Unknown meter movement testing. Soon to be calibration...

[Chris Wilson]

I bought two ostensibly the same D'Arsonval meter movements marked 0 to 500uA FSD.
Turns out they are not the same. I did the following test, which I THINK is the correct method. I connected two 1.5 volt batteries in series (as they were conveniently laying around with wires soldered to them) and a decade resistance box in series with them, and a meter. I started with a very high resistance and lowered it until I achieved FSD on one of the meters. I measured the voltage drop across the decade resistance box. I noted the resistance I had to set the box to in order to achieve FSD. Here are the figures for the two meters:

Meter 1: 2.939 volts and 6K resistance.   Meter 1 appears to be a 50uA, I think? Or have I got the decimal point wrong, and it's 500uA?


Meter 2 : 2.910 volts and 14.3k resistance.  Meter 2 appears to be a 20uA, I think? Or decimal point wrong again, and it's 200uA?

Oh dear, I should have listened to the nice man in the gown better....


 I am hopeless at maths, really HOPELESS

Thanks!

[vk6zgo]

Well,if your other figures are correct one is 500uA,& the other one is 200uA.

More quality control problems in the dear old PRC?