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Old 01-17-2007, 04:09 PM
debbie debbie is offline
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Default moving coil meter - please help

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
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Old 01-17-2007, 04:35 PM
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That's 100 times fsd, so it would attempt to move to a point 100 times farther than fsd. 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?
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Old 01-17-2007, 04:41 PM
debbie debbie is offline
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I'm thinking it would blow the meter
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Old 01-17-2007, 07:23 PM
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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.
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Old 01-18-2007, 12:28 AM
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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?"
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- Michael Faraday
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Old 01-18-2007, 12:59 AM
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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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