Rockwell provides a sample PLI program for a PLC-5 and a ControlLogix processor in their knowledgebase. The method shown in the examples
makes use of a PLI interface that is embedded in the PLC and conforms to the OpenBatch API. The drawback to this approach is that a PLI
program (or routine) has to be created for each phase defined in the Area Model and thus consumes PLC memory. Another approach is to provide a PC Based Phase interface that interacts with OpenBatch and the PLC (s). The PC Phase application can accommodate multiple Units with multiple phases (even parallel phases). The PC Phase application communicates with the PLC via an OPC I/O server or DDE I/O server whichever
is avialable and can communicate to the associated PLC based Equipment modules as needed. This will require a standardized PLC based equipment module structure that provides standardized Setpoint and Report data table area(s) and a mechanism to start the PLC based
Equipment Module as well as a mechinism to determine when the Equipment Module is complete. I have had experience with both PLC based phase
logic and PC Base Phase logic. If you would like to have a further discussion please contact me.
Open Batch, RS Batch, iBatch(Intellution)and even the DeltaV batch engine are derived from various revs of Sequentia (oBatch) source code. The Phase Logic Interface (PLI) is a data structure resident in the PLC for each Procedural Model Phase. The PLI is used to coordinate commands issued by the Batch server and the equipment control performed by the PLC.
The Industrial Applications team of Scheider Automation has good experiences developing integrated iBatch and Concept (IEC1131)batch control system applications. IAT has a well documented PLI interface and example code (Concept) on integrate S88 aware PLC equipment control sequences (running, aborting, holding, restarting, stopping) code in both SFC and FBD langauges with iBatch (Sequentia model).
Drop me an email if you require further assistance ([email protected]), or PLI sample code.
Regards Paul Bennison
IAT Process Control Team
919 855 1182
