YOKOGAWA EXAxt ZR22G, User Manual, Page: 120 / 211

<8. Detailed Data Setting>
8-7
IM 11M12A01-02E 16th Edition : Mar. 19, 2020-00
8.3.1 Setting the Alarm Values
(1) High-high and high alarm values
If high-high and high alarm values are set to ON, then alarms occur if measured valves exceed
the alarm set values.
(2) Low and low-low alarm values
If low-low and low alarm values are set, then alarms occur if measured values fall below the
alarm set values.
8.3.2 Alarm Output Actions
If the measured values of the oxygen concentration fluctuate between normal (steady state)
values and the alarm setting, alarm outputs may be frequently issued and canceled.
To avoid this, set the alarm delay and hysteresis for alarm canceling under the alarm output
conditions, as Figure 8.3 shows.
When a delay time is set, an alarm will not be issued so quickly even if the measured value differs
from the steady state and enters the alarm setpoint range.
If the measured value remains within the alarm setpoint range for a certain period of time (for the
preset delay time), an alarm will be issued. On the other hand, there will be a similar delay each
time the measured value returns to the steady state from the alarm setpoint range (canceling the
alarm status).
If hysteresis is set, alarms will be canceled when the measured value is less than or greater than
the preset hysteresis values.
If both the delay time and hysteresis are set, an alarm will be issued if the measured value is in
the alarm setpoint range and the delay time has elapsed.
For the alarm to be reset (canceled), the measured value must be beyond the preset hysteresis
value and the preset delay time must have elapsed.
Refer to Figure 8.3 for any further alarm output actions. The delayed time and hysteresis settings
are common to all alarm points.
Delay time:
5 seconds
7.5%
High limit alarm setpoint
5.5%
Oxygen concentration
Alarm output ON
OFF
Hysteresis
2.0%
A
B
C
D
Alarm range
Delay time:
5 seconds
Delay time:
5 seconds
F8.3E.ai
Figure 8.3 Alarm Output Action
In the example in Figure 8.3, the high limit alarm point is set to 7.5 vol%O
2
, the delay time is set to
five seconds, and hysteresis is set to 2 vol%O
2
.
Alarm output actions in each section in this figure are as follows:
A. Although the oxygen concentration value exceeds the high limit alarm setpoint, it falls below
the high limit alarm setpoint before the preset delay time of five seconds elapses. So, no
alarm is issued.
B. The oxygen concentration value exceeds the high limit alarm setpoint and the delay time
elapses during that measurement. So, an alarm is issued.
C. Although the oxygen concentration value falls below the hysteresis set value, the value rises
again and exceeds the hysteresis set value before the preset delay time elapses. So, the
alarm is not canceled.
D. The oxygen concentration value falls below the hysteresis set value and the preset delay
time elapses, so the alarm is canceled.