Yokogawa Multi Channel Oxygen Analyzer System ZR22/AV550G - Manual (Page 135)

IM 11M12D01-01E 8-9
8. Detailed Data Setting
8.2 Oxygen Concentration Alarm Setting
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 concentra-
tion 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% O2. 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
ᎏ 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.