Output points
- Last UpdatedJan 29, 2024
- 2 minute read
- PI System
- PI Interface for DNP3 3.3.1.38
- Interfaces
Output points control the flow of data from the Data Archive to any destination that is external to the Data Archive, such as a PLC or a third-party database. For example, to write a value to a register in a PLC, use an output point. Each interface has its own rules for determining whether a given point is an input point or an output point. For PI Interface for DNP3 output points, the point attribute for Location4 should be set to 0. For further explanation see Location4.
Note: When output points are required, implement an output point whitelist, which provides a defense against accidental or malicious changes to the control system.
Outputs are triggered for UniInt-based interfaces. That is, outputs are not scheduled to occur on a periodic basis. There are two mechanisms for triggering an output.
As of UniInt 3.3.4, event conditions can be placed on triggered outputs. The conditions are specified using the same event condition keywords in the extended descriptor as described below. The only difference is that the trigger point is specified with the SourceTag attribute instead of with the "event" or "trig" keywords.
For output points, event conditions are specified in the extended descriptor as follows: event_condition
|
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 point. 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." |