Vintage Analog OHM meter

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ben sorenson

Joined Feb 28, 2022
80
Hello, I picked a bunch of vintage electronics up at a flea market and came across this Simpson OHM meter I think it's called because it has the ohms sign on it. Any idea what these were used for? Can I use it to make an analog OHM Meter if so, how would I wire it? At what kind of battery or voltage would I use to wire it? Any help or ideas would be greatly appreciated.
 

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WBahn

Joined Mar 31, 2012
27,389
The first thing you need to do is determine the resistance of the meter coils and how much current is needed to get full-scale deflection.

The coil resistance should be large enough that you can get a good number just using any VOM you happen to have.

To get the full-scale deflection current, start with a large-value resistor in series with the meter and apply a voltage across both. The meter will likely show some sign of movement, though perhaps not a lot. That's fine. We want to start with a large resistance and work our way down so as to not damage the meter by slamming the needle against the stop. Decrease the resistance until the meter moves up to about half scale. At this point, you are getting close, so set yourself up to measure the actual current, either with a milliameter or by measuring the voltage across a known resistance (preferably with a 1% or better tolerance). Now adjust the voltage and/or resistance until you get a full scale deflection and note that current.

Once you have that, we can go from there.
 

ronsimpson

Joined Oct 7, 2019
2,385
This meter came out of a machine. It needs a battery and limit resistor. I don't know the circuit, but we can probably make something with a little thinking.

The meter, with no power reads "open". This gives us a clue to how it works.
 
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