A small PLC flexibly controls a complex system. What you can see is two rows of input and output relay terminals, corresponding indicator lights and PLC numbers, which are staggered up and down, just like an integrated circuit with dozens of feet. If anyone does not look at the schematic diagram to repair the faulty equipment, he will be helpless, and the speed of finding the fault will be particularly slow.
In view of this situation, we draw a table according to the electrical schematic diagram, paste it on the console or control cabinet of the equipment, and mark the electrical symbol corresponding to each PLC input and output terminal number, Chinese name, that is, the function description of each pin of similar integrated circuit. With this input and output table, electricians who understand the operation process or are familiar with the ladder diagram of the equipment can carry out maintenance.
But for those electricians who are not familiar with the operation process and can't see the ladder diagram, they need to draw another table: PLC input and output logic function table. This table actually explains the logical corresponding relationship between input circuit (trigger element, associated element) and output circuit (executive element) in most operation processes. Practice has proved that if you can skillfully use the input-output correspondence table and the input-output logic function table to repair electrical faults, you can also easily do without drawings.
