Yokogawa Single Channel Oxygen Analyzer System ZR22/ZR402 - Manual (Page 191)

IM 11M13A01-02E 12-6
12.2.2 Measures Taken When Alarms are Generated
12.2.2.1 Alarm 1: Oxygen Concentration Alarm
This alarm is generated when a measured value exceeds an alarm set point or falls
below it. For details on the oxygen concentration alarm, see Section 8.3, “Setting
Oxygen Concentration Alarms,” in the chapter on operation.
12.2.2.2 Alarm 6: Zero-point Calibration Coefficient Alarm
In calibration, this alarm is generated when the zero correction factor is out of the
range of 100
؎ 30% (refer to Section 9.1.3, “Compensation”). The following can be
considered the causes for this:
(1) The zero-gas oxygen concentration does not agree with the value of the zero-gas
concentration set “Calibration Setup.” Otherwise, the span gas is used as the zero
gas.
(2) The zero-gas flow is out of the specified flow (600 mL/min
؎60 mL/min).
(3) The sensor assembly is damaged and so cell voltage is not normal.
<Locating cause of failure, and countermeasures>
(1) Confirm the following and carry out calibration again: If the items are not within
their proper states, correct them.
a. If the indication for “Zero gas conc.” is selected in “Calibration setup,” the set
point 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 detailed data display by pressing the detail display key in the basic
panel display.
b. When the
᭢ key is pressed once, the cell voltage should be indicated on the top
line (Figure 12.5).
c. 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 approximately
؎10 mV.
Table 12.3 Oxygen Concentration and Cell Voltage
T12.3E.EPS
Oxygen concentration Cell voltage
(%O
2
) (mV)
1 % 67.1
21% 0