Wanting to Know More and More

http://www.industrial-ebooks.com/CBT_software/Troubleshooting_Basic_Electrical_Control_Circuits94.php

See this site: www.thelearningpit.com, there is a simulator (LogixPro 500 PLC Simulator). You can download it free for 15 days trial period. This website is good for PLC learners.

- MS

Just go here and down load their free PLR software. Its about all you would ever need to learn for basic ladder logic programing. Plus its user friendly too!

http://bb-elec.com

you might also find some programming help by going to youtube

there's a number of items there I've found interesting

Stub

good for you tonys. So what started you off.. the problem was equipment and program.

I suggest getting a PLC for your self and building a small test panel with some push buttons and selector switches (and a potentiometer if you want to get into analogue). PLCs are cheep now, and can usually be salvage from an obsolete piece of equipment. The biggest problem is getting hold of a copy of the programming software. If you only intend to use this for your own education, and not for commercial purposes, I don't see and ethical problem with "borrowing" a copy. Anyway, most PLC manufacturers have free demo versions.

While you state that you work with Allen Bradley, you might want to consider a less expensive make if you have to buy one. The differences in the instruction sets and the the ladder logic program structure between makes is minimal. Check Automation Direct. www.automationdirect.com they have some very inexpensive but powerful models and free programming software for some.

i thank everyone for theyre input, it all seems helpful. my comment tag is a question i get asked all the time by "the man." all i ever used was ab programs and software, i dont think anyone in alabama has heard of anything else. anywho thanks again. oh when i worked for a palletizer company we used alot of device ney by ab, what happened to it cause i havent seen it since i went into maint.

I do advise that you get hand's on experience in relation of the PLCs,,, I mean you have to learn a lot about all brands of the PLCs manufacturing companies in addition to Allen-Bradley plc's(this way you can increase your marketability).. Also you should work side by side with your colleagues (engineers & tech'es),,,, and the most important thing is to work by your hands, because we the human beings learn by doing,,,, that's it from,,,,,,,,,,,

• Obtain copies of other programs used elsewhere in the facility. Study them.
• Ask questions of the original programmer why things were done in certain ways.
• Ask for a copy of the facility's PLC programming standards, and study it.
• Enrol on a formal training course locally.

Go to www.plcs.net and download a copy of LogixPro. It's free for 30 days and then costs $32. Well worth it.

MattJohnson,

I got into PLC programming without any formal education in that topic, but with lots of related experience including Fortran IV (that dates me!). I suggest:

• If you aren't comfortable with Boolean logic (if, and, not, or...) become so. Any ladder rung, like any wired connection between push-buttons and relays, is essentially a statement of Boolean logic. This is the point where a text description of your desired function is translated into the logical equivalent.
• Make it a mantra to document, document, document. Yeah, you know why you did something---now. But, lay it down, do something else, and then do you remember all the quirks of why it was so?
• Before starting a project, write out in excruciating detail a sequence of operations for what is supposed to happen. How is each component supposed to operate; where is it located; what must come first; how do you start; how do you stop; what time delays are needed... A good and complete sequence of operations is the blueprint for your successful program.
• Realize the peculiarities of PLC programs--1) They are usually endless loops that execute the logic, update the outputs, check the hardware health, read the inputs, etc. 2) There are many ways to overcome hardware limits, such as interrupts. 3) Logic is solved sequentially, so the order of statements and order of rungs is sometimes critical to proper program function. As an example of this, consider how a 1-shot is programmed (not just referenced as an instruction).
• There is no such thing as two things happening simultaneously in a PLC program, unlike in hard-wired relays, etc.
• PLC's are not perfect and some instructions don't always function the way you expect them to, or even the way the software claims.
• If you are working on a safety issue, don't put it into the PLC logic, unless you are using one that is explicitly designed and certified for this use.
• It is best if the PLC always knows what is happening. Don't put relay contacts after an output, unless there is an input to let the PLC know the status of that relay.
• Become comfortable with subroutines. They can break a complex program into easily handled sections, and make it easy to design a big program and then create it in sections.
• Keep aware of instruction scan times. Make sure that the processor and program are looping fast enough to keep up with the status of the machine or process you are connected to. This will also dictate hardware--DC versus AC inputs or outputs, for example. If the timing is off, you will have unpredictable results. I'm sure that nearly every programmer can tell you stories of this.
  
• Finally, every programmer has his/her own way of writing a program. Some are shorter than others; some are easier to follow than others. Also, how a program is written will often be dictated by what hardware or operator interfaces are present. You might have bits that seem to have no reason to exist, but are referenced (and even controlled) by a totally separate piece of hardware.

The above comments are primarily aimed at programming in Ladder. There are a number of other recognized and standard programming languages for PLC's. Each one has its own strengths and peculiarities. Ladder just happens to be what nearly every industrial electrician can pick-up and understand the quickest. Also, as you move from one processor family or brand to another, you will find that the instruction set and even the programming format will change. Modicon's networks are unique and wierd to those who have not worked with them for a while. Some brands' math instructions required me to move the data into specific accumulator registers before executing the instruction and then to move the data out to where they would be used. Some had very liberal addressing space while others were limited. Addressing formats and limits have to be strictly adhered to--some may be octal, others decimal, even others hexadecimal. . . .

I hope you continue and succeed.

--John M.

Hello All,

First, John M.: that is the most compelling and straight-forward statement about PLC's (and programming in general) I've seen to date. PERIOD!!

Matt, get to the GE/Fanuc website. There are a LARGE number of tutorials that address the Modicon/Telemechnique/A-B infrastructure.

Last: I've been corrected that the tag line I use was actually Arthur C. Clarke. As to PLC's it is doubly true.

r/s

GLB