Yokogawa Integral Oxygen Analyzer ZR202 - Manual (Page 160)

IM 11M13A01-04E 12-6
(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 200
⍀ 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 k
⍀.
b. Display “Cell robustness” by specifying the parameter code A22. A good cell
(sensor) will show “5”, “Life > 1 year” (refer to Section 9.1.10).
12.2.2.3 Alarm 7: Span-point Calibration Coefficient Alarm
In calibration, this alarm is generated when the span gas ratio is out of the range of 0
Ϯ 18% (refer to Section 9.1.3, “Compensation”).
The following are suspected as the cause:
(1) The oxygen concentration of the span gas does not agree with the value of the span
gas set “Calibration setup”.
(2) The flow of the span gas is out of the specified flow value (600
Ϯ 60 ml/min).
(3) The sensor assembly is damaged and the cell voltage is abnormal.
<Search for cause of failure and taking measure>
(1) Confirm the following and carry out calibration again:
If the items are not within their proper states, correct them.
a. If the display “Span gas conc.” is selected in “Calibration setup” the set value
should agree with the concentration of span gas actually used.
b. The calibration gas tubing should be constructed so that the span 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 cell (sensor) is suspected as the cause of the alarm.
Replacement of the cell with a new one is necessary.
However, before replacement, carry out the procedure described in step (3) and later
of <Search for cause of failure and taking measure> in Section 12.2.2.2, “Alarm 6:
Zero-point Calibration Coefficient Alarm”.