A New State Machine Behaviour Model for Procedural Control Entities in Industrial Process Control Systems

Abstract

State machines are a popular way of modelling the behaviour of systems, including process control systems. However, there are also some problems with their use in this domain, in particular in the sub-domains of the control of continuous or batch processes. The problems originate from the fact that the continuous and batch processes are, in most cases, slow in their reaction; consequently, their control sequences should have a corresponding duration. However, at present, all state machine models are based on instantaneous sequences, with only the loop (or do) sequence having a duration. This paper presents a new state machine behaviour model for procedural control entities in industrial process control systems. The main feature of the new concept of state machine processing is the durability of all action sequences and not only the “do” or “loop” sequence, as is the case in the existing state machine formalisms. The new concept enables modelling of control software for slow continuous or batch industrial processes in a more straightforward manner and at the same time on a higher level of abstraction than with using traditional state machine formalisms. The new concept is demonstrated and validated by means of a case study, which addresses a control problem from a real industrial project. The validation demonstrates that the proposed concept has a significant advantage. The concept is applicable to other classes of slow response real time systems as well. DOI: http://dx.doi.org/10.5755/j01.itc.47.3.19630