PLC questions

Hello. I would like to know what the 4 different types of PLC instructions are, please?

Willis,

This is a rather ambigous question...There's lots of "types" of instructions. However if I had a gun to my head I would say there are Input instructions, Output Instructions, Math instructions, & Communication instructions...but the list goes on and on...

Scroll to the very top of this page and click on "learn PLCs".

Sorry willisj. The answer to that question only has meaning in the context of the class you are in. It certainly has very little meaning in a general sense. I think Mike has a pretty solid answer, although I would personally replace 'Communication Instructions' with 'Program Control Instructions'. But again, without any better constraints, it's a meaningless question.


Keith

Hey elevmike. Thanks for replying. I am starting to learn about plc's. Do the following sound anything like plc instructions also; ladder logic,mnemonics,sfc'c,or structured text?

Thanks for replying. I am starting to learn about plc's. Do the following sound anything like plc instructions also; ladder logic,mnemonics,sfc'c,or structured text?

willisj said:

Hey elevmike. Thanks for replying. I am starting to learn about plc's. Do the following sound anything like plc instructions also; ladder logic,mnemonics,sfc'c,or structured text?

Click to expand...

It's all in the context.. What you listed are types of programming, Like Basic, Pascal, Java, bla bla.. Instructions are within the programming language.

For example:

Types of cars would include sports car, economey car, SUV..etc..
All these cars have tires.. Radials, Bias ply, Whitewalls, snow tires... Asking what type of instructions, is like asking what type of tire, not what type of car.

Four kinds?

Good, bad, long, and short?

First I heard of it since I started with PLC2's in 1988.

Maybe this is a decent programming class, or instructor, for a change.

regards.....casey

kc9ih said:

Maybe this is a decent programming class, or instructor, for a change.

Click to expand...

I dobut it.. If this question comes from a class, then the answer hopefully is in the book. Having been in the field for umpteen years I'm struggling with it myself, and I think I'm pretty well versed on the subject..

willisj said:

Thanks for replying. I am starting to learn about plc's. Do the following sound anything like plc instructions also; ladder logic,mnemonics,sfc'c,or structured text?

Click to expand...

Three of those four are PLC programming languages and it's generally accepted that there are five.
Which is the odd one out? (hint: sfc is a mnemonic)

Google IEC 61131-3

We don't need no stinkin IEC 61131-3.

LM90 Forever!

Willis, if this is a class, where is it being taught ? It would be enlightening to view the course content.

I too would like to see the course content - I do get the idea that some of these courses use BBB ( bull**** baffles brains) to survive . Yes it is important to know about the various code entry methods , but can it really be a good idea to teach a newby STL (unless he comes from a background where he learnt STL in the course of his work) ? Ladder as we all know was developed for mechanical engineers - and it has to be said that it is a very friendly method of coding (particular for those used to the "American" method of electrical drawings where it can almost be direct transposed) .
It seem too much bias is placed on waffle and silly assignments , rather than just learning good coding practices like planning and structure .

I note somewhere here is a post asking for an OFF DELAY timer using only an ON DELAY timer - that was the way you had to do it with Omron in the dim and distant past - I too would like to see a few students complete this task in ladder before waffling on about totally unconnected (and uninteresting) subjects

four types? it's easy:
1. ones you know
2. ones you think you know
3. ones you heard of
4. ones you never heard of

Types

Thats an easy one.

There are "AND", "OR", "NOT" and "WHAT IF"

Since the class leans toward AB there are some things that may help. AB has a book called MicroMentor that gives some good decent explanations on using a micro plc..ie micrologix.
http://www.ab.com/plclogic/micrologix/micromn1.html

You can also download a free version of RSLogix for the 10 point Micrologix 1000 that cost approximately $100US: http://www.ab.com/plclogic/micrologix/1000/

Your original question was a little ambigious. The 3 main instructions used represent Normally Open contatcts -| |-, Normally Closed contacts -|/|- and Output energized -( )-.

The MicroMentor book and the PLC book seem to use 4 categories for instructions to go into, basic logic, timing/counting, data/numbers and advanced but not sure its really that simple. This may be the answer though.

As was mentioned, http://www.thelearningpit.com offers training software with a simulator that is based on AB systems.