My OP said that I did NOT intend to use an 'alternate' calibration method for EMC-related instruments - mostly because of comments during the proceeding years by Mr Woodgate et al on the this listserv.
There are some people that *do* read and carefully evaluate advice - scary, huh ?? Brian > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of John M > Woodgate > Sent: Friday, November 13, 2009 6:02 AM > To: [email protected] > Subject: Re: [PSES] equipment calibration process > > > In message > <[email protected]>, > "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> > writes > > >That said; without GUM, no decent traceable internal calibration is > >possible. So I suggest that you take a look at GUM first: > >http://en.wikipedia.org/wiki/Measurement_uncertainty > > I feel very sceptical about this subject. Granted that it is > necessary > to consider how accurate a result is, but there seems to be a lot of > disingenuous language designed to cover up that estimates of > accuracy > cannot be other than largely arbitrary, because the > quantities involved > are those which are inherently unknown - if they were known > they would > not be 'uncertainty'. > > Consider for example: > > Type A uncertainties are those that are evaluated by statistical > methods, > > meaning 'guessed using numbers' > > and Type B uncertainties are evaluated by other means. > > meaning 'guessed without any numbers being available.' > > Because of the close association of 'uncertainty' with > assessment and > certification of laboratories, it is becoming ritualized, > with implied > presumptions that uncertainty is some sort of 'fall from > perfection' or > even 'evil'. It isn't; it's an inherent property of this Universe. > > When threatened with increasing demands for more and more > complicated > evaluations of uncertainty and/or pressure to reduce it, I > suggest to > bear in mind that the required accuracy of a result depends > entirely on > what its to be used for, We don't measure the dimensions of > (agricultural) fields to the nearest millimetre, even though with a > laser tellurometer, we could measure to even smaller units. I have > coined the phrase 'measuring jelly (Jello) with a > micrometer' about some > EMC tests. > > This is particularly relevant to EMC, or any other > measurements relating > to limits. The permissible uncertainty isn't constant: close to the > limit it's very small (one hopes), but far from the limit in > can indeed > be 'agricultural'. If I measure an emission as -20 dB > referred to the > limit, an uncertainty of +/- 19.5 dB could be tolerated. In > practice, > +/- 6 dB should be acceptable without question. > > Another example is sound pressure level. A change of 1 dB is just > perceptible under instant comparison. With a 4-hour gap between > presentations, some people cannot detect a 3 dB change. But an > uncertainty of +/-1 dB is regarded as 'poor' in some circles. > > End of rant. > -- > This is my travelling signature, adding no superfluous mass. > John M Woodgate > > - > ---------------------------------------------------------------- > 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 <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > Graphics (in well-used formats), large files, etc. can be > posted to that URL. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > > - 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 <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
