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

[Florian Teply]

Am Mon, 23 Apr 2018 23:59:57 +0100
schrieb "Dr. David Kirkby" <drkirkby at kirkbymicrowave.co.uk>:

> 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.
> >

> 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.
>
Ah, probably I didn't get my wording precise. Just as you say, it looks
like they assume the resistors should have nominal value. Otherwise
they would need to list what they assume to be the nominal value, which
they don't. I was referring to the last column where they list the
measured deviation of +0.0107e11. In any case, I would consider unknown
resistances pretty odd as that would render the whole effort of
having 8.5 digits in the first place useless... So the only
explanation that would make sense is that the resistors should habve
nominal values. Unless of course the have individual values from
manufacture stored somewhere. But then it also wouldn't make sense to
not tell the owner of the device...

They don't spell out explicitlyy whether the test limits they give,
i.e. here +/- 0.0573e11 ohms would be their own measurement
uncvertainty or the instruments spec limits, but given the odd numbers
I'd expect it to be their measurement uncertainty. 

Best regards,
Florian