The EMCTLA's Technical Guidance Note No 39 may be relevant here.
These TGNs are guidance to UK test labs on how to apply the EMC directive and
EMC test standards.
You can get to TGN #39 via www.emctla.org.
If it doesn't answer your question completely, send an email to the EMCTLA's
Dear All
Gary Fenical of Laird Technologies told me about an interesting new report
from the Nasa Aviation Safety Reporting System.
You can download the report from: http://asrs.arc.nasa.gov/report_sets/ped.pdf
This May 2002 report concerns problems with Personal Electronic Devices
(PEDs) on
Dear Dan
You are correct, an IEC 61508 SIL is a property of an overall safety-related
function or system.
It cannot be applied to a constituent part.
However, IEC 61508 gives you a list of the things that you need to provide
safety-related systems designers with, so that they can decide how
Dear Bob
Just a point - smaller is not always better.
AVX and maybe some others make 0612 capacitors for decoupling. They are the
same size as the normal 1206 size but are metallised along their long edges.
This reduces their ESL considerably, to the extent that (according to
manufacturer's
Dear Nick
There are a number of useful links on the draft MID on our website A
HREF=http://www.cherryclough.com;
www.cherryclough.com/A under Useful links to EU directives (or go directly
to: A
Dear Ted
Your description of ground-loop prevention methods is very comprehensive, and
reminds me strongly of the years I spent designing consoles for Neve in the
70's - 80's.
Thank you very much for sharing this useful information with us.
These days most of my involvement with pro-audio is
Dear Mike
I'm sure professionals like yourself wouldn't dream of ever cutting a safety
ground.
Yet it does happen in pro-audio and video installations, even sometimes in
the Albert Hall in London at black tie concerts.
I know the US doesn't have laws equivalent to Europe's LVD, but I didn't
Dear Ken
Thank you for your reply. I am sure that most installers know what they are
supposed to do for electrical safety, but some seem very ready to cut safety
corners when hum appears in the audio signal. This is a worldwide problem in
pro-audio installations, of course, not a specifically
Dear Ted
OK, OK, after two postings making much the same point maybe I should have
been more careful to make it clear that I was only worried about the kind of
ground lift switches which disconnect the protective ground from the
chassis of the equipment. I have seen them used in pro-audio
Dear John
I was aware of the ability to mix Class I and II construction in a single
product, but as I understand it such a product must be treated as if were
simply Class I, in that it must have a protective ground connection via its
power cord.
I was sure that the AES would not condone
Dear Sergio
Many thanks for replying.
I have no problems with switches such as you describe, and have used them
myself.
It is switches that disconnect the protective earth, which I have also seen
(plus just plain disconnecting the green/yellow wire) that I am concerned
about.
All the very
Dear Group
Does anyone know if it is legally permissible in the USA to remove the safety
grounds from Class I equipment used in pro-audio systems and installations?
It has been a common practice over many many years in professional audio
systems and installations to 'lift the grounds' on
Just a short note to say a big 'Thank You' to the people who have read and
commented on the IEE's Guide on EMC and Functional Safety
(www.iee.org.uk/Policy/Areas/Electro) since my request for input from
emc-pstc members in January 2002.
Everyone who has commented to me has been generally in
Don't forget the European Product Liability Directive (85/374/EEC amended by
99/34/EC) and General Product Safety Directive (92/59/EEC).
Neither of these require any approvals or markings, but both require that the
state of the art in safety engineering is applied, and this implies the use
of
Dear John
My intention was simply to remind people (if any reminding was needed) that
achieving a presumption of conformity does not necessarily mean complying
with the EMC Directive.
Regards, Keith Armstrong
www.cherryclough.com
In a message dated 05/02/02 22:57:37 GMT Standard Time,
Dear Jim
Just a couple of points on your item 2, which you and most others are
probably well aware of anyway...
If you are making 'multifunction' equipment (e.g. a refrigerator with an LCD
display and internet browser) you may have to apply two different
product-family standards. For the
Dear Muriel
Separating CM from DM at the output of a LISN was covered by Michel
Mardiguian and Joel Raimbourg in a paper they presented at the IEEE EMC
Symposium held in Seattle in August 1999, titled: An alternate,
complementary method for characterising EMI filters (Volume 2 of the
Symposium
Dear John
You are setting up a straw man.
(Putting words into my mouth).
I have never said that I advised my clients in the manner you suggest below,
or that it was a good idea to do so.
Regards, Keith Armstrong
In a message dated 26/01/02 17:10:43 GMT Standard Time, j...@jmwa.demon.co.uk
Dear John
People put all sorts of things in contracts, some more crazy than others.
I wanted to establish the fact that there is nothing to stop a purchaser
placing a requirement on a supplier to apply the limits in IEC 61000-3-2 for
equipment that consumes 16A/phase, and you have confirmed
CherryClough@ao
l.comTo: j...@jmwa.demon.co.uk
cc:
emc-p
Dear John
Thank you for your replies.
A couple of points...
Optional application of standards: I believe there is nothing to stop
purchasers from using any IEC standards in their contracts with suppliers. So
a purchaser of a 30A/phase equipment could specify that the equipment must
meet the
Dear John
I understand the following statements to be true.
Please make corrections / comments where necessary.
1) EN 61000-3-2 only applies to equipment consuming up to 16A/phase, and
there are no mandatory harmonic limits in the EU (yet) for higher-powered
equipment, other than what the
Dear Ghery
I don't think I disagree very much with what you said below.
John Woodgate's summary yesterday was most interesting. He analysed the
reasons why harmonic mitigation at system and site level were not being
employed and concluded that:
It is almost axiomatic that the best overall
Dear Rich
Many thanks for your useful analyses.
I was wrong to suggest that the 'computer industry' is in denial about mains
harmonics - I realise that many people in that industry have made and are
making valuable contributions in that field.
But I am sure that the claims that there is 'no
Dear Gregg
I know of a number of companies that make these 'active harmonic
cancellation' units.
They are often called 'active harmonic filters' although their operating
principle is not based on filtering.
They seem to me to be an excellent idea, and can help avoid the need for
improving a
Dear Ghery
I am well aware of the undersized neutral problem, but given that we have a
legacy of buildings with undersized neutrals it is not a simple or low-cost
solution to uprate all their neutrals.
Anyway, harmonics in the mains distribution cause many more problems than
simply
Dear Ghery
There is plenty of evidence, for harmonic problems, especially in large
cities and large office buildings.
For example, an electricity supply engineer told me that in the financial
district in London there are buildings where they cannot fit any power factor
correction capacitors to
Dear all
Following comments made in the correspondence on 'EMC-related safety issues'
early in January I asked for everyone who was interested to read at least the
beginning of the IEE's guide and let me know their opinions.
Also to ask their colleagues and anyone else who might be interested.
Dear John
Sorry to be so late replying.
I am pleased that you now understand the situation that I attempted to
describe earlier, where an HCMOS inverter with an unterminated input was the
cause of surprisingly powerful radiated emissions at 200MHz, due to an
unfortunate, unlikely, but not
Dear Bob
Sorry to be so late replying.
Thank you for this reference, I was unaware of it.
I shall add it to my list of EMC-related safety references.
If anyone wants a copy of my list, I'll be pleased to email it to them in
Word format.
If anyone knows of any books, articles, or papers on the
Dear Ken
Sorry to be so late replying, but I have been unable to read any of the
correspondence in this thread for a week.
In an attempt to spare the emc-pstc more of our arguing I will not reply in
detail to three of your emails, one from the 6th Jan, and two from the 7th
Jan, because they
Dear Ken
Sorry to have taken so long to reply to this.
I haven't been able to read any of the contributions for a week.
I have to say that I don't recognise myself, or the IEE's guide on EMC and
Functional Safety or the 30+ respected and senior engineers who contributed
to it, or the IEE
Dear Ken
Sorry to have taken so long to reply to this. Pressure of work has kept me
away from the thread for a week.
I don't know where you get your maths from.
The usual formula (commonly available in a number of variants) for the
radiated emissions E in V/m at 10 metres due to a common-mode
Dear John
Sorry to have taken so long to reply.
We were talking about safety-related systems.
The general approach is to add additional back-ups to the safety related
system to provide it with necessary reliability as far as safety is
concerned, as I had hoped the examples in the full version
Dear John
Sorry to have taken so long to reply.
We will have to disagree over the educational value of the EMC + Compliance
Journal's Banana Skins column.
If you haven't seen anything that was CE marked but which was obviously not
compliant, then I think you must be lucky.
As I mentioned
Ken, I believe other postings on this topic this weekend clearly show that
electronic circuits which were not designed as radio receivers can possibly
be interfered with by the emissions from products which meet FCC/CISPR 22
limits, for a number of possible reasons, especially when the product
Taking Toms' calculations a little further
Typical thermocouple sensors have output voltages in the range 3 - 50
microvolts per degree C. So to create a 60C error in a thermocouple-based
temperature control system (see my recent posting about the RF immunity of a
blood sample incubator)
Yes, John, you are quite right in both your comments as far as you go:
1) You are not the only person who can dramatise an issue so as to encourage
people to debate it;
2) If you sold a single electronic safety-related circuit with a failure
probability of 10^ -9 to 100,000 customers the
A) I don't agree with Ken that: Emissions from a laptop are naturally
(without suppression) on the order of 10 uV/m to 100s of uV/m.
Maybe IBM PC clone laptops use similar enough architecture and chipsets and
design techniques to be this consistent (I don't know) but I have seen the
following
Ken, can we take it that in the posting below you are agreeing that
interference with non radio-receiving circuits from what you meant by
unintentional emitters is a possibility, albeit a worst-case one?
If my reading above is correct, how can you then go on to say that
...unintentional
Dear John
In previous postings from Ken Javor and myself, I believe that Ken (who I was
replying to in the fragment below) has made it clear that what he is really
concerned with is the kinds of emissions controlled by CISPR 22 and Title
47, part 15B of the US Code of Federal Regulations (I
Dear John
The incubator I described was already on the EU market in the latter half of
the 1990s, when I helped to test and fix it.
And I'm sorry to disappoint but I have already experienced several similar
examples I could quote, such as the electric blanket that would change its
heat
The one in a billion John refers to sounds very dramatic and difficult.
So it may be helpful to refer to IEC 61508 which is a recently-published
'basic safety publication' covering The functional safety of electrical /
electronic / programmable safety-related systems
IEC 61508 uses the
In a message dated 04/01/02 19:31:51 GMT Standard Time, j...@jmwa.demon.co.uk
writes:
The trick, I believe, is not to be in that position in the first place.
Design your products using the latest safety knowledge and test them well
to
discover if they have any weaknesses you did not
Dear Cortland
People can't simply say: ordinary semiconductors won't demodulate RF levels
produced by an unintentional radiator – even the smallest amount of RF can
be demodulated – there are no hysteresis or threshold effects in a PN
semiconductor junction or FET that is biased into its
Dear Ken
That is exactly what I am saying: under the EU's Product Liability Directive
a company can be held liable for unlimited damages with no proof of
negligence on the manufacturer's part.
It is of course a valid management decision to ignore a market that is almost
as large as USA/Canada
Dear Ken
That is precisely the point I was trying to make: all companies (and people)
always weigh up all the costs and risks that they know about and act
accordingly.
The problem arises when certain risks are unknown or ignored, for whatever
reasons.
I see it as part of every engineer's job
Dear Ken
I am truly sorry if I irritated you by misunderstanding your words, but I
took your posting to imply that electronic circuits which are not designed as
RF receivers would not respond very well to radio frequencies.
My example was not intended to be a full answer to your example (there
Dear All
A page on our website www.cherryclough.com has a useful list of EU directives
relating to electronic products (and not just the CE marking ones) and the
URLs where they and lists of their relevant standards can be downloaded from.
Not every possible directive is covered, but I think
As I understand the way the civil law section of the EU's Product Liability
Directive operates (I am not a lawyer) it does in fact place the burden of
proof on the manufacturer, who is effectively considered 'guilty until proved
innocent'.
I also understand that any number of manufacturers can
Hey, Ken, let's try to be realistic here!
Sure - we should try to get laws we don't like changed, but that isn't going
to happen overnight and in the meantime we have to operate within the law as
it stands.
Or are you suggesting immediate insurrection by product manufacturers?
(Outlaw
Does anyone else think that ordinary semiconductors doesn't respond to RF?
I have tested a product which was little more than an LM324 quad op-amp for
RF immunity using IEC 61000-4-3. This op-amp has a slew rate of
1V/micro-second on a good day with the wind in its favour. It was housed in
an
The IEE's guide on EMC and Functional Safety is concerned with helping
engineers and managers avoid legal problems - but I don't call this
appeasement, just good practice.
But the guide is also concerned with saving lives in a world where electronic
control of safety-related functions is
---BeginMessage---
Dear John
Maybe I should have been more explicit.
Over the course of this correspondence (and in earlier postings to emc-pstc)
you have cast doubt on the IEE's guide to EMC and Functional Safety without
being in any way specific.
Now you are saying that you haven't read it
---BeginMessage---
All I know about the issue of the laptop interfering with the compass is from
the IEE's Guide to EMC and Functional Safety, copied below:
*
A routine flight over Dallas-Fort Worth was disrupted when one of the
compasses suddenly shifted 10 degrees to the right. The
Dear Ken
I understand your concern and your comments, but all the IEE's guide was
trying to do was make people aware of the legal situation as it actually
exists - and recommend what engineers need to do to reduce their employers'
liability risks under present-day legislation. (Bearing in mind
The general impression in Europe is that the 'culture of blame' began in the
USA, leading to such warning messages as Do not use this appliance to dry
pet animals on microwave ovens. It often seems that legal trends begin in
the States and take about 10 years to get over to Europe.
It seems a
I believe there are great problems with the use of the phrase 'spurious
emissions' in any context save that of a standard or law which defines just
what that phrase means.
I sincerely hope I am not one of those who is ever ready to overstate the
importance of their station in life ! But I do
Once again, John, you seem to be trying to give a negative impression about
the IEE's guide on EMC and Functional Safety (which you now admit you haven't
read) instead of simply saying what it is that you think is wrong with it.
Of course I am passionate about the IEE guide - my colleagues and
I won't get into whether you were intending to impugn my truthfulness, and
shall assume you just used an unfortunate turn of phrase.
I had already said I was not aware of the previous communications on this
issue, so I could not have been aware that you were restricting the
discussion to the
Dear John
Quite a number of EMC and Safety experts took part in creating the IEE's
Guide on EMC and Functional Safety, including a lawyer who specialises in
high-tech issues. You will find their names listed at the end of the 'core'
of the guide (downloadable from
Dear all
There was a discussion about electromagnetic emissions and safety issues a
couple of weeks ago which I only caught the tail end of, so I hope my
comments below are relevant and useful.
I would also like to make a plea for assistance.
Spurious emissions and safety.
Even if we ignore
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