Verification of control logic based on process control event diagram

Computer based logic control has been widely used in chemical processes, which is responsible for safe and reliable start-up, shut-down and sequence control. Some incidents in the computer controlled processes occur not because of computer hardware failures but because of errors in the control logic. Achieving a safe control logic is the first step of designing a safe logic control system. In this paper an improved modelling representation, process control event diagram (PCED), is described and used to express the control logic and its effect on a process. The control logic is verified by qualitative simulation based on the PCED. The technique is illustrated by reference to a case study