What is Dry Input Contact

Discussion in 'General Electronics Chat' started by HallMark, Sep 4, 2013.

  1. HallMark

    Thread Starter Member

    Apr 3, 2011
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    Hello Friends,

    Somewhere I come to know about Dry Input Contact. Anybody can give me some detailed information about Dry Input Contact?

    What will be the circuit if I want to sense Dry Contact using Microcontroller?

    Regards,
     
  2. killivolt

    Active Member

    Jan 10, 2010
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    It's a relay contact. It will use a pull-up resistor connected to the Micro-controller input.

    http://en.wikipedia.org/wiki/Pull-up_resistor

    In the figure where you see the switch in line with the resistor, replace the switch with a relay. There are plenty of ways to control a relay, many are on this site.
     
  3. HallMark

    Thread Starter Member

    Apr 3, 2011
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    5
    Is that mean if I use Pullup on my microcontroller Pin. When ever Dry contact become active I can see Low voltage level on my pin ?
    Please correct me if I am wrong.
     
  4. killivolt

    Active Member

    Jan 10, 2010
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    It might be the opposite I'm not sure. I'm just learning this stuff myself.

    You will have to lookup other threads relating to this subject. All I can say is a dry contact is a switch, my direct reference with equipment I use it's a relay.

    But, I think it could be any switch. Someone else will have to help you or you can do some searches....
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A dry contact is one that does not switch the primary controlling current, some examples are input to PLC or Pic where the subsequent result is switched elsewhere, or an auxilliary contact on a motor Contactor or overload, that indicates to some other source that the contactor or O/L has been activated.
    Max.
     
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  6. #12

    Expert

    Nov 30, 2010
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    In my experience, "dry" means very little current, like 10 ma maximum. Dry contacts are gold plated to insure proper electrical contact in a circuit where the voltage is too low to penetrate a tiny oxide layer (a failure mode) and the current is too small to burn a new surface on the contacts when the contact resistance increases (a failure mode).

    If you use a dry contact to carry significant current, the gold layer will be burned off immediately and it will not qualify as a dry contact after that happens.

    (Different person, different application, different understanding.)
     
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  7. killivolt

    Active Member

    Jan 10, 2010
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    I'll go with that, without question.

    Only my equipment manufactures specs, relating to control over the dry contact in question. Has supposedly 1amp at 30v ac or dc.

    But, we both know they will push that to the limit. I will remember this.....
     
  8. killivolt

    Active Member

    Jan 10, 2010
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    Look what I found. I tried just looking up "Dry Contact" and didn't find much only when I asked "Where did the term dry contact come from / Electronics"

    http://en.wikipedia.org/wiki/Dry_contact


    I think the OP, deserves "The question of the Week award"
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Wikipedia.org
    No current
    : Dry contact can refer to a secondary set of contacts of a relay circuit which does not make or break the primary current being controlled by the relay. Usually some other contacts or device have the job of starting or stopping the primary current being controlled.

    Which could be a PLC etc, see post #5!
    Max.
     
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  10. killivolt

    Active Member

    Jan 10, 2010
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    I was just trying to point out, if their is a "Dry Contact" there must be a "Wet Contact" as well, and that

    e.g. Mercury Switch, which is about 24 - 40v. I didn't dispute your post.

    Regards,
    kv

    Edit: And if you'll note my #2nd post, that I said a relay "Which can be switch in several different ways" that would include PLC and other device remote switching.
     
  11. #12

    Expert

    Nov 30, 2010
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    I don't think I have ever heard anybody say, "wet contact" (or write it either).
    Probably because all contacts are considered to be, "not dry" unless you declare that they are dry.

    ps, My reference for 10 ma is the label on a relay that I have. That doesn't prove that dry contacts are rated at "less than 10 ma". It just proves that the relay I have is labeled as less than 10 ma.
     
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  12. HallMark

    Thread Starter Member

    Apr 3, 2011
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    5
    There is very useful information. In simple word we can say that it is something like Push Button.

    It transfers voltage on one pin to another pin. Somewhere I see some Fire-Alarm is using similar dry contact wondering how it works.
     
  13. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Relays, push buttons, micro switches, light switches, etc,etc,etc. Plugging into a receptacle if used as such.

    for micro's, you'll probably 'switch' the pin to common, or let it be pulled high. You need to know which.

    Mercury power switches are referred to as wet. I've run across them in various industries. With the myriad of contact configuration, it's not surprising that many dry contacts are not rated.
     
    Last edited: Sep 8, 2013
  14. strantor

    AAC Fanatic!

    Oct 3, 2010
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    My experience coincides with #12's experience; dry contact has always meant very low current. I haven't exactly heard of "wet contacts" but I have heard of "mercury wetted contacts." I have a mercury wetted rotary electrical connector (slipring assembly) on my desk, pretty cool gadget.
     
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