Trigger-based inputs
- Last UpdatedSep 16, 2024
- 2 minute read
For trigger-based input points, a separate trigger point must be configured.
Note: Location4 must be set to 0 for trigger-based input points.
An input point is associated with a trigger point by entering a case-insensitive string in the extended descriptor (ExDesc) PI point attribute of the input point of the form:
keyword=trigger_tag_name
where keyword is replaced by “event” or “trig” and trigger_tag_name is replaced by the name of the trigger point. There should be no spaces in the string. UniInt automatically assumes that an input point is trigger-based instead of scan-based when the keyword=trigger_tag_name string is found in the extended descriptor attribute.
An input is triggered when a new value is sent to the Snapshot of the trigger point. The new value does not need to be different than the previous Snapshot value to trigger an input, but the timestamp of the new value must be greater than (more recent than) or equal to the timestamp of the previous value. This is different than the trigger mechanism for output points. For output points, the timestamp of the trigger value must be greater than (not greater than or equal to) the timestamp of the previous value.
Conditions can be placed on trigger events. Event conditions are specified in the extended descriptor as follows:
Event='trigger_tag_name' event_condition
The trigger tag name must be in single quotes. For example,
Event='Sinusoid' Anychange
will trigger on any event to the PI Tag sinusoid as long as the next event is different than the last event. The initial event is read from the snapshot.
The keywords in the following table can be used to specify trigger conditions.
|
Event Condition |
Description |
|---|---|
|
Anychange |
Trigger on any change as long as the value of the current event is different than the value of the previous event. System digital states also trigger events. For example, an event will be triggered on a value change from 0 to "Bad Input," and an event will be triggered on a value change from "Bad Input" to 0. |
|
Increment |
Trigger on any increase in value. System digital states do not trigger events. For example, an event will be triggered on a value change from 0 to 1, but an event will not be triggered on a value change from "Pt Created" to 0. Likewise, an event will not be triggered on a value change from 0 to "Bad Input." |
|
Decrement |
Trigger on any decrease in value. System digital states do not trigger events. For example, an event will be triggered on a value change from 1 to 0, but an event will not be triggered on a value change from "Pt Created" to 0. Likewise, an event will not be triggered on a value change from 0 to "Bad Input." |
|
Nonzero |
Trigger on any non-zero value. Events are not triggered when a system digital state is written to the trigger tag. For example, an event is triggered on a value change from "Pt Created" to 1, but an event is not triggered on a value change from 1 to "Bad Input." |