How to apply uA current to test analog meter?

[dave356]

I have a few analog meters that I need to check and verify
for full scale swing.  Some of the meters have a magnetic shunt
attached to the side, some don't.  If I can adjust it, I will.
. 
What do I need to put together to apply 200ua into a 1000ohm meter.

School Me!!

[Ohm_My]

Hello Dave,

Here is a YT video that should cover what you would like to achieve. There is also a companion video for this as well worth looking at.



Good luck.

[floobydust]

Never connect the meter directly to a power supply, it's too easy to peg and damage. I use a series resistor of 1k-10k and an adjustable bench power supply.

[dave356]

Thanks ohm-my,
Just what I was looking for.
Very educational

[dave_k]

I have a few analog meters that I need to check and verify
for full scale swing.  Some of the meters have a magnetic shunt
attached to the side, some don't.  If I can adjust it, I will.
. 
What do I need to put together to apply 200ua into a 1000ohm meter.

School Me!!

Ohm's Law. You would use Ohm's Law.

V = I*R, or 0.0002*1000 = 0.2V.

Want to drive it with a higher voltage? Figure it out...

[gbaddeley]

I would put a 10K linear pot across a low voltage adjustable DC power supply, starting with a very low voltage (eg. 1 V). From the wiper, connect a 1K high precision resistor (1% or less) in series with the meter, and other terminal of meter to bottom of pot. Wind up the pot until the meter reaches full scale deflection. Wind up the supply if needed. Measure the voltage across the 1K resistor. The meter current is Im = Er / 1000.  Measure the voltage across the meter, the meter resistance is Rm = Em / Im.

Make sure the meter is oriented in its intended operating position. If it will be in a steel case, or will have nearby iron, mount it in the case.  Check the zero adjustment. These factors influence the full scale reading.