Callibration drift: temperature or voltage?

[Bob-O-Rama]

I've had a couple recent longer runs, like days in duration, where the calibration seems to drift significantly ( say 5% - 10% across the board ) with the GS-PRO-V5 and a scionix 2x2 probe. The temperature in the (cough) "lab" is changing with the seasons, but the range might be in the 65-72 *F range - so that may be it. The voltage displayed on the GS-PRO-V5 remains constant during the run. But I've observed that if I use a different probe at say 650v or 750v, and then set it back to 700v for the scionix one, it has to be calibrated. So I'm curious where that number comes from. Is it a measured value or is it a desired value?

[Sesselmann]

Bob,

I think you are asking me how the voltage display gets it's value.

Yes it is measured on the high side of the 1M load resistor and stabilised with a feedback circuit and a precision voltage regulator, so it should be accurate to within +-1V and repeatable.

The difference you are seeing could simply be lack of precision (decimal places) on the volt meter itself.

Temperature drift is more likely to affect the PMT voltage divider and crystal.

The GS-PRO doesn't have built in temperature compensation like the GS-MAX.

Steven