Electronics > Metrology

How important is DMM linearity for drift measurements?

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e61_phil:
Hi,

I'm currently developing a high voltage measurement system for drift measurements in the ppm range.  I wonder how important the linearity of the system is at the end? It is obvious to me, that a decrease in slope (gain) of the measurement would bring errors into the measurement, because 100ppm difference at 1kV could be "another 100ppm" at 5kV if the system isn't linear. But the error of even 1% non linearity (over say 10kV) looks, vey small for my purposes (100ppm drift at different voltages).

Am I wrong?

Thanks Philipp

ap:
Your question cannot be answered this way. You should specify what accuracy requirements you have absolute, what voltage you measure, and any known test system parameters, if they exist yet.
Any system has zero, gain and linearity inaccuracies and drifts. The measurement accuracy is always a combination of these. They usually should be combined according to GUM rules.
If you let us know more the group can certainly help.

e61_phil:
The goal is measuring drift in the single digit ppm range. The absolute values doesn't matter (1% is enough) but it must be rock stable over a couple of hours. The voltages are between 4kV and 10kV.

Kleinstein:
There is not just one measure of nonlinearity. The more important one are INL and DNL. With a drift measurement one does not care very much about good INL values, but the DNL should be reasonably good.

doktor pyta:
Probably You already know this but...

If You are measuring high voltages (DC, I assume) and You want to obtain nonlinearity in ppm region it is crucial to have well designed voltage divider. Typical HV resistors have typically 1...10 ppm/V voltage coefficient and using them at say 10kV can give few percent of nonlinearity error. Even famous Vishay Z201 have " <0.1 ppm/V". Also error due to self heating will be important.

I own two Fluke HV dividers for 10kV and for 30kV. First one is built using many 500k precision low tempco wirewound resistors. The second is also made using PWW resistors but the whole divider is inside big oil tank with stabilized temperature.

In other words this seems to be a difficult task.

P.S. I forgot about effect of corona and importance of guarding to prevent leakage.