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| Brymen BM869 - measurement of DCV linearity |
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| Dr. Frank:
Hello, following the very positive review of Dave about that instrument, I finally bought one, arriving right to-day. After a quick check against my calibration instruments, it really turns out to be very accurate and robust. Then I determined the linearity of the extended resolution DCV range, 5 4/5 digits. That mode promises 530,000 counts, and I wondered, if the last digit of that long scale would be useful. I used my Fluke 5442A, which has a proven non-linearity of < 0.1ppm. I measured the linearity on the 500mV and the 1V range and determined the max. deviation from a best fit line. All output values were averaged over 10-20 stable data from the BM869. Results from the tables reveal, that the A/D converter is linear to 2-3 counts or 4-6 ppm. That means, that all measurements using the normal 4 4/5 digits resolution are accurate to < 1 count on the last digit, if an exact F.S. calibration has been performed. Using the DCV extended resolution, the accuracy will approach 0.001% , if the instrument has been properly calibrated. Certainly, this may be only a short-term accuracy. Therefore I will monitor the stability of this instrument, to qualify the overall uncertainty, i.e. mid- and long-term accuracy, and thereby questioning the 0.02% specified uncertainty. Frank |
| retiredcaps:
Looking forward to seeing the results over a long period of time. Thanks for doing this even though I don't have a Brymen BM869. |
| Lightages:
Thanks Dr. Frank. I have found mine to be very stable over the long term. |
| Wytnucls:
--- Quote from: Dr. Frank on February 08, 2014, 08:58:30 pm ---Then I determined the linearity of the extended resolution DCV range, 5 4/5 digits. That mode promises 5,300,000 counts, and I wondered, if the last digit of that long scale would be useful --- End quote --- Don't you mean 530,000 counts? |
| Wytnucls:
Could you expand a little on the non-linearity of less than 0.1ppm of the Fluke 5442A. I have some trouble deriving that figure from the datasheet: http://www.testequipmentconnection.com/specs/FLUKE_5442A.PDF |
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