En Number - Reference that explains En Numbers Theory & Application

Hi Everyone,

I was unable to find any reference that explains En numbers theory & application except for in ISO/IEC Guide 43.

When I googgled, there is a NCSLI conference proceeding in 2006 entittled En Number 101. However, I need to pay to view the paper.

Advice anyone? Thanks in advance.

Can anyone help?

You might try the following link. In the 8 page document, there is a description of how to calcualte the En.

http://www.proficiency.org/Portals/0/ExamineWhyandHowsV2.pdf

Note that this is taken from one of the proficiency test providers. Other providers may have good explanations on their websites as well.

I believe another source is APLAC PT001 or APLAC PT002, both available at no charge.

http://www.aplac.org

...most of the references explained on how its calculated but not on why is it used.

Just in case there is a limitation for the use of En numbers that I need to be aware of.

Because of limited number of PT provider here and cost (if were to do it overseas), our lab send our own instruments to the National Lab (if they have the capability) or to our competitors as our own mean of interlaboratory comparisons. Hence, we produce our own interlaboratory comparison report and judge our capability based on the result.

Due to this, we need to know the reason behind En numbers and its scope of application to make sure that it is valid for our own application.

I hope in the future, we will have more PT providers here, if only someone could realize that quality is as important as producing goods..

The why is actually pretty simple: To let the participant know when the reported value, plus/minus the uncertainty, is what is known as an outlier. That means the value is outside the acceptable limits and a corrective action has to be initiated and investigated.

APLAC and the ABs have the ability to offer PT/ILC and also measurement audits. Having said that the availability does appear to be somewhat limited.

An ILC with the NMI and/or competitors is perfectly valid, but yes, the En score does have to be calculated and a report prepared. Contact me off-line and I may be able to refer someone to you to do the reporting, even perhaps run an ILC for you, located in India. No idea as to cost.

Hope this helps.

My concern on the self-calculated En value is that the measurement uncertanties factors taken into consideration maybe different from NMI/our competitors lab. Whereas in format PT program, well at least most of them, specify which factors are taken into consideration for a particular PT/calibration.

Thus, if the abs(En number) is more than 1, we are unable to identify whether there is an underlying problem or it is merely different considerations taken in regards to the measurement uncertainty calculation.

Any views on this? Or am I merely mistaken lol

I realize that this is over 5 years late, but if you deal with 17025 PT issues, this becomes important, and it's never the wrong time to bone up on 17025 issues!

Buckle up, folks!

The En number is merely a percentage of your measured value to the reference value, corrected with the square root of the sum of the squares of your uncertainty and the uncertainty of the reference value.

If your absolute En number is over 1, then your corrected measurement is GREATER than your uncertainty. That would indicate 1 or a combination of four causes, assuming your reference value and reference uncertainty are valid:

1) Your uncertainty is incorrect
2) Your measurement is incorrect
3) Your measurement equipment is faulty
4) Your measurement procedure is faulty

1 and 2 are most often typos on your part, and are easily corrected. 3 and 4 are system issues that MUST be addressed in some way prior to your next 17025 audit, and would ultimately require a corrective action.

Also, the .pdf posted above is a good calculation reference. I recommend saving it for your convenience.

I hope this helps someone save some time and heartache!