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How to troubleshoot with a PLC

How to troubleshoot with a PLC is the most common practice.

PLC Technician

Troubleshooting PLC itself is a much less common practice. As PLCs are so reliable. PLC (Programmable Logic Controllers) where designed specifically to be more reliable thank a computer, and more simple so a maintenance technician could work with them, including use them to troubleshoot the machine and automation control process.

The PAC (Process Automation Controller) on the other hand is much more complicated as it is a customized industrial computer, designed with computer IT and programmers in mind, not the maintenance technician or electrician. Likewise, the PAC is a lot less useful for troubleshooting machines and automation control systems. Actually, in that respect, the PAC is the opposite due to its complicity. It is more common end-users (process and manufacturing maintenance personnel)  will be troubleshooting the PAC itself more than using it as troubleshooting tool for the machine. Read on to learn why…

Given that PLC vendor’s intent was to make the PLC easy for the maintenance electrician to use, beyond just using ladder logic as programming language, the added many great software tools to aid the maintenance electrician in troubleshooting machines. You wont find most of these PLC troubleshooting software tools and design features in a PAC. Below are just a few examples. At the end of this article will be a link to read about more. To learn about all of the PLC troubleshooting tools and techniques, and to master PLC troubleshooting, there is currently only one way, attend a hands-on PLC Troubleshooting Training Seminar in St. Louis.

How to troubleshoot with a PLC | Basics

In the real world, 99% of the time, the problem with a machine or process is not the PLC, it is an Input or Output. In other words, it is one of the hundreds of sensors, switches, solenoids, etc. gone bad, out of adjustment or not be made. If the people who wrote the PLC program used PLC programming best practices, the PLC program will be well documented ladder logic. (A symbolic programming language as easy to troubleshoot as looking at a ladder and seeing what rung is broke on the ladder. )

Given the above, based on symptoms reported, you search PLC program for the input or output not working, then trace back through the ladder logic to find out what contact is not being made and that is the sensor or switch causing the problem that you need to look at out in the real world. most of the time that is how you troubleshoot with a PLC, simple as that and takes about 4 minutes to find root cause. (If you have been properly trained by BIN95.)

But … in real life it is not always simple, just most of the time with a PLC. There can be intermittent problems, analog problems, poor management of automation equipment in your facility, etc.

FYI:  Management of PLCs in your facility is also taught in BIN95 PLC Training seminars.

Those little more complex PLC troubleshooting instances that occasionally come up is where PLC troubleshooting software tools that vendors provide, come in. Read How to troubleshoot PLC Allen Bradley to learn more. Below are a few excerpts…

For more cumbersome troubleshooting like intermittent problems, RSLogix 500 has great tools like the Histogram, Custom Data Monitors, trend charts, writing your own diagnostics rungs using Latch bit, etc.

Rslogix 500 Custom Data Monitor    RSLogix 5000 Trend Charts

One example of real world troubleshooting we teach, which is not in books or software, is using RSLogix 500 program “Compare Tool” (Compare Tool may be in your version of RSLogix 5000, or as a separate software for PACs. Or you might not have the tool if you are using PACs, instead of PLCs to control your machinery.) Those not spending years maintaining a PLC/PAC controlled facility may not be aware of the common scenario of one employee on one shift changing the program, and the rest don’t know it. If the troubleshooter suspects that, they can use the program compare and once again within about 15 minutes, find the problem.

PLC Troubleshooting tool

System Data Tables and other data tables found in a PLC (like RSLogix 500) are great troubleshooting tools too, but are not in PACs (like RSLogix 5000). This is another major factor contributing to the use of PACs resulting in increased troubleshooting and downtime. In BIN95’s instructor based PLC training, we also teach best practices in writing PLC programs, so attendees can identify if they are being used before purchasing new machines or systems controlled by PLCs. (Like RSLogix 5000 programmer compensating for missing data table files in their tag naming conventions, for example.) Having a program that was written using PLC programming best practices, with the end user in mind (customer who has to maintain equipment for the next 10-20 years), greatly reduces troubleshooting time. … continued at https://bin95.com/rslogix-5000-troubleshooting.htm

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July 24, 2017 - Posted by | Education, Electrical, maintenance, manufacturing, PLC, PLCProfessor, Skill Shortage

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