Latching a logic signal

Discussion in 'General Electronics Chat' started by Dritech, May 17, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    I am using a current sensor to switch off a relay when a particular motor exceeds its current limit. I want the relay to remain off until a reset button is pressed. What type of latching IC or circuit can I use to achieve this please? Ideally it have to be a simple circuit or a single IC.

    Thanks in advance.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the current sensor is N.C. then place a N.O. contact on the sensing relay in series with its coil, place a reset or arming N.O. P.B. in parallel with the N.O. contact.
    The current sensor will have to have returned to its N.C. state to enable a reset.
    Max.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The simplest part is the one you already have: the relay itself. Put a normally open relay contact in series with the relay coil. When the current sensor breaks the circuit this contact will keep it off until the reset button is pressed.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Here's one way to do ErnieM's suggested circuit. The reset switch won't energize the relay unless the current limit switch is closed (indicating no overcurrent).

    Reset Latch.gif
     
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Or if you want logic.
     
    Dritech likes this.
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also post #2;)
    Max.
     
  7. profbuxton

    Member

    Feb 21, 2014
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    Simple method: Use a magnetically latched relay. These have two coils operating the same contact set. One coil "sets" the relay and the other coil "resets" the relay. Use your Current sensing to "reset" the relay to off and a pushbutton to "set" the relay to on.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Sorry Max, didn't mean to slight you. :p
     
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Thanks for the replies :)
     
  10. strantor

    AAC Fanatic!

    Oct 3, 2010
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    you're welcome
     
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