UniInt End User
Download 1.93 Mb.
|
PI BASemAPI
- Navigate this page:
- Output Points
- Trigger Method 1 (Recommended)
Unsolicited InputsSome interfaces do not poll for data. Rather, the foreign device (Distributed Control System, PLC, SCADA, etc.) is in control of what type of data is sent to the interface and when it is sent. For unsolicited data input, the value of Location4 is meaningless to UniInt. The interface may make use of Location4 for some other PI tag configuration value. Please see the interface documentation for a description of how Location4 is used for unsolicited input tags. Output PointsOutput points control the flow of data from the PI Data Archive to any destination that is external to the PI Data Archive, such as a PLC or a third-party database. For example, to write a value to a register in a PLC, one would use an output point. Each interface has its own rules for determining whether a given point is an input point or an output point. There is no de facto PI point attribute that distinguishes a point as an input point or an output point. Outputs are triggered for UniInt-based interfaces. That is, outputs are typically 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 under “Trigger-Based Inputs.” The only difference is that the trigger tag is specified with the SourceTag attribute instead of with the “event” or “trig” keywords. Otherwise, the behavior of event conditions described under ‘Trigger-Based Inputs” is identical for output points. For output points, event conditions are specified in the extended descriptor as follows: event_condition Trigger Method 1 (Recommended)For trigger method 1, a separate trigger point must be configured. The output point must have the same point source as the interface. The trigger point can be associated with any point source, including the point source of the interface. Also, the point type of the trigger point does not need to be the same as the point type of the output point. The output point is associated with the trigger point by setting the SourceTag attribute of the output point equal to the tag name of the trigger point. An output 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 value that was sent to the Snapshot to trigger an output, but the timestamp of the new value needs to be more recent than the previous value. If no error is indicated, then the value that was sent to the trigger point is also written to the output point with the same timestamp as the trigger point. If the output is unsuccessful, then an appropriate digital state that is indicative of the failure is usually written to the output point. If an error is not indicated, the output still may not have succeeded because the interface may not be able to tell with certainty that an output has failed. Download 1.93 Mb. Share with your friends:
|