Calibration
Calibration
Thermo Fisher Scientific
Model 42
i
Trace Level Instruction Manual
4-15
The analyzer does a one point NO
2
span coefficient calculation,
corrects the NO
2
reading for converter inefficiency, and then adds the
corrected NO
2
to the NO signal to give a corrected NO
x
signal.
If the analyzer calculates a NO
2
span coefficient of less than 0.96, either
the entered NO
2
concentration is incorrect, the converter is not being
heated to the proper temperature, the instrument needs servicing (leak
or imbalance), or the converter needs replacement or servicing. The
NO
2
analog output will reflect the NO
2
concentration generated by
GPT, any NO
2
impurity, and the NO
2
zero offset.
The recorder response will be as follows:
Z
+
100
x
URL
]
NO
[
=
scale)
(%
esponse
Recorder R
NO
OUT
2
2
Where:
URL = Nominal upper range limit of the NO
2
channel, ppm
12.
Record the NO
2
concentration and the analyzer's NO
2
response.
13.
Maintaining the same F
NO
, F
O
, and F
D
, adjust the ozone generator to
obtain several other concentrations of NO
2
over the NO
2
range (at least
five evenly spaced points across the remaining scale are suggested).
14.
Record the stable responses and plot the analyzer's NO
2
responses
versus the corresponding calculated (using the above equation for
[NO
2
]
OUT
) concentrations and draw or calculate the NO
2
calibration
curve.
Note
It is important that the curve be linear within
±
1 % FS over the NO
2
range. If the curve is nonlinear, the analyzer is not operating correctly,
(possible leak, or converter failure, etc.), and should be serviced. Assuming
the curve is linear, subsequent data should be reduced using this NO
2
calibration curve response.
▲
Using the Calibration Factors menu can change the calibration factors.
This is often useful in a troubleshooting situation. However, after the above
calibration procedure is completed, all subsequent data reduction depends
on the calibration parameters, remaining the same as during the initial
calibration.
▲
