Interface to the pi system Version 37 and Greater

Outline of Operation

Log messages are recorded either in the PI log file or the PI application log file. The PI log file is named Pi\PiLog\pimsg_yymmdd.dat and is renewed daily. Its information is more about the status of PI than the interface. The status of the interface is recorded in the PI application log file Pipc\Dat\Pipc.log. This file is never renewed and is the responsibility of the system administrator to handle its backing up and/or deleting.

The interface begins by searching the PI Point Database for all tags configured with the PointSource code specified in the interface startup file. It records these tags in dynamic group structures in computer memory based on logical grouping (for example, one list per scan class, per point type). If any tag makes reference to a PI tag that is not present in the PI point database, a message indicating this is logged and the tag is rejected by the interface.

Data is retrieved from the gateway upon request. The conditions under which this happens are specified either by individual PI tags or by the interface startup file as described in the Interface Startup File section on page 15. See, also, the Input Tags section below. When the interface receives data it is filtered through the exception and compression criteria of each PI tag.

When the interface process has completed these initial tasks, it enters a permanent loop in which it processes input and output tags. This loop is repeated until the interface is stopped. The actions taken within this loop are described below.

Input Tags

Scan-Based

An input tag can be configured to be updated at a regular time interval specified by any one of a set of user-defined scan classes. The interval of each scan class is based from and controlled by the interface. When a scan class’s time interval expires, the data for the tags that are configured for that scan class is requested. 32 tags for a particular scan class are retrieved from the gateway at a time, until all tags for that scan class are collected. For information about defining scan-based input tags, see the description of “/f” in the Interface Startup File section on page 17.

Event-Based

An input tag can be configured to send data to PI on an event, based on the exception of the data from a separate PI point. When the value of this separate PI point changes, the data for the actual tag is requested from the gateway. For information about setting up an exception tag, see the ExDesc heading of the Tag Definition section on page 11.

Output Tags

Output tags are serviced by the interface to collect data from PI and send it to the gateway based on the exception of a separate PI tag (referred to as a “source” tag). When the value of this source tag changes, it is sent both to the gateway and to the output tag itself. This keeps a record of data that was sent to the gateway. For more information about setting up an output tag, see the Source heading of the Tag Definition section on page 11. If a tag is defined to be an output tag, its settings override any settings that apply to input tags.

If an output tag requires the destination tag to be a PI tag, the PI Performance Equation utility should be used (see the PI2 System manual, Part I or the PI Data Archive for Windows NT and Unix manual).

Tag Attributes Update

Approximately every two minutes the interface checks for any messages from PI indicating that a PI tag has been added to, edited in or deleted from the PI point database. It then makes appropriate changes to its own tag lists. An edited tag in PI is handled within the interface by deleting the tag from its tag list and adding it back in with the new tag definition. The updated information comes into effect from that time onward, without having to stop the interface.

Event Counter Tags

An event counter (also known as an IORates counter) can be used to monitor data being processed within the interface. Each event counter counts the number of times a particular event occurs, calculates a rate and sends it to PI. The rate is based on a 10-minute average and represents the number of events per minute. The interface increments the event counters assigned to it whose definitions are located in the file Pipc\Dat\IoRates.dat. This file is used by multiple PI client applications for similar purposes. The format of the file is as follows:

• 
  Comment lines preceded by a *
  * RampSoak interface exceptions IORate tag
  RmpSk_Exc, 27
  *
  * PI-YGW interface exceptions IORate tag
  

YGW_Except, 22
*
* PI-YGW input data received IORate tag

Each entry must have a PI tag name and a unique counter number (counters 35-50 are reserved for system applications). The interface will use the tag in this file whose event counter matches the event counter number passed by the “/ec” option in the interface startup file. Although Uniint supports multiple uses of this argument, it can only be used once for this interface.

For example, if IORates.dat file was defined as it is in the example above and the first occurrence of “/ec” in the interface startup file was /ec=22, the interface would use the PI tag “YGW_Except” to store its rate of exceptions. See the description of the “/ec” argument in the Interface Startup File section on page 16 for more information.

The tag specified in the IORates.dat file must be defined in PI and use a different point source than that of the interface (the default point source L is adequate).

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