[VAC] Re: transformer/converter question

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx>]

I never though measuring the voltage drop across a shunt as indirect
measurement. Just dividing the current between the large current and
giving a small current for a panel meter.

AC clip on ammeters work by transformer action. Transformers don't pass
DC from winding to winding, because the amplitude tends to not change.
DC clip on ammeters work by hall effect where a magnetic field (constant
or varying) varies the resistance of a slab of silicon. Transformer type
clip on ammeters have predictable calibration. Hall effect devices need
individual calibration and amplification to drive a meter or readout. I
consider these INDIRECT measurements.

Where an AC clip on ammeter may be had for as little as $40, the last
good DC one I saw was $600.

If you set up a 1 milliohm shunt, you can use your DVM on DC millivolts
and read amps directly and won't have to take it out of the circuit. A
standard meter shunt drops 50 millivolts full scale, though I've seen
some that drop 100 millivolts full scale.

Gerald J.