[volt-nuts] Would you be concerned if the manufacturer does not have an uncertainty budget, so can't provide uncertainties in a calibration?

[Dr. David Kirkby]

On 21 April 2018 at 09:32, Florian Teply <usenet at teply.info> wrote:

> Am Fri, 20 Apr 2018 14:37:22 +0100
> schrieb "Dr. David Kirkby" <drkirkby at kirkbymicrowave.co.uk>:
>
> > The columns below, from left to right are
> >
> > Device type (whether the DUT is floating, or grounded one side).
> > Resistor setting (ohms)
> > Votage (V)
> > Measurement time (Long or Short)
> > Test limits (+/- ohm)
> > Test results (ohm)
> >
> > FLOAT 1E6 100 SHORT +/- 0.0086E6 -.0019E6
> > FLOAT 1E7 100 LONG +/- 0.0063E7 -.0016E7
> > FLOAT 1E8 100 LONG +/- 0.0073E8 -.0027E8
> > FLOAT 1E9 100 LONG +/- 0.0093E9 -.0032E9
> > FLOAT 1E10 100 LONG +/- 0.0273E10 +.0095E10
> > FLOAT 1E11 100 LONG +/- 0.0453E11 +.0080E11
> > FLOAT 1E11 100 SHORT +/- 0.0550E11 +.0086E11
> > FLOAT 1E11 10 LONG +/- 0.0546E11 +.0113E11
> > GROUND 1E7 100 LONG +/- 0.0065E7 -.0017E7
> > GROUND 1E11 10 LONG +/- 0.0573E11 +.0107E11
> >
> > That strikes me that the assumption is the values are what their
> > nominal values are, but I wonder how accurate they are.
> >
> I might be wrong, but to me it seems like the resistors are not
> exactly nominal but slightly off. But the uncertainty of the
> measurements is larger than the deviation. Or were you referring to the
> notion that the uncertainties are symmetrically distributed? I'd be
> pretty surprised if the uncertainties were asymmetrical for that
> matter.
>
> Best regards,
> Florian
>


Florian,

how do you determine that the resistors are not assumed to be the nominal
value?

As far as I can see, taking the example of a 1e11 ohm resistor grounded at
one end (very last entry on table), the meter should read 1e11 +/-
0.0573e11 ohms. My meter read 0.010e11 ohms high, so was in spec, as
0.010e11 is less than 0.0573e11. As far as I can determine, the fact the
permissable range of the meter is +/-x, rather than +x, -y, means the
nominal values are assumed.

I put the complete cal certificate here.

http://www.kirkbymicrowave.co.uk/tmp/1-9690444179-1-combined-file.pdf

What I also find a bit odd, is the 16340A RC box used for calibrating the
meter, is itself not due for calibration for over a year.

I am awaiting a call/email from the calibration manager at Keysight (UK),
and I've been advised Keysight (UK) have contacted Keysight in the USA to
see what they can provide, as a calibration *with* uncertainties is listed
on the Keysight (USA) website.

I have no formal requirement for needing the uncertainties, but I am a bit
worried the fact that Keysight (UK) seem to use a resistance box that is
calibrated less than once/year, and can't provide the uncertainties, and as
far as I can tell (although you disagree), it would appear the nominal
value of the resistors are used. . It does not exactly inspire a lot of
confidence.

Dave