CLOUGLOBAL
09.06.2021

Melon Weight

Hello Subscriber

Last weekend I've bought a watermelon. The fact itself is not very spectacular, but it's a good example for different aspects of metering.
I did a calibration by measuring the weight. The weighting scale has a resolution of 1 g.
So we have a measurement uncertainty of +/- 0.444 g. (We skip the remaining decimals because a 1 ppm test result would be OK for us.)
Measuring the weight twenty times hasn't shown any difference, so we have zero standard deviation. So, for a measurement uncertainty budget calculation, I would continue with a coverage factor of 2, which means 95% probability that all measurement results are within the same range.
Since the supermarket scale was showing 5 grams more and with a valid calibration mark, we have to deal with additional uncertainties.
a) my scale is not calibrated
b) we have no reference temperature for comparison
c) the melon weight is drifting.
So I can't use the melon as a transfer standard to calibrate my weight scale.
Also, the long time stability of a melon is just so so.

Conclusion:
Keep your measurement equipment calibrated and traceable to international standards. Only this makes sure, that your measurement results are accurate and repeatable.

CL2052

The difference between adjustment and calibration

Calibration means the comparison of a unit under test with test equipment with higher accuracy.
CL710K11B

Repeatability Test for Energy Meters

Another new test introduced by the IEC62052-11 Edition 2 is the repeatability test.
Thank you for your interest and stay safe.

Reinhard Günther
and the CLOUGLOBAL Team
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