moving coil meter - please help

Discussion in 'Homework Help' started by debbie, Jan 17, 2007.

  1. debbie

    debbie Thread Starter New Member

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    God this makes me look thick!
    What would happen if a moving coil meter with fsd of 10mA had a 1A circuit momentarily connected to it? I'm not sure of this or the suitabilty of such action:confused:
  2. thingmaker3

    thingmaker3 Moderator Staff Member

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    That's 100 times fsd, so it would attempt to move to a point 100 times farther than fsd.:D Well, not really. It would simply move very hard and fast to wherever the magnetic fields become parallel

    Mechanical stops (the little peg) would prevent this, of course. This is colloquially known as "pegging the meter."

    Now... if we assume that the meter coil can handle 120% to 200% of fsd current - what happens when we send 10,000% fsd current through said coil?
  3. debbie

    debbie Thread Starter New Member

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    I'm thinking it would blow the meter
  4. beenthere

    beenthere AAC Fanatic!

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    Hi,

    A quick application might not. The pointer should make a loud tick against the stop. I'd want to check response afterward.
  5. thingmaker3

    thingmaker3 Moderator Staff Member

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    "Blowing the meter" typically means burning off the insulation from the coil. How hot the coil needs to be for this to happen depends on what type of insulating varnish is used. (They have different ratings.) How fast the wire gets to the bad temperature depends on how much current goes through it, how big around it is, and what the ambient temperature is.

    How many seconds in "momentarily" or "quick?" :D
  6. beenthere

    beenthere AAC Fanatic!

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    Hi,

    Actually, there's another aspect to "blowing the meter". I got one wet and, thinking it was low pressure, tried to blow the water out with an air hose. The air pressure blew the coil into a long knot. Didn't hurt the coil, though.
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