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PI BASemAPI
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- Location4
- Zero and Span Attributes
CompressingIf the compressing attribute is set to 1 (ON), then the following compression specifications are used to filter the data that is passed from the Snapshot to the Archive. CompDev, CompMin, CompMax, CompDevPercentThese are the compression specifications. CompDev is the compression deviation; CompMin is the compression minimum time; and CompMax is the compression maximum time. CompDevPercent and CompDev are related by: CompDev = CompDevPercent * Span / 100 where Span is defined by the Span PI point attribute. The “swinging door compression” algorithm is used to filter the data. The algorithm is described in the PI Server Reference Guide manual. ScanBy default, the Scan attribute has a value of 1, which means that scanning is turned on for the point. Setting the scan attribute to 0 turns scanning off. If the scan attribute is 0 when the interface starts, a message is written to the pipc.log and the tag is not loaded by the interface. There is one exception to the previous statement. If any PI Point is removed from the interface while the interface is running (including setting the scan attribute to 0), SCAN OFF will be written to the PI Point regardless of the value of the Scan attribute. Two examples of actions that would remove a PI Point from an interface are to change the point source or set the scan attribute to 0. If an interface specific attribute is changed that causes the tag to be rejected by the interface, SCAN OFF will be written to the PI point. Location4For interfaces that support scan-based collection of data, Location4 defines the scan class for the PI point. The scan class determines the frequency at which input points are scanned for new values. For more information, see the description of the /f parameter in the Interface Startup Parameters section beginning page 3. Zero and Span AttributesZero and Span attributes are required for PI point types of Int16 and Float16 because the values of Zero and Span attributes affect the data representation in the Archive for these point types. Zero and Span attributes for other point types may have an affect on the data collection especially if the compression and exception specifications are specified using the percentage point attributes. For more information, see PI Server Reference Guide. Do not define the Zero and Span attributes for digital PI points on a PI 3 Server node, because PI sets them internally when a digital point is created. Zero will be set to 0 and the Span will be set to the number of digital states in the set. Download 1.93 Mb. Share with your friends:
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