Wednesday, August 24, 2016

EMC & Its Role In Reliability


EMC and Its Role In Reliability

by Ken Javor, EMC Compliance

Totally anecdotal, but this just happened to me.

My wife uses a powered wheelchair. A very high end, high quality chair. We were on vacation driving north and had just crossed the 45th parallel in the state of Michigan. The 45th parallel anywhere is halfway between the equator and the North Pole. In Michigan it’s also halfway to nowhere, and it was there my wife’s chair broke down.

The chair weighs close to 250 pounds empty, and is not much fun to move around less the electric motors, especially say up and down the handicap van’s ramp. The chair has enough smarts to give you a code when something fails. Maybe not the correct code, but a code. In this case, it told us the joystick module had gone bad, so we called a repair place and got one ordered to be sent to the place we were headed. I mentioned we were in the middle of nowhere, but we had pulled over in a cell phone-serviced spot just off I-75 because I was supposed to support a telecon with a customer and I had been looking for just such an oasis.

While looking at the chair, I saw a cable had been abraded and the sheathing was damaged and so were internal wires. I repaired those, and although that cable had nothing to do with the joystick module, once I got it repaired the fault code changed to bad power module cable. We haven’t priced the joystick module, because essentially price was no object with the chair stalled at the side of the road north of the 45th parallel, but I know it will be well north of $500 US. Seeing a new code unrelated to the joystick module did not lighten my mood.

Several days later after cooling our heels at what is called the “tip of the mitt”, the northern most point of Michigan’s lower peninsula, the new joystick module arrived and I installed it and got the same cable fault code as before and no life from the chair. So I removed all the chair plastic covers and traced the cable from the joystick module back to its other end, and I ended up at two plastic connectors with various wires emanating, and ferrite cores around them.

Now we are finally getting near the end of the shaggy dog story. Or maybe not the end, but the beginning of the end. Or maybe just the end of the beginning. But I digress.

One of those connectors or a wire/pin connection within had loosened and when I pushed on it, the chair woke up and worked. So clearly an intermittent. The chair is several years old, so this was not some sort of infant mortality problem, nor something to be caught by QA before shipping the chair. The ferrite cores I mentioned earlier are not the typical snap-on type, but they are actual toroids around which one could wind a choke or transformer. But they weren't so wound; they were just encircling the cables. Anyway, pushing on one of the two cores caused the intermittent to change states, so clearly over time that heavy core bouncing around the cable had caused something to open up.

So the lesson here is that adding EMI fixes can actually decrease reliability. Stating that in some circles where EMC is held to be a reliability issue is nigh on to heresy and can literally cause a violent argument. I could tell that story, but I won’t.

But it is in fact the case that adding parts decreases reliability – it’s just probability theory. Snapping a core around a cable at the last minute may be attractive and relatively risk-free on a piece of portable electronics, but when it is a vehicle and/or people’s lives depend on its functionality, then the modification must be subjected to review.

Related to this problem, I once worked a spacecraft that had a long RS-232 cable interface, for which they had chosen some very fast logic family, and the cable was electrically long relative to the transition time. There was considerable ringing on leading and trailing edges, and there was an expressed concern that such ringing could look like an extra bit. The fix here was to slow down the rise time (the data rate was OTOO 100 kbits/sec), but no one wanted to change anything, so I suggested one of these press-in connector filters (ee-seal by Quell), and that was demonstrated to work. But the ancient program manager, confronted with this news, asked the question: “Do capacitors fail open or closed?” The answer was “closed.” The program manager, the recipient of no telling how many whippings by Murphy, responded, “Not on my spacecraft,” and that was that.

Intelligence guided by experience.

Mr. Javor has worked in the EMC industry for over 30 years. He is a consultant to government and industry, runs a pre-compliance EMI testing facility, and curates the Museum of EMC Antiquities, a collection of radios and instruments that were important in the development of the discipline, as well as a library of important documentation. He can be reached at ken.javor@emccompliance.com. 

CISPR 35 Published - Multimedia Immunity

CISPR 35 – How does it compare with CISPR 24?

by Ghery Pettit, Pettit EMC Consulting LLC

After 15 years of work in CISPR Subcommittee I, the IEC Central Office published CISPR 35 Edition 1.0 on Tuesday, August 16, 2016. The IEC webstore link is https://webstore.iec.ch/publication/25667. In the US, ANSI has the standard available on their website as well. Go to www.ansi.org and type in CISPR 35 in the search window for standards. You must purchase a copy of the standard to see what the specific requirements are.

Now that CISPR 35 is finally published, the questions that you want answered are: What is the same as CISPR 24? What has changed? What is new?

The full title of the standard is, "CISPR 35:2016 Electromagnetic compatibility of multimedia equipment - Immunity requirements"

The abstract, off the IEC webstore page, states,

"CISPR 35:2016 applies to multimedia equipment (MME) having a rated AC or DC supply voltage not exceeding 600 V. The objectives of this document are:

- to establish requirements which provide an adequate level of intrinsic immunity so that the MME will operate as intended in its environment in the frequency range 0 kHz to 400 GHz; and
- to specify procedures to ensure the reproducibility of tests and the repeatability of results."

Before going into any details, please note that CISPR 35, like other CISPR standards, uses dated references to other standards. Thus, the laboratory must use the version called out in the standard, even if a newer version is available. A particular example where this is necessary is in the use of IEC 61000-4-5:2005 for surge testing. A newer version is available on the IEC website, but CISPR Subcommittee I has determined that for the time being the 2005 version is the one to use.

So, what is different between CISPR 24 (ITE immunity) and CISPR 35?

A key difference is that CISPR 24 provides guidance on testing different types of devices while CISPR 35 focuses on “functions” of the EUT. For example, in the annexes of CISPR 24 there are annexes aimed at telephony terminal equipment, data processing equipment, local area networks, printers and plotters, etc. The annexes in CISPR 35, on the other hand, deal with broadcast reception function, print function, scan function, display and display output functions, musical tone generating function, networking functions, audio output function and telephony function. Testing to CISPR 35 need only be performed for the primary function(s) of the product.

The general types of immunity tests are the same in both CISPR 24 and CISPR 35. There are a few key differences, however.

For continuous RF electromagnetic field disturbances, CISPR 35 adds the option of testing in a TEM cell (IEC 61000-4-20) or a reverberation chamber (IEC 61000-4-21) to the testing method used in CISPR 24 (IEC 61000-4-3). Thus, CISPR 35 offers more choice in testing environments. CISPR 35 adds spot frequencies of 1800 MHz, 2600 MHz, 3500 MHz and 5000 MHz to be tested. 3 V/m is the required test level for all these tests (swept from 80 MHz to 1000 MHz and spot frequencies as noted above). There are additional spot frequencies required in CISPR 35 for equipment with a primary function of telephony. Devices processing analog composite video signals (for example, PAL, NTSC or SECAM) have a relaxation from performance criteria A to performance criteria B test testing within +/- 1.5 MHz of a relevant subcarrier frequency. The key item to note in this is that laboratories that were equipped to test to CISPR 24 will now have to purchase new test equipment to allow performing radiated immunity testing above 1 GHz and manufacturers of equipment to be tested must be prepared for the addition test time and expense associated with this testing.

Table 2 providing immunity requirements for analogue/digital data ports is an expansion of the requirements contained in CISPR 24. Testing requirements unique to CPE (customer premise equipment) xDSL ports has been added. The test level for continuous induced RF disturbances has been changed. In CISPR 35 this is 3 V from 0.15 MHz to 10 MHz. From 10 MHz to 30 MHz this test level decreases with the logarithm of the frequency to 1 V and is 1 V from 30 MHz to 80 MHz.

Immunity requirements in Table 3 for DC network power ports are the same in CISPR 35 as they are in CISPR 24, except for the change in test level for continuous induced RF disturbances noted above.

There are some changes in Table 4 for AC mains power ports, as well. The change noted above for test levels for continuous induced RF disturbances applies here, as well. For voltage dips and dropouts the voltage reduction is stated in terms of the residual voltage, rather than amount of reduction, although the actual requirements are the same. In addition, CISPR 35 provides requirements for either 50 Hz and 60 Hz distribution systems for the remaining reductions.

Table 5 provided requirements on EUT arrangement with respect to whether the EUT is intended for table top, floor standing, either table top or floor standing, rack mounting or “other” operational arrangement.

CISPR 35 is very much like CISPR 24, except where the two standards are different. If you are familiar with CISPR 24 you have a good start on understanding CISPR 35. However, you must obtain and read CISPR 35 carefully to ensure that you test your product correctly to show compliance with the new standard. And make sure the lab has the new test equipment needed for radiated immunity testing above 1 GHz.

A past president of the IEEE EMC Society, Ghery S. Pettit has worked in the areas of TEMPEST and EMC for the past 40 years, working at the Naval Electronic Systems Engineering Center, Vallejo, Martin Marietta Denver Aerospace, Tandem Computers, Intel Corporation and now as an independent consultant.  He is presently the Vice Chair of CISPR SC I and will take the Chair’s position on November 1, 2016.  He has been active in CISPR standardization work since 1998, initially as a member of the USNC IEC / CISPR G TAG and now as a member of the USNC IEC / CISPR I TAG, USNC IEC / SC77B TAG, CISPR SC I WG2 and WG4, in addition to the leadership position noted above.  Mr. Pettit is also a member of ASC® C63 SC 1.

Ghery has written 8 papers and articles for publication and contributed a chapter for the 2nd Edition of the ARRL’s Radio Frequency Interference Handbook.  He is a member of the dB Society and serves as a Technical Advisor for the ARRL in the area of EMC.  He holds an Amateur Extra class ham license (N6TPT) and is an instrument rated private pilot.

Mr. Pettit may be reached at Ghery@PettitEMCConsulting.com or at (360) 790-9672.

Saturday, June 25, 2016

Britain after Brexit, with the accent on EMC


Editor's Note (Updated June 27, 2016): Britain has voted to leave the European Union, a monumental decision that’s triggering some serious alarm bells throughout the country. As it stands, many UK laws and regulations are determined by EU legislation and it’s not immediately clear what the EMC standards ramifications in Britain will be during the two year transition and in the future after that.

There’s still a long road ahead, and many of the concerns expressed by the EMC standards community are likely to be addressed in the coming negotiations. Panic is obviously not the way to go, and to understand the issues with more clarity, I've asked John Woodgate and Keith Armstrong, product regulations/EMC consultants and standards experts in England, to provide some initial analysis. Both of these consultants are based in England, so have a unique perspective as events unfold. As the transition takes place, you can depend on Interference Technology to help inform and clarify the issues as the transition progresses.


In the meantime, we would invite your comments on the issue. See below.

K. Wyatt


Britain after Brexit, with the accent on EMC - Part 1

by John M. Woodgate, BSc(Eng) C.Eng MIET SMIEEE FAES HonFInstSCE

(June 24, 2016) - What is the future for Britain after the historic 'Brexit' vote to leave the European Union? It's very early days – as early as you can get, in fact – but there are some signs. Controlling factors can be described as 'Dame Luck and the Lame Duck'.  Dame Luck is market sentiment, always volatile but in this case reason appears to be holding. The British stock market bubbled up before the vote, so the post-vote fall has really returned the market to where it was ten days ago. The Lame Duck is Prime Minister David Cameron, who says he will resign, but not till October, so until then the government will be hamstrung, both at home and abroad.

This may not matter if enough of British industry takes advantage of the drop in the value of the pound sterling to combat rising material costs by increasing export sales. There are always some with enough insight (and low enough debt) to do that. Every economic change allows someone to make money, and it doesn't have to be bankers. The EU leaders are pressing for a quick resolution, perhaps even shorter than the two-year period embedded in the treaties. That is likely to benefit industry, especially if British leaders use that appeal for speed to toughen their negotiations.

So what does this mean for EMC? We are in the age of world markets, so obviously British industry will continue to fulfil all significant market entry requirements, such as respecting EU Directives and applying European standards (ENs). If Britain joins EFTA (European Free Trade Association), it will continue to participate in CEN and CENELEC, but with changed voting rights. If it doesn't join, it can choose whether to apply EU Directives (or a variant thereof) and CEN/CENELEC or ISO/IEC/CISPR standards, whichever is advantageous. ETSI standards are a different matter, while ETSI is nominally and originally 'European Telecommunication Standards Institute', it is de facto an independent non-governmental body, with world-wide activity, and there seems no reason why anything should change regarding British participation.

Of course, all this could be wildly wrong, and disasters forecast by the 'Remain' faction may happen. But most events are not beyond our control. We just have to be clever enough to control them correctly.

Britain after Brexit, with the accent on EMC - Part 2

by Keith Armstrong, Consultant, Cherry Clough Consultants Ltd.

Yes it is big news, but I don't feel that I have anything very significant to say about how the issues you mention might be affected.

All I can say is that, from my point of view as a design consultant, whatever country I am working in (most recently Australia, New Zealand, Belgium and England, UK) if my customers want to sell to the EU they must declare compliance to all relevant EU Directives and most find that easiest to do by declaring that they have applied all the relevant standards that have been notified under those Directives in the OJEU. 

As far as I can see, this process and its associated documentation is exactly the same for any country in the world that is outside the EU – as it is for manufacturers in Belgium and in the UK (both of whom are currently Member States within the EU).

I suppose that if the UK actually left the EU (which is by no means a certainty, and anyway would most likely take 2 or more years to happen) UK experts would no longer be involved with creating EN standards. But as EN standards are mostly based on international standards anyway, and UK experts would still be involved on those international committees, I don't see any big changes happening.

It is interesting to note that even though the UK is still a Member State within the EU, it has not yet published National Regulations corresponding to the new EMC or LV Directives which came into force on 20th April 2016 (2104/30/EU and 2014/35/EU respectively). 

Normally we in the UK would have seen draft UK Regulations at least a year in advance of the date when new EU Directives required National Regulations to be enforced, but not this time.

Quite possibly this same situation applies to all the other EU Directives which came into force on that date, too.

I am told that enquiries by others were told by the responsible UK government departments that they were waiting for the outcome of the referendum.  

So it is already the case that manufacturers in the UK have National Regulations that are not harmonized with the corresponding EU Directives, just like manufacturers in China, Japan, the USA, or anywhere else outside the EU!