On Tue, 12 Jul 2016 02:08:04 +0100, John Woodgate <jmw1...@btinternet.com> wrote:
> Slight under-compensation would cause a brief overshoot to 138 V. In my > opinion, probes can't be calibrated except with the scope they are > exclusively used with. Covering the cal adjuster with a sticker shows a deep > misunderstanding of how passive probes work. Agreed. Performance of passive probes strongly depends to the oscilloscope, so I think it should always be calibrated with a specific oscilloscope channel. EURAMET cg-7 (calibration of oscilloscopes), https://www.euramet.org/get/?tx_stag_base%5Bfile%5D=3611&tx_stag_base%5Bidentifier%5D=%252Fdocs%252FPublications%252Fcalguides%252FEURAMET_cg-7__v_1.0_Calibration_of_Oscilloscopes.pdf&tx_stag_base%5Baction%5D=downloadRaw&tx_stag_base%5Bcontroller%5D=Base also says "For multi-channel systems, the measurement result must be related with the corresponding oscilloscope channel. A probe calibration is only valid in combination with the calibrated oscilloscope (indicated in the calibration certificate). The probe calibration must be clearly related to the applied channel." Regards, Tom > From: Schaefer, David [mailto:dschae...@tuvam.com] > Sent: Monday, July 11, 2016 10:50 PM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: [PSES] Oscilloscope probe calibration > > All, > > We're seeing an issue with scope probes, and I'd appreciate suggestions, or > just information on how others handle calibration. I've got two problems > with passive scope probes. > > First, probe compensation. Compensation depends on the capacitance of the > scope being used, so the probe would be adjusted to match that capacitance. > Well if the cal house is using a different scope, they'll adjust it to match > their capacitance, which may not be what we need. Also, many times the cal > sticker then covers the adjustment port, implying the user should not be > adjusting that value. I disregard the stickers, but it isn't a good habit to > get into. > > Second, we're seeing variance between in cal probes based on what they're > measuring. I had four probes measuring a 1 microsecond rise time transient > signal. All were within 5% of the expected peak voltage. Next, all four > probes measured a 5 ns rise time transient. Three peak voltages were within > 10-15% of the measured 100V(not great, but acceptable). The fourth > consistently read around 138 V. Nearly 40% off, just by changing the rise > time. 5 ns might be at the edge of the probe's bandwidth, but I'd expect a > decrease in level, not an increase. > > These were all calibrated probes, and three were identical models. The one > that was way off wasn't the odd model. Our cal house measures a DC voltage > for accuracy, and bandwidth. > > What's causing the inaccuracy? How can I prevent this problem in the future? > Moving to all active probes isn't an option right now. > > Thanks, > > David Schaefer > > - > ---------------------------------------------------------------- > 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 <mailto: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 <mailto:sdoug...@ieee.org> > > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > > David Heald <dhe...@gmail.com <mailto: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) > 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) 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>
