Monitoring systems in sequential program control arrangements

Abstract

A monitoring system in a sequential program control arrangement comprises an operation detecting portion for detecting operating states of components of the sequential program control arrangement for machinery, a memory for storing reference operating states at sequential check steps, a difference detecting section for detecting a difference between an actual operating state detected by the operation detecting portion and the reference operating state, a control section for causing the difference detecting section to compare the actual operating states detected successively with the reference operating states at corresponding check steps respectively, then after a first check step at which the differnece between the actual operating state and the reference operating state is detected, to compare the actual operating state of the first check step with the reference operating state at each of check steps between the first check step and a second check step ahead of the first check step by a predetermined step number, and further after a third check step at which the reference operating state is coincident with the actual operating step of the first check step, to compare the actual operating states with the reference operating states at check steps ahead of the third check step respectively, and a checking section for checking the operation of the machinery based on the differences detected by the difference detecting section.