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

Greg Burnett gbusg at comcast.net
Wed Sep 22 04:39:51 UTC 2010

```Bill,

Yes, "Out of 10 volts, 1uv is 0.1ppm." But take another look at Frank's statement. He's referring to 0.1x divided output uncertainty, for which the uncertainty becomes 1ppm, as he states. (This is for the case where Input = 10Vdc and Output = 1Vdc.) The key to understanding this is that the 720A's linearity is spec'd relative to *Input*, not output (as Frank is careful to point out).

Greg

----- Original Message -----
From: "WB6BNQ"
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Monday, September 20, 2010 6:28 PM
Subject: Re: [volt-nuts] Fluke 720A Kelvin Varley Divider Questions

Frank,

...Out of 10 volts, 1uv is 0.1ppm.

------clip-----

Bill....WB6BNQ

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Frank wrote:
The 720A is specified "0.1ppm linearity error of input" for a setting S of 1.1 ..0.1.
That means, if you apply 10V input voltage ("Input" is the crucial word!), it gives an error of 1µV.
Related to the output (linearity!!!), that means the 0.1x divided output of 1V is unsecure 1µV, i.e. 1ppm of output, or 1ppm of ratio.
```