Any Volt meter Repair men.

Gerald J.

There might be a bit of information on the lower face of the meter scale, perhaps fs=1ma and r=100 ohms. Though on a custom meter those may not appear. Its common for a 1 ma meter to have a 100 ohm resistance, a 100 microamp meter to have 1000 ohms, and the movement itself to have something on the order of 90% of that resistance because putting most of the movement resistance in the moving coil gets the best torque for moving the pointer. I had a meter maker once tell me that when I specified 2K for a 100 microamp meter that he'd use more wire in the movement coil to get that greater power. When I later decided I needed 1K and took my test meter apart it had all of that added 1K in the series resistor, which I shipped to him to counter his letter. Never heard from him again.

So for a 1m meter, I'd guess that wire wound resistor is probably in the range of 11 ohms.

Gerald J.

Soundguy

Yes it works. By using a 100 volt supply with a 100K series resistor to get 1 ma, the resistance of the meter whether 100 ohms or cut in half by the shunt resistor doesn't change the current much. Difference between 100100 and 100050 ohms, out in the .05% range, and when the meter indication is probably not more accurate than 3% of full scale, that current change is far smaller than insignificant.

The same ratios apply with 100 volts 1 megohm and a 100 microamp meter.

It works best with a relatively high voltage, poorest with a low voltage like 1.5 volts. There for a 1 ma meter the series resistor would be 1.5K, so the two conditions are 1.5 volts 1600 ohms and 1550 ohms a change of 3%. Which could be compensated for by going for a point 3% above half scale rather than half scale.. if the meter could be trusted to be read to 3% and could indicate to 3% which some laboratory meters might.

Gerald J.

Soundguy

Gerald J.

Soundguy

Is a "tach" or "dwell" function?

Since it is basically for testing DC voltage and current, I wonder WHY an inductor would be needed?

A sort of filter choke perhaps?

I have a meter that sounds similar to your's. I'll take a look tomorrow to see what brand and model it is, although it seems to me it IS a SUN.

If its a 1 ma meter the 2 volt multiplier will be 1.9K and the 20 volt multiplier will be 19.9K. and the meter movement 100 ohms. At least that's how I'd have made it. A 1 ma meter movement is fairly sturdy and readily available. A more sensitive movement gets to be a bit fragile and doesn't stand up well in the work environment.

Gerald J.