[sdiy] Ohms-Per-Volt

[Glen]

I was reading a calibration procedure in an old service manual, and the
goal of one test in particular is to measure the AC voltage present at the
instrument's output terminals, while different musical notes are played on
the instrument's keyboard. The manual says to connect a voltmeter to the
instrument's output terminals. (So far, so good.)

Then it says to be sure and use the 1000 Ohms-per-Volt setting of your
multi-meter to make the measurements. This is almost certainly intended to
make sure your particular voltmeter meter "loads" the circuit to the same
degree theirs did.

The problem is, my volt meter is a modern DMM with a very high impedance. I
would like to emulate the impedance of their older d'arsonval style meter,
but I really don't know how to calculate their meter's impedance, since
they only gave the Ohms-per-Volt spec of their meter, but didn't tell me
the full-scale voltage of their meter. If I knew the impedance of their
meter, couldn't I just add a shunt resistor across my test leads to emulate
their older meter with lower impedance? I think this would work if only I
knew the original impedance.

Anyone have any suggestions?

For reference, the signals to be measured should fall between 0.2 VAC and
16 VAC. That should help narrow things down ever so slightly. Of course,
there is also the problem of meter impedance varying with frequency. I have
no way to estimate how their meter and mine compare in that regard, but I
thought that it would be good to at least try and emulate the "DC" (or
should that be 60 Hz?) loading of their meter.


thanks for any suggestions,
Glen Berry