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Teledyne API Model 200A NO
X
Analyzer Instruction Manual, 02246, Rev. G, DCN 5247
7.10 Calibration Quality
After calibration is complete, it is very important to check the QUALITY of the calibration. The
calibration of the M200A involves balancing several sections of electronics and software to
achieve an optimum balance of accuracy, noise, linearity and dynamic range.
The following procedure checks the Slope and Offset parameters in the equations used to
compute the NO, and NO
x
concentrations. It is important that they fall within certain limits with
respect to themselves and to each other. For an explanation of the use of these terms in the
concentration calculation see Section 5.2.2.5.
The slope and offset parameters are similar to the span and zero pots on an analog instrum
ent.
Just as in the analog instrument, if the slope or offset get outside of a certain range, the
instrument will not perform as well.
The slope value will be slightly different on the NO and NO
x
channels. This is due to slight
differences in pneumatic resistance in each pathway. If the slopes are significantly different,
there is a calibration error or a cross port leak in the switching valve. If there is a sudden change
in slopes after a calibration, that usually indicates a change in reaction cell pressure. This
generally requires a Factory Calibration covered in Section 9.1.6.
The offset value gives inform
ation about the background signal level. Check the observed offset
value against the factory value in Table 2-2-6. If significantly higher, check Section 9.1.6
. Also,
after calibration check the AutoZero reading and compare it against the factory checkout value.
Increasing readings are a predictor of problem
s.
7-35
PRINTED DOCUMENTS ARE UNCONTROLLED