Temperature/Pressure Compensation (Tpc) - Teledyne 200E Instruction Manual

Theory of Operation
Instrument slope and offset values recorded during the last calibration can be viewed on the
front panel. NO SLOPE, NOX SLOPE, NO OFFS and NOX OFFS are four of the test
parameters accessible through the <TST TST> buttons.

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
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.

RCELL
=
TP _ FACTOR A 

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.
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.
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:
A
=
B 1
186
concentration. When the TPC feature is enabled (default
X
 
TEMP ( K ) ( 7 in
× 
B 
 
323 ( K ) RCEL
rcell _ temp ( K
= +
1 [(
323 ( K )
7 (" Hg )
+
[(
rcell _ pressure ("
rcell _ temp (
= +
C 1 [(
323 ( K )
box _ temp ( K
= +
D 1 [(
298 ( K )
Model 200E Instruction Manual
 
Hg ) SAMP ( in Hg
× 
C 
 
( in Hg ) 29.92 ( in Hg
)
− ×
) 1 RCTEMP _ TPC
− ×
) 1 RCPRESS
Hg )
K )
− ×
) 1 SPRESS _ TPC
)
− ×
) 1 BXTEMP _ TPC
  
BOX TEMP ( K )
× 
D  
  
) 298 ( K )
_ GAIN ]
_ TPC _ GAIN ]
_ GAIN ]
_ GAIN ]
044100102 Rev A
Eq 10-5
Eq 10-6
Eq 10-7
Eq 10-8
Eq 10-9