[Test-Equipment] Simple DC Voltage Standard?

[Gary Schafer]

I evaluated one of Joe's boards a few years ago and they are not bad. They
do change with supply voltage and especially ambient temperature. You have
to pay close attention to air currents in the room and need a stable room
temperature. But that is only if you are getting down into the low
millivolts calibration range. 

I have an HP3456A DVM and a Fluke transfer standard, both of which are
pretty stable for comparison purposes.

But for a small DVM calibration or an analog meter they will be fine and you
don't have to worry about temperature.

The cheapest way to go is to buy one of the voltage reference chips from
Mouser and build it on a small board. It only takes a couple of resistors
and a cap. It is best to feed it from a small regulated supply. The AD587 is
one chip. They are only a few dollars and come in different voltages. Right
out of the box without any trim pot attached they will be plenty close
enough for an analog meter calibration.

Short of that I would use your fluke DVM to calibrate the 410 against.

I, like Eric have also measured 1.5 volt AA batteries and find new ones to
be in the 1.6 volt range.

If I remember right the calibration procedure for the old heathkit vtvm was
to use a 1.5 volt battery as a reference at 1.5 volt. That was a C cell and
they may be closer to 1.5 volts but I haven't checked any in a long time.

73
Gary  K4FMX

> -----Original Message-----
> From: test-equipment-bounces at mailman.qth.net [mailto:test-equipment-
> bounces at mailman.qth.net] On Behalf Of Dino Papas
> Sent: Monday, February 28, 2011 9:48 PM
> To: Discussion of Electronic Test Equipment
> Subject: Re: [Test-Equipment] Simple DC Voltage Standard?
> 
> Barry - you might want to take a look at Joe Geller's voltage standards:
> 
> http://gellerlabs.com/Voltage%20References.htm
> 
> if you want more accuracy that a "standard battery."  I got one a while
> back and found it compared very well with my Agilent 34405A DMM (and
> most surprisingly with my very old Heathkit auto-ranging DMM).
> 
> Dino KL0S
> 
> On Feb282011, at 2023 PM, Barry wrote:
> 
> > I recently refurbished an HP-410B and want to perform a simple DC
> voltage calibration.   The problem is I don't have anything that I'm
> really certain is all that close to the 1V standard I need.  I have a
> variable-voltage supply and with a simple voltage divider, I can hit 1V
> easily but without something to properly measure it, I don't know when
> it's spot on 1V.
> >
> > I have a Fluke 25 DMM, an old Triplett 630-NA, and an HP-410C - none
> of which are in known calibration.  The Fluke and Triplett agree, but
> the HP410C reads a little lower than either of those for the same
> voltage.
> >
> > For example, if I set the variable supply through the divider so that
> the Fluke and Triplett both see exactly 1V, the HP410C reads about
> 0.85V.  Of course, without any of them in known calibration, I don't
> know which one would be correct.
> >
> > What I was wondering is how close should a fresh AA battery be to
> exactly 1.5V?  From what I can find online, all the specs state a AA
> battery's "nominal" voltage is 1.5V but I'm not sure how close to
> exactly 1.5V is considered "nominal".
> >
> > Oddly, the HP410C measures a fresh AA batttery at exactly 1.5V while
> the other two see it as about 1.625V.  I'm pretty sure 1.625V is quite
> high for a "nominal" AA and perhaps the Fluke and Triplett are both out
> of calibration about the same amount.
> >
> > Any suggestions on a "dirty" way to get really close to 1.0V?  I also
> have a Tek 465B 'scope but that, too, isn't calibrated so not sure how
> that might help get me where I want to be with this.
> >
> > Thanks,
> > Barry - N4BUQ
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