Which setup do you use to measure your references on the long run, to calculate drift and compare them?
Hello,
for the first: I try to get as many calibrations as possible from calibrated equipment. In best case I have the calibration report so that I can narrow down the uncertainity of the calibration points after some years.
2nd: I do dayly intercomparisons of my ADCs (ADC13 is one of the most stable) and known good references.
So I can detect unusual drifts. E.g. the jump on LTZ#1 by -1.9 ppm on day ~820 (green dots) due to a short on the unbuffered output.
I use a relay scanner with latching signal relays for this. (low heat generation). After each switching I wait some time to let the thermals settle.
But i still dont understand if a cheaper DMM in the 200mV-range would affect the drift-measurement or if the selfdrift of the DMM-selfdrift would cancel out during the long-time measurement. Maybe someone can point out how its done?
Also: I still would need a good reference with a known low drift to calculate the absolute drift of each of my LTZ1000A-references, is that correct?
lets do the math:
- 30 ppm error in 10V range are 300 uV.
- 50 ppm error in 100mV range only 5 uV. (assuming that the error is larger in the 100mV range against the native 10V range).
And yes you will need a well aged known good reference so that you can do differential measurements.
LTZ1000 references tend all to drift down over time.
So I use my well aged LTZ#2 as reference for the new references LTZ#3-#6 to do weekly ageing measurements.
Several ADC´s measure the absolute value and 2 DMMs in 100mV range the difference to LTZ#2.
These questions emerged because i now have my 7x LTZ1000A-reference which i want to measure.
Welcome to the club.
Before starting with ageing experiments I would fully characterize the references as good as I can.
(Tempco, variation of power supply, EMI sensitivity (changes when using battery supply, or laying the hand over cables, mobile phone ...), tilting, ....).
With best regards
Andreas