Yokogawa Integral Oxygen Analyzer ZR202 User Manual

Page 168

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IM 11M12A01-05E

12-5

12. Troubleshooting

<Locating cause of failure, and countermeasures>
(1) Confirm the following and carry out calibration again: If the items are not within

their proper ranges, correct them.

a. If the indication for “Zero gas conc.” is selected in “Calibration setup,” the set

value should agree with the concentration of zero gas actually used.

b. The calibration gas tubing should be constructed so that the zero gas does not leak.

(2) If no alarm is generated as a result of carrying out re-calibration, it is suspected that

improper calibration conditions were the cause of the alarm in the preceding calibra-
tion. In this case, no specific restoration is necessary.

(3) If an alarm is generated again as a result of carrying out re-calibration, deterioration

of or damage to the sensor assembly is suspected as the cause of the alarm. Replace-
ment of the cell with a new one is necessary. However, before replacement, carry out
the following:
Check the cell voltages when passing the zero gas and span gas.

a. Display the cell voltage with the parameter code A11.
b. Check whether or not the value of the displayed cell voltage is very different from

the theoretical value at each oxygen concentration. Confirm the theoretical values of
the cell voltage in Table 12.3. Although it cannot be generally specified as to what
extent the difference from the theoretical value is allowed, consider it to be approxi-
mately 610 mV.

Table 12.3 Oxygen Concentration and Cell Voltage Oxygen concentration

Oxygen concentration (% O

2

) Cell voltage (mV)

1%

67.1

21%

0

T12.3.EPS

(4) Confirm whether deterioration of or damage to the sensor assembly that caused the

alarm has occurred abruptly during the current calibration in the following procedure:
Check the history of the span gas ratio with the parameter codes A50 and A51.
Check the history of the zero gas ratio with the parameter codes A60 through A69.
The larger the parameter code number, the older the displayed data. Changes in
deterioration of the sensor can be seen.

(5) If deterioration of the sensor assembly has occurred abruptly, it may show that the

check valve, which prevents moisture in the furnace from getting into the calibration
gas tubing, has failed. If the gas in the furnace gets into the calibration gas tubing, it
condenses and remains in the gas tubing. The sensor assembly is considered to be
broken for the reason that the condensation is blown into the sensor assembly by the
calibration gas during calibration and so the cell cools quickly.

(6) If the sensor assembly has been gradually deteriorating, check the sensor assembly

status in the following procedure:

a. Display “Cell resistance” by specifying the parameter code A21. A new cell will

show a cell resistance value of 200V or less. On the other hand, a cell
(sensor) that is approaching the end of its service life will show a resistance value
of 3 to 10 kV.

b. Display “Cell robustness” by specifying the parameter code A22. A good cell

(sensor) will show “5,” “Life > 1 year” (refer to Section 10.1.15).

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