1. Junior Member
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## Programmable Logic Controllers

Just wondering what the recommendations are out there for learning about PLC's, textbooks or online and who? Thanks!

2. Senior Member
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Can't give a review because I don't work with them, but my book is the one the local union uses to teach them: Frank D. Petruzella's Programmable Logic Controllers 3rd Edition.

I have to keep reminding myself that 2005 was a significant time ago when it comes to technology, though.

3. gar
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revlution4:

A PLC in its earliest form was a stored program digital computer using a specialized language that simulated relay logic for control of something.

Today PLCs have been extended to perform many other functions than just logical circuits, such as math functions.

You need to know how to design or work with logical circuits. This means knowing how to work with AND, OR, NOT, timers, retentive memory, and transitional contacts.

The truth tables for AND, OR, and NOT describe their function. The word OR usually means inclusive. Meaning any one or more inputs to an OR will produce an output. An OR or AND can have many inputs. There is also an exclusive OR written as XOR and is only a two input function. The XOR produces an output only when the two inputs are different, and no output when the inputs are the same.

You will probably learn more by buying an inexpensive PLC, studying its manual, and creating programs than by trying to study some text book. There are some functions that will be common to all PLCs and others that are unique to specific PLCs.

For ordinary machine control logic I would never use a PLC in a sequencer mode, use only combinatorial logic.

Sequential mode should only be used where it uniquely fits the application, and that is not in a general machine application.

Learn about logical circuits first, then study a specific PLC.

You will learn the most and quickest from hands on experience.

.

4. Rockwell Automation has the best training, however it is specific to Allen Bradley PLCs.
Expect to pay \$600 a day.
https://www.rockwellautomation.com/g...overview.page?

What I would recommend is to take a basic two day class, then get your hands on a PLC and practice programming.

AB has a nice book about \$10 called MicroMentor, it may be out of print, but well written its meant to go along with their Micro Logix PLC line, in particular the ML 1000 series.
A DC version of a ML1000 is about \$100, and the starter software is free

here are a couple of good plc forums
https://www.mrplc.com/
http://www.plctalk.net/qanda/

Koldwater Technology has some good interactive DVDs

And again I want to emphasize that you must have hands on to learn PLCs, book learning is not enough!!

5. If you can understand ladder logic diagrams you already know quite a bit of what you will need to know. Proper syntax and other procedures is most of the rest and can have some variances between units. This gets you through for most basic programming functions, there can be more complex functions but they are explained in users manuals and help pages in the software help files. As mentioned you might be better off buying an inexpensive controller and learn just by playing around with some of your own mock programming.

Automation Direct has some Clic PLC's you can purchase for under \$100. Their program software is free and downloadable from their site. In fact you can write all the programs you want with the software and even check it for syntax type errors, but to be able to actually have an output react to input conditions you really need to load that program into the controller and run it.

6. Also I forgot that the trend in PLC communications is TCP/IP (Ethernet), learn as much as you can about Ethernet, routers, switches, subnets, domains,....

7. GMc
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Originally Posted by revlution4
Just wondering what the recommendations are out there for learning about PLC's, textbooks or online and who? Thanks!
If you have the opportunity to take a trip to Charleston, SC I highly suggest you take a class at Ron Beaufort Training, LLC , you will not be sorry.

You can get a very good idea of his GREAT ability to teach by reading some of his posts at PLCs.net, just search for Ron Beaufort.

I personally have taken a cople of his classes and have always wanted to go back and take a PID class but never made it.
Last edited by GMc; 10-31-17 at 03:23 PM.

8. If you can afford it buy a used plc (processor and few i/o cards)
perhaps ebay or a salvage yard
get the interface sw for a computer
free odf manuals for the mfg
And start playing

9. Junior Member
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Thank you all for the replies, I will do some more research into the various items. I do understand some basic ladder logic, I just need to expand on it more and implement it.

10. gar
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revlution4:

From your last post it seems that your basic need is to understand logical circuits.

Suppose you have four binary signals A, B, C, and D. Binary signals are two state signals. Variuos names are assigned to these two states. Typical names are TRUE and FALSE, 1 and 0, CLOSE and OPEN, etc. Various logical functions are defined by what is called a truth table. So signal A can be either T or F, and the same for the other logical signals.

A truth table for two inpits has 4 possible input combinations. 00, 01, 10, and 11. The truth table for AND has a 1 for its output only when both inputs are 1s. Whereas an inclusive OR, usually described by the word OR, only has a 0 output when both inputs are 0.

Note that the logical function NOT is a single input function where the output is the opposite of the input.

If we have a logical signal A, then the NOT of A is often written as /A or A with a bar over it. If we write a logical equation like A and B and NOT C = D, then D is true only when A and B are true, and C is NOT true.

So an electrically latched relay could be described as :
A or ( D and NOT C ) = D
where D is the output.

If C is not asserted, meaning NOT C is TRUE, and A is asserted momentarily, then D remains on after A is lost because of the parallel path, the OR function, maintains D on. D can only be dropped out if C is asserted making NOT C a 0 while A is still not asserted. Sounds like double talk, but try thinking this way.

To create an exclusive OR function write ( A and NOT B ) or ( NOT A and B ) = D

.

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