Interface to the pi system Version 37 and Greater
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- DigitalSet (PI3 only)
- InstrumentTag
- Typical Value
- Other Parameters
Tag DefinitionDigStartCode, DigNumber (PI2 only)If the tag is of type D. these fields specify where its corresponding digital state strings are located in the PI2 digital state table. The DigStartCode specifies the position in the table of the first digital state is. The DigNumber specifies the number of further states in the table that are to be associated with the tag. For example, if a the digital state table contained four states in a row from 22 to 25 that were to be associated with a tag, that tag’s DigStartCode and DigNumber would be set to 22 and 3, respectively. See the PI2 Digital State Table section on page 9 for more information about digital states. DigitalSet (PI3 only)If the tags is of type Digital, this field specifies which digital state set it corresponds to. The digital states that will be used for this tag are those found in the specified digital state set. See the PI3 Digital State Sets section on page 10 for more information about digital states. ExDescThis field is the extended descriptor of a tag. It is used for defining the source of an event for event-based input tags. The Event-Based heading of the Input Tags section on page 5 describes the operation of event-based tags. The tag that is monitored for the event is specified here in the following format: EVENT=<PI_Tag> For example, EVENT=CTD158 Here, the interface will request data for the tag only when the PI tag CDT158 receives an exception. Only the occurrence of the exception is recognised by the interface and the actual value of CDT158 is ignored. If it is necessary to include other information in the ExDesc field, this can be separated from the event keyword using a comma. For example, if the ExDesc contained
The interface would then recognise only the EVENT keyword and the comment would be ignored. Note: If the ExDesc field is used for specifying that a tag is event-based, it will override scan class information specified by Location4. See the Location4 section below. InstrumentTagThis field contains the full name of the Yokogawa point with which a PI tag is associated, including the Yokogawa data type. The data type must be separated from the tag name by a comma. For example, FIC0417,PV. For input tags, this represents the Yokogawa point that the data is to be collected from. For output tags, it represents the Yokogawa point that data is to be written to. Lower-case letters are not valid for an instrument tag. Location1This field is used to specify whether a PI tag is an input tag (from Yokogawa to PI) or an output tag (from PI to Yokogawa). Valid values are from 0 to 3 and are described in the following table:
A clipped value is forced to be within the bounds of the PI range by setting values that are outside the range of the PI tag to the limit of the range. For example, if the Zero and Span of a tag were 50 and 200, and the output value was 270, it would be changed to 250. If the value for the same tag was 20, it would be changed to 50. See the Zero/Span section below for more details about the range of a PI tag. Location4This field is used to specify the scan class number (and, subsequently, the data access type) for an input tag. The scan period and data access type of each scan class is specified in the startup file. See the description of “/f” and “/g” in the Interface Startup File section on page 15. If a tag is to be read by PI exception, Location4 does not need to be configured. See the ExDesc section above for information about how to set up an exception point. PointSourceA point source is a character defined in every tag to group together all tags collected from a collective source. The interface will look for all tags that have a particular point source defined. The PI tag’s point source must match the point source character defined by the “/ps” argument in the interface startup file (see “/ps” in the Interface Startup File section on page 19). The point source for character may be any printable ASCII character except C, Q, T, @ and ? are reserved for PI2 and C, L, R, T and 9 are reserved for PI3. PointTypeThis field specifies the point type of a PI point. Use R (PI2) or Float64/Float32 /Float16 (PI3) for real data, I (PI2) or Int32/Int16 (PI3) for integer data and D (PI2) or Digital (PI3) for digital data. For PI2, real data can stored in the archive as SCALED or FULL precision. For SCALED real data, the input value is stored as a scaled value between 0 and 32767 in the PI archive. FULL precision real data is saved as a 4 byte floating point value. For PI3, the equivalent of SCALED and FULL data types are Float16 and Float32, respectively. Values which can be less than 0 should be saved as real data since the range for PI integers is between 0 and 32767. If input value of integer point is minus, the digital state INT_MINUS will be written to PI. See the Digital States section on page 9 above for more information. The interface supports Float64 data for PI3 input points only and not for output data to DCS. Float64 data is always put to snapshot thus no exception reporting is done. Note: It is not necessary that the data type of a Yokogawa point match the data type of its corresponding PI tag. For example, a Yokogawa point of type real may correspond to a PI digital tag. To do conversions, however, the interface may need to truncate some values for PI to be able to store them. ScanThe Scan flag is used by the interface to control processing of a PI tag. A tag with a scan value of ON will be serviced by the interface. Setting the scan field to OFF will cause the interface to delete that tag from its structure of tags. The digital state value of SCAN OFF will be written to the tag when its scan flag has been turned off. Change it back to ON to enable data collection for the tag to resume. SourceTagThis field is used for defining the source of an event for event-based output tags. When the value of the PI tag specified in this field changes, it is sent both to the current tag and out to its corresponding Yokogawa point. For more information about the operation of output tags, see the Output Tags section on page 5. Typical ValueThis field is not used by the interface but must be set to a value that lies within the range of the tag. See the Zero/Span section below for more information about a tag’s range. Zero/SpanThis field specifies the range of the PI tag’s zero and span. For input tags, if the value of a Float16 or Int16 tag is outside of its specified range, either the digital state UnderRange or OverRange will be written to the tag. If the tag is specified as a Float32 or Int32, the input value is written to PI even when it is out of range. For output tags, the value being sent to the DCS can be checked and changed according to the range of the tag. See the Location1 section above for more information about output tag values. This range is also used to determine the compression dead-band width in engineering units when using the CompDev or CompDevPercent(PI3) or DeviationUnits (PI2) field. For more information about these fields, see the PI2 System manual, Part I or the PI Data Archive for Windows NT and Unix manual. Other ParametersOther PI tag fields that need to be configured are listed below. The configuration of these fields is regardless to the interface. For information about configuring these fields, see the PI2 System manual, Part I or the PI Data Archive for Windows NT and Unix manual.
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