Yokogawa Integral Oxygen Analyzer ZR202 - Manual (Page 173)

IM 11M12A01-05E 12-10
(4) The reference gas is mixing into the measuring gas and vice versa.
When such mixing occurs, since the deference between oxygen partial pressures on the
sensor anode and cathode sides becomes smaller, the measured value shows a lower
value. See Section 11.1.2 to check that the sensor has been properly installed. An error
which does not indicate Error-1 may occur in the sensor. If the sensor assembly is loose,
or if there is any damage to the O-ring, the measured gas will leak into the reference gas
or vice versa. Because of a low oxygen partial pressure between the reference and
measurement sides, the oxygen concentration reading is high, and the humidity reading
is low. In this case, the sensor assembly needs to be reinstalled (see Section 11.1.2). In
such a case, be sure to remove the O-ring and replace it with a new one. In addition, if
any crack is found, replace the sensor assembly with a new one (see Section 11.1.2,
earlier in this manual).
CAUTION
See the cell robustness in function A22 for sensor quality.
12.3.2 Measured Value Lower Than True Value
<Causes and Countermeasures>
(1) The measuring gas pressure becomes lower.
If an increment of the measured value due to pressure change cannot be neglected, take
appropriate measures (see Section 11.1.1 (1)).
(2) Moisture content in a reference gas changes (decreases) greatly.
Changes in the moisture content contained in the instrument air will cause an error of
the humidity measurement (vol% H
2
O or kg/kg). If this error cannot be ignored, use a
gas in which the moisture content is constant, such as instrument air in almost dry
condition, as a reference gas.
(3) The calibration gas (zero gas) is leaking in the detector.
If the zero gas is leaking in the detector because of a failure of the valve in the calibra-
tion gas tubing system, the measured value will show a slightly lower value than normal.
Check the valves in the calibration gas tubing system for leakage. For manual valves,
check them after confirming that they are in the fully closed state.