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voltmeter. Impedance is the biggest difference
between analog and digital voltmeters.
Since most digital voltmeters have 50
times more impedance than analog
voltmeters, digital meters are more
accurate when measuring voltage in
high resistance circuits.
For example, if you are using a low
impedance (20,000 ohms per volt) analog
meter on the 20 volt scale (the voltmeter
represents 400,000 ohms resistance to the
circuit) to measure voltage drop across a
1,000,000 ohm component in a circuit, two
and a half times as much current is
flowing through the meter than through
the component. You are no longer
measuring just that component, but the
component plus your meter, giving you a
false reading of the actual voltage drop
across the component. This situation
might lead you to believe the voltage at the
component is low or that there is high
resistance somewhere in the circuit or
that the component is defective when it is
just the meter you are using.
If you use a digital meter with 10 million
ohms of impedance to test the same
component, only 1/10 of the current will
flow through the meter, which means it
has very little effect on the circuit bei...
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