I recently separated from gov't service and am used to using mil standards.
When I was hired at my current place of employment they told me that they used a 10:1 accuracy ratio.
I was impressed, but now that I'm here I can't find any references to it.
They say they are 17025 compliant (not certified). Does anyone have a reference for accuracy ratios in the 'real world"? I have found a couple instances already of not even meeting the industry standard of 4:1.
Any help would be greatly appreciated
Here is a link to a white paper written by Keith Bennett and Howard Zion of Transcat addressing TUR. They reference the old Z540 quality standard which ISO is replacing but the concepts are universal to all Metrology quality standards.
http://www.transcat.com/media/pdf/TUR.pdf
Not to sound like a smart ass but you have a great opportunity to bring your company to this century.
10:1 test accuracy ratio predates me (schooling 1983), I recall 4:1 being in place back then. Accuracy ratio evolved to Uncertainty ratio in the 90s, the main difference being the actual performance of the instrument under test was included in the evaluation of measured value.
As the ratios shrunk so the evaluation of the result evolved, 4:1 or better simple guardbanding is normally used, less than that I use a 2% FAR (2% False Acceptance Ratio). These are methods of evaluation that hopefully help to ensure that not only is the instrument in tolerance upon completion but also increases the odds of it being in tolerance at the end of the cycle.
Sorry for the rant, I'm old and the last Mohican here.
Paul Reese of Baxter Healthcare presented a noteworthy paper at the 2016 NCSLI Conference on the history of calibration and requirements. He provided this history:
* 1960 MIL-C-45662 - Required a 10:1 TAR
* 1988 MIL-STD-45662A - Required a 4:1 TAR
* 1994 Z540.1-1994 - Retained a 4:1 TAR
* 2006 Z540.3-2006 - Described a 2% FAR along with Measurement Uncertainty Ratio of 4:1
However, because your company claims to be compliant to ISO 17025, there is no mention on the use of TAR or TUR but the requirement that you have an estimation of uncertainty of measurements for all calibrations. ISO 17025 also points to the VIM for acceptable definitions and the VIM definition for calibration also stipulates that measurement uncertanties be defined for calibrations.
I'd like to read up on FAR but don't see anything that looks relevant in google. If you have a link to some reading material or literature you'd advise I'd be interested.
FAR = False Accept Risk
ANSI/NCSL Z540.3-2006 discusses FAR as a method to ensure that measurement quantities are within specified tolerances by stating that the FAR shall not exceed 2%.
A good reference for this topic is Integrated Sciences Group and their Analytical Metrology Handbook Part 3 - Analyzing Measurement Decision Risk:
"One measure of the 'out-the-door' quality of a calibration lab or a testing organization is the probability that equipment parameters that are accepted as being in-tolerance are actually out-of-tolerance. This probability is called false accept risk or consumer risk."
Scott Mimbs formerly of NASA presented a superb paper at the 2009 NCSLI Conference where he presented 'NASA's Approach to Measurement Quality Assurance' and shared data that showed that if your calibrated equipment inventory has a total In-Tolerance Rate above 89% that all things considered equal your FAR would be below 2% and thus meet the requirements of Z540.3.
Thanks for the info! Looks like a I have a lot of reading to do :|
It gets confusing between all the different regs a company can follow.
My boss sometimes pulls out some military references, but he can't tell me what we follow or don't.
The most I got him to commit to is the 17025 compliant
Bama Kid gave the correct answer or you can just report the uncertainty