Does ISO 17025 Require Point By Point Measurement Uncertainty on Reports?

[Bob Collins]

Weekly I find myself having the same discussion regarding providing point-by-point uncertainties on calibration reports. My feeling is yes since standards, resolution, etc may not be the same throughout the range being certified. However other believe the 17025 does not specifically require this. What is the correct answer

[Hershal]

In truth, ISO/IEC 17025 does not require a point by point listing of measurement uncertainty. MU covering a range is equally acceptable under the Standard provided the MU applies to any point in the range.

Now, where the rub comes in is what do your customers want/need, and what does your accrediting body (AB) require, if you are accredited?

Hope this helps.

Hershal

[CalGuy]

ISO 17025 is an evil International Standard. It seems to have been wriiten for National and Standards type laboratories. It is not written for the most common users, In-House Labs and Commercial Labs. But ISO/IEC 17025 Sec 5.10.3.1 (c) states;

"where applicable a statement on the estimated uncertainty of measurement; Information on uncertainty is needed in test reports when it is relevant to the validity or application of the test results, when a client's instruction so requires, or when the uncertainty affects compliance to a specification limit"

So basically measurement uncertainty is in the hands of the client (end user) and they need to ask a few questions. I have seen too many customers wanting uncertainty data (Increased Cost) for mundane every day items (Handheld DMM, Oscilliscopes, Function Generators etc). This can lead to situations where you are paying 1-4 times as much for the calibration as you would for a brand new instrument. So before asking for measurement uncertainty data I would reccommend asking (UUT=Unit Under Test);

1) Is the UUT used as a check or reference standard? (Standard Resistors, Meter Calibrators, Multifunction Calibrators)

2) Do I need to calculate measurement uncertainty for the instruments I am calibrating with the UUT?

3) What are the cost differences for calibration, calibration with data, calibration with data and uncertainty statement, calibration with data and measurement uncertainties?

Simple TAR's (Test Accuracy Ratio) or the old 4:1 rule seems sufficient for 90% of the instruments I see every year (Approx 17,000/year) Maybe 9% should have data and the final 1% would require actual uncertainty data.

Well thats my Hope this helps anybody so they do not send me another 3% Analog Oscilloscope asking for Measurement Uncertainty because I am pretty certain that it is not accurate!

[Graeme]

Originally Posted by CalGuy

... ISO/IEC 17025 Sec 5.10.3.1 (c) states;

"... or when the uncertainty affects compliance to a specification limit."

Of the clause you quoted, it this the phrase that is usually understood to require uncertainty reporting in the case of "borderline" measurements?

I have heard and seen some people say that if a calibration result is within the range (specification limit +/- uncertainty), then reporting the uncertainty is required. Is that correct? Or is there another way to do it?

[Charles Wathen]

I think CalGuy has some excellent valid points. As he mentioned, I'm a CalGuy for an internal company. We do not perform measurement uncertanty (yet). We are going to be using the old TAR method BUT for critical standards, I will be reporting measurement uncertainty where I feel that it will benifit the actual measurement where there is a chance that the uncertainty of the measurement will impact production.

Another issue I have is the cost of reporting "as found data". I'm in several arguments with my counter parts in other divisions over this. My feeling is the actual data is needed only when you find an out of tolerance condition; otherwise, simply reporting on the cal cert "within mfg specs" is good enough for me. I've even asked my counter parts what they do with all this as found data, and they said it's for auditors (LOL). So in other words, they do nothing with all this data but pay an additional 20% for the extra information.

[CalGuy]

That brings up a good point. This was the reason that if an item is at 70% or more of specified tolerance then I would adjust it to nominal to ensure being within tolerance +/- the measurement uncertainty.
Ex. Nominal 1.000 V
Tol. is +/-0.010 V
Actual is 1.009 V (0.009 is 90% of Tolerance)
Uncertainty is +/- 0.002 V

Is this unit received In Tolerance or Out of Tolerance? It is "Indeterminite"... I would not want to be answering the phone the days Cal certificates went out saying: Condition Received... Indeterminite. I would call this instrument In Tolerance then adjust to nominal.

My basic point is that ISO 17025 has taken the aspect of equipment accuracy out of the normal technicians hands and put it into the hands of Statisticians and Mathmatical Engineers (some of who couldn't operate a basic piece of equipment). The time required to calculate and interpret the measurement uncertainty on all the varying pieces of equipment and standards is mind boggling. A standard 1 Ohm resistor not much of a problem but how about a 9k-26 GHz Spectum Analyzer or a 10M-20 GHz Signal Generator with AM/FM/PM?

Also 5.10.3.1 is for Test Report which I ASSuME is for Test Labs. Calibration Certificates are covered under 5.10.4, which is even more bad news. Section 5.10.4.2 states..."When a statement of compliance with a specification is made omitting the measurement results and associated uncertainties, the laboratory shall record those results and maintain them for possible future reference."
Translation: When I do a calibration for a customer who requires an accredited cal but does not require data, then I must still take the data and store it and thus charge the same as if data was requested.

The last part of 5.10.4.2 is the kicker..."When statements of compliance are made, the uncertainty of measurement shall be taken into account."
This is the part that really gets me. Did they make this statement so vague on purpose? Taken into account... Does this mean Calculated and applied to readings? Looked at and discarded as "Inconsequential"? Documented and shown for each data point taken?

Until industries see that many of the things required in 17025 are not necessary for there applications they are being applied to then the cost for calibration and testing wil increase significantly. Has anyone seen the price changes for Agilent Technologies calibration services lately? You get about 5 or 6 different prices depending on what you ask for. Of course the highest is always the 17025 version. I think costs will eventually force companies to maybe switch to ISO 100012 or a rewrite of 17025.

[Charles Wathen]

Originally Posted by CalGuy

My basic point is that ISO 17025 has taken the aspect of equipment accuracy out of the normal technicians hands and put it into the hands of Statisticians and Mathmatical Engineers (some of who couldn't operate a basic piece of equipment). The time required to calculate and interpret the measurement uncertainty on all the varying pieces of equipment and standards is mind boggling. A standard 1 Ohm resistor not much of a problem but how about a 9k-26 GHz Spectum Analyzer or a 10M-20 GHz Signal Generator with AM/FM/PM?

Hehe, for a headache, look at this uncertainty analysis:
http://www.thunderscientific.com/ref...25rhuncert.pdf

I doubt most of us could even follow this. I know because I just did one myself a few months back on our humidity ability with a General Eastern C1 calibrator and a chilled mirror. Since I'm green to measurement uncertainty, it took me almost a full 8 hour day to perform mine using Uncertainty Analyzer software by Dr. Howard Castrup of Integrates Science Group at home to avoid interruptions. I was fortunate that I took Dr. Howard's class for a full week, and found it difficult at times, and I don't consider myself that "dumb" when it comes to calibration, but Howard's software is very easy to follow. I even had the opportunity to have the Dr visit my facility for almost 4 hours, and he evaluated my use and made some improvements to his software.

I'm just fortunate that ISO17025 is a reference document only for us.

[Graeme]

Originally Posted by Charles Wathen

Hehe, for a headache, look at this uncertainty analysis:
http://www.thunderscientific.com/ref...25rhuncert.pdf

I doubt most of us could even follow this. ... I was fortunate that I took Dr. Howard [Castrup]'s class for a full week, ...

We need a new Smiley -- "Pulling Hair Out!" (For those of us who still have any, of course.)

I agree with Charles, that example is a bit difficult to follow, especially at 2230 when I should be shutting down the confuser instead of visiting the Cove! On the other hand, if you skim over the calculus that paper does give a very good example of the type of analysis that often needs to be done. Now, we have to keep in mind that (a) a two-pressure humidity chamber is a primary standard, (b) relative humidity does have very complex interactions that only a physicist could love, and (c) the author certainly has a higher degree than I do!

Also the theory is - or so I have been told - that for "a measurement system" this only has do be fully done once and then reduced to either a single number or software code, and re-verified every now and then.

The problem is, I (most of us?) am too short-staffed and spend too much time firefighting to do it consistently. Also I don't have enough equipment to make a dedicated system for each type of measurement! For example, I have one HP 8902A: is is used about 50% for calibrating communications and navigation system test sets, 30% for calibrating signal generators, and the rest of the time for attenuation and other miscellaneous calibrations. That's three different workstations and three different "measurement systems" and so would require three different uncertainty analyses. (Or, I really need two more 8902A units and then the three analyses - but the lab is a department of a major airline and you can see in the papers what the money situation is.)

I've taken one uncertainty course myself but it was over ten years ago. I'm planning on taking a half-day intro that Dr. Castup is doing after the NCSL conference this summer, and if I can ever get someone else to pay for it I will go through one of his full courses and get the software.

Actually, my customers don't even want a certificate - all they want is a new sticker on the instrument right now. The only ones we print (they're all in the computer - it's automatic) are where they must have a report of value to use the instrument. As for uncertainty - I evaluate it when writing a cal procedure and apply guardbands if needed but we don't report it - and if we did the customers would not know what to do with it. So for me doing uncertainty the way 17025 wants it is not feasible or economic and to that extent I agree with CalGuy's assessment of the standard. On the other hand, it is also an idealized goal to strive for ... a benchmark of some kind.