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11.3
Measures to be taken when measured
values indicate abnormalities
The cause that the measured value indicates an abnormal value is not necessarily a failure of
the equipment. Rather, there are many cases in which the measured gas itself is in an abnormal
state or due to external factors that disturb the operation of the equipment. This section explains
the causes and remedies for when the measured value indicates the following phenomena.
(1) The measured value shows a higher value than the actual value.
(2) Measured value shows lower value than actual value
(3) Measured values occasionally show abnormal values
11.3.1
The measured value is higher than the actual value
<Cause and remedy>
(1) The pressure of the measured gas increases.
Oxygen concentration measurement value X when the pressure of the measured gas becomes
higher by Δ p (kPa) than at the time of calibration (vol%O
X=Y[1+(Δ p/101.30)]
Y: Measured oxygen concentration at the same pressure as at calibration (vol%O
If the change in the measured value due to pressure fluctuation cannot be ignored, measures
must be taken. Consider the following points and make possible improvements in each
process.
• Consider the following points and make possible improvements in each process.
• Is it possible to perform calibration under the average measured gas pressure (furnace
pressure)?
(2) The amount of moisture contained in the comparison gas changes greatly (increases)
If the air at the detector installation site is used as a comparator gas, a large change in
the amount of water contained in the air may cause an error in the measured oxygen
concentration value (vol%O
moisture content, such as instrumented air that is almost dry, as the comparison gas.
Changes in the amount of water in the combustion exhaust gas can also be considered as
an error factor. Normally, this amount of error is negligible.
(3) Calibration gas (span gas) is leaking into the detector.
If span gas leaks into the detector due to a defective valve installed in the calibration gas
piping system, the measured value will show a higher value. Check valves in the calibration
gas piping system (needle valves, check valves, solenoid valves for automatic calibration,
etc.) for leaks. In the case of a manual valve, check that the valve is fully closed before
checking for leaks. Also, check that there is no leakage at the joint part of the piping.
(4) The comparison gas enters the measurement gas side, or the measurement gas enters the
comparison gas side.
The difference in oxygen partial pressure between the anode and cathode sides of the
sensor is reduced, so the measured value indicates a higher value. Check your detector's
manual to ensure there are no sensor installation problems.
An error that does not appear as alarm 016 may have occurred in the sensor. In addition,
if the metal O-ring is not tightened sufficiently or if the seal surface is damaged or dirty, the
measured gas or comparison gas may be leaking. Visually inspect the sensor. If any cracks
are found, replace the sensor assembly with a new one.
(NOTE)
The data such as cell health displayed on the detailed display screen should also be used as a reference for judging the
quality of the sensor.
). If this error cannot be ignored, use a gas with a constant
2
<11. Troubleshooting>
) is as follows.
2
11-11
)
2
IM 11M13G01-02EN
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