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<12. Troubleshooting>
12-10
IM 11M13A01-04E
12.3.2 Measured Value Lower Than True Value
<Causes and Measures>
(1) The measuring gas pressure becomes lower.
Where an increment of the measured value due to pressure change cannot be neglected, take
measures referring to Subsection 12.3.1 (1).
(2) Moisture content in a reference gas changes (decreases) greatly.
If air at the analyzer installation site is used for the reference gas, large change of moisture
content in the air may cause an error in measured oxygen concentration value (vol%O
2
).
When this error is not ignored, use a gas in which moisture content is constant such as
instrument air in almost dry condition as a reference gas.
In addition, change of moisture content in exhaust gas after combustion is also considered as a
cause of error. However, normally this error is negligible.
(3) Calibration gas (zero gas) is mixed into the sensor due to leakage.
If the zero gas is mixed into the detector due to leakage as a result of failure of the valve provided
in the calibration gas tubing system, the measured value shows a value a little lower than
normal.
Check valves (needle valves, check valves, solenoid valves for automatic calibration, etc.) in the
calibration gas tubing system for leakage. For manual valves, check them after confirming that
they are in fully closed states.
(4) Combustible components exist in the sample gas. If combustible components exist in the sample
gas, they burn in the sensor and thus oxygen concentration decreases. Check that there are no
combustible components.
(5) Temperature of the sensor cell reaches 750°C or more.
If the sensor temperature is 750°C or higher, this may indicate that sample gas has leaks into the
reference gas side, corrosion. Also check that the thermocouple resistance is no greater than
15Ω.
12.3.3 Measurements Sometimes Show Abnormal Values
<Cause and Measure>
(1) Noise may be mixing in with the converter from the detector output wiring.
Check whether the equipment is securely grounded.
Check whether or not the signal wiring is laid along other power cords.
(2) The converter may be affected by noise from the power supply.
Check whether or not the converter power is supplied from the same outlet, switch, or breaker as
other power machines and equipment.
(3) There may be a crack in the sensor or leakage at the sensor-mounting portion.
If the indication of concentration varies in synchronization with the pressure change in the
furnace, check whether or not there is a crack in the sensor or whether the sensor flange is
sticking tightly to the probe-attaching face with the metal O-ring squeezed.
(4) There may be leakage in the calibration gas tubing
In the case of a negative furnace inner pressure, if the indication of concentration varies with
the pressure change in the furnace, check whether or not there is leakage in the calibration gas
tubing.