Incorrect for product safety, there would be no 'gray area'. Per the error 
band, the temperature measurement exceeds limits. It is important to not 
confuse the 'accuracy method' in Guide 115 with the calculated UoM. Limits per 
instrument accuracy are only part of measurement uncertainty, and in fact, 
Guide 115 specifically indicates that if the uncertainty affects compliance 
with specification limits, the UoM calculation is the appropriate method for 
error bands.

For EMC - it is all magic and hand-waving, and your ability to concoct an 
engineering rationale in the report.

My favorite challenge to NRTLs is to demonstrate that their repeating error 
repeatability of measurement (type A) has normal distribution.


From: Balmukund Vyas [] 
Sent: Tuesday, September 20, 2016 9:17 PM
Subject: Re: [PSES] Measurement Accuracy

in general, the test standards prescribe the accuracy / type of equipments and  
method to be used for testing. This means that measurement uncertainty has been 
specified indirectly. In such cases, where we are following these guidelines, 
the pass/fail decision can be taken based on the limits given in standard , 
without taking into account the uncertainty. If any of these guidelines are not 
being followed and resulting in higher uncertainty, the decision of pass/ fail 
needs to taken after due consideration of measurement uncertainty.
More and more standards are now defining uncertainty factors in details for 
example EMC standards; however I agree that many are still not very clear, 
requiring engineering judgment to be taken.
Best regards
B M Vyas
From: Boštjan Glavič [] 
Sent: Wednesday, September 21, 2016 9:22 AM
Subject: Re: [PSES] Measurement Accuracy
Measurement uncertainty depends on instruments used, method used etc. Each lab 
has to do calculation of measurement uncertainty for particular method. 
Measurement uncertainty becomes critical when results are close to the limit.
High uncertainty means you have more chance to be in »a grey area« where result 
needs to be defined as pass or fail. Laboratory needs to inform the client 
about value of measurement uncertainty if requested.
Example, if your measurement uncertainty of temperature measurement method with 
thermocouples is 3°C, limit according to standard is 85°C and you measure 84°C 
then you are in a grey area. In this case you can make result as Pass however 
client needs to be informed about your measurement uncertainty.
ISO GUIDE 115 give you some guidance how to do calculation, but no document 
specifies limits of measurement uncertainty.
Hope it helps.
Best regards,
From: Brian O'Connell [] 
Sent: Wednesday, September 21, 2016 12:54 AM
Subject: Re: [PSES] Measurement Accuracy
ISO, International Standardization Organization, Guide to the Expression of 
Uncertainty in Measurement, GUM
ISO, General Requirements for the Competence of testing and calibration 
laboratories, ISO 17025
From: Richard Nute [] 
Sent: Tuesday, September 20, 2016 1:18 PM
Subject: Re: [PSES] Measurement Accuracy
I was wondering if anyone was aware of any guidance documents that provided 
acceptable levels of uncertainty when conducting various tests.
I didn’t know what “uncertainty” is, so I did a Google search and found this 
Of particular interest is 1.2, which discusses “pass-fail.”  In both product 
safety and EMC compliance, the result is “pass” or “fail.”  The document says:
“Often, a test is not a measurement: tests normally lead to a ‘yes/no’ answer 
or a ‘pass/fail’ result. (However, measurements may be part of the process 
leading up to a test result.)”
So, our standards specify tests and test limits, pass or fail.  
Just looking for some additional guidance documents or standards that would 
help me convince the powers that be that such errors are unacceptable.
Well, according to the document, you need to take into account what you call 
“errors” as they are not errors but different measurements that need to be 
accounted for in determining the “pass-fail.”
At the end of the document are two references, which are much more detailed.

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