YOKOGAWA EXAxt ZR22G, User Manual, Page: 193 / 211

<12. Troubleshooting>
12-12
IM 11M12A01-02E 16th Edition : Mar. 19, 2020-00
(3) Calibration gas (span gas) is mixing into the detector due to leakage.
If the span gas is mixing 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
higher 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. In addition, check the tubing joints for leakage.
(4) The reference gas is mixing into the measuring gas and vice versa.
Since the difference between oxygen partial pressures on the sensor anode and cathode
sides becomes smaller, the measured value shows a higher value.
An error which does not appear as the Error1 may occur in the sensor. Sample gas and/or
the reference gas may be leaking. Visually inspect the sensor. If any crack is found, replace
the sensor assembly with a new one.
Referring to Section 11.1.3, check if there is a problem with the sensor mounting. If things
are abnormal but there is no error indication, then maybe the sensor assembly isn’t properly
secured, the O-ring seal is dirty, the measurement gas and ratio gas are leaking into each
other (if measurement gas pressure is high, then it may leak into ratio gas, and vice versa);
as oxygen partial pressure difference between ratio gas and measurement gas is small, the
oxygen concentration in measured gas will read high and the humidity value will read low.
Replace the sensor assembly as shown in 11.1.3, and be sure to replace the metal O-ring
with a new one.
If the sensor is cracked, the symptoms will be the same – low humidity measured value.
Perform a visual inspection, and – if a crack is found – replace the sensor assembly as
described in 11.1.3.
NOTE
Data such as cell robustness displayed in the Detailed-data display should also be used for
deciding sensor quality as references.
12.3.2 Measured Value Lower (Higher for Humidity Analyzer)
Than True Value
<Causes and Countermeasures>
(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 detector 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
) or
humidity value (vol% H
2
O or kg/kg).
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 detector 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 a fully closed situation.
(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.