testing analogue meter for sensitivity

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
So I found a couple of analogue meters in my box and I have no idea what sensitivity they are, if they are 100 micro amps I can use them in my power supply, how do I go about checking this?

they are actually signal meters.
 

Reloadron

Joined Jan 15, 2015
4,508
The sensitivity of an analog meter is expressed as Ohms/Volt. Using the meter movement of the old Simpson 260 just as an example the full scale current of the meter movement is 50 uA. The sensitivity is the reciprocal of the full scale current is the sensitivity so 1/0.000050 = 20,000 Ohms/Volt. Likewise if the Ohms/Volt sensitivity is known the full scale current would be 1/20,000 = 0.000050 Amp (50 uAmp).

A 100 uA meter movement full scale would be 1/0.000100 = 10,000 Ohm/Volt sensitivity.

Ron
 

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
How do I go about finding the amount of current it takes to push the needle to the far end of the scale?
 

danadak

Joined Mar 10, 2018
3,577
Use a pot, like 1 M ohm, maybe 100K, in series, and adjust for full scale,
then measure V across pot, then R of pot, using a DMM.

Imeter = Vpot / Rpot.

Or use a DMM as current measurement in series with pot and meter, adjust pot
until max deflection, DMM will tell you current.


Regards, Dana.
 

LesJones

Joined Jan 8, 2017
2,319
Assuming the meters are moving coil the basic meter movement will have quite a low resistance so for this test it can be ignored. The meter is unlikely to be less than 50 uA FSD so we will start with 50 uA. Connect the meter in series with a 180 K resistor and 9 volt battery. (Note. The polarity must be correct.) If the meter is 50 uA FSD it will just read full scale. If it is hard on the stop it is less than 50 uA FSD. Try to judge what fraction of full scale it is reading. For example if it reads half full scale it is probably 100 uA FSD. Confirm your estimate by changing the resistor value to give this current. The meter should read just full scale. You will have to take into account that the battery may not be exactly 9.00 volts.
If the meter was originally a volt meter then it will have a built in resistor in series with the basic meter movement so this would distort the results of this test.
Les.
 
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