Pi bailey Sem api interface Manual
Download 2.52 Mb.
|
PI BASemAPI, UniInt Interface User Manual
- Navigate this page:
- Diagram of Hardware Connection
| Serial Based Interface
The semAPI software handles all of the Bailey communications protocol and thereby makes it possible for the PI interface to communicate to Bailey ICI modules via a variety of transport methods (serial, Ethernet, and SCSI). Server class machines often have inferior serial ports. Server class machines are not required for most interfaces and should not be used, especially not when serial port connections are required. Diagram of Hardware ConnectionPrinciples of OperationThe PI Bailey semAPI interface supports the major Bailey point types for reading data from the Bailey Infi90. It also supports data output to the Bailey Infi90 system via the Analog and Digital Report functions. All data read by the interface come from the Bailey system as exception reports. Bailey generates an exception report whenever the value or the status changes, or when a specific amount of time has elapsed since the last report (exception maximum time). Data is output to Bailey with any change in the related value or the event time in PI. The most common network topology used by the interface is peer-to-peer. With this approach, the interface process and semAPI software reside on the same computer. The computer is physically connected via serial, SCSI or Ethernet cable to a Bailey communications module, which is connected to the Bailey Infi90 network. At startup, the interface retrieves all the PI tags for the specified point source and processes only those tags with matching ICI number. The interface builds the tags into a sequential list keyed by list index position. The interface attempts to initiate communication with the Bailey communications modules via calls to Bailey semAPI libraries. These, in turn, establish a device driver process to talk to the Bailey communications module. The Bailey device driver handles physical and low-level protocol communication. Via the semAPI call, the interface then establishes the tags in the Bailey communications module point table. After all points are established and connected, the interface enters the data collection phase. The interface keeps reading exception data from the Bailey communications module until the maximum number of exceptions specified in the interface startup parameters have been reached or ten read exception calls have been made. The interface checks for output events to be processed. Whenever output tags are triggered within PI, data will be sent to the Bailey system. If more than two minutes have been passed since the last PI point database check, the interface will check for point database changes. Tags are added, modified, or deleted from the interface if necessary. When the interface encounters ten consecutive communication errors with the ICI, the interface will attempt to clear the error by going through the error recovery procedure. The error recovery starts with disconnecting from the semAPI. Then the interface goes back to the startup phase of the operation, as described in the beginning of the manual. This auto error recovery feature normally clears problems caused by line noise. However, hardware failure will still require human intervention. Note: Since the ICI point table can only buffer one exception for each point, it is possible for the interface to miss exception reports for Bailey tags that are changing values too rapidly. For example, if the control engineer has configured an RCM to reset itself after the operator has set the RCM to the ‘on’ state, the PCU module will generate two exception reports within a second. Most likely, the interface will not be able to catch the first exception report before it is over-written by the second exception on the ICI module. Download 2.52 Mb. Share with your friends:
|