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


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) (
) (
) (
(
) (
) ( 7
) (
) (
_
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
(Equation 9-5)
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.
 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.
 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.
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.
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:
] _ _ × ) 1
) ( 323
) ( _
[( + 1 = GAIN TPC RCTEMP
K
K temp rcell
A
(Equation 9-6)
] _ _ × ) 1
) (" _
) (" 5
[( + 1 = GAIN TPC RCPRESS
Hg pressure rcell
Hg
B
(Equation 9-7)
] _ _ × ) 1
) ( 323
) ( _
[( + 1 = GAIN TPC SPRESS
K
K temp rcell
C
(Equation 9-8)
] _ _ × ) 1
) ( 298
) ( _
[( + 1 = GAIN TPC BXTEMP
K
K temp box
D