[Test-Equipment] Simple DC Voltage Standard?

[Eric Lemmon]

Barry,

I used a recently-calibrated Fluke 87 DVM to measure a dozen fresh AA cells,
and they all were 1.618 to 1.620 volts.  The voltage of any dry (alkaline)
cell will vary slightly with temperature and the length of time since
manufacture.  Just holding a cell in your hand for a minute will change its
voltage.  Moreover, I would never rely on an ordinary dry cell to provide a
calibration source.  That's why "standard cells" are made.

73, Eric Lemmon WB6FLY
 

-----Original Message-----
From: test-equipment-bounces at mailman.qth.net
[mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Barry
Sent: Monday, February 28, 2011 5:24 PM
To: test-equipment at mailman.qth.net
Subject: [Test-Equipment] Simple DC Voltage Standard?

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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