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plc programming

plc programming

(OP)
Anybody please help me,

I am new to plc, but after learning basics i got project to work on it.I was introdced with electrical cad diagram from which i should design ladder diagram.Since I learned PLC with concepts and conditions never came across to build ladder logic with electrical diagram.Pls anyone come forward and help me with some examples so i can easily understand the concept to get logic conditions from electrical diagrams.

RE: plc programming

There is little we can do for you...

1) Programing a PLC requires you to fundamentally understand what the circuitry and hardware can be made to do and what it needs to do. If you cannot find a way to understand the electrical diagrams to this level you cannot proceed.

2) Once you understand the electrical diagram you need to work from a specification. The specification is a document that describes the system's expected function. Think about a dishwasher. It will have several electrical apparatus that need to work in an organized, sequential manner to realize its proper function. A specification will be a recipe that explains all the states the dishwasher needs to pass thru to accomplish its task. As the PLC programmer you would normally look to the customer. This could also be your project leader or it could be yourself - if you're expected to fully understand the system. Someone needs to develop a detailed written specification.

To summarize: A PLC programmer is not handed an electrical diagram and told, "Program the PLC". He is handed an electrical diagram or list and a detailed specification. From these he or she can then proceed to program the PLC in a deliberate, successful manner.

Keith Cress
kcress - http://www.flaminsystems.com

RE: plc programming

Agree with above. You have to understand the system/diagram so you can program it. Cause and effect. Typically your circuit diagrams are design to model after ladder logic program.

RE: plc programming

(OP)
Thanks for the replies,my problem is it is an old machine with relays,more buttons,indicators and wiring .So to modify it with plc and touchscreen,I was introduced with its electrical diagram to create ladder for plc. I feel tough to understand the conditions of its working with it.So is there any way to understand with the help of electrical diagram or so.

RE: plc programming

If the machine still works you can use it or operate it in all manners needed to FULLY exercise it. You then write the aforementioned specification as a list of functions and user adjustments. You need to list all the subsystems in use during the machine's various functions.

Back to the dishwasher:
Prewash cycle
1) Fill
* Turn on water valve
* Turn on Prewash light
* Wait for water level to reach -full-
* Start time-out timer if fill switch or water source have failed
2) Once full
* Turn off water valve
* Run motor forward
* Do for X minutes
* Stop motor

Prewash Drain
* Run motor in reverse
* Start time-out for pump out
* Stop motor
* Turn off Prewash light

Etc etc until done with all states.

Then, you need to understand your circuit diagram to understand how you can control the various electrical apparatus with the PLC.

Keith Cress
kcress - http://www.flaminsystems.com

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