Expanded Uncertainty vs. Accuracy Requirement (including concept of guardbanding)

W

w6553

#1
Hi

A testing Standard requires the equipment accuracy to be 3%. The calibation certifcate shows the expanded uncertainty of the equipment is 3.4%. Is this means that the equipment is not comply with the Standard?

Wayne
 
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Polly Pure Bread

#2
Re: Expanded Uncertainty vs. Accuracy Requirement

Hi

A testing Standard requires the equipment accuracy to be 3%. The calibation certifcate shows the expanded uncertainty of the equipment is 3.4%. Is this means that the equipment is not comply with the Standard?

Wayne
Hi Wayne,

What’s the source of uncertainty?
 
W

w6553

#3
Re: Expanded Uncertainty vs. Accuracy Requirement

HI dQAppentice,

The calibartion equipemnt used to calibrate my equipment has expanded uncertainty 2%. Does accuracy of my equipment depend on the sources of calibration uncertainty?
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#4
Re: Expanded Uncertainty vs. Accuracy Requirement

In this case the uncertainty is higher than th accuracy, so it means that your measurement using this device will have a larger uncertainty. That in turn means that the true value of the measurement, expressed at 95% confidence will be the indicated value, plus or minus the uncertainty. Now, the instrument may truly be accurate in its measurements, but when the uncertainty is considered, then all contributions together mean the true value of th measurement may or may not be the indicated value.

I would address this by guardbanding to reduce the effect of the uncertainty on the pass/fail decision.
 
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