The threshold (in primary units) at which the
conditional expression would be evaluated to
false. Defines the hysteresis for analog
triggers. Not applicable for digital triggers.
Figure 5-12: General Setup Dialog Box – Control/Alarm Setpoints Tab
Using Numeric Triggers
For numeric (analog) triggers, you can specify two thresholds for each
trigger to provide hysteresis (dead band) for setpoint operations.
The Operate Limit defines the operating threshold, and the second
Release Limit defines the release threshold for the trigger. The trigger
thresholds are specified in primary units.
If you do not want to use hysteresis for the trigger, set the Release Limit
to the same value as the Operate Limit.
Using Binary Triggers
Binary (digital) triggers like digital inputs and relays are tested for
ON/CLOSED or OFF/OPEN status.
In the PM135, the binary events are level-sensitive events. An event is
asserted all the time while the corresponding condition exists.
Delaying Setpoint Operations
Two optional delays can be added to each setpoint to extend monitoring
triggers for a longer time before reaching a decision on whether the
expected event occurred or not. When a delay is specified, the logical
controller changes the setpoint status only if all conditions are asserted for
a period of at least as long as the delay time.