PLC Fault Finding & Troubleshooting Guide

Understanding how a PLC works and using a logical approach is the key to successfully fault finding a PLC systems.

Some fairly simple techniques can be used to fault find the PLC. The easiest is probably the half split technique. This however relies on knowing where the various check points are for the PLC system.

Our courses are based on understanding simple diagrams and then using them to fault find, delegates cannot believe how simple it is once you know where the check points are and how to check them and are then confident to say wether the signal is present or not. Check and then go on.

8 simple check points and you know where the PLC fault is.

There are possibly 4 places where the PLC program can reside, you need to know where they are and how to keep them all the same, not easy with some PLCs. If you have ever lost the documentation you used to have from your Allen Bradley PLC, this is the reason.

· Where is the problem ? Is it the PLC or is it a sensor or relay?

· How do I know the PLC is OK .

· How do i know if the PLC has a program,without the use of a laptop?

· The Led on the output card means i am getting voltage out right? does it?

· What exactly happens in between? ,theres more than just a program in the CPU

· How exactly does it scan the program? Do I need to know?

· What is this Watchdog Timer? Is it that important?

· Can I use the same output twice? That’s bad programming isn’t it?

· A PLC is a logic controller, so use a logical approach to fault find it.

· What are the 5 check points, without a laptop?

· What are the 8 simple check points ?

· The PLC is in RUN, that means theres a program right? does it?

· Where do I get the documentation for the program?

· FORCING a bit and toggling a bit is pretty much the same yeah? depends on which PLC

· We couldn’t even get online to the PLC, whats that all about.?

Our delegates are always amazed that by following the logical approach we teach works every time.

Within the first hour of the course delegates are able to identify exactly where the problem is within the PLC Control System.