Yokogawa Multi Channel Oxygen Analyzer System ZR22/AV550G - Manual (Page 224)

IM 11M12D01-01E 12-14
cell emf
1st calibration
2nd calibration
3rd calibration
O
2
value
0.51%
21%
F12.11E.eps
Example: When the second calibration
result is compared with the first, the change
in slope indicates sensor degradation.
However, when the third calibration
result is compared with the second,
the slope has not changed, only the
zero offset, suggesting clogging
and pressure effects
Fig. 12.11 Cause of alarm
(2) Conditions for generating an alarm
When the current result and the two previous results -- for the oxygen concentration
resulting in a given cell emf -- are compared, if both of the following conditions are
satisfied then an alarm is issued:
A B C
21% 0.51%
O
2
value
Current calibration
Previous calibration
Calibration
before previous one
1 A-B
м
0.125%O 2
2 B-C
м
0.125%O 2
cell emf mV
Fig. 12.12 Conditions for alarm
A repeatability of 0.125% O
2
on the 0 to 25% range is determined from the specified
precision. (25% O
2
x 0.5% = 0.125% O
2
)
However, the following restrictions apply:
(a) When either span or zero calibration is performed, not both, the results are ignored
in applying the above criteria.
(b) If calibrations are separated by an interval of less than 5 days, then the results are
ignored in applying the above criteria.
(3) Conditions for releasing alarm status
(a) If calibration results show improvement compared with previous results ? e.g.
higher cell emf ? then it is assumed that clogging has been cleaned away, or the
cell replaced. Alarm status and previous data are cleared.
(b) If you clear the calibration history, then alarm status and past calibration data is
also cleared.
(c) If you disable alarm functions, then alarm status is cleared (but calibration history
is not cleared
. (4) What to do when an alarm occurs
It is possible that the detector tip filter is clogged. Refer to Sec. 11 Inspection and
Maintenance ( on Maintenance for cleaning procedure ).