Instruction manual

SM425 INSTRUCTION MANUAL 8.0 DETAILED DATA SETTING
8.3.2 Alarm Output Actions
The oxygen concentration alarms have two programmable parameters, delay and hysteresis, which can
be used to minimize unwanted alarm action when the process oxygen level is near an alarm set point.
Delay is the time in seconds that the process must continuously be in an alarm state before the alarm is
issued or continuously out of the alarm state before the alarm is cleared. Hysteresis is the concentration
band on the “safe” side of an alarm set point, through which the process oxygen concentration must pass
before the alarm will clear. Delay and hysteresis settings are common to all of the alarms. Delay and
hysteresis can be deactivated by setting their values to zero.
Figure 8-4 illustrates the effects of delay and hysteresis.
Figure 8-4 Alarm Output Action
In the example in Figure 8-4, the high-limit alarm point is set to 7.5% O
2
, the delay time is set to five
seconds, and hysteresis is set to 2% O
2
.
Alarm output actions in this figure are as follows:
1. In “A” Although oxygen concentration value exceed the high-limit alarm set point, it falls lower
than the high-limit alarm set point before the preset delay time of five seconds elapses. No alarm
is issued.
2. In “B” Oxygen concentration value exceeds the high-limit alarm set point and the delay time
elapses during that measurement. An alarm is activated.
3. In “C” Although oxygen concentration value falls lower than the hysteresis set value, the value
rises again and exceeds the hysteresis set value before the preset delay time elapses. The alarm
is not cleared.
4. In “D” Oxygen concentration value falls below the hysteresis set value and the preset delay time
elapses, the alarm is cleared.
124 42500001 REV A