<8. Detailed Data Setting>
8-8
IM 11M12D01-01E
8.2 Setting Oxygen Concentration Alarms
You can set four oxygen concentration alarm settings: High High (HH), High (H), Low (L) and Low
Low (LL). If an alarm occurs while the basic panel display is displayed then an alarm mark appears
on the display, and at the same time the oxygen concentration display color of the channel in alarm
status turns orange. An orange status display lamp also lights at the top of the corresponding channel
card. If the function contact outputs are allocated to alarms then the corresponding contact output also
occurs. Here we explain how to set this alarm action.
8.2.1 Setting the Alarm Values (Individual Settings)
The alarm values can be set individually for all channels and for all averaging groups.
1) High High (HH) and High (H) alarms
An alarm occurs when the measured value is bigger than the alarm limit. The alarm settings
can be in the range 0 to 100% O
2
. However you need to enable each alarm set point (HH, H) by
setting it to “ON” rather than “OFF”.
2) Low (L) and Low Low (LL) alarms
An alarm occurs when the measured value is smaller than the alarm limit. The alarm settings
can be in the range 0 to 100% O
2
. However you need to enable each alarm set point (LL, L) by
setting it to “ON” rather than “OFF”.
8.2.2 Alarm Delay Time and Hysteresis (Applies to All Alarm Settings)
If the measured oxygen concentration fluctuates between the normal value and the alarm setting then
alarm status will keep turning ON and OFF. You can reduce this annoyance by setting alarm action
delay and hysteresis.
Delayed alarm action prevents immediate alarm output after measurement value goes outside an
alarm limit; alarm status is entered only if the alarm stays outside the limit for the delay time. The delay
time also affects release of alarm status.
The effect of hysteresis is similar-delaying alarm action and release-except that it is an offset value
rather than a time: to release an alarm, the alarm has to move (the hysteresis value) inside the alarm
setting. You can combine delay with hysteresis to both minimize spurious alarms and lengthen brief
(but valid) alarm output.
The action of delay and hysteresis are illustrated in Figure below. Alarm delay and hysteresis settings
apply to all alarm settings for all channels and all averaging groups.
A . Although the measured value exceeds the high alarm setting, within the delay time of 5 sec., it
falls within (alarm setting ─ hysteresis) so no alarm is output.
B. The measured value stays outside the alarm setting for longer than the delay time, so an alarm is
output, delayed by the delay time.
C . Although the measured value falls within (alarm setting ─ hysteresis) it does not stay there for
the delay time, so the alarm is not released.
D. After the measured value falls within (alarm setting ─ hysteresis) and stays there for the delay
time, the alarm is released.
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