Can Uncertainty be larger than the Specification on a Certification

adamt

Involved In Discussions
#21
Thanks Jerry for your post,

The question is not a 4 to 1 calibration in this case(that is a issue with Z540.3) The question is under current 17205 and ILAC rules at this point. The UUT is not that accurate and is well spec'ed by the manufacture. The calibration equipment used by the cal lab was the same equipment or equivalent to the calibration equipment called out in the service manual for the UUT.

To bring people back to the question:

Can the Uncertainty listed on a 17205 logo accredited certification with uncertainties listed on the certification be larger than the specification of the UUT and still call the unit to be within manufactures specifications.

I am still talking back and forth with the accrediting body that the certification was listed under. I have went up the food chain and I have been told by this accreditation body YES and NO FIVE different times:mg:. Meaning that there people don't have a consistent stance on the issue either.

So how can I blame the calibration lab.

This issue has been since JUNE. Is there any auditors(Hershal?) that wont to take a this on and give guidance on why this is such a difficult issue.
Sorry I will not name the Accreditation body or the calab. Though I would really like to.
 
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rickpaul01

Involved in HankyPanky
#22
You?ve stated what the cal lab did, and then asked if they can do what they did. Maybe you should come at it from a different angle. What if you sent out an RFQ to a half a dozen labs and asked them to quote the uncertainty?
 

Jerry Eldred

Forum Moderator
Super Moderator
#23
Wow!!! Very funny standard quote lines. But also, great thoughts on doing the RFQ for uncertainty. That is a very good idea.
 

adamt

Involved In Discussions
#24
Thank you for your response!

Well the funny thing is the lab in question has certified this unit for three years previous they decided to add the specification of the UUT into the uncertainty budget this year witch made the uncertainty larger than the specification. This is not a difficult calibration or a very accurate one. The way they came up with the uncertainty is in question.

I think you are missing the point of the the question. It really does not mater in this conversation what the unit is unless of course it is a ideal UUT with unrealistic performance. It is not.

Again the question: On an logo accredited 17205 certification can the uncertainty listed be larger than the specification of the UUT.

I ask anyone that does uncertainty budgets for there lab What would you do? Would you accept this certification?

I'm not trying to be difficult or a jerk about this. I just am trying to find out if there is a rule on this and if it is a common thing. The way I was taught was that it can not be. Has that changed? Anyone have documentation?

This is a instrument we calibrate customers instruments with. Now that the uncertainty is larger we have an uncertainty that is larger for our customers.
 

Jerry Eldred

Forum Moderator
Super Moderator
#25
My short answer is no. My technical thinking is it is not a performance verification. If accreditation scope does everything in 2 Sigma ~95% confidence, you can't even do the math to provide any confidence at all of the measured value. I have disqualified vendors for using "shoddy" methods where a less accurate standard is used to "calibrate" a more accurate "UUT." And I have called such measurands in accredited certs I have done "non-accredited." I don't personally accept such invalid (in my opinion) measurements.

Is it a violation of ISO17025? I don't know for certain. Perhaps send the certificate to their AB, and state you believe it is a violation. If it is, the question will be answered. If it is not, get them to give you something in writing. If you need those uncertainties for your accredited measurements, there is also risk of you being in violation (if this is a violation). That, to me, elevates its importance beyond whether or not it is a good quality measurement (which I believe it is not). It is a matter of your labs compliance as well.

If you don't want to post details publicly, I would be curious about what the measurand value is, and what standard was used. If you'd care to send via a PM, I might be able to give a fuller opinion. There are cases where "that's just plain ridiculous" when a much better standard should have been used; and other cases where that may be as good as it gets.
 

adamt

Involved In Discussions
#26
Thanks Jerry for your input

If you look back on the previous pages some of your questions will be answered.

I have named the AB and given some of the particulars of the certification in question.

To bring everyone up to speed. I have been in contact with the cal lab and the AB since June 2012. Yes it has been 4 months. I have had multiple answers from the AB on my question. Yes/No FIVE different times:mg:!!!!!! Every time I go farther up the food change I get a different answer. I do not blame the cal lab for bad work just bad uncertainty budget calculations but if the AB gives such wishy washy answers I guess I can not put to much blame on them.

The cal labs answer to my questions was to leave out the specification of the UUT( to make me happy) (In my opinion should have never been there to begin with) to make the uncertainty smaller than the specification of the UUT.

What gets me is that there has been no real answer to my question. Everyone wants to blame the lab, UUT , STD or the calculations. To me that is a concern but is not the point of the conversation.

The Question: Can the uncertainty listed on a logo accredited 17205 certification be larger than the manufactures specification and still say the UUT passes calibration? That is all I really wont to know. Though I do like all the discussion.

If there is no rule that you need to have an uncertainty less than the UUT specification(given the specification is not unrealistic and the UUT's repeatability is good and of course all the other contributors you figure into the budget are not a factor)then what is the point.

Lets get my micrometer out and I'll calibrate all your gauge blocks.
 
J

jimatsntc

#27
Can Uncertainty be larger than the Specification on a Certification? my answer is yes.... but if your question is its acceptable? my answer is big "NO"....

using poor standard+poor method of calibration+poor technical skill & etc.= poor calibration

and poor calibration result poor uncertainty....
 

adamt

Involved In Discussions
#28
Have another update for you that are following this thread. The AB says there is nothing prohibiting the said calibration lab from listing uncertainties larger than the specification and still calling the certification with manufactures spec.

They will be looking at this at a future shin dig. I have concerns about other such suppliers ( I'm sure you all have such examples) but again if there is so much wiggle room with the ABs on accreditation I can not blame them to much.

So we pay our dues to the ABs and still need to audit our accredited suppliers?

I would love to get some more input to this question. Any 17205 auditors, managers, AB personal or just people with an opinion have any input on this? I have not had good luck with any of mine.

Remember the UUT is good condition with realistic specifications. The standards that calibrated the UUT are appropriate for the calibration.

The Question:
Can the uncertainties listed on a logo accredited 17205 certification be larger than the UUT factory's specification and still call it within manufactures specification?
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#29
Adamt, happy to take it on. Sorry to take so long, I was on a two-weeker in Asia.

Anyway, I first reply, buried long back, is that yes, it is entirely possible that the uncertainty on an accredited cert is larger than the specification or tolerance.

Jerry is correct that it is not desirable or suggested. Uncertainty depends on many factors. If it can be assumed (risky, I know the three words) that the cal lab's standards are all calibrated with lower uncertainty, and environmental issues are controlled, and there are no other significant influences, then the UUT will drive the high uncertainties.

However, if the UUT is not the main driver, then that would mean that the standards, the environment, or some other significant effect is driving the uncertainty.

It is also possible, even likely, the uncertainty was calculated incorrectly.

If I were going into the cal lab and was aware of this situation, one of the first things I would want to see is the PT/ILC for that discipline. Then a demonstration of that type calibration, and sit down and calculate the uncertainty.

It is possible this is a one-off, which would suggest calculation. If more than that, suggests a systemic issue.

The cal lab's AB should not give an answer in truth without some investigation, other than to say it is possible. BTW, if it is the one where I am senior staff, let me know, and I will get an answer.

One other thing, if you continue to get a runaround, you can lodge a formal complaint with the AB. They are required to follow-up, required under ISO/IEC 17011 and ILAC requirements.

Hope this helps.
 

adamt

Involved In Discussions
#30
Hershal,

Glad your back. To bring you up to date. I have lodged a complaint with the AB and the response was that they do not believe the final measurement uncertainty should be larger than the UUT's specification BUT there is nothing prohibiting the lab in doing so. They will be looking to maybe change that in there policy next year.

In talking to the cal lab they included the UUT's specification in the final uncertainty calculations. I said that is not the way I was taught to calculate uncertainty. The class I took years ago and my CCT prep and test I don't remember ever adding the UUT's specification in the final uncertainty calculation. Am I right? This cal lab and the calibration is Accredited 17205. (It's not one of yours ):)

This then brought up the original question. This is still my question.

As many have asked about the UUT and the standards being used. They are both good units with realistic specifications with none of the contributors large enough make the uncertainty problems. It's the question of final uncertainty being larger than the specification and the cal lab calling it within manufacturer's specification.

If the uncertainty is larger than the spec. How can you say that it is within spec?

If your are not doing the uncertainty calculations wrong and you have good equipment and at least 4:1 TUR. Then how can the uncertainty be larger than the specification and call the cal good?

Is there a standard that states this one way or the other?

Am I :deadhorse:???????
 
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