This is a multi-part message in MIME format.
Dear Gert, please see my replies below, in-line at the appropriate locations.
-------------- Original message ----------------------
From: "Gert Gremmen" <[email protected]>
> Neven,
>
> While I understand your point of view,
> I object against your arguments..
> I preferred to read some sound proof
> instead of suggestions and statements like
> ---------
> Ethernet devices, as well as other high-speed devices that
> utilize balanced differential pairs, are very sensitive to CM-DM conversion
> ---------
> I am not at all convinced that this is the case.
>
> I have the followoing arguments:
>
> - Most high speed receiver chips do have a
> decent common mode rejection. A few
> percent of asymmetry will not have any
> impact on the receiption quality.
NP: A few percent of asymmetry will not have impact? "Decent CM rejection"? I
was not talking here about CM rejection. I wrote about the issues I see that
are related to conversion. 10Vrms immunity test level means 25Vpk calibrated
level or 12.5V at the DUT. 1% conversion puts 125 mV differentially to the Rx
which has ~50 mV sensitivity (Ethernet).
The situation is similar the other way regarding the emission. The level of
LCL suggested by CISPR22 2005 puts the differential amplitude of 10 BaseT,
which is up to 5.6V, right about the limit line, i.e. it is designed to make
10BaseT about to fail. 58 dB conversion at 10 MHz as specified by CISPR22 and
worst-case 5.6V (135 dBuV) signal of 10BaseT at 10 MHz result in 77 dBuV CM.
The QP limit for ClassB is 74 dBuV. I admit I am using here the worst-case,
but I am also calculating only with the DM-signal, not even adding the CM
generated form the DUT - so I am not far off.
> This can be proved easily by adding a grounding
> resistor at one input terminal of say 1kOhm introducing tens
> of percents of asymmetry.
> I also noted multiple times that adding serial impedances
> such as 20-30 ohms resistor or cm- coils
> (used to suppress EMI = common mode current)
> do not impact error rates (there was no error rate: 0 faults
NP: Adding 1kOhm from one line to GND probably affected the emission levels,
but I would not expect it to considerably affect the transmission i.e. Bit
Error Rate. Adding 20-30 ohms to the max length of cable is going to
considerably degrade the cable reach.You should be are looking at the
attenuation of the UTP and 100 Ohm load impedance. The resistors are going to
further and considerably attenuate the available signal, that will reduce the
cable reach. I guess you used a short cable, not max length (at least 100 m,
some folks want more although it is out of the IEEE spec).
>
>
> -Most (all) high speed cards do have a transformer with
> a considerable amount of CM to DM suppression.
> 20 dB is the minimum one may expect.
> Before reaching the receivers the CM component
> introduced on purpose by a ISN will be substantially
> attenuated by it.
>
NP: 20 dB of CM-DM rejection/conversion is nothing considering the levels of
the signal, sensitivity, emission and immunity, as I described above. The
conversion-rejection from the Ethernet transformer should be better than 40
dB, at some frequencies much more, but it is gets less important as the
frequency goes higher, beyond the spectrum of the signal..
> -The decoupling part of the ISN/CDN generally
> consists of a Common mode coil with
> extreme low leakage field (read substantial symmetry)
> for the frequencies the ISN is designed for.
> This CM coil recovers (by design) the major part
> of the introduced asymmetry.
NP: The CMC in the ISN/CDN can be pretty good, with high CM-CM and low CM-DM
properties. No argument here. The problem is, if you look at the basic circuit
for an ISN/CDN, the coupling circuit between the DUT-port and the CMC. If that
coupling circuitry is built asymmetrically, as I have observed, then on top of
the coupled CM signal, the line will also "receive" converted DM signal as a
result of conversion in that section of the CDN/ISN. This puts the DUT under
extra "stress" of not being exposed to CM-only (as intended) but of the added
(unintentional) DM signal. This can cause a DUT to look as it fails, because
e.g. using the example from above, 10Vrms level and 1% conversion, can put 125
mV in a circuit with large tolerance to CM but with 50mV differential
sensitivity.The other way around, even a theoretically perfectly differential
Ethernet signal, with no CM on top of it, can be converted by the ISN and look
as it fails - WITH THE CONVERSION LEVELS AS CURRENTLY SPECIF!
IED BY
THE STANDARDS - aghain as I described above.
>
> As long as the Diff Mode properties
> as a 1-2-4 times 2-port of the ISN can be proved to cover
> more then the spectrum of the signal that needs
> to be transmitted through it, i am not afraid
> of using one.
NP: I read this as if you don't care how much conversion ISN/CDN creates, all
that matters to you is that the DM properties are such to allow the
transmission of the signal. I am happy it works for you. It does not work for
me.
>
> Most transmission problems in ethernet connections relate
> to frequency dependent attenuation, (aging and humidity)
> high voltage CM (50-60 Hz) voltage introduced by
> mains cabling close to the UTP,
>
> TIP: do you have a large ethernet building installation
> which underperforms heavily ? Add a grounding
> resistor of 100 K to chassis ground on one wire of
> each of the pairs. Good chance that you
> have a capacitively coupled mains voltage
> in Common Mode on your UTP pairs.
NP: The Ethernet transformers have really large CM isolation in the 50-60 Hz
range, achieved by the transformers and (depending on the center-tap capacitor
value) on the center taps. Coupled mains frequency (on the UTP-side) is not
going to have any considerable effect on the receiver. I am not talking here
about power-line cross. Adding 100k form line to GND is going to violates the
high voltage isolation requirement, unless coupled through a suitable HV cap.
I have not seen this, even tough I have seen a couple of Ethernet devices in
my life.
>
> Waiting your reaction WITH arguments.
NP: I hope I answered, at least to a satisfactory extent, to your objections.
I really hope this is sufficient, and I believe a person who understands the
issues discussed might be able to see it. I do not intend to enter into a
situation in which you request that I prove everything I write, as I do not
expect everyone on this list to be interested or expert in all these matters,
so with kind regards I am concluding this discussion with you.
Respectfully, Neven.
>
> Gert Gremmen
>
> ce-test, qualified testing
>
> ________________________________
>
> Van: [email protected] namens [email protected]
> Verzonden: do 10-5-2007 19:39
> Aan: [email protected]
> Onderwerp: Re: ISN for Conducted Emission in accordance to CISPR 22 Ed
5.2:2006
>
>
>
> Thanks to everyone who replied off- and online. I am trying to look into the
> TECHNICAL aspects of these standards, and unfortunately my conclusion is
that
> they still haven't been thoroughly examined by anyone who has much
experience
> with the details and issues related to differential high-speed multi-pair
> interfaces, such as balance, conversion, and how to measure these
parameters. I
> spent a number of years in that area, and I am still not sure what
measurement
> method is better and more appropriate (it can depend on what you are trying
to
> see), and consequently what measured levels of balance and conversion are
"true"
> - as they depend on how they are measured. One thing that appears evident is
> that a single-pair measurement is not appropriate as e.g. 4-pair interface
> exhibits coupling between all 4 pairs (8 lines) and relation between the
> common-mode and differential mode (i.e. conversion) when only one pair is
driven
> is not the same as when the whole cable is driven by the !
> common
> mode (or all 4 pairs are driven by differential mode). The lack of the
> appropriate measurement method for balance is the major reason why the levels
> of
> LCL for SLCE ISN and the required balance for CDN cannot be properly
> (realistically) defined, which in turn allows manufacturers of these devices
to
> build couplers with various characteristics that can easily cause apparent
> failures.
>
> That's one of the reasons why I find the currently available standards
> inappropriate. I do not question the intent of the standards, as I believe
it is
> good, but as Ken Hall pointed out it appears there is positive voting going
on,
> without fully understanding the technical (and economic) implications. The
> methods in the standards are plausible, i.e., they seem to make sense to
someone
> with general technical background in EMC, but at the detailed level of the
> specific application, e.g. Ethernet, they do not take into account the
related
> issues, which make some methods (IMO) completely unsuitable. That's why I
> currently strongly prefer clamp-methods - they don't affect the cable
> characteristics.
>
> I know many have observed considerable differences in results (SLCE and
> Immunity) depending on the test method, as e.g. in the mentioned paper as
well
> as in numerous conversations I had with test-engineers as well as in my
> first-hand observations, but I wish to draw attention of the EMC community
to
> things that I see as the root-cause of these effects and that I believe very
few
> people actually looked at the same level. Before they are thoroughly
understood
> I don't think we are ready for the standards in question in their current
form
> and for CDN/ISN devices currently on the market.
>
> I do not sit on these standards and I am in no way associated with the
> committees. All my observations are coming from reading the standards and
> papers, my personal experience with issues observed on many projects across
many
> companies worldwide, and from my lab work trying to measure and understand
these
> issues, especially conversion mechanisms and balance in the Ethernet and
other
> high-speed differential-signaling world.
>
> Regards, Neven
>
>
>
> -------------- Original message ----------------------
> From: "Grace Lin" <[email protected]>
> > Hello Ken,
> >
> > Thank you for pointing out the paper. Sorry, I missed your presentation.
I
> > remember my friends discussed the topic after attending your presentation.
> > I believe the concern they had were measuement instrument and necessity.
> >
> > I have a difficulty to understand the technical implications of telcom port
> > requirement. I am not challenging the CISPR committee. I just need some
> > help to understand the requirement/necessity. Telcom port measurement is
> > through the conducted method. A telecom port does not directly connect to
> > (interfere) public utility/power network. If it radiates, it should be
> > covered by the radiated emission measurement.
> >
> > From a manufacturer point of view, telecom port measurement is not a big
> > deal if products pass. Labs don't add additional fee for this test. For
> > in-house testing, there is not much work to setup a test site (using the
> > conducted emission site plus an ISN and adaptors).
> >
> > Best regards,
> > Grace
> >
> > On 5/10/07, Hall, Ken <[email protected]> wrote:
> > >
> > > Hello Grace,
> > >
> > > This topic has been argued and discussed, multiple papers, in CISPR/I AND
> > > CISPR/G since the early 80's. The problem may be/is political. However,
with
> > > a few countries voting against the LCL requirements they ended up in the
> > > standard because > 75% of the voting countries approved.
> > >
> > > We need to influence every countries voting membership to only vote
> > > positive if they understand the technical implications of a standard.
> > > Attached is a paper from IEEE EMC 2001.
> > >
> > > Regards,
> > >
> > > KEn
> > >
> > > ------------------------------
> > > *From:* [email protected] [mailto:[email protected]] *On Behalf Of *Grace
> > > Lin
> > > *Sent:* Thursday, May 10, 2007 4:00 AM
> > > *To:* [email protected]
> > > *Subject:* Re: ISN for Conducted Emission in accordance to CISPR 22 Ed
5.2
> > > :2006
> > >
> > >
> > > Hi Neven,
> > >
> > > Thank you for the detail comments. I suggest you write a paper to the
> > > IEEE International Symposium on EMC. There are many EMC experts
attending
> > > this Symposium, including many equipment manufacturers, rule makers, and
> > > government agencies. The Symposium record is distributed worldwide and
kept
> > > forever. This is a good way to get attention and make friends.
> > >
> > > Grace
> > >
> > >
> > > On 5/9/07, [email protected] <[email protected]> wrote:
> > > >
> > > > Be careful if you want to use ISN for Cinducted Emission or Immunity
> > > > testing of Ethernet or any other high speed differential-pair
interface. I
> > > > just could not resist to reply, because of so poor specifications which
> > > > allow the ISN to cause APPARENT failures, and can cost the industry
> millions
> > > > to "fix" problems that do not exist. I tried to talk with a major
vendor
> of
> > > > these devices, offering help to make them actually appropriate for use
> with
> > > > high-speed diff-pair interfaces ( e.g. Ethernet), but there appears to
> > > > be absolutely no interest. It appears there is too much politics and
> > > > marketing, as opposed to engineering, that dictates how these devices
are
> > > > constructed (and specified). The cost is paid by the industry who is
then
> > > > forced to follow the standards. I have worked on many cases where
after a
> > > > reported emission failure, measured using ISN, the clamp-method ( e.g.
> > > > VOltage and Current Clamp method) resulted in very different and
passing
> > > > result.
> > > >
> > > > So here are some of my thoughts on this topic.They are mostly based on
> > > > the use of CDN/ISN for Immunity, but they really equally apply to both
> SLCE
> > > > and Immunity.
> > > >
> > > > * The most recent 6100-4-6 standard specifies the common-mode
(CM)
> > > > impedance Zcm (Table 3) at the EUT-port of the coupling device
> > > > * It also specifies that the Common-to-Differential mode
> > > > conversion (defined by Longitudinal Conversion Loss or LCL) of the CDN
> > > > should be better than the conversion of a cable or the equipment
connected
> > > > to the cable, whichever conversion is lower, i.e. whichever LCL value
is
> > > > larger (Note in 6.2.1.2)
> > > > * The standard recognizes that a given method and coupling device
> > > > may not be appropriate for all types of devices under test, so it
allows
> for
> > > > alternate test methods. Specifically, in 6.2 it says:
> > > >
> > > > "If CDNs are not suitable or available, other injection methods can be
> > > > used".
> > > >
> > > > * The note in 6.2.1.2, regarding common to differential mode
> > > > conversion, recognizes that the CDNs for multi-pair balanced lines
(e.g.
> > > > UTP) may not be suitable:
> > > >
> > > > "Often, clamp injection needs to be applied to multi-pair balanced
> > > > cables,
> > > > because suitable CDNs might not be available." *
> > > >
> > > > *What defines "suitable" can be the major limiting factor
> > > >
> > > >
> > > > * Rules for selecting appropriate method are given in 7.1. The
> > > > main deciding factor for selection of the method is (again): "are the
CDNs
> > > > suitable?", which could result in a subjective decision
> > > > * Conversion can be a problem with the currently available CDN
and
> > > > can make it not-suitable for Ethernet lines
> > > > * Relatively well designed RJ45/Ethernet devices can have
between
> > > > -40 dB and -46 dB conversion (2%-1% impedance balance)
> > > > * Ethernet devices, as well as other high-speed devices that
> > > > utilize balanced differential pairs, are very sensitive to CM-DM
> conversion
> > > > * It is critical that the conversion characteristics of any
> > > > coupling devices be at least the same if not better than the conversion
> > > > by
> > > > the well-designed signal lines used for the application
> > > > * In practice, on multi-pair balanced cables where all wires are
> > > > coupled (e.g. 8 wires of a CAT5 UTP), it is not easy to:
> > > > - specify how to measure conversion
> > > > - measure conversion
> > > > - specify required levels of conversion
> > > > * Lack of clear and appropriate method for measuring conversion
> > > > can also be a problem with currently pending draft CISPR22 emission
> > > > standard.
> > > > * The problem lies in the fact that the CDN/ISN is inserted into
> > > > an otherwise well-balanced line. The design of the CDN/ISN is not
balanced
> > > > (the standards lack realistic requirement and appropriate verification
> > > > method) and it creates mode-conversion, which can create apparent CM
> > > > emission and susceptibility. This condition does not resemble the
> realistic
> > > > situation were the cable is fairly balanced and uninterrupted
> > > > * Conversion by the CDN/ISN can be well beyond the conversion
> > > > characteristics of the cable. The currently specified test method for
> > > > measuring conversion (or LCL) is not appropriate for multi-pair
> interfaces.
> > > > * Test equipment should not increase the conversion by
introducing
> > > > imbalance considerably higher than that of the cable. Conversion by
the
> test
> > > > equipment artificially increases the test levels beyond the
> characteristics
> > > > of the measured device and intended cabling, causing apparent failures
> > > >
> > > >
> > > > * Therefore, unless better CDN/ISN devices are constructed
(and/or
> > > > better-defined in the standards), I recommend methods using clamps
(e.g.
> > > > Voltage and Current Clamp method), which preserve integrity of the used
> > > > cabling and allow testing in more realistic environment. The
CM-impedance
> > > > requirement that can be of some concern with the clamp-methods is not
hard
> > > > to meet, at least for 4-pair differential interfaces, but that is
another
> > > > topic.
> > > >
> > > > I hope it helps make your decision.
> > > >
> > > >
> > > >
> > > > Regards, Neven
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > -------------- Original message ----------------------
> > > > From: < [email protected]>
> > > > > Hi,
> > > > > this may be easier than you think (or wish).
> > > > > To my knowledge there are only two manufacturers at the moment: Teseq
> > > > > and Fischer.
> > > > >
> > > > > Regards,
> > > > > Ari Honkala
> > > > >
> > > > >
> > > > > On 5/8/07, wendy <[email protected] > wrote:
> > > > >
> > > > > Dear All,
> > > > >
> > > > >
> > > > >
> > > > > My company intends to purchase the above mentioned.
Will
> > > > > someone recommend any brand/model that compiles to the latest
> > > > > requirements?
> > > > >
> > > > >
> > > > >
> > > > > Regards,
> > > > >
> > > > > Wendy Nya
> > > > >
> > > > > -
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> > > >
> > > > ---------- Forwarded message ----------
> > > > From: <[email protected]>
> > > > To: < [email protected]>
> > > > Date: Tue, 8 May 2007 11:17:17 +0000
> > > > Subject: RE: ISN for Conducted Emission in accordance to CISPR 22 Ed
5.2
> > > > :2006
> > > > Hi,
> > > > this may be easier than you think (or wish).
> > > > To my knowledge there are only two manufacturers at the moment: Teseq
> > > > and Fischer.
> > > >
> > > > Regards,
> > > > Ari Honkala
> > > >
> > > >
> > > >
> > > > On 5/8/07, wendy <[email protected] > wrote:
> > > > >
> > > > > Dear All,
> > > > >
> > > > >
> > > > >
> > > > > My company intends to purchase the above mentioned. Will someone
> > > > > recommend any brand/model that compiles to the latest requirements?
> > > > >
> > > > >
> > > > >
> > > > > Regards,
> > > > >
> > > > > Wendy Nya
> > > > > - ----------------------------------------------------------------
> > > > > This message is from the IEEE Product Safety Engineering Society
> emc-pstc
> > > > > discussion list. Website: http://www.ieee-pses.org/
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> > > > > Scott Douglas [email protected] Mike Cantwell [email protected]
> > > > >
> > > > > For policy questions, send mail to:
> > > > >
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> > > > >
> > > > > All emc-pstc postings are archived and searchable on the web at:
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> > > >
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> > > >
> > > > http://www.ieeecommunities.org/emc-pstc
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--- Begin Message ---
Neven,
While I understand your point of view,
I object against your arguments..
I preferred to read some sound proof
instead of suggestions and statements like
Ethernet devices, as well as other high-speed devices that
utilize balanced differential pairs, are very sensitive to CM-DM conversion
I am not at all convinced that this is the case.
I have the followoing arguments:
- Most high speed receiver chips do have a
decent common mode rejection. A few
percent of asymmetry will not have any
impact on the receiption quality.
This can be proved easily by adding a grounding
resistor at one input terminal of say 1kOhm introducing tens
of percents of asymmetry.
I also noted multiple times that adding serial impedances
such as 20-30 ohms resistor or cm- coils
(used to suppress EMI = common mode current)
do not impact error rates (there was no error rate: 0 faults
-Most (all) high speed cards do have a transformer with
a considerable amount of CM to DM suppression.
20 dB is the minimum one may expect.
Before reaching the receivers the CM component
introduced on purpose by a ISN will be substantially
attenuated by it.
-The decoupling part of the ISN/CDN generally
consists of a Common mode coil with
extreme low leakage field (read substantial symmetry)
for the frequencies the ISN is designed for.
This CM coil recovers (by design) the major part
of the introduced asymmetry.
As long as the Diff Mode properties
as a 1-2-4 times 2-port of the ISN can be proved to cover
more then the spectrum of the signal that needs
to be transmitted through it, i am not afraid
of using one.
Most transmission problems in ethernet connections relate
to frequency dependent attenuation, (aging and humidity)
high voltage CM (50-60 Hz) voltage introduced by
mains cabling close to the UTP,
TIP: do you have a large ethernet building installation
which underperforms heavily ? Add a grounding
resistor of 100 K to chassis ground on one wire of
each of the pairs. Good chance that you
have a capacitively coupled mains voltage
in Common Mode on your UTP pairs.
Waiting your reaction WITH arguments.
Gert Gremmen
ce-test, qualified testing
_____
Van: [email protected] namens [email protected]
Verzonden: do 10-5-2007 19:39
Aan: [email protected]
Onderwerp: Re: ISN for Conducted Emission in accordance to CISPR 22 Ed 5.2:2006
Thanks to everyone who replied off- and online. I am trying to look into the
TECHNICAL aspects of these standards, and unfortunately my conclusion is that
they still haven't been thoroughly examined by anyone who has much experience
with the details and issues related to differential high-speed multi-pair
interfaces, such as balance, conversion, and how to measure these parameters. I
spent a number of years in that area, and I am still not sure what measurement
method is better and more appropriate (it can depend on what you are trying to
see), and consequently what measured levels of balance and conversion are
"true" - as they depend on how they are measured. One thing that appears
evident is that a single-pair measurement is not appropriate as e.g. 4-pair
interface exhibits coupling between all 4 pairs (8 lines) and relation between
the common-mode and differential mode (i.e. conversion) when only one pair is
driven is not the same as when the whole cable is driven by the !
common
mode (or all 4 pairs are driven by differential mode). The lack of the
appropriate measurement method for balance is the major reason why the levels
of LCL for SLCE ISN and the required balance for CDN cannot be properly
(realistically) defined, which in turn allows manufacturers of these devices to
build couplers with various characteristics that can easily cause apparent
failures.
That's one of the reasons why I find the currently available standards
inappropriate. I do not question the intent of the standards, as I believe it
is good, but as Ken Hall pointed out it appears there is positive voting going
on, without fully understanding the technical (and economic) implications. The
methods in the standards are plausible, i.e., they seem to make sense to
someone with general technical background in EMC, but at the detailed level of
the specific application, e.g. Ethernet, they do not take into account the
related issues, which make some methods (IMO) completely unsuitable. That�s why
I currently strongly prefer clamp-methods � they don�t affect the cable
characteristics.
I know many have observed considerable differences in results (SLCE and
Immunity) depending on the test method, as e.g. in the mentioned paper as well
as in numerous conversations I had with test-engineers as well as in my
first-hand observations, but I wish to draw attention of the EMC community to
things that I see as the root-cause of these effects and that I believe very
few people actually looked at the same level. Before they are thoroughly
understood I don�t think we are ready for the standards in question in their
current form and for CDN/ISN devices currently on the market.
I do not sit on these standards and I am in no way associated with the
committees. All my observations are coming from reading the standards and
papers, my personal experience with issues observed on many projects across
many companies worldwide, and from my lab work trying to measure and understand
these issues, especially conversion mechanisms and balance in the Ethernet and
other high-speed differential-signaling world.
Regards, Neven
-------------- Original message ----------------------
From: "Grace Lin" <[email protected]>
> Hello Ken,
>
> Thank you for pointing out the paper. Sorry, I missed your presentation. I
> remember my friends discussed the topic after attending your presentation.
> I believe the concern they had were measuement instrument and necessity.
>
> I have a difficulty to understand the technical implications of telcom port
> requirement. I am not challenging the CISPR committee. I just need some
> help to understand the requirement/necessity. Telcom port measurement is
> through the conducted method. A telecom port does not directly connect to
> (interfere) public utility/power network. If it radiates, it should be
> covered by the radiated emission measurement.
>
> From a manufacturer point of view, telecom port measurement is not a big
> deal if products pass. Labs don't add additional fee for this test. For
> in-house testing, there is not much work to setup a test site (using the
> conducted emission site plus an ISN and adaptors).
>
> Best regards,
> Grace
>
> On 5/10/07, Hall, Ken <[email protected]> wrote:
> >
> > Hello Grace,
> >
> > This topic has been argued and discussed, multiple papers, in CISPR/I AND
> > CISPR/G since the early 80's. The problem may be/is political. However, with
> > a few countries voting against the LCL requirements they ended up in the
> > standard because > 75% of the voting countries approved.
> >
> > We need to influence every countries voting membership to only vote
> > positive if they understand the technical implications of a standard.
> > Attached is a paper from IEEE EMC 2001.
> >
> > Regards,
> >
> > KEn
> >
> > ------------------------------
> > *From:* [email protected] [mailto:[email protected]] *On Behalf Of *Grace
> > Lin
> > *Sent:* Thursday, May 10, 2007 4:00 AM
> > *To:* [email protected]
> > *Subject:* Re: ISN for Conducted Emission in accordance to CISPR 22 Ed 5.2
> > :2006
> >
> >
> > Hi Neven,
> >
> > Thank you for the detail comments. I suggest you write a paper to the
> > IEEE International Symposium on EMC. There are many EMC experts attending
> > this Symposium, including many equipment manufacturers, rule makers, and
> > government agencies. The Symposium record is distributed worldwide and kept
> > forever. This is a good way to get attention and make friends.
> >
> > Grace
> >
> >
> > On 5/9/07, [email protected] <[email protected]> wrote:
> > >
> > > Be careful if you want to use ISN for Cinducted Emission or Immunity
> > > testing of Ethernet or any other high speed differential-pair interface. I
> > > just could not resist to reply, because of so poor specifications which
> > > allow the ISN to cause APPARENT failures, and can cost the industry
> > > millions
> > > to "fix" problems that do not exist. I tried to talk with a major vendor
> > > of
> > > these devices, offering help to make them actually appropriate for use
> > > with
> > > high-speed diff-pair interfaces ( e.g. Ethernet), but there appears to
> > > be absolutely no interest. It appears there is too much politics and
> > > marketing, as opposed to engineering, that dictates how these devices are
> > > constructed (and specified). The cost is paid by the industry who is then
> > > forced to follow the standards. I have worked on many cases where after a
> > > reported emission failure, measured using ISN, the clamp-method ( e.g.
> > > VOltage and Current Clamp method) resulted in very different and passing
> > > result.
> > >
> > > So here are some of my thoughts on this topic.They are mostly based on
> > > the use of CDN/ISN for Immunity, but they really equally apply to both
> > > SLCE
> > > and Immunity.
> > >
> > > � The most recent 6100-4-6 standard specifies the common-mode (CM)
> > > impedance Zcm (Table 3) at the EUT-port of the coupling device
> > > � It also specifies that the Common-to-Differential mode
> > > conversion (defined by Longitudinal Conversion Loss or LCL) of the CDN
> > > should be better than the conversion of a cable or the equipment connected
> > > to the cable, whichever conversion is lower, i.e. whichever LCL value is
> > > larger (Note in 6.2.1.2)
> > > � The standard recognizes that a given method and coupling device
> > > may not be appropriate for all types of devices under test, so it allows
> > > for
> > > alternate test methods. Specifically, in 6.2 it says:
> > >
> > > "If CDNs are not suitable or available, other injection methods can be
> > > used".
> > >
> > > � The note in 6.2.1.2, regarding common to differential mode
> > > conversion, recognizes that the CDNs for multi-pair balanced lines (e.g.
> > > UTP) may not be suitable:
> > >
> > > "Often, clamp injection needs to be applied to multi-pair balanced
> > > cables,
> > > because suitable CDNs might not be available." *
> > >
> > > *What defines "suitable" can be the major limiting factor
> > >
> > >
> > > � Rules for selecting appropriate method are given in 7.1. The
> > > main deciding factor for selection of the method is (again): "are the CDNs
> > > suitable?", which could result in a subjective decision
> > > � Conversion can be a problem with the currently available CDN and
> > > can make it not-suitable for Ethernet lines
> > > � Relatively well designed RJ45/Ethernet devices can have between
> > > -40 dB and -46 dB conversion (2%-1% impedance balance)
> > > � Ethernet devices, as well as other high-speed devices that
> > > utilize balanced differential pairs, are very sensitive to CM-DM
> > > conversion
> > > � It is critical that the conversion characteristics of any
> > > coupling devices be at least the same if not better than the conversion by
> > > the well-designed signal lines used for the application
> > > � In practice, on multi-pair balanced cables where all wires are
> > > coupled (e.g. 8 wires of a CAT5 UTP), it is not easy to:
> > > � specify how to measure conversion
> > > � measure conversion
> > > � specify required levels of conversion
> > > � Lack of clear and appropriate method for measuring conversion
> > > can also be a problem with currently pending draft CISPR22 emission
> > > standard.
> > > � The problem lies in the fact that the CDN/ISN is inserted into
> > > an otherwise well-balanced line. The design of the CDN/ISN is not balanced
> > > (the standards lack realistic requirement and appropriate verification
> > > method) and it creates mode-conversion, which can create apparent CM
> > > emission and susceptibility. This condition does not resemble the
> > > realistic
> > > situation were the cable is fairly balanced and uninterrupted
> > > � Conversion by the CDN/ISN can be well beyond the conversion
> > > characteristics of the cable. The currently specified test method for
> > > measuring conversion (or LCL) is not appropriate for multi-pair
> > > interfaces.
> > > � Test equipment should not increase the conversion by introducing
> > > imbalance considerably higher than that of the cable. Conversion by the
> > > test
> > > equipment artificially increases the test levels beyond the
> > > characteristics
> > > of the measured device and intended cabling, causing apparent failures
> > >
> > >
> > > � Therefore, unless better CDN/ISN devices are constructed (and/or
> > > better-defined in the standards), I recommend methods using clamps (e.g.
> > > Voltage and Current Clamp method), which preserve integrity of the used
> > > cabling and allow testing in more realistic environment. The CM-impedance
> > > requirement that can be of some concern with the clamp-methods is not hard
> > > to meet, at least for 4-pair differential interfaces, but that is another
> > > topic.
> > >
> > > I hope it helps make your decision.
> > >
> > >
> > >
> > > Regards, Neven
> > >
> > >
> > >
> > >
> > >
> > >
> > > -------------- Original message ----------------------
> > > From: < [email protected]>
> > > > Hi,
> > > > this may be easier than you think (or wish).
> > > > To my knowledge there are only two manufacturers at the moment: Teseq
> > > > and Fischer.
> > > >
> > > > Regards,
> > > > Ari Honkala
> > > >
> > > >
> > > > On 5/8/07, wendy <[email protected] > wrote:
> > > >
> > > > Dear All,
> > > >
> > > >
> > > >
> > > > My company intends to purchase the above mentioned. Will
> > > > someone recommend any brand/model that compiles to the latest
> > > > requirements?
> > > >
> > > >
> > > >
> > > > Regards,
> > > >
> > > > Wendy Nya
> > > >
> > > > -
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> > >
> > > ---------- Forwarded message ----------
> > > From: <[email protected]>
> > > To: < [email protected]>
> > > Date: Tue, 8 May 2007 11:17:17 +0000
> > > Subject: RE: ISN for Conducted Emission in accordance to CISPR 22 Ed 5.2
> > > :2006
> > > Hi,
> > > this may be easier than you think (or wish).
> > > To my knowledge there are only two manufacturers at the moment: Teseq
> > > and Fischer.
> > >
> > > Regards,
> > > Ari Honkala
> > >
> > >
> > >
> > > On 5/8/07, wendy <[email protected] > wrote:
> > > >
> > > > Dear All,
> > > >
> > > >
> > > >
> > > > My company intends to purchase the above mentioned. Will someone
> > > > recommend any brand/model that compiles to the latest requirements?
> > > >
> > > >
> > > >
> > > > Regards,
> > > >
> > > > Wendy Nya
> > > > - ----------------------------------------------------------------
> > > > This message is from the IEEE Product Safety Engineering Society
> > > > emc-pstc
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> > > For help, send mail to the list administrators:
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> > > Jim Bacher: [email protected] David Heald: [email protected]
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> > - ---------------------------------------------------------------- This
> > message is from the IEEE Product Safety Engineering Society emc-pstc
> > discussion list. Website: http://www.ieee-pses.org/
> >
> > To post a message to the list, send your e-mail to [email protected]
> >
> > Instructions: http://listserv.ieee.org/request/user-guide.html
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> > List rules: http://www.ieee-pses.org/listrules.html
> >
> > For help, send mail to the list administrators:
> >
> > Scott Douglas [email protected] Mike Cantwell [email protected]
> >
> > For policy questions, send mail to:
> >
> > Jim Bacher: [email protected] David Heald: [email protected]
> >
> > All emc-pstc postings are archived and searchable on the web at:
> >
> > http://www.ieeecommunities.org/emc-pstc
> >
> >
> >
>
> -
> ----------------------------------------------------------------
> This message is from the IEEE Product Safety Engineering Society
> emc-pstc discussion list. Website: http://www.ieee-pses.org/
>
> To post a message to the list, send your e-mail to [email protected]
>
> Instructions: http://listserv.ieee.org/request/user-guide.html
>
> List rules: http://www.ieee-pses.org/listrules.html
>
> For help, send mail to the list administrators:
>
> Scott Douglas [email protected]
> Mike Cantwell [email protected]
>
> For policy questions, send mail to:
>
> Jim Bacher: [email protected]
--- End Message ---
