[volt-nuts] 7061 statistics , dont understand

Fabio Eboli FabioEb at quipo.it
Tue Apr 24 20:59:02 UTC 2012


I had a confirmation from Fred Schneider
that reports the following:
"I turned on a fluke 731a 10V source and the 7061.
It is now running since 16:00 after 30 minutes warm up.
The display started with 0-000.220 prg, in a few minutes it was 240,
an hour later 244 and 3 hour later still 244.
I just did a reset and after half a minute the meter shows 0-000.242
After a few minutes is 243, probably will go to 244 again"

Thanks to Fred for dedicating his time to do the test,
the fact that the two meters have the same behaviour suggests
that there isn't a fault on mine in particular.

Am I correct that the meter should show
a standard deviation of something like 2E-6,
given the previous readings?

Fabio.


Fabio Eboli <fabioeb at quipo.it> ha scritto:

> Hello, after bulding the cables as per previous post,
> and trying to test them, I'm having a problem understanding
> 7061 statistics calculations.
> Maybe it's some simple thing happening,but I cannot understand.
> I set up the meter in program mode, statistics, output=standard
> deviation, 7 digits filter off.
> Soon the meter started showing strange numbers, too high for me.
> So I cleared the history file and repeated the measures with few
> points and after tried calculating the values also by hand.
>
> 13 Samples (comma as decimal divider):
>
> 9,999964
> 9,999961
> 9,999961
> 9,999961
> 9,999962
> 9,999958
> 9,99996
> 9,99996
> 9,999964
> 9,999962
> 9,99996
> 9,999958
> 9,999958
>
> meter's calculated values:
> mean=9,999961
> variance=5,587935E-008
> SD=2,363881E-004
>
> hand calculated values:
> mean=9,9999606923
> variance=4,064E-012
> SD=2,016E-006
>
> What's happening?
>
> Fabio.
>
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