I was surprised to see that no one came up with
the classic simple answer regarding the meter
internal R post...
-
-
Two Potentiometers, a 9 volt battery and one or two
resistors will do the trick.
-
Assume the movement to be 50 uA unless otherwise
known "in stone" that it is another value. I have
surplus meters with full scale 1mA indicated, but
having micro amp movements.
-
One must construct a simple current loop using
a few simple parts.
-
Limit the max current to a "safe value" that will
not peg (slam) the movement hard (might actually
bend the meter needle). Pick a value like 47K min
as your soft limit value, placed in series with a
250K linear pot and the meter movement.
Observe polarities...
-
Adjust the series linear pot for full scale deflection
of the meter. Leave the meter reading full
scale and apply a second pot as described
just below.
-
Place the second pot in parallel with the meter
and adjust it for half scale on the meter. A
250 ohm pot is probably a good value to use.
-
With the 250 ohm pot set at some position
which drops the meter reading from full, to
half scale.... the meter and the 250 ohm pot
share equal current. Thus.... their values are
equal. Measure the value across the pot and
you have your meter movement resistance.
-
In step one, you might decrease the value of
the 47K resistor to obtain full scale meter
readings on higher current meter movements.
-
A 1 milli amp "mA" movement might use
a 4700 ohm resistor as your testing safe
limit value.
-
cheers
skipp
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>Anyone know of a procedure where I can determine the internal resistance
>without damaging the meter movement? or, am i SOL? Some are uA meters,
>some volts and some watts -- so who knows what the intended range was.
>Thanks,
>Gerry, W1VE
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