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. Brian From: Balmukund Vyas [mailto:balmukund.v...@ymllabs.com] Sent: Tuesday, September 20, 2016 9:17 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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 [mailto:bostjan.gla...@siq.si] Sent: Wednesday, September 21, 2016 9:22 AM To: EMC-PSTC@LISTSERV.IEEE.ORG 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, Bostjan From: Brian O'Connell [mailto:oconne...@tamuracorp.com] Sent: Wednesday, September 21, 2016 12:54 AM To: EMC-PSTC@LISTSERV.IEEE.ORG 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 http://www.bipm.org/en/publications/guides/gum.html Brian From: Richard Nute [mailto:ri...@ieee.org] Sent: Tuesday, September 20, 2016 1:18 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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 reference: https://www.wmo.int/pages/prog/gcos/documents/gruanmanuals/UK_NPL/mgpg11.pdf 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. Rich - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
