A pearl-based multi-loop and multi-sequence controller

The growing complexity of industrial automation systems is accompanied by the requirement for improved system dependability. From this point of view, when designing distributed, hierarchically organized automation systems, some high-level languages have to be used not only for software implementation but also for software design. Although the use of high-level programming languages for higher hierarchical levels is standard, this is not the case at the field-level where programmable controllers are placed, allowing the block oriented definition of closed-loop and sequence-controllers. Furthermore, a transparent multi-tasking software implementation is mostly missing. On the other hand, the real-time process-oriented automation language PEARL and its extension Multicomputer PEARL represents a standard allowing the scheduling of concurrent closed-loop and sequence control tasks for distributed systems in a very transparent way. The degree of transparency, achievable by its module concept, as well as its high-level multitasking and process-I/O concept, recommends PEARL not only for software implementation but, as well, for software design. A PEARL-oriented software design will also improve software dependability significantly, if it is systematically transformend to another implementation language wanted, e.g. the language C. In this paper, a controller will be decribed that can be graphically configurated and parametrized. The controller software has been designed in a PEARL-oriented way and has been implemented in PEARL as well. The system allows in a conceptually fully consistent way graphical, block-oriented configuration of closed-loop and sequence controllers beeing realized as independently scheduled tasks of programmable sample-time and interrupt, respectively. Control and sequence tasks can be mutually dependent via the process-I/O, and synchronized via RECEIVE/TRANSMIT communication blocks.