[volt-nuts] Integrator errors from dielectric soakage?

[Bruce Griffiths]

Charles Morris wrote:
> I recently repaired a Weston 4442 (3.5 digit dual-slope DVM) which had
> a failure of the integrating cap. It had decreased in value from 2.2
> uf to 0.42 uf; a radial-lead green "box" containing an unknown
> dielectric) Not having a suitable polystyrene or Teflon cap in the
> junk box, I used a handy polyester cap (looks like an orange-drop but
> white epoxy).
>
> Any ideas as to how much error the (presumably) Mylar integrator cap
> will introduce? In other words, will such error be significant in a
> mere 3.5 digits? (I imagine that Weston would have used a less
> expensive cap if it would do the job). The absolute value isn't
> important due to the dual-slope technique, but time-variant storage
> effects are...
>
> I have an HP 4.5 digit DVM and a MAX6385 (2.5 volt) reference, but no
> "volt-nuts"-league meters or standards, other than a 596.5 ohm 0.01%
> resistor ;)
>
> thanks
> Charles
>
>
>    
The effect will depend on the dual slope integration time and could be 
as high as 1% depending on the particular capacitor.

Bruce