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Connecting separate circuits help needed

  1. Apr 5, 2012 #1
    I'm a graduate engineer at a manufacturing plant and unfortunately my lack of experience shows. Today I had the simple job of connecting the output of a limit switch on a circuit from a machine to the input terminal of a robot on a separate circuit. Both use 24v DC. I failed horribly. Probably because I attempted to use a single wire and evidently electricity needs to flow in a loop.

    As both machines were running of the mains wouldn't there already be a loop present? And at the risk of sounding even more silly, does there need to be a loop, or are the electrons just trying their best to get to ground (0v)? I was actually under the impression 24v would travel to 0 volts through a single line no matter what the conditions.

    Finally what would be the best way to wire these two circuits together. Maybe the 24v from limit switch should be run through a relay to isolate the circuit and having a second wire run between the machine neutral and the robot neutral? I honestly have no idea. I will try and draw up a little diagram in paint.

    Thanks in advance for any assistance. This is really eating at me, and I it would help me out a lot. Pretty confused at the moment.
  2. jcsd
  3. Apr 5, 2012 #2


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    Generally when hooking two machines together in this manner, the machine that is 'signaling the other machine' provides a set of contacts (switch) that open and close appropriately. This set of contacts will be isolated from the signaling machine.
  4. Apr 5, 2012 #3


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    ergwell, Welcome to Physics Forums!

    Are there no electricians at your manufacturing plant? You are dealing with one of the most basic types of electrical connections. No one needs a degree to do this task.

    I am awaiting the diagram you promised. Please include as much detail as possible...that will make suggestions you receive more useful.
  5. Apr 6, 2012 #4
    Thank you Supernova, this is the advice I have heard. I'm unsure how to wire it up but it's a great start. Thanks.

    Bobby, I realise how basic this should be, hence it eating at me and my turning to a forum for guidance. We have two electricians at the plant, but unfortunately they don't speak much english so while they could likely easily wire it themselves, there is not the ability for them to explain it to me. I have included a diagram of the circuit as I understand it, any help would be greatly, greatly appreciated. The machine is pretty much a black box to me. When I connect directly from the 24V on the machine part of the diagram to the 0v of the robot I get no reading on the multimeter.
  6. Apr 6, 2012 #5
    Forgot to attach my crude diagram.

    Attached Files:

  7. Apr 7, 2012 #6
    This seems like a pretty common scenario and from what I've read something you guys handle very easily. Could someone please take a couple of minutes to explain it to me, it would really mean a lot. Thanks.
  8. Apr 7, 2012 #7


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    ergwell, I have studied your "crude diagram" and cannot help because it is confusing and or wrong.

    The limit switch inside the Machine, when closed, sends +24 volts to the point marked "0 V". That can't be. I would expect to see only one output from the machine...one wire, and it would have on it either +24 volts or zero volts. This I would call the "status signal" to be sent to the "Robot". But when I look at your diagram of the Robot I find two inputs: +24V and 0V.

    If anyone is to give you some help or advice to resolve this, you need to provide an accurate wiring diagram. Do those units have any documentation? Any connection or wiring diagrams? Without these we out here are helpless and cannot be helpful.
    Last edited: Apr 7, 2012
  9. Apr 8, 2012 #8
    Youre right but thanks for having a look at it. I guess i mean to say the potential difference when the switch is open is 24v and when closed its obviously zero, but i get 24v between that path and the neutral. Im back there tuesday, if i cant figure it out by then ill take some photos and find the documentation.
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