If we want to be really technical


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Posted by Sherman in Idaho [72.47.153.112] on Saturday, February 01, 2014 at 15:02:24 :

In Reply to: Re: amp gauge explained posted by JohnD [71.246.81.71] on Saturday, February 01, 2014 at 10:16:56 :

A volt meter is really an ammeter, since it's a moving current (amps) that produces the variable magnetic field that "pushes against" the fixed magnetic field provided by the permanent magnet inside the meter. In that sense, the only difference between an ammeter and a voltmeter is the gauge of the wire. An ammeter might have one turn of fat wire and a voltmeter might have 1000 turns of thin wire.

But there's another complication too -- whether it's a "moving coil" meter or a "moving magnet" meter. All voltmeters, and the more sensitive ammeters are "moving coil" designs, but less sensitive (and cheaper) ammeters, like most vehicles have, are "moving magnet" designs. This avoids having to get a high current through the meter springs or thin pieces of flexible wire.

There are true voltmeters that don't require an current flow at all to make the pointer move. They're called electrostatic voltmeters, and they're just a calibrated version of the way static electricity attracts things. You only find them in laboratory equipment, mostly really old (pre-war) instruments.



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