Yokogawa Single Channel Oxygen Analyzer System ZR22/ZR402 - Manual (Page 198)

IM 11M12A01-03E 12-14
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
11.1.2, 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 11.1.2.
(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 Than True Value
<Causes and countermeasures>
(1) The measuring gas pressure becomes lower.
Where an increment of the measured value due to a pressure change cannot be
neglected, take measures per Section 11.1.1, (1).
(2) Moisture content in a reference gas changes (decreases) greatly.
A change in moisture content contained in the instrument air, which is used for the
reference gas, may cause an error in the measured humidity value (vol% H
2
O or kg/
kg).When this error is not ignored, use a drier or dehumidifier to make the
instrument air constant (to be almost dried) as a reference gas.
(3) Calibration gas (zero gas) is leaking in the detector.
If the calibration gas is leaking in the detector due to a faulty valve provided in the
calibration gas tubing system, the measured value shows a value a little lower than
normal.
Check valves in the calibration gas tubing system for leakage. When manual valves
are used, check them after confirming that they are in fully closed states.
12.3.3 Measurements Sometimes Show Abnormal Values
<Cause and countermeasures>
(1) Noise may be mixing in with the converter from the detector output wiring.
Check whether the converter and detector are 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) Poor wiring contact
If there is poor contact in the wiring, the sensor voltage or thermocouple emf
(voltage) may vary due to vibration or other factors.
Check whether or not there are loose wiring connections or loose crimping (caulking)
at the crimp-on terminal lugs.
(4) 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.
(5) 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.