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
>  >
> 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 

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
>  >
> 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> >
> 
> -
> 
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