Brian, I will hazard a guess that the cal labs are referring to a situation where there is an analog scale (such as for a bulb thermometer or a VOM) instead of a digital readout. In such cases, there will be differences in the readings that are reported, due to parallax and/or how different people interpolate between the scale tick marks. If this is the case I would agree that the lab ought to be able to provide a best uncertainty based only on their standards; this best uncertainty can assume that the tick marks have a resolution better than or equal to their uncertainty. If an instrument with lower resolution tick marks is provided for calibration, the actual uncertainty will be less than the best uncertainty. Best Regards, Mike
Michael Heckrotte Engineering Manager, CCS (408) 463-0885 ext. 121 fax: (408) 463-0888 [email protected] From: [email protected] mailto:[email protected]]On Behalf Of Brian O'Connell Sent: Monday, November 01, 2004 8:22 AM To: [email protected]; [email protected] Subject: IEC 17025 certs I am reviewing potential calibration contractors, and have noted the following, or similar, on some of their IEC17025-referenced certs. The following is noted when there is no uncertainty listed for some measurements and/or instruments: "The uncertainty of scale verification is highly dependent on local conditions such as the resolution of the scale. Any statement of best uncertainty would therefore be misleading..." Huh ?!?! According to clause 5.4.6 of IEC17025 "A calibration lab ... shall have and shall apply a procedure to estimate the uncertainty of measurement for all calibrations and types of calibrations". The purpose of listing a specific scope accreditation is to state what can be expected from a facility and its techs. If the accreditation agency cannot support its audit with empirical data, under specific test conditions, then of what use is the IEC17025 certificate ? (Not a rhetorical question). I need to verify that, after instrument and measurement uncertainty, that the contractor can give me at least a 4:1 TAR. luck, Brian ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
