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Suspected static discharge

Discussion in 'General Electronics Discussion' started by Steve Ford, Oct 13, 2017.

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  1. Steve Ford

    Steve Ford

    Oct 13, 2017
    Hi, i have a duress button connected to a dry contact panel via a cable run of about 89mtrs.
    Every so often I am getting "phantom" activations which i believe are caused by the length if the cable run.
    I have been advised that placing a capacitor across the button contacts may resolve this issue
    The cable being used is fig 8. 24 awg

    Any advise appreciated.

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It could be static, but it is far more likely to be pickup of interference on your long antenna.

    I guess that your long run of wire isn't shielded cable.

    Replacing the cable with coax would probably help, but you might get away with a capacitor at one or both ends. These will reduce the speed of operation, but for a button press i don't think that is an issue. Try 0.1uF at the end furthest from the switch first, that may be all you need.
  3. Bluejets


    Oct 5, 2014
    If all else fails, fit a small interposing relay.
    Arouse1973 likes this.
  4. dorke


    Jun 20, 2015
    89 Meters is a long nice antenna.
    It can pick-up fluorescent light ignition,old car ignition, working tool (like a drill) etc.

    Do you know what type of "input" there is at the dry contact panel?

    The Coax solution would be very costly,twisted pair may be o.k.
    A capacitor filter like Steve suggested may help,
    you can add(depending on "input type") a series small resistor(say 100) near the input to create a more effective filter.
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