Scott, Thanks for this, please see my PM.
All the best, Doug On Tue, Jan 13, 2015 at 9:45 AM, Scott Aldous < 00000220f70c299a-dmarc-requ...@ieee.org> wrote: > Hi Doug, > > Rather than start with the number to plug into the formula in the > standard, it would be more helpful to start with the MSA and derive what > number should be plugged into the formula. I am curious to see what others > think, but I agree with you in that I believe that a +/-1% stated accuracy > would correspond to a 1% value for "a" (not 2%). > > Looking at IEEE 1547.1, A.1, it is consistent for the standard to use > twice the nominal or stated value for test parameters. The slope of the > ramp function includes not only the MSA, but the time-delay setting plus > manufacturer's stated detection time of the EUT (added together to obtain > "z"). The value used for calculating the slope (in the denominator) is > twice "z". The value for the hold time is also a minimum of 2 times the > time-delay setting (footnote 40 on page 47). The standard seems to have > been written with the assumption that a 2x factor is sufficient margin for > test accuracy for each parameter that is a source of error. > > In terms of voltage or frequency, it is irrelevant whether the EUT > measurement is on the high or low side of the test instrument measurement. > The magnitude of the error is the important bit. The standard requires the > voltage/frequency ramp to be half the stated accuracy, which I would > interpret to mean half the maximum magnitude of error for any given > measurement. An example: If the MSA is +/-1% of the reading, and the > voltage as measured by the test instrument is 100V, then for any specific > measurement the EUT measurement is no lower than 99V (1% error) or no > higher than 101V (1% error). > > It is important to note that this interpretation results in a slower > overall ramp, which is more conservative. For the example above, if the > value to be used in the formula were assumed to be 2% rather than 1% > (corresponding to 2V rather than 1V), then the ramp would be twice as fast. > I would argue that if a slower ramp than is absolutely required is used, it > still should be acceptable since it will result in a more accurate test > result. A faster than required ramp is not acceptable. > > As a side note, the picture gets a bit more complicated when we dive into > exactly what the MSA means. Is it +/-1% of reading? full scale? This should > be specified by the manufacturer but I don't know if that is always the > case. If stated in terms of percentage of reading, than a strict reading of > the standard requires the slope to be varied as the PUT is varied during > the ramp. Also, what to do if the MSA isn't symmetrical, such as +1%/-2%, > since you don't know for any given test if the error will be on the high or > low side? > > On Mon, Jan 12, 2015 at 9:44 PM, Nyffenegger, Dave < > dave.nyffeneg...@bhemail.com> wrote: > >> Seems to be related to measurement uncertainty which I see expressed as >> a single absolute value (in the ISO acoustic measurement standards) which I >> also assumed was the equivalent of +/- 1/2 of the value. >> >> >> >> -Dave >> >> >> >> *From:* Doug Powell [mailto:doug...@gmail.com] >> *Sent:* Tuesday, January 13, 2015 12:31 AM >> *To:* EMC-PSTC@LISTSERV.IEEE.ORG >> *Subject:* [PSES] Manufacturer's Stated Accuracy (MSA) >> >> >> >> In my reading of private and government web sites plus a few test >> standards, "manufacturer's stated accuracy" is a commonly used term and in >> every case I could find, it seems +/- some percentage is the normal way of >> stating accuracy. However, I also find in IEEE 1547.x the "+/-" is >> omitted. So it is not clear, would 1% MSA mean +/- 1% or +/- 0.5%? >> >> >> >> My interpretation of a 1% accuracy which does not specify "+/-" is >> that this is a shorthand way of specifying the same thing. As in a 1% >> deviation from a center point which is the nominal value. Or stated in >> statistics fashion, you should expect an infrequent measurement of +/- 3 >> standard deviations from nominal under a normal curve. >> >> >> >> In the case of the voltage & frequency variation tests of IEEE 1547 >> and programming the test ramps, this becomes an important factor. >> >> >> >> Any discussion on this is appreciated. >> >> >> >> Thanks, - doug >> >> Douglas Powell >> http://www.linkedin.com/in/dougp01 >> >> - >> ---------------------------------------------------------------- >> >> 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) <http://www.ieee-pses.org/list.html> >> 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> >> - >> ---------------------------------------------------------------- >> >> 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) <http://www.ieee-pses.org/list.html> >> 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> >> > > > > -- > Scott Aldous > Compliance Engineer > Google > 650-253-1994 > scottald...@google.com > - > ---------------------------------------------------------------- > > 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) <http://www.ieee-pses.org/list.html> > 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> > -- Douglas E Powell doug...@gmail.com Skype: doug.powell52 http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- 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>
