Need help on calibration result analysis

[Rachel]

Can someone enlighten me whether my analysis is correct for the calibration results? See attached pic.

I only have the relative expanded measurement uncertainty % in the report. From there, I used the formula : Relative Expanded Measurement Uncertainty (REU) = (EU / y) to calculate the expanded measurement uncertainty. And found out that the test result for 4.00 cNm is out of tolerance.

Thanks.

 

[greif]

What is the expanded uncert, and what value is y?

 

[Rachel]

What is the expanded uncert, and what value is y?

Relative Expanded Measurement Uncertainty (REU) = (EU / y)

y is the measured value = 4.00

28.9% = EU/4.00
EU = 1.156

 

[greif]

You appear to be comparing the measured value to the uncertainty to get your percentage; this does not make sense.
Comparing the tolerance interval (4.4-3.6) to the uncertainty would make some sense.
You may want to evaluate the ratio of uncert to the tolerance interval first, then eval the measured value and decide if it passes or fails.

A common desired uncert to tolerance range is 4:1
How to Calculate Test Uncertainty Ratio - isobudgets

 

[BradM]

Hello Rachel!!

Well... it looks like we might want to look a little deeper into how you're calculating the relative expanded uncertainty values. Your calibration assessment at "4" was spot on, yet it shows a failure.

Was the calibration performed by an accredited organization? They should have listed an expanded uncertainty traceable to an SI unit (like cN.m).

 

[Rachel]

Hello Rachel!!

Well... it looks like we might want to look a little deeper into how you're calculating the relative expanded uncertainty values. Your calibration assessment at "4" was spot on, yet it shows a failure.

Was the calibration performed by an accredited organization? They should have listed an expanded uncertainty traceable to an SI unit (like cN.m).

Hi BradM,

This instrument calibrated by an accredited vendor. All these values are taken from their calibration report with only Relative Expanded Uncertainty (%) given. I'm not sure how the vendor get those percentage. They did not list out the expanded uncertainty in the report.

Thus, I can only derived the EU from the formula I mentioned earlier on:

Relative Expanded Measurement Uncertainty (REU) = (EU / y)

For the measured value 4.00, the EU I calculated is 1.156, meaning +/-1.156

If the EU is taken into account, the result will be 4.00 +/-1.156. I interpreted that as a fail because it falls outside the tolerance limits (3.600 - 4.400)

 

[BradM]

I totally understand your scenario. Question... on the calibration certificate, did they not report pass/fail?

If it was me, I would pose this back to them. You paid good money for documentation that should clearly show you what they did and the results.

 

[greif]

I was unfamiliar with Relative Measurement Uncertainty; now that I have looked at that I see that it is a measure of "goodness".
It appears that they are not stating that the measured value is out of tolerance, but are stating that the measurement uncertainty is too large for the magnitude of the measured value.
They did not list expanded uncertainty on the report? Is this a 17025 accredited cal lab? Iso 17025 requires the reporting of uncertainty.

 

[Rachel]

I totally understand your scenario. Question... on the calibration certificate, did they not report pass/fail?

If it was me, I would pose this back to them. You paid good money for documentation that should clearly show you what they did and the results.

Unfortunately, they did not report pass/fail. Only a remark in their report: " The user should determine the suitability of the instrument for its intended use."

 

[Rachel]

I was unfamiliar with Relative Measurement Uncertainty; now that I have looked at that I see that it is a measure of "goodness".
It appears that they are not stating that the measured value is out of tolerance, but are stating that the measurement uncertainty is too large for the magnitude of the measured value.
They did not list expanded uncertainty on the report? Is this a 17025 accredited cal lab? Iso 17025 requires the reporting of uncertainty.

Yes, they are accredited calibration lab. That's why I'm puzzled, they should provide EU instead of REU