[volt-nuts] Prema 6048 zero offset problems

[Bruce Griffiths]

Result of nonlinearity and dc offset combined?

Bruce

> 
>     On 19 January 2018 at 00:57 "David C. Partridge" <david.partridge at perdrix.co.uk> wrote:
> 
>     Starting with a warmed up Prema 6048, if I power it off and then on, select
>     20V DC range, 4 second integration and connect to the 10V output of a Fluke
>     732A, I get a reading of:
> 
>     +10.000047
> 
>     If I reverse the polarity of the cables and allow the reading to settle down
>     for a minute, I get a reading of:
> 
>     -10.000006
> 
>     If I short the inputs of the meter, I get a reading of:
> 
>     +0.000105
> 
>     which is different from the +0.000020 which I would have expected from the
>     readings of the 732A output.
> 
>     Proceeding on the assumption that the meter has stored a zero offset of
>     -105uV
> 
>     I then press the ZERO button to null out the offset and then reconnect the
>     732A in normal polarity I get an incorrect reading of:
> 
>     +10.000153
> 
>     This is not what I would expect to see - I would expect to see a reading of
>     +10.000047 - 0.000105 = +09.999942 This calculation
> 
>     I then reverse the inputs and get a reading of:
> 
>     -10.000113
> 
>     which is close to the expected reading of -10.000006 - 0.000105 = -10.000111
> 
>     I have mailed Prema about this problem, and will let you know what they have
>     to say.
> 
>     Cheers
>     David Partridge
> 
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