Re: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents

[Douglas Smith]

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

[Ken Javor]

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

[ce-test, qualified testing bv - Gert Gremmen]

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

[Ken Javor]

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

[Doug Smith]

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

[Ken Javor]

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

[Amund Westin]

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:
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Re: [PSES] Fwd: [PSES] Current probe for CM currents

[Ken Javor]

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

[John Allen]

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

[Richard Marshall]

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

[McDiarmid, Ralph]

" 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

[ce-test, qualified testing bv - Gert Gremmen]

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

[Doug Smith]

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

[Ken Javor]

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

[Ed Price]

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

[Ken Javor]

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

[Bill Owsley]

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 Wyatt]

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 
>  
>  
> -
> 
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