[R-390] Meters

[Roy Morgan]

At 06:06 PM 4/30/03 -0400, Barry Hauser wrote:
   There was
>a procedure for measuring DC resistance without burning out the armature
>coil.  Probably can find it in the Pearls of Wisdom on Al's R-390A FAQ site.

In Summary:

1) Arrange a source of voltage with a current limiting resistor to make the 
meter read full scale.  1-1/2 volt penlight cell and a 1500 ohm resistor, 
for instance, would work for a 1 ma meter movement. If you use variable 
resistors, make sure you don't over drive the meter.

2) While the circuit is operating, put resistors in parallel with the METER 
until it reads half scale.

3) The value of the parallel resistance is equal to the internal resistance 
of the meter.

Note: R-390A line level meters are AC detecting and include an internal 
rectifier. They will deflect upwards with applied voltage of either 
polarity. Their resistance is likely non-linear to some degree, but the 
above method will give you an approximation of the overall 
meter-plus-rectifier resistance.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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