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Turning Relay back on

  1. Jun 22, 2015 #1
    I'm trying to figure out a way to turn a relay back on with a sensor. This relay is attached to a device that is plugged into a wall. I was thinking of using a non-invasice current sensor but I don't know if there will be a significant current change, if any, once I turn the device on, if the relay is still turned off.

    Is there a sensor to check the change in capacitance of the wire that is turned on?
  2. jcsd
  3. Jun 22, 2015 #2


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    Staff: Mentor

    You kind of already asked this question here: https://www.physicsforums.com/threads/how-to-tell-a-wire-is-plugged-in.817417/

    Did the replies in that thread not help you?
  4. Jun 22, 2015 #3
    They are helpful on how to measure current without using current. But now I'm curious on if there is a sensor to turn a relay back on. I don't believe these methods suggested would work besides the "quantum oscillator " which I do not fully understand.

    I was worried if I responded to that thread that it wouldn't be viewed.
  5. Jun 22, 2015 #4


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    Science Advisor

    Yes, there are sensors but we need more information to answer your question.
    The world is more complex than you realise. If you ask the right question you will get the right answer.
    We require feedback from you to identify what your question actually means.
    Can you produce a circuit diagram of what you have and describe the feature what you want to change or add.
  6. Jun 23, 2015 #5


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    Gold Member

    You need to provide at least a block diagram that lets us see visually what functionality you are trying to achieve. What's this relay hooked to? Where does it get power? Why did it turn off?

    Why can't you just hook up a switch or sensor to turn it back on.

    I'm sure your actual application and issues are in your questions somewhere, but I can't really figure it out.

    Details details details. We can't read minds.
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