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#1
01-17-2007, 04:09 PM
 debbie New Member Join Date: Jan 2007 Location: oxfordshire Posts: 2

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
#2
01-17-2007, 04:35 PM
 thingmaker3 Super Moderator Join Date: May 2005 Location: Rural, Oregon GMT -8 Posts: 5,072 Blog Entries: 6

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?
__________________
"I want to establish in your mind very clearly that you must not think I deny all that I do not admit. On the contrary, I think there are many things which may be true, and which I shall receive as such hereafter, though I do not as yet receive them; but that is not because there is any proof to the contrary, but that the proof in the affirmative is not yet sufficient for me"

Last edited by thingmaker3; 01-17-2007 at 04:39 PM.
#3
01-17-2007, 04:41 PM
 debbie New Member Join Date: Jan 2007 Location: oxfordshire Posts: 2

I'm thinking it would blow the meter
#4
01-17-2007, 07:23 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

Hi,

A quick application might not. The pointer should make a loud tick against the stop. I'd want to check response afterward.
#5
01-18-2007, 12:28 AM
 thingmaker3 Super Moderator Join Date: May 2005 Location: Rural, Oregon GMT -8 Posts: 5,072 Blog Entries: 6

"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?"
__________________
"I want to establish in your mind very clearly that you must not think I deny all that I do not admit. On the contrary, I think there are many things which may be true, and which I shall receive as such hereafter, though I do not as yet receive them; but that is not because there is any proof to the contrary, but that the proof in the affirmative is not yet sufficient for me"
#6
01-18-2007, 12:59 AM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

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.

 Tags coil, meter, moving

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