Posted by KEB1 on May 19, 2010 at 19:54:57 from (97.124.140.124):
In Reply to: Electrically Weird? posted by GUIDO on May 19, 2010 at 19:15:10:
What you're seeing is an artifact of the way digital multimeters work. A digital meter has very high input impedance (millions of ohms), which means it takes very little current (millionths of an amp) to operate the meter. Even at 60 Hz, the stray capacitance between the table top and the power wiring provides plenty of current.
Small currents can also be induced in loops...try holding the meter leads in your fingers, one in each hand, and see what it reads. You'll be reading the voltage induced in the electrical loop formed by your body and the meter leads from the stray magnetic fields created by the AC power wiring.
Mechanical analog meters require some flow of current through the meter to physically move the needle, and had input impedances measured in thousands of ohms, or even hundreds of ohms for cheapie meters. With a relatively low imput impedance, stray capacitance can't pass enough curent to operate the meter, and you don't get these kinds of stray readings.
Hope this helps a little....kind of hard to explain without getting into a lot of engineering terminology, but there's nothing at all surprising about what you're seeing. A lot of time has been wasted in electronics labs getting erroneous readings because the engineers and techs don't understand this phenomenon.
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