What should be the basic knowledge to learn PLC?

What?

Why?

When?

Where?

Types?

Features, software?

How to configure?

How to program?

Learning about PLC’s is understanding  what you are trying to control, a single PLC can be programmed to replace thousands of relays. PLCs can be programmed using standards-based programming languages.  A graphical programming notation called Sequential Function Charts is available on certain programmable controllers.

Programming and troubleshooting skills

First you have to understand the logic that rules the CPU - central processing unit - of an PLC.

A program for PLC is build in steps (rungs), like a ladder. This is why it is called: "ladder logic programing ".

When a program is running, the CPU first reads all the rungs and after that takes action. So, at the end of readings "he" close/open contacts or turn on/off relays based on how the process is altered in time.

Let's take a short example: we have a button B whit a NO (normal open) contact and a motor M. We start the program and the CPU starts to read. First it sees that B is not pressed so he decide not to turn on M.

He continue the readings and taking decisions until the CPU is turned off. So, after a while we press B. Now, CPU see B pressed, so at the end of the reading will turn M on and keeps it on as long as we keep B pressed.

When we depressed B, by removing the finger, the CPU reads that and at the end of the reading takes the decision to turn M off!!! Notice here that short delay between depressing B and turning off M?!? This can became very frustrating when programming!!!

Above is a simple example but the situation becomes complicated when the rungs are much more complex!

But, in essence, if you understand this logic, a PLC course, practice and time is what you need!

For more information you can read IEC61131 part3!

Good luck!

There are two basic knowledge in order to adapt the PLC, One is you must have a thorough knowledge and experience in troubleshooting MEP system and the second is, you know how to work on computer system. Without these two (2) basic knowledge, you will find yourself a hard-time working in PLC. Hope this helps give you an idea.