Hi All, Although the CT-1.... probes from Tek are good probes and are widely used current probes in general have some limitations that can cause errors:
1) The capacitance from the probe body to the wire through the probe is stated as 1.5 pF for the CT-1, if I remember correctly. This value is not unlike many probes, but remember that 1.5 pF at 1 GHz is only 160 Ohms. This can affect the circuit so the probe should always be used near the ground end of a circuit to minimize the effect. Put a second probe around the cable from the first to measure how much signal current is capacitively coupling to the probe body. In one case with another probe I saw 30% of the rising edge of a current pulse leaving on the probe cable. See: http://emcesd.com/tt061999.htm and http://emcesd.com/tt2005/tt050105.htm on my website. 2) The CT-1 (not sure of the other members of the family), at least several years ago when I was at Bell Labs, showed a significant electric field response when used to measure ESD generated currents. In one case I remember, the error was 25% but it can be larger. This can be checked by a "null experiment." Solder a stub on the wire you are going to measure the current in and put the probe on the stub, clipping off the any of the stub that protrudes past the probe body. The measurement result should be zero since no current is flowing in the probe, but the stub exposes the current probe to the electric field on the wire. You may be amazed at what you see! I have been surprised a number of times over the years with several different probes. 3) Never assume a current probe just measures current until you can prove it by experiment for your particular setup. Many are spec'ed in a nice lab test setup which is not usually the case for most measurements I do. There is much more information like the above on my website, published papers, and my book and seminars on this topic. Doug John McAuley wrote: >Hi > >I thought this probe comprised the Tektronix CT1, CT2 or Ct6. > >These have a 1V/A characteristic into a 50ohm load and bandwidth from 10kHz >to 1 GHz depending on model. > >http://www.tek.com/site/ps/0,,60-12572-INTRO_EN,00.html > >Regards > >John > >John McAuley >www.cei.ie >[email protected] >***************************************************************** >DISCLAIMER: The information contained in this e-mail may be confidential and >is intended solely for the use of the named addressee. Access, copying or >re-use of the e-mail or any information contained therein by any other >person is not authorised. If you are not the intended recipient please >notify us immediately by returning the e-mail to the originator > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On Behalf Of Richard >Marshall >Sent: 19 April 2008 12:45 >To: [email protected] >Subject: CISPR15 Current probe > >Re; " Folks, in the CISPR 15 loop antenna there is a current probe >specified. Can >anyone direct me to a source please? I'm struggling. Thanks, Derek Walton >L F Research" > >There are adequate specification details in CISPR16-1-4 Annexe C, but no >design info. there. > >I reckon that this "current probe" is a toroidal ferrite current transformer >with a load resistor and possibly a calibration tweaking resistor. > >My company has made generally similar (but usually split-core) devices for >other EMC applications and will be happy to design/make/calibrate a special >for you if you cannot find an off-the-shelf item. > >Richard >Richard Marshall Limited, The Dappled House >30 Ox Lane, Harpenden, Herts. AL5 4HE, UK > >Phone: +44 (0)1582 460815 >Email: [email protected] >Website: www.design-emc.co.uk > >- >---------------------------------------------------------------- >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/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] > >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/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] > >All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > > > -- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: [email protected] \ _ / ] \ _ / Web: http://www.dsmith.org - 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/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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
