UniInt End User
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PI BASemAPI
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- Scan-based Inputs
- Trigger-based Inputs
Input PointsInput points are used to write data to the PI Data Archive. 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. Input points can be scan-based, trigger-based, or unsolicited. Scan-based InputsFor scan-based input points values are sent to the points on a periodic basis. Scanning periods are defined by the /f parameter on the startup-command-line of the interface. The first appearance of the /f parameter on the command-line is referred to as the first scan class, the second appearance of the /f parameter is referred to as the second scan class, and so on. The Location4 PI point attribute is used to associate an input point with a given scan class. For example, to associate a particular input point with scan class 1, set Location4 to 1 for the point. Trigger-based InputsFor trigger-based input points, a separate trigger point must be configured. 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”, “trig” or “trigger” and trigger_tag_name is replaced by the name of the trigger point. 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. As of UniInt 3.3.4, conditions can be placed on trigger events. Event conditions are specified in the extended descriptor as follows: Download 1.93 Mb. Share with your friends:
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