[Test-Equipment] Simple DC Voltage Standard?

[Bill Fuqua]

   Most people have access to an accurate meter via friends or
work. They can simply check it there. If you are looking for a
cheap and easy solution that may be it especially if you need
a variable calibration source.
    You can get from time to time the standard board used in
HP's 8.5 digit meter, if you want a really precise standard. We have gotten 
a 8 or 10 of those
for the lab at work. They usually go for around $100 each. I think my 
present source has dried up.
These are often rejected by HP after calibrating due to an occasional noise 
flicker but
work very well 99.99% of the time.
    You can buy a precise regulator chip but you should still verify your 
circuit works properly somehow.
An interesting note. The LM399 is available again. It is an active Zener 
diode with a temperature regulator
on the chip. Can't remember the supplier but I believe they have an 
improved version.
   People used to take the plastic thermo insulating shell off these and 
attach them to
crystals and other things to regulate their temperatures. Naturally you had 
to surround
the whole mess with thermo insulation.


73
Bill wa4lav


At 01:37 AM 3/1/2011 -0500, you wrote:


>-----Original Message-----
>From: Fuqua, Bill L
>
>
>
>Simplest solution to calibrate an analog volt meter is to use a battery,
>variable voltage divider ( 10k or so) and a cheap digital volt meter across
>the input to the analog voltmeter.
>Any loading effects will not be an issue as long as you don't remove the
>digital voltmeter.
>Oddly as it may seem the Horbor Freight  $4.95 3.5 digit multimeter is
>accurate to plus or minus least digit.
>I have tried many of these and they seem quite consistant in DC. Not so in
>AC however.
>   One down side to these cheap digital multimeters is that the input
>resistance is 1MOhm.
>Just set the voltage divider output to the full scale value you want to
>calibrate your meter with both meters in parallel and set it.
>
>
>***Er.please tell us just how you know that the cheap digital multimeter is
>calibrated correctly to begin with????
>
>Brian G.
>
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