[sdiy] Ohms-Per-Volt

[John L Marshall]

1000 Ohms/Volt means that the meter movement is 1 mA full scale. Resistors
in series with meter set the voltage range. 1000 Ohms/Volt is not very
sensitive. My first meter, when I was a kid, was 20 k ohms per volt, a 50 uA
full scale meter.

DMMs should have a frequency response specification, at least the Flukes do.

Take care,
John
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Pacific Northwest Synthesizer Meeting
August 9, 2003
www.sound-photo.com
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----- Original Message ----- 
From: "jhaible" <jhaible at debitel.net>
To: <synth-diy at dropmix.xs4all.nl>; "Glen" <mclilith at charter.net>
Sent: Friday, May 30, 2003 1:08 AM
Subject: Re: [sdiy] Ohms-Per-Volt


> Hi Glen,
>
> If the text is rather old, 1000 Ohm / Volt might mean "at least
> 1000 Ohms / Volt". (I remember a time when recommendations
> to buy a decent voltmeter actually said something like this.
> We're spoilt with the high impedance of modern instruments
> nowadays.
>
> (Of course you can always connect a simple resistor in parallel to
> your DVM if you need a lower impedance ...)
>
> But I see a different problem here:
> Frequency response.
> Many DVMs can do 50Hz accurately in their AC mode, but
> get much worse on higher frequencies.
>
> I would use a scope and "watch" the amplitude.
>
> JH.
>
>
>
>
> > 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
> >
>
>