Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
Pretty much everything by Gert looks incorrect or possibly a some typos. More turns on the core gives you less output over most of the frequency range but more output at the very low end of the frequency. Zt = M/L * Zo in the flat region of the frequency response where Zo is the 50 Ohm load on the probe, M the mutual inductance between the probe and measured circuit an L is the inductance of the probe coil. M goes up as the number of turns but L goes up as the square of the turns. This is the result of the low pass filter formed by the probe coil and 50 Ohm load. Doug Smith Sent from my iPhone IPhone: 408-858-4528 [tel:408-858-4528] Office: 702-570-6108 [tel:702-570-6108] Email: d...@dsmith.org Website: http://dsmith.org On Sun, Jan 31, 2016 at 23:05, ce-test, qualified testing bv - Gert Gremmen wrote: As a rule of thumb the transfer impedance (Zt) is the load impedance of your SA ( = 50 Ohm) multiplied by the square of the applied windings on your probes core. You should load the probe with a low impedance (attenuation) network (1 Ohm ->50 Ohm) to reduce Zt and limit the number of windings. The latter gives you better control on frequency response, while more windings give more output signal and extends the lowest usable frequency . So it's a trade off between sensitivity, and frequency response. It's not so different from classical signal transformer analysis, you should be familiar with. A Zt of less than 10 Ohm will give good accuracy for common CM currents. If you try to shield your home-made probe, make sure the shield is discontinuous with low capacitance, otherwise it will short the magnetic field in the core. As usual with rule of thumbs, this is not an exhaustive analysis of Zt, but very usable in terms of learning what's going on. Regards, Ing. Gert Gremmen Approvals manager + ce marking of electrical/electronic equipment + Independent Consultancy Services + Compliance Testing and Design for CE marking according to EC-directives: - Electro Magnetic Compatibility 2004/108/EC - Electrical Safety 2006/95/EC - Medical Devices 93/42/EC - Radio & Telecommunication Terminal Equipment 99/5/EC + Improvement of Product Quality and Reliability testing + Education Web: www.cetest.nl (English) Phone : +31 10 415 24 26 --- This e-mail and any attachments thereto may contain information that is confidential and/or protected by intellectual property rights and are intended for the sole use of the recipient(s) named above. Any use of the information contained herein (including, but not limited to, total or partial reproduction, communication or distribution in any form) by persons other than the designated recipient(s) is prohibited. If you have received this e-mail in error, please notify the sender either by telephone or by e-mail and delete the material from any computer. Thank you for your co-operation. -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Monday 1 February 2016 03:41 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents Doug's point is well taken. If you know the probe's transfer impedance, and you know it works properly (is well-shielded) then instead of just "getting a number" and trying to lower it you can work against a computed current limit that radiates at or below the RE limit which is the actual goal. BTW, SAE ARP 6236 shows how you can measure your probe's transfer impedance. Ken Javor Phone: (256) 650-5261 > From: Doug Smith > Reply-To: > Date: Sun, 31 Jan 2016 16:21:19 -0800 > To: > Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM > currents > > That is why it is very difficult to make current probes well shielded > enough and certainly with a flat transfer impedance that covers a few > decades of frequency. The cost of a good current probe, for instance > an > F-33-1 or F-61 is less than what it has already cost your company in > time lost. > > Doug > > Douglas C. Smith > University of Oxford Course Tutor > D C Smith Consultants > PO Box 60941 > Boulder City, NV 89006 > Email: d...@dsmith.org > Web: http://www.dsmith.org > Web: http://emcesd.com > Tel: 702-570-6108 > Mobile: 408-858-4528 > > On Sun, 31 Jan 2016 17:49:08 -0600, Ken Javor > wrote: > You needed a metal shield to prevent capacitive coupling. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >>> From: Amund Westin >>> Reply-To: Amund Westin >>> Date: Sun, 31 Jan 2016 20:21:48 +0100 >>> To: >>> Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents >>>> A clamp-on ferrite with a few turn
Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
Have to disagree about the transfer impedance formula. The transfer impedance is certainly dependent on the number of windings, but it is also dependent on the relative permeability of the core around which it is wound, and also the diameter of the ferrite core (the probe actually senses the magnetic field circulating around a wire, and that field falls off in proportion to distance). The core material has a magnetizing inductance, and unless the measurements are made at frequencies above which the magnetizing inductance is a high impedance relative to load (50 Ohm) impedance, the transfer impedance rolls off with decreasing frequency. The probe works off Faraday's Law, and the output potential is proportional to the time rate of change of the magnetic flux in the core around which the turn are wrapped. The magnetic field intensity B is the magnetic field H multiplied by the core permeability. But one must also take into account the core diameter. H = I / 2 pi r, so that a probe that has a small diameter sees a significant change in H at the inner core diameter vs. the outer core diameter. Therefore in computing the transfer impedance, one must integrate the current behavior as a function of radius, and get a log [r] type fictional dependence. With larger diameter probes (four/five inches) this is less of a factor. What is dependent on load impedance is the impedance the probe inserts in a wire around which it is clamped. I referenced this in my first response on this thread: the inserted impedance is the transfer impendence divided by the turns ratio, which is just the number of windings. Ken Javor Phone: (256) 650-5261 > From: "ce-test, qualified testing bv - Gert Gremmen" > Reply-To: "ce-test, qualified testing bv - Gert Gremmen" > Date: Mon, 1 Feb 2016 08:05:32 +0100 > To: > Conversation: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > > As a rule of thumb the transfer impedance (Zt) is the load impedance of your > SA ( = 50 Ohm) multiplied > by the square of the applied windings on your probes core. You should load > the probe with > a low impedance (attenuation) network (1 Ohm ->50 Ohm) to reduce Zt and limit > the number of windings. > The latter gives you better control on frequency response, while more windings > give more > output signal and extends the lowest usable frequency . So it's a trade off > between sensitivity, and frequency response. > > It's not so different from classical signal transformer analysis, you should > be familiar with. > > A Zt of less than 10 Ohm will give good accuracy for common CM currents. > If you try to shield your home-made probe, make sure the shield is > discontinuous with low capacitance, otherwise > it will short the magnetic field in the core. > > As usual with rule of thumbs, this is not an exhaustive analysis of Zt, but > very usable in terms of > learning what's going on. > > > Regards, > > Ing. Gert Gremmen > Approvals manager > -- > -- > > > + ce marking of electrical/electronic equipment > + Independent Consultancy Services > + Compliance Testing and Design for CE marking > according to EC-directives: > - Electro Magnetic Compatibility 2004/108/EC > - Electrical Safety 2006/95/EC > - Medical Devices 93/42/EC > - Radio & Telecommunication Terminal Equipment 99/5/EC > + Improvement of Product Quality and Reliability testing > + Education > > Web: www.cetest.nl (English) > Phone : +31 10 415 24 26 > --- > This e-mail and any attachments thereto may contain information > that is confidential and/or protected by intellectual property rights > and are intended for the sole use of the recipient(s) named above. > Any use of the information contained herein (including, but not > limited to, total or partial reproduction, communication or > distribution in any form) by persons other than the designated > recipient(s) is prohibited. If you have received this e-mail in error, > please notify the sender either by telephone or by e-mail and > delete the material from any computer. > Thank you for your co-operation. > > -Original Message- > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sent: Monday 1 February 2016 03:41 > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > > Doug's point is well taken. If you know the probe's transfer impedance, and > you know it works properly (is well-shielded) then instead of just &quo
Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
As a rule of thumb the transfer impedance (Zt) is the load impedance of your SA ( = 50 Ohm) multiplied by the square of the applied windings on your probes core. You should load the probe with a low impedance (attenuation) network (1 Ohm ->50 Ohm) to reduce Zt and limit the number of windings. The latter gives you better control on frequency response, while more windings give more output signal and extends the lowest usable frequency . So it's a trade off between sensitivity, and frequency response. It's not so different from classical signal transformer analysis, you should be familiar with. A Zt of less than 10 Ohm will give good accuracy for common CM currents. If you try to shield your home-made probe, make sure the shield is discontinuous with low capacitance, otherwise it will short the magnetic field in the core. As usual with rule of thumbs, this is not an exhaustive analysis of Zt, but very usable in terms of learning what's going on. Regards, Ing. Gert Gremmen Approvals manager + ce marking of electrical/electronic equipment + Independent Consultancy Services + Compliance Testing and Design for CE marking according to EC-directives: - Electro Magnetic Compatibility 2004/108/EC - Electrical Safety 2006/95/EC - Medical Devices 93/42/EC - Radio & Telecommunication Terminal Equipment 99/5/EC + Improvement of Product Quality and Reliability testing + Education Web: www.cetest.nl (English) Phone : +31 10 415 24 26 --- This e-mail and any attachments thereto may contain information that is confidential and/or protected by intellectual property rights and are intended for the sole use of the recipient(s) named above. Any use of the information contained herein (including, but not limited to, total or partial reproduction, communication or distribution in any form) by persons other than the designated recipient(s) is prohibited. If you have received this e-mail in error, please notify the sender either by telephone or by e-mail and delete the material from any computer. Thank you for your co-operation. -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Monday 1 February 2016 03:41 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents Doug's point is well taken. If you know the probe's transfer impedance, and you know it works properly (is well-shielded) then instead of just "getting a number" and trying to lower it you can work against a computed current limit that radiates at or below the RE limit which is the actual goal. BTW, SAE ARP 6236 shows how you can measure your probe's transfer impedance. Ken Javor Phone: (256) 650-5261 > From: Doug Smith > Reply-To: > Date: Sun, 31 Jan 2016 16:21:19 -0800 > To: > Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM > currents > > That is why it is very difficult to make current probes well shielded > enough and certainly with a flat transfer impedance that covers a few > decades of frequency. The cost of a good current probe, for instance > an > F-33-1 or F-61 is less than what it has already cost your company in > time lost. > > Doug > > Douglas C. Smith > University of Oxford Course Tutor > D C Smith Consultants > PO Box 60941 > Boulder City, NV 89006 > Email: d...@dsmith.org > Web: http://www.dsmith.org > Web: http://emcesd.com > Tel: 702-570-6108 > Mobile: 408-858-4528 > > On Sun, 31 Jan 2016 17:49:08 -0600, Ken Javor > wrote: > You needed a metal shield to prevent capacitive coupling. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >>> From: Amund Westin >>> Reply-To: Amund Westin >>> Date: Sun, 31 Jan 2016 20:21:48 +0100 >>> To: >>> Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents >>>> A clamp-on ferrite with a few turns of wire and connected to a >>>> spectrum >>> analyzer, worked out to be a good tool for measuring CM currents on >>> single cables. It gave me some measured numbers [dBuV], and then I >>> worked >> on trying >>> to get the numbers down :) >>>> But when I placed the home-made probe on wires / cables inside a >> noisy rack, >>> problems started. The probe picked up almost all kinds of >>> frequencies, even when no cables or wires where going through the probe >>> (ferrite). >>>>>> This lesson told me that a simple home-made current probe >> works good on a >>> stand-alone cable, but it does not work that good then measurements
Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
Doug's point is well taken. If you know the probe's transfer impedance, and you know it works properly (is well-shielded) then instead of just "getting a number" and trying to lower it you can work against a computed current limit that radiates at or below the RE limit which is the actual goal. BTW, SAE ARP 6236 shows how you can measure your probe's transfer impedance. Ken Javor Phone: (256) 650-5261 > From: Doug Smith > Reply-To: > Date: Sun, 31 Jan 2016 16:21:19 -0800 > To: > Subject: Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > > That is why it is very difficult to make current probes well shielded > enough and certainly with a flat transfer impedance that covers a few > decades of frequency. The cost of a good current probe, for instance an > F-33-1 or F-61 is less than what it has already cost your company in > time lost. > > Doug > > Douglas C. Smith > University of Oxford Course Tutor > D C Smith Consultants > PO Box 60941 > Boulder City, NV 89006 > Email: d...@dsmith.org > Web: http://www.dsmith.org > Web: http://emcesd.com > Tel: 702-570-6108 > Mobile: 408-858-4528 > > On Sun, 31 Jan 2016 17:49:08 -0600, Ken Javor > wrote: > You needed a metal shield to prevent capacitive coupling. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >>> From: Amund Westin >>> Reply-To: Amund Westin >>> Date: Sun, 31 Jan 2016 20:21:48 +0100 >>> To: >>> Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents >>>> A clamp-on ferrite with a few turns of wire and connected to a spectrum >>> analyzer, worked out to be a good tool for measuring CM currents on single >>> cables. It gave me some measured numbers [dBuV], and then I worked >> on trying >>> to get the numbers down :) >>>> But when I placed the home-made probe on wires / cables inside a >> noisy rack, >>> problems started. The probe picked up almost all kinds of frequencies, even >>> when no cables or wires where going through the probe (ferrite). >>>>>> This lesson told me that a simple home-made current probe >> works good on a >>> stand-alone cable, but it does not work that good then measurements are >>> carried out closed to other noisy sources. Then you might need a more >>> professional current clamp. >>>>>> #Amund >>>>>>>>>>>> Fra: Ken Javor [mailto:ken.ja...@emccompliance.com] >>> Sendt: 15. januar 2016 17:53 >>> Til: EMC-PSTC@LISTSERV.IEEE.ORG >>> Emne: Re: [PSES] Fwd: [PSES] Current probe for CM currents >>>>>> I think it is important to not lose sight of the original >> query that started >>> this thread. The query was about whether placing a current probe around a >>> cable perturbed the current to be measured. >>>> There is no doubt that radiated emissions can originate within an >> equipment >>> enclosure separately from driving common mode currents on a cable, but that >>> wasn't the query. In fact, the poster was probing cables within a >> large rack >>> (enclosure) looking for a source within an enclosure. >>>> Ken Javor >>> Phone: (256) 650-5261 >>>>>> _ > > From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org >>> <mailto:00f5a03f18eb-dmarc-requ...@ieee.org> > >>> Reply-To: Bill Owsley mailto:wdows...@yahoo.com> > >>> Date: Fri, 15 Jan 2016 07:26:08 + >>> To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG> > >>> Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents >>>> If you can measure common mode noise on a cable, you have a >> problem from the >>> port !! >>> Note the world famous Ott's math on this effect in his 1st edition. Might >>> be in his 2nd too. >>>> I have used both e-field and h-field (current clamp) at the same time. >>> We are engineers so figure out how I did that! >>> And since some of the work is below 30 MHz, I have also added a >> loop antenna >>> for a 3rd measurement. >>> My approach is if I find any emission, locally, near field, bench stuff, >>> that varies by position over the area of the product, then I have a >> problem. >>> E-field scan,using a o'scope probe. H-field scan usually using a personally >>> built small loop, and any other sort of scan, conducted or radiated, that I >>> can make up at the moment. >>> I work for a homogeneous field in the scans over the area of the product. >
Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
That is why it is very difficult to make current probes well shielded enough and certainly with a flat transfer impedance that covers a few decades of frequency. The cost of a good current probe, for instance an F-33-1 or F-61 is less than what it has already cost your company in time lost. Doug Douglas C. Smith University of Oxford Course Tutor D C Smith Consultants PO Box 60941 Boulder City, NV 89006 Email: d...@dsmith.org Web: http://www.dsmith.org Web: http://emcesd.com Tel: 702-570-6108 Mobile: 408-858-4528 On Sun, 31 Jan 2016 17:49:08 -0600, Ken Javor wrote: You needed a metal shield to prevent capacitive coupling. Ken Javor Phone: (256) 650-5261 > From: Amund Westin > Reply-To: Amund Westin > Date: Sun, 31 Jan 2016 20:21:48 +0100 > To: > Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > > A clamp-on ferrite with a few turns of wire and connected to a spectrum > analyzer, worked out to be a good tool for measuring CM currents on single > cables. It gave me some measured numbers [dBuV], and then I worked on trying > to get the numbers down :) > > But when I placed the home-made probe on wires / cables inside a noisy rack, > problems started. The probe picked up almost all kinds of frequencies, even > when no cables or wires where going through the probe (ferrite). > > > > This lesson told me that a simple home-made current probe works good on a > stand-alone cable, but it does not work that good then measurements are > carried out closed to other noisy sources. Then you might need a more > professional current clamp. > > > > #Amund > > > > > > > > > > > > Fra: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sendt: 15. januar 2016 17:53 > Til: EMC-PSTC@LISTSERV.IEEE.ORG > Emne: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > > > I think it is important to not lose sight of the original query that started > this thread. The query was about whether placing a current probe around a > cable perturbed the current to be measured. > > There is no doubt that radiated emissions can originate within an equipment > enclosure separately from driving common mode currents on a cable, but that > wasn't the query. In fact, the poster was probing cables within a large rack > (enclosure) looking for a source within an enclosure. > > Ken Javor > Phone: (256) 650-5261 > > > > _ > > From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org > <mailto:00f5a03f18eb-dmarc-requ...@ieee.org> > > Reply-To: Bill Owsley mailto:wdows...@yahoo.com> > > Date: Fri, 15 Jan 2016 07:26:08 + > To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG> > > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > If you can measure common mode noise on a cable, you have a problem from the > port !! > Note the world famous Ott's math on this effect in his 1st edition. Might > be in his 2nd too. > > I have used both e-field and h-field (current clamp) at the same time. > We are engineers so figure out how I did that! > And since some of the work is below 30 MHz, I have also added a loop antenna > for a 3rd measurement. > My approach is if I find any emission, locally, near field, bench stuff, > that varies by position over the area of the product, then I have a problem. > E-field scan,using a o'scope probe. H-field scan usually using a personally > built small loop, and any other sort of scan, conducted or radiated, that I > can make up at the moment. > I work for a homogeneous field in the scans over the area of the product. > My assumption is that if I find a homogeneous field, then there are no or > low emission gradients which can equate to a field at a distance. So get > creative, and redundant, by different methods for measuring the emissions. > Ironic, I am good at mashing all emissions, and then they hand me an > intentional radiator and ask that I don't kill the fundamental. What ? You > mean I have to pick what to mash, and what not to mash? > Ok, so I caught on quick enough to keep the job. > > > ps. I suffer from not being able to use a leaky enclosure. I don't get any > shielding for the products. > Cable shielding that is bogus terminated, but at the low frequencies of > interests, it works. > Then I have to deal with the higher frequencies, the harmonics !!! > Plastic covers and pcb and cables up to 15 KW or more of digital BS to make > an analog signal. > And then 'normal' digital signals for the ADC circuits all in the middle of > this. > Management is like, we have done it this way for over 25 years and so we are > not changing it now. > It works (I have to make it work) so do
Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
You needed a metal shield to prevent capacitive coupling. Ken Javor Phone: (256) 650-5261 > From: Amund Westin > Reply-To: Amund Westin > Date: Sun, 31 Jan 2016 20:21:48 +0100 > To: > Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents > > A clamp-on ferrite with a few turns of wire and connected to a spectrum > analyzer, worked out to be a good tool for measuring CM currents on single > cables. It gave me some measured numbers [dBuV], and then I worked on trying > to get the numbers down :) > > But when I placed the home-made probe on wires / cables inside a noisy rack, > problems started. The probe picked up almost all kinds of frequencies, even > when no cables or wires where going through the probe (ferrite). > > > > This lesson told me that a simple home-made current probe works good on a > stand-alone cable, but it does not work that good then measurements are > carried out closed to other noisy sources. Then you might need a more > professional current clamp. > > > > #Amund > > > > > > > > > > > > Fra: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sendt: 15. januar 2016 17:53 > Til: EMC-PSTC@LISTSERV.IEEE.ORG > Emne: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > > > I think it is important to not lose sight of the original query that started > this thread. The query was about whether placing a current probe around a > cable perturbed the current to be measured. > > There is no doubt that radiated emissions can originate within an equipment > enclosure separately from driving common mode currents on a cable, but that > wasn't the query. In fact, the poster was probing cables within a large rack > (enclosure) looking for a source within an enclosure. > > Ken Javor > Phone: (256) 650-5261 > > > > _ > > From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org > <mailto:00f5a03f18eb-dmarc-requ...@ieee.org> > > Reply-To: Bill Owsley mailto:wdows...@yahoo.com> > > Date: Fri, 15 Jan 2016 07:26:08 + > To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG> > > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > If you can measure common mode noise on a cable, you have a problem from the > port !! > Note the world famous Ott's math on this effect in his 1st edition. Might > be in his 2nd too. > > I have used both e-field and h-field (current clamp) at the same time. > We are engineers so figure out how I did that! > And since some of the work is below 30 MHz, I have also added a loop antenna > for a 3rd measurement. > My approach is if I find any emission, locally, near field, bench stuff, > that varies by position over the area of the product, then I have a problem. > E-field scan,using a o'scope probe. H-field scan usually using a personally > built small loop, and any other sort of scan, conducted or radiated, that I > can make up at the moment. > I work for a homogeneous field in the scans over the area of the product. > My assumption is that if I find a homogeneous field, then there are no or > low emission gradients which can equate to a field at a distance. So get > creative, and redundant, by different methods for measuring the emissions. > Ironic, I am good at mashing all emissions, and then they hand me an > intentional radiator and ask that I don't kill the fundamental. What ? You > mean I have to pick what to mash, and what not to mash? > Ok, so I caught on quick enough to keep the job. > > > ps. I suffer from not being able to use a leaky enclosure. I don't get any > shielding for the products. > Cable shielding that is bogus terminated, but at the low frequencies of > interests, it works. > Then I have to deal with the higher frequencies, the harmonics !!! > Plastic covers and pcb and cables up to 15 KW or more of digital BS to make > an analog signal. > And then 'normal' digital signals for the ADC circuits all in the middle of > this. > Management is like, we have done it this way for over 25 years and so we are > not changing it now. > It works (I have to make it work) so don't change anything. Sucks to be me > - but I do like a challenge. > > > > > > > > > > > > > > > > _ > > > From: Ken Wyatt mailto:k...@emc-seminars.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 > > > All emc-pstc postings are archived and searchable on
[PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
A clamp-on ferrite with a few turns of wire and connected to a spectrum analyzer, worked out to be a good tool for measuring CM currents on single cables. It gave me some measured numbers [dBuV], and then I worked on trying to get the numbers down :) But when I placed the home-made probe on wires / cables inside a noisy rack, problems started. The probe picked up almost all kinds of frequencies, even when no cables or wires where going through the probe (ferrite). This lesson told me that a simple home-made current probe works good on a stand-alone cable, but it does not work that good then measurements are carried out closed to other noisy sources. Then you might need a more professional current clamp. #Amund Fra: Ken Javor [mailto:ken.ja...@emccompliance.com] Sendt: 15. januar 2016 17:53 Til: EMC-PSTC@LISTSERV.IEEE.ORG Emne: Re: [PSES] Fwd: [PSES] Current probe for CM currents I think it is important to not lose sight of the original query that started this thread. The query was about whether placing a current probe around a cable perturbed the current to be measured. There is no doubt that radiated emissions can originate within an equipment enclosure separately from driving common mode currents on a cable, but that wasn't the query. In fact, the poster was probing cables within a large rack (enclosure) looking for a source within an enclosure. Ken Javor Phone: (256) 650-5261 _ From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org <mailto:00f5a03f18eb-dmarc-requ...@ieee.org> > Reply-To: Bill Owsley mailto:wdows...@yahoo.com> > Date: Fri, 15 Jan 2016 07:26:08 + To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG> > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents If you can measure common mode noise on a cable, you have a problem from the port !! Note the world famous Ott's math on this effect in his 1st edition. Might be in his 2nd too. I have used both e-field and h-field (current clamp) at the same time. We are engineers so figure out how I did that! And since some of the work is below 30 MHz, I have also added a loop antenna for a 3rd measurement. My approach is if I find any emission, locally, near field, bench stuff, that varies by position over the area of the product, then I have a problem. E-field scan,using a o'scope probe. H-field scan usually using a personally built small loop, and any other sort of scan, conducted or radiated, that I can make up at the moment. I work for a homogeneous field in the scans over the area of the product. My assumption is that if I find a homogeneous field, then there are no or low emission gradients which can equate to a field at a distance. So get creative, and redundant, by different methods for measuring the emissions. Ironic, I am good at mashing all emissions, and then they hand me an intentional radiator and ask that I don't kill the fundamental. What ? You mean I have to pick what to mash, and what not to mash? Ok, so I caught on quick enough to keep the job. ps. I suffer from not being able to use a leaky enclosure. I don't get any shielding for the products. Cable shielding that is bogus terminated, but at the low frequencies of interests, it works. Then I have to deal with the higher frequencies, the harmonics !!! Plastic covers and pcb and cables up to 15 KW or more of digital BS to make an analog signal. And then 'normal' digital signals for the ADC circuits all in the middle of this. Management is like, we have done it this way for over 25 years and so we are not changing it now. It works (I have to make it work) so don't change anything. Sucks to be me - but I do like a challenge. _ From: Ken Wyatt mailto:k...@emc-seminars.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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Fwd: [PSES] Current probe for CM currents
The cover story of the November issue of IN Compliance magazine deals with this effect when in injecting current on cables: http://incompliancemag.com/magazine/past-issues/ The bottom line is that using an injection clamp as a current probe introduces resistance that detunes standing waves while not affecting the average current on the cable. Ken Javor Phone: (256) 650-5261 From: John Allen Reply-To: John Allen Date: Tue, 19 Jan 2016 12:30:10 - To: Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Richard & Folks (at least in the UK) FWIW, I was at the R&S ³Demystifying EMC² Seminar at Reading yesterday, and there was very clear and informative talk (³Demystifying the uses and selection of cable ferrites²) on the correct/incorrect uses of ferrites from Glen Wallis at Wurth so if anyone can get to one of his presentations,, or even get the Notes, I can recommend it. Also, it was an extremely good Seminar overall! John Allen W.London, UK From: Richard Marshall [mailto:richard.marshal...@btinternet.com] Sent: 19 January 2016 11:24 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Just as Gert and Ralf say, ferrites used for EMC purposes are , if the ferrite material is properly chosen for the frequency range concerned, predominately RESISTIVE not inductive. Therefore they damp out resonances, rather than tune them. The resistive impedance is however limited, and so they are best placed where the interference current is highest, that is at the current maximum of the most serious resonance. See ³Cores and Cables in EMC Design and Test: A get it right first time guide² in ³The EMC Journal² for March 2013, pages 19-24 and subsequent issues.Available in the archive at www.compliance-club.com/ <http://www.compliance-club.com/> Richard Richard Marshall Laboratories, 30 Ox Lane, Harpenden, Herts.,AL5 4HE, UK +44 (0)1582 460815 www.design-emc.co.uk <http://www.design-emc.co.uk> Member of the EMC Industry Association From: McDiarmid, Ralph [mailto:ralph.mcdiar...@schneider-electric.com] Sent: 18 January 2016 22:46 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents " I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. " Seems to me that it's akin to adding resistance to an L-C network to provide better damping. So, these ferrites are lossy? I suppose that makes sense. ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: "ce-test, qualified testing bv - Gert Gremmen" To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/16/2016 01:41 AM Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Doug et al, If I understand well, the ferrite creates a virtual end of cable for EUT2, allowing the cable to resonate ?? Interesting case, but not completely fair, as there a 2 EUT that in this situation would require ferrite at both end of the cable. I have not seen this effect yet on a single EUT with cabling in 20 year of testing. I have seen reductions too small to justify the ferrites use, and I have seen spurious frequencies go up , in the case of multiple cable situations. And yea, it is possible that 2 compliant EUT connected together can exceed limits, even without adding ferrites. Theoretically EUT should be tested with lambda/2 length of cabling for each frequency peak -as a worst case-, instead we have chosen to test EUT using a single length of cable , accepting the risk of a null effect for certain frequencies and resonance for others. In addition the termination impedance of the cables is undefined, ranging from open for not connected cables to shorts for other. CISPR 22 makes an effort to stabilize the mains cabling by using AMN for each. Unfortunately most AMN do not have a defined CM/DM impedance above 30 MHz, their upper design frequency. Measuring CM current using the current clamp is the best way to avoid these effects, if the cables common mode termination impedance is frequency independent and around a typical value of 150 Ohms. This effectively suppresses any resonances and nulls. Unfortunately (again) this is extremely difficult to realize this at frequencies above 150 -200 MHz. This idea was the basis for the propositions a few years ago to terminate all cables in a radiated test setup with ferrite clamps at their ends. The idea is that the input CM impedance of a set of ferrites is around 150 ohms, and in any case better as open or short. I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high p
Re: [PSES] Fwd: [PSES] Current probe for CM currents
Richard & Folks (at least in the UK) FWIW, I was at the R&S "Demystifying EMC" Seminar at Reading yesterday, and there was very clear and informative talk ("Demystifying the uses and selection of cable ferrites") on the correct/incorrect uses of ferrites from Glen Wallis at Wurth - so if anyone can get to one of his presentations,, or even get the Notes, I can recommend it. Also, it was an extremely good Seminar overall! John Allen W.London, UK From: Richard Marshall [mailto:richard.marshal...@btinternet.com] Sent: 19 January 2016 11:24 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Just as Gert and Ralf say, ferrites used for EMC purposes are , if the ferrite material is properly chosen for the frequency range concerned, predominately RESISTIVE not inductive. Therefore they damp out resonances, rather than tune them. The resistive impedance is however limited, and so they are best placed where the interference current is highest, that is at the current maximum of the most serious resonance. See "Cores and Cables in EMC Design and Test: A get it right first time guide" in "The EMC Journal" for March 2013, pages 19-24 and subsequent issues.Available in the archive at <http://www.compliance-club.com/> www.compliance-club.com/ Richard Richard Marshall Laboratories, 30 Ox Lane, Harpenden, Herts.,AL5 4HE, UK +44 (0)1582 460815 <http://www.design-emc.co.uk> www.design-emc.co.uk Member of the EMC Industry Association From: McDiarmid, Ralph [mailto:ralph.mcdiar...@schneider-electric.com] Sent: 18 January 2016 22:46 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents " I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. " Seems to me that it's akin to adding resistance to an L-C network to provide better damping. So, these ferrites are lossy? I suppose that makes sense. ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: "ce-test, qualified testing bv - Gert Gremmen" To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/16/2016 01:41 AM Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents _ Hi Doug et al, If I understand well, the ferrite creates a virtual end of cable for EUT2, allowing the cable to resonate ?? Interesting case, but not completely fair, as there a 2 EUT that in this situation would require ferrite at both end of the cable. I have not seen this effect yet on a single EUT with cabling in 20 year of testing. I have seen reductions too small to justify the ferrites use, and I have seen spurious frequencies go up , in the case of multiple cable situations. And yea, it is possible that 2 compliant EUT connected together can exceed limits, even without adding ferrites. Theoretically EUT should be tested with lambda/2 length of cabling for each frequency peak -as a worst case-, instead we have chosen to test EUT using a single length of cable , accepting the risk of a null effect for certain frequencies and resonance for others. In addition the termination impedance of the cables is undefined, ranging from open for not connected cables to shorts for other. CISPR 22 makes an effort to stabilize the mains cabling by using AMN for each. Unfortunately most AMN do not have a defined CM/DM impedance above 30 MHz, their upper design frequency. Measuring CM current using the current clamp is the best way to avoid these effects, if the cables common mode termination impedance is frequency independent and around a typical value of 150 Ohms. This effectively suppresses any resonances and nulls. Unfortunately (again) this is extremely difficult to realize this at frequencies above 150 -200 MHz. This idea was the basis for the propositions a few years ago to terminate all cables in a radiated test setup with ferrite clamps at their ends. The idea is that the input CM impedance of a set of ferrites is around 150 ohms, and in any case better as open or short. I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. Not enough cases to draw final conclusions, however. Would love to hear any other experiences from members on this list. Gert Gremmen -Original Message- From: Doug Smith [ <mailto:d...@emcesd.com> mailto:d...@emcesd.com] Sent: zaterdag 16 januari 2016 1:52 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Everone, Here is an interesting case wher
Re: [PSES] Fwd: [PSES] Current probe for CM currents
Just as Gert and Ralf say, ferrites used for EMC purposes are , if the ferrite material is properly chosen for the frequency range concerned, predominately RESISTIVE not inductive. Therefore they damp out resonances, rather than tune them. The resistive impedance is however limited, and so they are best placed where the interference current is highest, that is at the current maximum of the most serious resonance. See "Cores and Cables in EMC Design and Test: A get it right first time guide" in "The EMC Journal" for March 2013, pages 19-24 and subsequent issues.Available in the archive at www.compliance-club.com/ Richard Richard Marshall Laboratories, 30 Ox Lane, Harpenden, Herts.,AL5 4HE, UK +44 (0)1582 460815 <http://www.design-emc.co.uk> www.design-emc.co.uk Member of the EMC Industry Association From: McDiarmid, Ralph [mailto:ralph.mcdiar...@schneider-electric.com] Sent: 18 January 2016 22:46 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents " I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. " Seems to me that it's akin to adding resistance to an L-C network to provide better damping. So, these ferrites are lossy? I suppose that makes sense. ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: "ce-test, qualified testing bv - Gert Gremmen" mailto:g.grem...@cetest.nl> > To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> , Date: 01/16/2016 01:41 AM Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents _ Hi Doug et al, If I understand well, the ferrite creates a virtual end of cable for EUT2, allowing the cable to resonate ?? Interesting case, but not completely fair, as there a 2 EUT that in this situation would require ferrite at both end of the cable. I have not seen this effect yet on a single EUT with cabling in 20 year of testing. I have seen reductions too small to justify the ferrites use, and I have seen spurious frequencies go up , in the case of multiple cable situations. And yea, it is possible that 2 compliant EUT connected together can exceed limits, even without adding ferrites. Theoretically EUT should be tested with lambda/2 length of cabling for each frequency peak -as a worst case-, instead we have chosen to test EUT using a single length of cable , accepting the risk of a null effect for certain frequencies and resonance for others. In addition the termination impedance of the cables is undefined, ranging from open for not connected cables to shorts for other. CISPR 22 makes an effort to stabilize the mains cabling by using AMN for each. Unfortunately most AMN do not have a defined CM/DM impedance above 30 MHz, their upper design frequency. Measuring CM current using the current clamp is the best way to avoid these effects, if the cables common mode termination impedance is frequency independent and around a typical value of 150 Ohms. This effectively suppresses any resonances and nulls. Unfortunately (again) this is extremely difficult to realize this at frequencies above 150 -200 MHz. This idea was the basis for the propositions a few years ago to terminate all cables in a radiated test setup with ferrite clamps at their ends. The idea is that the input CM impedance of a set of ferrites is around 150 ohms, and in any case better as open or short. I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. Not enough cases to draw final conclusions, however. Would love to hear any other experiences from members on this list. Gert Gremmen -Original Message- From: Doug Smith [ <mailto:d...@emcesd.com> mailto:d...@emcesd.com] Sent: zaterdag 16 januari 2016 1:52 To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Everone, Here is an interesting case where a ferrite core can actually perform an impedance matching function and increase emissions on a cable: <http://emcesd.com/tt120199.htm> http://emcesd.com/tt120199.htm Doug On Fri, 15 Jan 2016 09:40:22 -0800, Ed Price mailto:edpr...@cox.net> > wrote: I would add a caution to Ken's comment about common mode cable currents > creating RE. Yes, the CM currents certainly do create RE, but you need > to probe the cables at several intervals to understand those current > paths. It is not immediately obvious that all CM current flowing on a > cable at one end of a cable does
Re: [PSES] Fwd: [PSES] Current probe for CM currents
" I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. " Seems to me that it's akin to adding resistance to an L-C network to provide better damping. So, these ferrites are lossy? I suppose that makes sense. ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: "ce-test, qualified testing bv - Gert Gremmen" To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/16/2016 01:41 AM Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Doug et al, If I understand well, the ferrite creates a virtual end of cable for EUT2, allowing the cable to resonate ?? Interesting case, but not completely fair, as there a 2 EUT that in this situation would require ferrite at both end of the cable. I have not seen this effect yet on a single EUT with cabling in 20 year of testing. I have seen reductions too small to justify the ferrites use, and I have seen spurious frequencies go up , in the case of multiple cable situations. And yea, it is possible that 2 compliant EUT connected together can exceed limits, even without adding ferrites. Theoretically EUT should be tested with lambda/2 length of cabling for each frequency peak -as a worst case-, instead we have chosen to test EUT using a single length of cable , accepting the risk of a null effect for certain frequencies and resonance for others. In addition the termination impedance of the cables is undefined, ranging from open for not connected cables to shorts for other. CISPR 22 makes an effort to stabilize the mains cabling by using AMN for each. Unfortunately most AMN do not have a defined CM/DM impedance above 30 MHz, their upper design frequency. Measuring CM current using the current clamp is the best way to avoid these effects, if the cables common mode termination impedance is frequency independent and around a typical value of 150 Ohms. This effectively suppresses any resonances and nulls. Unfortunately (again) this is extremely difficult to realize this at frequencies above 150 -200 MHz. This idea was the basis for the propositions a few years ago to terminate all cables in a radiated test setup with ferrite clamps at their ends. The idea is that the input CM impedance of a set of ferrites is around 150 ohms, and in any case better as open or short. I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. Not enough cases to draw final conclusions, however. Would love to hear any other experiences from members on this list. Gert Gremmen -Original Message- From: Doug Smith [mailto:d...@emcesd.com] Sent: zaterdag 16 januari 2016 1:52 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Everone, Here is an interesting case where a ferrite core can actually perform an impedance matching function and increase emissions on a cable: http://emcesd.com/tt120199.htm Doug On Fri, 15 Jan 2016 09:40:22 -0800, Ed Price wrote: I would add a caution to Ken's comment about common mode cable currents > creating RE. Yes, the CM currents certainly do create RE, but you need > to probe the cables at several intervals to understand those current > paths. It is not immediately obvious that all CM current flowing on a > cable at one end of a cable does not necessarily flow at the other end of that cable. > Especially where cables are bundled, or where they pass closely along > a chassis or structural member, there are possibilities for that > current to couple off of the cable. The current flow will follow the > impedances, both at the ends and at other fortuitous nodes. This is > one of the reasons that a ferrite absorber might work much better at > one position along a cable than at another position and also why RE > might be dependent on something as obscure as cable bundle tightness. > > Ed Price > WB6WSN > Chula Vista, CA USA > > > > From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Friday, > January 15, 2016 8:53 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > > > I think it is important to not lose sight of the original query that > started this thread. The query was about whether placing a current > probe around a cable perturbed the current to be measured. There is no > doubt that radiated emissions can originate within an equipment > enclosure separately from driving common mode currents on a cable, but > that wasn't the query. In fact, the poster was pro
Re: [PSES] Fwd: [PSES] Current probe for CM currents
Hi Doug et al, If I understand well, the ferrite creates a virtual end of cable for EUT2, allowing the cable to resonate ?? Interesting case, but not completely fair, as there a 2 EUT that in this situation would require ferrite at both end of the cable. I have not seen this effect yet on a single EUT with cabling in 20 year of testing. I have seen reductions too small to justify the ferrites use, and I have seen spurious frequencies go up , in the case of multiple cable situations. And yea, it is possible that 2 compliant EUT connected together can exceed limits, even without adding ferrites. Theoretically EUT should be tested with lambda/2 length of cabling for each frequency peak -as a worst case-, instead we have chosen to test EUT using a single length of cable , accepting the risk of a null effect for certain frequencies and resonance for others. In addition the termination impedance of the cables is undefined, ranging from open for not connected cables to shorts for other. CISPR 22 makes an effort to stabilize the mains cabling by using AMN for each. Unfortunately most AMN do not have a defined CM/DM impedance above 30 MHz, their upper design frequency. Measuring CM current using the current clamp is the best way to avoid these effects, if the cables common mode termination impedance is frequency independent and around a typical value of 150 Ohms. This effectively suppresses any resonances and nulls. Unfortunately (again) this is extremely difficult to realize this at frequencies above 150 -200 MHz. This idea was the basis for the propositions a few years ago to terminate all cables in a radiated test setup with ferrite clamps at their ends. The idea is that the input CM impedance of a set of ferrites is around 150 ohms, and in any case better as open or short. I have been experimenting with this and in several cases using a ferrite clamp at the end of cabling seems to "stabilize the spectrum", increasing low peaks and reducing high peaks. Not enough cases to draw final conclusions, however. Would love to hear any other experiences from members on this list. Gert Gremmen -Original Message- From: Doug Smith [mailto:d...@emcesd.com] Sent: zaterdag 16 januari 2016 1:52 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents Hi Everone, Here is an interesting case where a ferrite core can actually perform an impedance matching function and increase emissions on a cable: http://emcesd.com/tt120199.htm Doug On Fri, 15 Jan 2016 09:40:22 -0800, Ed Price wrote: I would add a caution to Ken's comment about common mode cable currents > creating RE. Yes, the CM currents certainly do create RE, but you need > to probe the cables at several intervals to understand those current > paths. It is not immediately obvious that all CM current flowing on a > cable at one end of a cable does not necessarily flow at the other end of > that cable. > Especially where cables are bundled, or where they pass closely along > a chassis or structural member, there are possibilities for that > current to couple off of the cable. The current flow will follow the > impedances, both at the ends and at other fortuitous nodes. This is > one of the reasons that a ferrite absorber might work much better at > one position along a cable than at another position and also why RE > might be dependent on something as obscure as cable bundle tightness. > > Ed Price > WB6WSN > Chula Vista, CA USA > > > > From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Friday, > January 15, 2016 8:53 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > > > I think it is important to not lose sight of the original query that > started this thread. The query was about whether placing a current > probe around a cable perturbed the current to be measured. There is no > doubt that radiated emissions can originate within an equipment > enclosure separately from driving common mode currents on a cable, but > that wasn't the query. In fact, the poster was probing cables within a > large rack > (enclosure) looking for a source within an enclosure. > > Ken Javor > Phone: (256) 650-5261 > > > > _ From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org> > Reply-To: Bill Owsley > Date: Fri, 15 Jan 2016 07:26:08 + > To: > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > If you can measure common mode noise on a cable, you have a problem > from the port !! > Note the world famous Ott's math on this effect in his 1st edition. > Might be in his 2nd too. > > I have used both e-field and h-field (current clamp) at the same time. > We are engineers so figure out how I did that! > And since some of th
Re: [PSES] Fwd: [PSES] Current probe for CM currents
Hi Everone, Here is an interesting case where a ferrite core can actually perform an impedance matching function and increase emissions on a cable: http://emcesd.com/tt120199.htm Doug On Fri, 15 Jan 2016 09:40:22 -0800, Ed Price wrote: I would add a caution to Ken's comment about common mode cable currents creating RE. Yes, the CM currents certainly do create RE, but you need to probe the cables at several intervals to understand those current paths. It is not immediately obvious that all CM current flowing on a cable at one end of a cable does not necessarily flow at the other end of that cable. Especially where cables are bundled, or where they pass closely along a chassis or structural member, there are possibilities for that current to couple off of the cable. The current flow will follow the impedances, both at the ends and at other fortuitous nodes. This is one of the reasons that a ferrite absorber might work much better at one position along a cable than at another position and also why RE might be dependent on something as obscure as cable bundle tightness. Ed Price WB6WSN Chula Vista, CA USA From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Friday, January 15, 2016 8:53 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents I think it is important to not lose sight of the original query that started this thread. The query was about whether placing a current probe around a cable perturbed the current to be measured. There is no doubt that radiated emissions can originate within an equipment enclosure separately from driving common mode currents on a cable, but that wasn't the query. In fact, the poster was probing cables within a large rack (enclosure) looking for a source within an enclosure. Ken Javor Phone: (256) 650-5261 _ From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org> Reply-To: Bill Owsley Date: Fri, 15 Jan 2016 07:26:08 + To: Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents If you can measure common mode noise on a cable, you have a problem from the port !! Note the world famous Ott's math on this effect in his 1st edition. Might be in his 2nd too. I have used both e-field and h-field (current clamp) at the same time. We are engineers so figure out how I did that! And since some of the work is below 30 MHz, I have also added a loop antenna for a 3rd measurement. My approach is if I find any emission, locally, near field, bench stuff, that varies by position over the area of the product, then I have a problem. E-field scan,using a o'scope probe. H-field scan usually using a personally built small loop, and any other sort of scan, conducted or radiated, that I can make up at the moment. I work for a homogeneous field in the scans over the area of the product. My assumption is that if I find a homogeneous field, then there are no or low emission gradients which can equate to a field at a distance. So get creative, and redundant, by different methods for measuring the emissions. Ironic, I am good at mashing all emissions, and then they hand me an intentional radiator and ask that I don't kill the fundamental. What ? You mean I have to pick what to mash, and what not to mash? Ok, so I caught on quick enough to keep the job. ps. I suffer from not being able to use a leaky enclosure. I don't get any shielding for the products. Cable shielding that is bogus terminated, but at the low frequencies of interests, it works. Then I have to deal with the higher frequencies, the harmonics !!! Plastic covers and pcb and cables up to 15 KW or more of digital BS to make an analog signal. And then 'normal' digital signals for the ADC circuits all in the middle of this. Management is like, we have done it this way for over 25 years and so we are not changing it now. It works (I have to make it work) so don't change anything. Sucks to be me - but I do like a challenge. _ From: Ken Wyatt - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald: - This message is from the IEEE Product Safety Engin
Re: [PSES] Fwd: [PSES] Current probe for CM currents
No argument, and once a cable is electrically long, the probe must be scanned down the length of the cable looking for maxima. Along those lines, the Henry Ott equation referenced by someone else is only valid for electrically short cables. Aschenberg and Grasso extended the equation to the case where the cable is electrically long, treating the cable in that case as a tuned dipole. http://emcesd.com/tt2006/mat-cmi.pdf Ken Javor Phone: (256) 650-5261 > From: Ed Price > Reply-To: Ed Price > Date: Fri, 15 Jan 2016 09:40:22 -0800 > To: > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > I would add a caution to Ken's comment about common mode cable currents > creating RE. Yes, the CM currents certainly do create RE, but you need to > probe the cables at several intervals to understand those current paths. It > is not immediately obvious that all CM current flowing on a cable at one end > of a cable does not necessarily flow at the other end of that cable. > Especially where cables are bundled, or where they pass closely along a > chassis or structural member, there are possibilities for that current to > couple off of the cable. The current flow will follow the impedances, both > at the ends and at other fortuitous nodes. This is one of the reasons that a > ferrite absorber might work much better at one position along a cable than > at another position and also why RE might be dependent on something as > obscure as cable bundle tightness. > > Ed Price > WB6WSN > Chula Vista, CA USA > > > > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sent: Friday, January 15, 2016 8:53 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > > > I think it is important to not lose sight of the original query that started > this thread. The query was about whether placing a current probe around a > cable perturbed the current to be measured. > > There is no doubt that radiated emissions can originate within an equipment > enclosure separately from driving common mode currents on a cable, but that > wasn't the query. In fact, the poster was probing cables within a large rack > (enclosure) looking for a source within an enclosure. > > Ken Javor > Phone: (256) 650-5261 > > > > _ > > From: Bill Owsley <000000f5a03f18eb-dmarc-requ...@ieee.org> > Reply-To: Bill Owsley > Date: Fri, 15 Jan 2016 07:26:08 + > To: > Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents > > If you can measure common mode noise on a cable, you have a problem from the > port !! > Note the world famous Ott's math on this effect in his 1st edition. Might > be in his 2nd too. > > I have used both e-field and h-field (current clamp) at the same time. > We are engineers so figure out how I did that! > And since some of the work is below 30 MHz, I have also added a loop antenna > for a 3rd measurement. > My approach is if I find any emission, locally, near field, bench stuff, > that varies by position over the area of the product, then I have a problem. > E-field scan,using a o'scope probe. H-field scan usually using a personally > built small loop, and any other sort of scan, conducted or radiated, that I > can make up at the moment. > I work for a homogeneous field in the scans over the area of the product. > My assumption is that if I find a homogeneous field, then there are no or > low emission gradients which can equate to a field at a distance. So get > creative, and redundant, by different methods for measuring the emissions. > Ironic, I am good at mashing all emissions, and then they hand me an > intentional radiator and ask that I don't kill the fundamental. What ? You > mean I have to pick what to mash, and what not to mash? > Ok, so I caught on quick enough to keep the job. > > > ps. I suffer from not being able to use a leaky enclosure. I don't get any > shielding for the products. > Cable shielding that is bogus terminated, but at the low frequencies of > interests, it works. > Then I have to deal with the higher frequencies, the harmonics !!! > Plastic covers and pcb and cables up to 15 KW or more of digital BS to make > an analog signal. > And then 'normal' digital signals for the ADC circuits all in the middle of > this. > Management is like, we have done it this way for over 25 years and so we are > not changing it now. > It works (I have to make it work) so don't change anything. Sucks to be me > - but I do like a challenge. > > > > > > > > > > > > > > > _ > > From: Ken Wyatt > > - >
Re: [PSES] Fwd: [PSES] Current probe for CM currents
I would add a caution to Ken's comment about common mode cable currents creating RE. Yes, the CM currents certainly do create RE, but you need to probe the cables at several intervals to understand those current paths. It is not immediately obvious that all CM current flowing on a cable at one end of a cable does not necessarily flow at the other end of that cable. Especially where cables are bundled, or where they pass closely along a chassis or structural member, there are possibilities for that current to couple off of the cable. The current flow will follow the impedances, both at the ends and at other fortuitous nodes. This is one of the reasons that a ferrite absorber might work much better at one position along a cable than at another position and also why RE might be dependent on something as obscure as cable bundle tightness. Ed Price WB6WSN Chula Vista, CA USA From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Friday, January 15, 2016 8:53 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents I think it is important to not lose sight of the original query that started this thread. The query was about whether placing a current probe around a cable perturbed the current to be measured. There is no doubt that radiated emissions can originate within an equipment enclosure separately from driving common mode currents on a cable, but that wasn't the query. In fact, the poster was probing cables within a large rack (enclosure) looking for a source within an enclosure. Ken Javor Phone: (256) 650-5261 _ From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org> Reply-To: Bill Owsley Date: Fri, 15 Jan 2016 07:26:08 + To: Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents If you can measure common mode noise on a cable, you have a problem from the port !! Note the world famous Ott's math on this effect in his 1st edition. Might be in his 2nd too. I have used both e-field and h-field (current clamp) at the same time. We are engineers so figure out how I did that! And since some of the work is below 30 MHz, I have also added a loop antenna for a 3rd measurement. My approach is if I find any emission, locally, near field, bench stuff, that varies by position over the area of the product, then I have a problem. E-field scan,using a o'scope probe. H-field scan usually using a personally built small loop, and any other sort of scan, conducted or radiated, that I can make up at the moment. I work for a homogeneous field in the scans over the area of the product. My assumption is that if I find a homogeneous field, then there are no or low emission gradients which can equate to a field at a distance. So get creative, and redundant, by different methods for measuring the emissions. Ironic, I am good at mashing all emissions, and then they hand me an intentional radiator and ask that I don't kill the fundamental. What ? You mean I have to pick what to mash, and what not to mash? Ok, so I caught on quick enough to keep the job. ps. I suffer from not being able to use a leaky enclosure. I don't get any shielding for the products. Cable shielding that is bogus terminated, but at the low frequencies of interests, it works. Then I have to deal with the higher frequencies, the harmonics !!! Plastic covers and pcb and cables up to 15 KW or more of digital BS to make an analog signal. And then 'normal' digital signals for the ADC circuits all in the middle of this. Management is like, we have done it this way for over 25 years and so we are not changing it now. It works (I have to make it work) so don't change anything. Sucks to be me - but I do like a challenge. _ From: Ken Wyatt - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Fwd: [PSES] Current probe for CM currents
I think it is important to not lose sight of the original query that started this thread. The query was about whether placing a current probe around a cable perturbed the current to be measured. There is no doubt that radiated emissions can originate within an equipment enclosure separately from driving common mode currents on a cable, but that wasn¹t the query. In fact, the poster was probing cables within a large rack (enclosure) looking for a source within an enclosure. Ken Javor Phone: (256) 650-5261 From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org> Reply-To: Bill Owsley Date: Fri, 15 Jan 2016 07:26:08 + To: Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents If you can measure common mode noise on a cable, you have a problem from the port !! Note the world famous Ott's math on this effect in his 1st edition. Might be in his 2nd too. I have used both e-field and h-field (current clamp) at the same time. We are engineers so figure out how I did that! And since some of the work is below 30 MHz, I have also added a loop antenna for a 3rd measurement. My approach is if I find any emission, locally, near field, bench stuff, that varies by position over the area of the product, then I have a problem. E-field scan,using a o'scope probe. H-field scan usually using a personally built small loop, and any other sort of scan, conducted or radiated, that I can make up at the moment. I work for a homogeneous field in the scans over the area of the product. My assumption is that if I find a homogeneous field, then there are no or low emission gradients which can equate to a field at a distance. So get creative, and redundant, by different methods for measuring the emissions. Ironic, I am good at mashing all emissions, and then they hand me an intentional radiator and ask that I don't kill the fundamental. What ? You mean I have to pick what to mash, and what not to mash? Ok, so I caught on quick enough to keep the job. ps. I suffer from not being able to use a leaky enclosure. I don't get any shielding for the products. Cable shielding that is bogus terminated, but at the low frequencies of interests, it works. Then I have to deal with the higher frequencies, the harmonics !!! Plastic covers and pcb and cables up to 15 KW or more of digital BS to make an analog signal. And then 'normal' digital signals for the ADC circuits all in the middle of this. Management is like, we have done it this way for over 25 years and so we are not changing it now. It works (I have to make it work) so don't change anything. Sucks to be me - but I do like a challenge. > > > > > > From: Ken Wyatt > To: EMC-PSTC@LISTSERV.IEEE.ORG > Sent: Thursday, January 14, 2016 8:24 PM > Subject: [PSES] Fwd: [PSES] Current probe for CM currents > > > > Ken is correct. Near field probes are good for finding sources, but current > probes are better for characterizing the emissions from cables. However, if > the EUT has a leaky enclosure, or other radiating structures besides cables, > you'll really need to monitor the emissions from a distance while you're > troubleshooting. I've found a distance of 1m works well. For small EUTs, I > place them at one end of a bench and set up a small monitoring antenna and > spectrum analyzer at the other. I've written many articles on this technique. > Take a look at The EMC Blog in EDN.com <http://edn.com/> . I also wrote an > article on how to make and use current probes for Interference Technology. > > Kenneth Wyatt > Wyatt Technical Services > Woodland Park, CO > k...@emc-seminars.com > Sent from my iPhone. > > Begin forwarded message: > >> From: Ken Javor >> Date: January 14, 2016 at 5:14:36 PM MST >> To: EMC-PSTC@LISTSERV.IEEE.ORG >> Subject: Re: [PSES] Current probe for CM currents >> Reply-To: Ken Javor >> >> Re: [PSES] Current probe for CM currents IMO, a near field probe gets you >> back to where Bill Owlsley was at: you are X dB over the limit on the test >> site, so you wave a probe around and look for X dB reduction in signal from >> whatever change was made, hoping the probe picks up something proportional to >> the RE field at three or ten meters. >> >> Whereas with a current probe, even without any site testing, a common mode >> conducted emission (CMCE) limit can be determined based on the three or ten >> meter RE limit, and then the design work is done on the cable before any >> testing at any site. >> >> Ken Javor >> Phone: (256) 650-5261 >> >> >> >> From: "McDiarmid, Ralph" >> Reply-To: "ralph.mcdiar...@schneider-electric.com" >> >> Date: Thu, 14 Jan 2016 14:20:33 -0800 >> To: &g
Re: [PSES] Fwd: [PSES] Current probe for CM currents
If you can measure common mode noise on a cable, you have a problem from the port !! Note the world famous Ott's math on this effect in his 1st edition. Might be in his 2nd too. I have used both e-field and h-field (current clamp) at the same time. We are engineers so figure out how I did that! And since some of the work is below 30 MHz, I have also added a loop antenna for a 3rd measurement. My approach is if I find any emission, locally, near field, bench stuff, that varies by position over the area of the product, then I have a problem. E-field scan,using a o'scope probe. H-field scan usually using a personally built small loop, and any other sort of scan, conducted or radiated, that I can make up at the moment. I work for a homogeneous field in the scans over the area of the product. My assumption is that if I find a homogeneous field, then there are no or low emission gradients which can equate to a field at a distance. So get creative, and redundant, by different methods for measuring the emissions. Ironic, I am good at mashing all emissions, and then they hand me an intentional radiator and ask that I don't kill the fundamental. What ? You mean I have to pick what to mash, and what not to mash? Ok, so I caught on quick enough to keep the job. ps. I suffer from not being able to use a leaky enclosure. I don't get any shielding for the products. Cable shielding that is bogus terminated, but at the low frequencies of interests, it works. Then I have to deal with the higher frequencies, the harmonics !!!Plastic covers and pcb and cables up to 15 KW or more of digital BS to make an analog signal. And then 'normal' digital signals for the ADC circuits all in the middle of this. Management is like, we have done it this way for over 25 years and so we are not changing it now. It works (I have to make it work) so don't change anything. Sucks to be me - but I do like a challenge. From: Ken Wyatt To: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Thursday, January 14, 2016 8:24 PM Subject: [PSES] Fwd: [PSES] Current probe for CM currents Ken is correct. Near field probes are good for finding sources, but current probes are better for characterizing the emissions from cables. However, if the EUT has a leaky enclosure, or other radiating structures besides cables, you'll really need to monitor the emissions from a distance while you're troubleshooting. I've found a distance of 1m works well. For small EUTs, I place them at one end of a bench and set up a small monitoring antenna and spectrum analyzer at the other. I've written many articles on this technique. Take a look at The EMC Blog in EDN.com. I also wrote an article on how to make and use current probes for Interference Technology. Kenneth WyattWyatt Technical Services Woodland Park, COken@emc-seminars.comSent from my iPhone. Begin forwarded message: From: Ken Javor Date: January 14, 2016 at 5:14:36 PM MST To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Current probe for CM currents Reply-To: Ken Javor Re: [PSES] Current probe for CM currentsIMO, a near field probe gets you back to where Bill Owlsley was at: you are X dB over the limit on the test site, so you wave a probe around and look for X dB reduction in signal from whatever change was made, hoping the probe picks up something proportional to the RE field at three or ten meters. Whereas with a current probe, even without any site testing, a common mode conducted emission (CMCE) limit can be determined based on the three or ten meter RE limit, and then the design work is done on the cable before any testing at any site. Ken Javor Phone: (256) 650-5261 From: "McDiarmid, Ralph" Reply-To: "ralph.mcdiar...@schneider-electric.com" Date: Thu, 14 Jan 2016 14:20:33 -0800 To: Subject: Re: [PSES] Current probe for CM currents Would a Near Field probe be a better choice? ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: Ken Javor To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/13/2016 01:22 PM Subject: Re: [PSES] Current probe for CM currents A current probe measures the net current on the conductor within its opening. The impedance of the circuits attached to that conductor may affect how much current flows through the conductor, but not the measurement thereof. Ken Javor Phone: (256) 650-5261 From: Amund Westin Reply-To: Amund Westin Date: Wed, 13 Jan 2016 18:48:23 +0100 To: Subject: [PSES] Current probe for CM currents Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web an
[PSES] Fwd: [PSES] Current probe for CM currents
Ken is correct. Near field probes are good for finding sources, but current probes are better for characterizing the emissions from cables. However, if the EUT has a leaky enclosure, or other radiating structures besides cables, you'll really need to monitor the emissions from a distance while you're troubleshooting. I've found a distance of 1m works well. For small EUTs, I place them at one end of a bench and set up a small monitoring antenna and spectrum analyzer at the other. I've written many articles on this technique. Take a look at The EMC Blog in EDN.com. I also wrote an article on how to make and use current probes for Interference Technology. Kenneth Wyatt Wyatt Technical Services Woodland Park, CO k...@emc-seminars.com Sent from my iPhone. Begin forwarded message: > From: Ken Javor > Date: January 14, 2016 at 5:14:36 PM MST > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Current probe for CM currents > Reply-To: Ken Javor > > IMO, a near field probe gets you back to where Bill Owlsley was at: you are X > dB over the limit on the test site, so you wave a probe around and look for X > dB reduction in signal from whatever change was made, hoping the probe picks > up something proportional to the RE field at three or ten meters. > > Whereas with a current probe, even without any site testing, a common mode > conducted emission (CMCE) limit can be determined based on the three or ten > meter RE limit, and then the design work is done on the cable before any > testing at any site. > > Ken Javor > Phone: (256) 650-5261 > > > From: "McDiarmid, Ralph" > Reply-To: "ralph.mcdiar...@schneider-electric.com" > > Date: Thu, 14 Jan 2016 14:20:33 -0800 > To: > Subject: Re: [PSES] Current probe for CM currents > > Would a Near Field probe be a better choice? > ___ > > > Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | > Regulatory Compliance Engineering > > > > From: Ken Javor > To: EMC-PSTC@LISTSERV.IEEE.ORG, > Date: 01/13/2016 01:22 PM > Subject: Re: [PSES] Current probe for CM currents > > > > A current probe measures the net current on the conductor within its opening. > The impedance of the circuits attached to that conductor may affect how much > current flows through the conductor, but not the measurement thereof. > > Ken Javor > Phone: (256) 650-5261 > > > From: Amund Westin > Reply-To: Amund Westin > Date: Wed, 13 Jan 2016 18:48:23 +0100 > To: > Subject: [PSES] Current probe for CM currents > > Planning to do some EMI troubleshooting with a «homemade» current probe. > Probing a lot of cables inside a rack and try to find the source. > Will make a current probe by a ferrite core (two halves, a few turns wire and > coax plug) as many EMI experts have posted on the web and on this forum. > Then find the Zt[dBohm], so make a measurement on a cable and verify the > readings on the spectrum. > > But when clamping on the current probe, which is a ferrite, does that change > the cable impedance and therefore actually changes the real current flow, so > my reading will not be true? ... or am I missing some fundamental theory > here? ... > > #Amund > > > - > > > 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 > > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > <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/ > <http://product-compliance.oc.ieee.org/> can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> > Instructions: http://www.ieee-pses.org/list.html > <http://www.ieee-pses.org/list.html> (including how to unsubscribe) > <http://www.ieee-pses.org/list.html> <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > <http://www.ieee-pses.org/listrules.html> > > For help, send mail to the list administrators: > Scott Douglas > Mike Cantwell > > For policy questions, send mail to: > Jim Bacher > David Heald > > > __ > This email has been scanned by the Symantec Email Security.cloud servi
Re: [PSES] Current probe for CM currents
On 1/14/2016 5:20 PM, McDiarmid, Ralph wrote: Would a Near Field probe be a better choice? That's good for finding a source. but as Ken points out, its not accurate enough for quantitative evaluation. FWIW... a SA chamber or an OATS aren't all that hot either,according to a 2001 paper.* *Reproducibility and Uncertainty in Radiated Emission Measurements at Open Area Test Sites and in Semi-anechoic Chambers Using a Spherical Dipole Radiator, Tae-Weon Kang and Hyo-Tae Kim IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 43, NO. 4, NOVEMBER 2001 677 Cortland Richmond - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Current probe for CM currents
IMO, a near field probe gets you back to where Bill Owlsley was at: you are X dB over the limit on the test site, so you wave a probe around and look for X dB reduction in signal from whatever change was made, hoping the probe picks up something proportional to the RE field at three or ten meters. Whereas with a current probe, even without any site testing, a common mode conducted emission (CMCE) limit can be determined based on the three or ten meter RE limit, and then the design work is done on the cable before any testing at any site. Ken Javor Phone: (256) 650-5261 From: "McDiarmid, Ralph" Reply-To: "ralph.mcdiar...@schneider-electric.com" Date: Thu, 14 Jan 2016 14:20:33 -0800 To: Subject: Re: [PSES] Current probe for CM currents Would a Near Field probe be a better choice? ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: Ken Javor To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/13/2016 01:22 PM Subject: Re: [PSES] Current probe for CM currents A current probe measures the net current on the conductor within its opening. The impedance of the circuits attached to that conductor may affect how much current flows through the conductor, but not the measurement thereof. Ken Javor Phone: (256) 650-5261 From: Amund Westin Reply-To: Amund Westin Date: Wed, 13 Jan 2016 18:48:23 +0100 To: Subject: [PSES] Current probe for CM currents Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web and on this forum. Then find the Zt[dBohm], so make a measurement on a cable and verify the readings on the spectrum. But when clamping on the current probe, which is a ferrite, does that change the cable impedance and therefore actually changes the real current flow, so my reading will not be true? ... or am I missing some fundamental theory here? ... #Amund - 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 All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html <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/ <http://product-compliance.oc.ieee.org/> can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> Instructions: http://www.ieee-pses.org/list.html <http://www.ieee-pses.org/list.html> (including how to unsubscribe) <http://www.ieee-pses.org/list.html> <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html <http://www.ieee-pses.org/listrules.html> For help, send mail to the list administrators: Scott Douglas Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald __ This email has been scanned by the Symantec Email Security.cloud service. __ - 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 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 <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/ <http://product-compliance.oc.ieee.org/> can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ <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 <http://www.ieee-pses.org/listrules.html> For help, send mail to the list administrators: Scott Douglas mailto:sdoug...@ieee.org> > Mike Cantwell mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher mailto:j.bac...@ieee.org> > David Heald 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 All emc-pstc postings are archived and searchable on the web at: http://
Re: [PSES] Current probe for CM currents
Would a Near Field probe be a better choice? ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: Ken Javor To: EMC-PSTC@LISTSERV.IEEE.ORG, Date: 01/13/2016 01:22 PM Subject: Re: [PSES] Current probe for CM currents A current probe measures the net current on the conductor within its opening. The impedance of the circuits attached to that conductor may affect how much current flows through the conductor, but not the measurement thereof. Ken Javor Phone: (256) 650-5261 From: Amund Westin Reply-To: Amund Westin Date: Wed, 13 Jan 2016 18:48:23 +0100 To: Subject: [PSES] Current probe for CM currents Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web and on this forum. Then find the Zt[dBohm], so make a measurement on a cable and verify the readings on the spectrum. But when clamping on the current probe, which is a ferrite, does that change the cable impedance and therefore actually changes the real current flow, so my reading will not be true? ... or am I missing some fundamental theory here? ... #Amund - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald __ This email has been scanned by the Symantec Email Security.cloud service. __ - 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 Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Current probe for CM currents
If I understand the message below, it¹s not that fuzzy. One can predict electric field intensity in the far field as a function of cable cm current. So there is a number to work with from the get-go. Of course the final check has to be an RE test, but if the cm current meets the computed cm limit, than the RE from that cable should meet the RE limit. Ken Javor Phone: (256) 650-5261 From: Bill Owsley <00f5a03f18eb-dmarc-requ...@ieee.org> Reply-To: Bill Owsley Date: Thu, 14 Jan 2016 07:21:02 + To: Subject: Re: [PSES] Current probe for CM currents Ok, so call me lazy, real lazy ! clamp on your probe, measure a number, and then work to reduce that number by twice what is needed to meet the limit, then re-test. Repeat, if necessary. The really big trick in this process is knowing how to reduce the measured number of the problem that has shown up. Sucks to be you. ps. I have used that same technique for years. It works really well when done with relative measurements. pps. a couple of products needed more than halving the number measured at the beginning. ppps. correct fixes usually kill the problem, not just reduce it. But there are exceptions. > > > > > > From: Ken Javor > To: EMC-PSTC@LISTSERV.IEEE.ORG > Sent: Wednesday, January 13, 2016 4:25 PM > Subject: Re: [PSES] Current probe for CM currents > > > > Re: [PSES] Current probe for CM currents > I re-read the query and see I didn¹t address the actual question. The current > probe inserts an impedance given by the transfer impedance divided by the > winding turns ratio. Once you have measured the transfer impedance and > computed the inserted impedance, you can then judge the inserted impedance > against the cable impedance itself to assess any perturbation of the quantity > to be measured. > > Ken Javor > Phone: (256) 650-5261 > > > > From: Ken Javor > Date: Wed, 13 Jan 2016 15:15:55 -0600 > To: > Conversation: [PSES] Current probe for CM currents > Subject: Re: [PSES] Current probe for CM currents > > A current probe measures the net current on the conductor within its opening. > The impedance of the circuits attached to that conductor may affect how much > current flows through the conductor, but not the measurement thereof. > > Ken Javor > Phone: (256) 650-5261 > > > > From: Amund Westin > Reply-To: Amund Westin > Date: Wed, 13 Jan 2016 18:48:23 +0100 > To: > Subject: [PSES] Current probe for CM currents > > Planning to do some EMI troubleshooting with a «homemade» current probe. > Probing a lot of cables inside a rack and try to find the source. > Will make a current probe by a ferrite core (two halves, a few turns wire and > coax plug) as many EMI experts have posted on the web and on this forum. > Then find the Zt[dBohm], so make a measurement on a cable and verify the > readings on the spectrum. > > But when clamping on the current probe, which is a ferrite, does that change > the cable impedance and therefore actually changes the real current flow, so > my reading will not be true? ... or am I missing some fundamental theory here? > ... > > #Amund > > > - > > > 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 > > > 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 > Mike Cantwell > > For policy questions, send mail to: > Jim Bacher > David Heald > > - > > 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 > > 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: h
Re: [PSES] Current probe for CM currents
Ok, so call me lazy, real lazy ! clamp on your probe, measure a number, and then work to reduce that number by twice what is needed to meet the limit, then re-test. Repeat, if necessary. The really big trick in this process is knowing how to reduce the measured number of the problem that has shown up. Sucks to be you. ps. I have used that same technique for years. It works really well when done with relative measurements. pps. a couple of products needed more than halving the number measured at the beginning. ppps. correct fixes usually kill the problem, not just reduce it. But there are exceptions. From: Ken Javor To: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Wednesday, January 13, 2016 4:25 PM Subject: Re: [PSES] Current probe for CM currents Re: [PSES] Current probe for CM currentsI re-read the query and see I didn’t address the actual question. The current probe inserts an impedance given by the transfer impedance divided by the winding turns ratio. Once you have measured the transfer impedance and computed the inserted impedance, you can then judge the inserted impedance against the cable impedance itself to assess any perturbation of the quantity to be measured. Ken Javor Phone: (256) 650-5261 From: Ken Javor Date: Wed, 13 Jan 2016 15:15:55 -0600 To: Conversation: [PSES] Current probe for CM currents Subject: Re: [PSES] Current probe for CM currents A current probe measures the net current on the conductor within its opening. The impedance of the circuits attached to that conductor may affect how much current flows through the conductor, but not the measurement thereof. Ken Javor Phone: (256) 650-5261 From: Amund Westin Reply-To: Amund Westin Date: Wed, 13 Jan 2016 18:48:23 +0100 To: Subject: [PSES] Current probe for CM currents Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web and on this forum. Then find the Zt[dBohm], so make a measurement on a cable and verify the readings on the spectrum. But when clamping on the current probe, which is a ferrite, does that change the cable impedance and therefore actually changes the real current flow, so my reading will not be true? ... or am I missing some fundamental theory here? ... #Amund - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - 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 All emc-pstc postings are archived and searchable on the web at:http://www.ieee-pses.org/emc-pstc.htmlAttachments 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.htmlFor help, send mail to the list administrators: Scott Douglas Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Current probe for CM currents
I re-read the query and see I didn¹t address the actual question. The current probe inserts an impedance given by the transfer impedance divided by the winding turns ratio. Once you have measured the transfer impedance and computed the inserted impedance, you can then judge the inserted impedance against the cable impedance itself to assess any perturbation of the quantity to be measured. Ken Javor Phone: (256) 650-5261 From: Ken Javor Date: Wed, 13 Jan 2016 15:15:55 -0600 To: Conversation: [PSES] Current probe for CM currents Subject: Re: [PSES] Current probe for CM currents A current probe measures the net current on the conductor within its opening. The impedance of the circuits attached to that conductor may affect how much current flows through the conductor, but not the measurement thereof. Ken Javor Phone: (256) 650-5261 From: Amund Westin Reply-To: Amund Westin Date: Wed, 13 Jan 2016 18:48:23 +0100 To: Subject: [PSES] Current probe for CM currents Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web and on this forum. Then find the Zt[dBohm], so make a measurement on a cable and verify the readings on the spectrum. But when clamping on the current probe, which is a ferrite, does that change the cable impedance and therefore actually changes the real current flow, so my reading will not be true? ... or am I missing some fundamental theory here? ... #Amund - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Current probe for CM currents
A current probe measures the net current on the conductor within its opening. The impedance of the circuits attached to that conductor may affect how much current flows through the conductor, but not the measurement thereof. Ken Javor Phone: (256) 650-5261 From: Amund Westin Reply-To: Amund Westin Date: Wed, 13 Jan 2016 18:48:23 +0100 To: Subject: [PSES] Current probe for CM currents Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web and on this forum. Then find the Zt[dBohm], so make a measurement on a cable and verify the readings on the spectrum. But when clamping on the current probe, which is a ferrite, does that change the cable impedance and therefore actually changes the real current flow, so my reading will not be true? ... or am I missing some fundamental theory here? ... #Amund - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
[PSES] Current probe for CM currents
Planning to do some EMI troubleshooting with a «homemade» current probe. Probing a lot of cables inside a rack and try to find the source. Will make a current probe by a ferrite core (two halves, a few turns wire and coax plug) as many EMI experts have posted on the web and on this forum. Then find the Zt[dBohm], so make a measurement on a cable and verify the readings on the spectrum. But when clamping on the current probe, which is a ferrite, does that change the cable impedance and therefore actually changes the real current flow, so my reading will not be true? ... or am I missing some fundamental theory here? ... #Amund - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald: