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NO Reed switch in a magnetic field?

  1. Nov 9, 2012 #1
    NO Reed switch in magnetic field. What I'm wondering is, a normaly open switch is closed in the presents of a changing magnetic field. Would the switch be closed when the field is present but not changing? I'd rather use a Hall sensor but know very little in how I would hook that up to my reed switch and the DC power supply. Frist, I guess how does a NO reed swich behave. Any one?

    Thanks for your responses
    Robin Hooper
  2. jcsd
  3. Nov 9, 2012 #2


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    Hi Robin

    A reed switch NORMALLY operates in a non-changing magnetic field ie. if you hold a magnet close to a reed switch and leave it there in position and the reed will stay closed

  4. Nov 10, 2012 #3


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    You apply DC to the solenoid, this creates a steady magnetic field and causes the reed switch to be held closed. The reed stays that way until you switch off the field.
  5. Nov 10, 2012 #4
    Thanks guys, exactly the answer I was looking for, just needed it to be confirmed.

    Many Thanks
  6. Nov 10, 2012 #5
    Most Hall modern hall sensors are easy to use, the pin devices. It will have a pin for ground, another for power, and a third to tell you when the field is present.
    Most run off of 3-5 volts and have whats called on open collector or open drain output.
    This means that the output appears disconnected when no field is present, but is shorted to ground when a field is present.
    The output is not as tough as your reed switch in that it can usually only handle a few tens of milliamps. Also, you cannot "pull" the output voltage above the devices supply voltage without fear of damage.

    These parts are much smaller, somewhat cheaper, and are usually sensitive to which pole is facing them. Unlike the reed relay, they can be toggled for the life of the instrument without fear of wear.
    There are numerous variations for mounting alternatives, output signal alternatives, sensitivity, operating voltage and so forth. Digi-Key is a good place to search, find data sheets, and/or buy them.
  7. Nov 16, 2012 #6
    An informative reply, thanks Mike.

    I'm not an electrical anything but you gave me food for thought, a direction allways helps.
  8. Nov 17, 2012 #7
    So I went to Didikey and found some reed switches. Some of the choices are 'must operate' and 'must release'. I imagine this is where ones choices NO or NC. and that is what I'm not able to decifer between the two states. What's confusing is that one type lists 'must operate' but does not indicate 'must release'. Which is which?

    Thanks for all your help thus far
    Last edited: Nov 17, 2012
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