[volt-nuts] Fluke 720A Kelvin Varley Divider Questions

[Greg Burnett]

Welcome Charlie,

According to Fluke's specs, the 720A's stability of linearity is 0.1ppm/30 
days. ...and +/- 1.0ppm of input/yr for dial settings of 1.1 to 0.1. So, 
because the 720A can be self-calibrated by the user (you), I'm guessing 
that, based on your requirements, you'd want to do another self-calibration 
every so often.

If you buy a 720A on the used market, be careful that its switches are OK 
and that it doesn't have any oil leaking out of any of its resistors.

Best,
Greg

----- Original Message ----- 
From: "Myers, Charlie" <Charlie_Myers at dell.com>
To: <volt-nuts at febo.com>
Sent: Sunday, September 19, 2010 12:36 PM
Subject: [volt-nuts] Fluke 720A Kelvin Varley Divider Questions


Hi to everyone,

I am new to this group and have a keen interest in precision and accurate 
voltage references and metrology.  I am using a pair of Fluke 732A Reference 
Voltage Sources for my voltage standards and a Fluke 5440B Direct Voltage 
Calibrator in my home lab. I am thinking about acquiring a Kelvin Varley 
voltage divider for a number of lab uses including scaling of my 10 volt 
standards so that I can calibrate my Fluke 5440B and, in turn, various DMMs. 
The most precision DMM I own is an HP 3457A 6 ½ digit multimeter which can 
be extended to 7 ½ digits by adding the contents of the 7th digit register 
to the displayed reading.

My question is how stable are the Fluke 720A dividers over time, i.e., if I 
have one that is in calibration (+/- 0.1 ppm accuracy and linearity) will it 
tend to stay that way over the course of years assuming that I don't apply 
excessive voltage, dissipate excessive power, or otherwise abuse the 
divider?  Or will it need to be calibrated on an annual basis to keep it 
within reasonable specifications?  I don't require +/- 0.1 ppm accuracy but 
I would like to maintain somewhere between +/- 0.5 ppm accuracy and  +/- 
1ppm accuracy over time.

All advice and comments are welcome.  For me, this is a new area of learning 
and adventure.

Thanks.

Charlie

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