Quick question about PLC testing

Edgar · Oct 22, 2004

I am new in the field so bare with me please. I just programmed this PLC controlling this machine. I want to test my process to see if it works without actually using the real outputs (motors, pump contactors, solenoid valves...) So what is the best way to do that? Can I just unplugged the fields outputs wires from the PLC (what are the risks involved with that) or is it better to use the spare outputs that I have on my PLC.
Thanks

bentleya · Oct 22, 2004

Edgar,
Usually you can isolate the outputs with fuses, breakers, etc.
Depending on your equipment, most processes are dependent on things actually happening (i.e. sensors making, starter feedback, etc.)so your logic may not work completely.
Hope this helps...

elevmike · Oct 22, 2004

1'st question is what make/model PLC & software are you using??

Bentlya has a good point, no feedback from the system usually makes testing a bit more involved. In my case I have a "test tower", a small model of a fully working elevator. It has all the buttons, switches indicators and so on, but that's a pretty big investment for just one project... So you may have to disconnect the terminal strips on your I/O and force the inputs, and watch for the desired results..

Answer the question, and I'm sure you can get some real spicific answers..

Mike.

Edgar · Oct 22, 2004

You are right. I thought about it after I posted my topic. Anyway I am using a Siemens S7-200 (CPU 214) running on Step 7 MicroWin 32. So like you said I may have to force the inputs. I think that's better cause I can check everything I need. Can I just disconnect the terminal strips with no problems?

elevmike · Oct 22, 2004

Im not sure about the Siemens, but most current model PLCs have removable terminal strips on the I/O modules. Check your manuals before prying on them..

Edgar · Oct 26, 2004

Can I just disconnect all the I/O wires from the terminal block one by one (I have about 20 inputs and 20 outputs so it's not that many.
My concern is will this cause any spikes, surges, or...
Will it be safe for the system as long as those wires do not touch each other?

GregPLC · Oct 26, 2004

Well, first off you need to verify your outputs. If an output is energized, and you suddenly disconnect it, are you okay with it turning off? Will something very large move when you do this on your machine? Check your energized I/O, see what it will effect. Otherwise, I don't see any issues that you mentioned.

Greg

Polle · Oct 26, 2004

Edgar, do you mean you want to test the program without having to run the machine?
In this case, you might load the program in a spare PLC with some switches connected to the inputs. This way you can 'play' the machine yourself by activating the inputs manually.
For S7-300, Siemens sells I/O modules with switches instead of a terminal block, but if they don't exist for s7-200 you can make it yourself easilly.

Polle

Edgar · Oct 26, 2004

Yes I want to test the program without having to run the machine, and I do not have any spare PLCs.

lanman · Oct 26, 2004

As mentioned in a post earlier this week, it's a good idea to map all of your physical IO to internal bits, then use thes bits throughout the program. During testing, these bits can be mapped to other internal bits, rather than the physical io addresses. The inputs can then be simply toggled on/off, rather than having to use forces.
What this also allows you to do is simulate feedback from the outputs. For example, if an output controls an air cylinder, then the cylinder probably has a couple of reed switches connected to inputs. Using the IO mapping method, it's easy have your cylinder output also turn on the expected inputs. Using timers, you can even simulate the time required to extend/retract the cylinder. With a little imagination, you can simulate almost anything.

ishmaelgd · Oct 26, 2004

Trip all your breakers before you test

Goody · Oct 27, 2004

Why not test it 'live' like the rest of us...........

and like the rest of us..... your hand hovering 3mm away from the e stop

joby · Oct 27, 2004

goody is right

Paulus · Oct 27, 2004

Rock-On Goody....

BobB · Oct 27, 2004

Don't Siemens have a simulator????? Just about everone else does.

Quick question about PLC testing

Edgar

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bentleya

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elevmike

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Edgar

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elevmike

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Edgar

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GregPLC

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Polle

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Edgar

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lanman

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Paulus

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