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Calibrating the Model
CGA 351
Recommended
Calibration Gas
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Setup and Calibration
To calibrate the CGA 351 analyzer, the following steps must be
completed:
•
introduce the chosen calibration gas
•
regulate the calibration gas flow rate
•
adjust the calibration setting as required
Proceed with the instructions in this section to calibrate the analyzer.
To properly calibrate the zirconia oxygen sensor, a calibration gas of
known composition must be used. The following calibration gas is
recommended by GE Infrastructure Sensing:
•
5 ppm O
in N
2
2
IMPORTANT:
The gas cylinder must be certified as to the exact
composition of the calibration gas.
A calibration gas containing only CO is not recommended, since the
analyzer will not respond correctly to dry calibration gases that do not
contain H
. However, CO may be used if moisture is added to the gas
2
by passing it through a saturator or bubbler.
Uncertainty in the oxygen content of the calibration gas may be a
significant source of error in the calibration process. A standard
certificate of analysis has an uncertainty in the smaller component of
±5%. For the recommended calibration gas, this means an oxygen
range of 4.5–5.5 ppm, and the corresponding potential calibration
errors shown in Table 4-1 below are introduced.
Table 4-1: Calibration Uncertainty
ppm O
T(°C)
2
4.5
5.0
700
5.5
As shown in Table 4-1 above, a calibration uncertainty of about
±0.95% is introduced by the calibration gas uncertainty alone.
December 2004
∆mV
mV
225.317
+2.209
223.108
0.00
221.110
–1.03
%Error
+0.99
0.00
–0.90
4-31
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