Discrete Logic Control Research Articles

Synthesis of Microprogram Discrete Logic Control Systems

Synthesis of Microprogram Discrete Logic Control Systems

Where others fear to tread [programmable automation controllers (PACs) and programmable logic controllers (PLCs)

Until relatively recently, PLCs dominated the automation space, but, as plants cut costs and reduce system upgrade funding, engineers must continue to improve the plant while keeping overall costs low. Many plants are successfully implementing a strategy to locally optimise their processes by intelligently applying new technology to increase efficiency at bottlenecks. Local optimisation of processes requires higher speed signal acquisition and more sophisticated analysis operations, such as machine vision, Fourier transforms, order analysis and model-free adaptive control. The traditional PLC architecture, with I/O scanning and ladder logic, works well for sequential, discrete logic control, but extending this architecture to build in the more advanced functions required for local optimisation is often not practical. PACs combine the floating point processors, wide range of networking options and sophisticated programming tools more usually found on the PC with the industrial I/O and ruggedness usually associated with PLCs. The use of programmable automation controllers (PACs) in process control and automation is growing rapidly. In many applications, however PACs are not replacing PLCs; rather engineers use them to expand process monitoring and control into areas where PLCs fear to thread.

A case study in hybrid process safety verification

A recently developed, model-based methodology for the verification of chemical process safety is applied to a batch fertiliser production process. The latter is modelled within a discrete/continuous modelling framework to represent the hybrid characteristics of a processing system involving batch operations as well as discrete logic control. The optimisation-based safety verification technique aims at determining whether the process and its control system are able to satisfy the safety and operability specifications despite the possibility of human error and equipment failure. The results of the analysis are compared to those of different safety verification procedures proposed in the past. The feasibility and benefits of using rigorous, model-based techniques as opposed to qualitative methods for safety assessment are highlighted.