Electronic – the test voltage of a ohmmeter


Ohmmeters don't appear to make LEDs conduct which gives overestimates in the resistance measured (tested with a R1//(R2+LED) parallel circuit). So what is the voltage they apply to the circuit, assuming it is conventional? I assume it depends on the range selected (I seriously doubt it will apply 1V to a mOhm branch), but to what extent?

Best Answer

If it's a DVM I'd think along these lines: -

Smallest resolution in ohms is probably 0.1 ohms and smallest resolution in volts might be 1mV. This leads to the conclusion that the current used in the lowest ohm range is probably: -

\$\dfrac{1mV}{0.1\Omega}\$ = 10mA.

Given that the lowest ohm range will probably go-over range at 200 ohms, the maximum voltage it likely produces is 4 volts across 200 ohms.