The cause place investigation method null of the abnormality in programming the ladder sequence

摘要

PURPOSE:To shorten the production stop time and to reduce the loss by logically tracing back a program of the ladder sequence system with an abnormality as a retrieval key to automatically clear up the cause position of the abnormality. CONSTITUTION:Plural blocks 31, 32, 33... each of which has an output instruction part 2 whose state is determined by the logic of a condition instruction part 1 having a relay are connected like a ladder. A process I where the output instruction part having an abnormal state is used as the retrieval key and its value is searched in all blocks, a process II where the validity of the block corresponding to the logical operation result of the condition instruction part of the found block is decided, a process III where all operatable relays are searched at the time when the block is valid, a process IV where the found relay is used as the next retrieval key to repeat processes I to III, and a process V where results for a failure in search of blocks and relays are outputted are provided. If an abnormality occurs, the program is automatically logically traced back with this abnormality as the retrieval key to automatically clear up the cause position of the abnormality.