Performance of logic controllers in industrial environment

The performance of programmable logic controllers (PLCs) in an industrial environment is investigated. A survey is first presented which briefly deals with the general adaptation and suitability of programmable controllers in some Swedish plants. The reasons behind the decision to use or not to use PLCs in safety systems are then investigated. The aspects of a burner control system for a certain boiler are considered. Safety and risk aspects are discussed in terms of reliability, installation, and the human element. The study shows the superiority of PLC systems over conventional relay technology, but also that PLCs are seldom used in safety connections mainly due to nontechnical factors such as human conservatism.<>