This is, for me, good stuff. I adore the physics of measurements. Mr. Dudek has provided a link to a good info source that I was remiss for not including. On this general subject of test data acceptance, please note that all such UL guides are at
<www.ul.com/global/eng/pages/offerings/services/programs/dap/tools/> To re-state my original question - what does the CFR say about temperature measurement in reference to the NRTL program ? Brian > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of Dudek, > John (Corcom) > Sent: Tuesday, June 16, 2009 12:25 PM > To: [email protected] > Subject: RE: T-Couple Calibration > > From UL's website, acceptance of thermocouple guidelines > for DAP participants. > > http://www.ul.com/global/eng/documents/offerings/services/pro grams/dap/tools/Equipment_Thermocouple.pdf > > Regards > John F. Dudek > Manager, Product Safety Engineering > Corcom Products, Tyco Electronics Corp. > Mundelein, Il. USA > 847-573-6534 telephone > 847-680-0340 fax direct to PC > Mailto:[email protected] > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf > Of Brian O'Connell > Sent: Tuesday, June 16, 2009 12:27 PM > To: [email protected] > Subject: RE: T-Couple Calibration > > I buy thermocouple wire on separate spools so that I can > control the twisted pair, then cut the twisted pairs into > 1.5m segments. Then I choose a pair from the first third and > a pair from the last third of the spools to verify. No > complaints from any auditors to date. For calibration, look > at ASTM E207/E220/E563 - but there are easier, more > reasonable ways to verify instruments and temperature sensors. > > I have not seen any particular requirement in 29 CFR 1910.7 > for NRTL thermocouple-based measurements/calibration. I > would be very interested in any additional information that > could be provided for NRTL temperature measurement requirements. > > Let us talk about this concept called 'temperature', because > I have seen some non-credible temperature data from CBTLs and NRTLs. > > Temperature measurements are recorded for a small surface > area of a larger mass, for a single instance in time. > Temperature is a scalar quantity. Do not think of > temperature measurements as vector quantities, and do not > consider a temperature measurement to represent a 'constant' > characteristic. > > The NIST polynomials' accuracy for the common stuff (J, K, > T) has a theoretical yield of about than 0.1 degC error > through the full scale. The NIST polynomial error can be > improved an order of mag for a delimited temperature range. > > The reported accuracy of some instruments that are used for > typical engineering measurements are about the same is the > resolution (about 0.1 degC), which is not practical, and > maybe not possible. For any of these common t/c types, the > voltage gradient across a thermocouple wire pair is on the > order of 100s of microvolts or perhaps 10's of millivolts > for most product safety Type Test measurements. So the > sensitivity of the thermocouple and its variable lead > resistance and t/c attachment thermal impedance and thermal > shunting and non-isothermal routing of t/c leads, the > accuracy of the instrument, and the ambient noise conditions > all conspire to make the resultant temperature measurement > uncertainty, at best, 2 degC. > > And a lab that reports temperatures to 0.1 degC is delusional. > > There are some research/academic labs that may be able to > control a test so the measurement uncertainty is 1 degC or > better - but the practice is not reasonable for the > engineering measurements in a product safety lab. > > Let the shouting begin. > > Brian > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf > Of American Idle > Sent: Tuesday, June 16, 2009 8:38 AM > To: [email protected] > Cc: [email protected] > Subject: Re: T-Couple Calibration > > You could pull the whole spool off and make your 2nd > junction from the last bit, then re-wrap the whole spool :-) > > I talked to a UL team lead on their DAP/ISO 17025 program > and he had the following comments; > > -This requirement is based on a CTL decision > -You must validate one TC from the beginning of the spool > and one from the end of the spool with an RTL Calibrator or > water bath method > -You risk all your previous data if the last TC you make > from the spool doesn't calibrate right > > He also stated that this requirement may change in the > future because it doesn't make a lot of sense (and suggested > that I bring this particular issue up for discussion if I > happened to know anyone who sits on the Standards Commitee!). > > As another poster stated, you may be better off purchasing > pre-made thermocouples. The only risk there is if your > manufacturer goes out of business, your calibration > certificates may become invalid. > > -Ken Arenella > > On Tue, Jun 16, 2009 at 9:50 AM, > <[email protected]> wrote: > > While we are on the subject. Anyone have an inexpensive > solution to the big NRTL's new > Calibrated Thermocouple requirement? > > As I read the spec it requires calibrating the first and > last T-Couple off of the spool > minimum. Takes me a couple years to use 500ft. So I would > technically only need to Calibrate > one a year. > > Thanks in advance > > John Merrill > Principal Product Safety Engineer > Schneider Electric - 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. 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