[volt-nuts] 3458A calibration

[Randy Scott]

> The effect of dielectric absorption can be minimised by
> ensuring that the average voltage across the integrator feedback
> capacitor remains low over the integration cycle.
> HP/Agilent have several patents covering this aspect of DVM
> integrator runup cycles.

Are you referring to what HP calls their "charge-balancing" A/D converter where during the run-up phase of the conversion they attempt to keep the output of the integrator balanced around 0 volts?

The Agilent 34401A does something like this and then uses a second, fast A/D converter to replace the run-down phase.

> However the runup cycle of the 3458 unlike some other
> HP/Agilent DVMs doesn't appear to use this technique.
> Later HP DVMs do use such techniques.

It would seem that with an A/D, like the 3458A's, that relies on multi-slope run-down, it would be advantageous to keep the integrator output as high as possible at the end of the run-up phase to maximize the resolution achieved during run-down.

Randy.