Wednesday, September 24, 2014

The Annual IEEE EMC Show in Dresden, Plus Elephant #4 ‘The Zip Code Lottery in Achieving Product Compliance'



Hurrah!! The 3D EM software has arrived and I have started to familiarize myself with it. I am going to enjoy this. Reading through the features, it is extremely powerful and looks perfectly suited to simulating the automotive test fixture. It always seems to take me about 40 hours at the keyboard to get up to speed with a new software package, so it will be a while. Meantime ....,

The Annual IEEE EMC Show – Why Dresden?

Last time we covered the vendors’ motives for attending a show, and made the claim that, despite the self-declared importance of the largest vendors, technical paper attendees rule when it comes to the survival of symposiums. Here is why: -

Shows come into existence when a small number of like-minded individuals (usually members of an engineering society) have a common interest in an emerging engineering discipline. Sooner or later it makes sense to meet up to share knowledge, often through the mechanism of technical presentations. This draws vendors like bees to a honey pot, and right from the start a ‘table-top’ sideshow becomes part of the event. As attendee numbers grow, so does the size of the sideshow. Exhibition hall fees soon make up a sizable part of the show revenue, which is why the largest of the EMC exhibitors see themselves as indispensable to a show’s survival. But when did you ever see even the largest vendor actually go out on a limb and pay for their own event on a scale equivalent to the annual IEEE EMC show? Why would anyone attend? It is like asking someone to subscribe to a technical journal with nothing but advertisements in it.

Vendors need to face facts, they are a sideshow, beholding to the symposium organizers; not the other way around.


The Presentation Attendee’s Tale


Given their importance, what draws a technical presentation attendee to a show?

Obviously, the papers/ workshops being presented. Now. unless they have a thousand dollars or two burning a hole in their pocket, these attendees are likely to be employer backed and likely be responsible for the EMC compliance of that company’s products. If newly appointed, an employer with an ounce of sense will want the new appointee ‘up to speed’ as quickly as possible. If the attendee is mid-level experienced, a worldly-wise employer will want that knowledge kept up to date. If highly experienced, the employer better keep that ‘hard to replace’ employee sweet should they wish to retain him/her.

Attendee Motivators

For the new guy, being responsible for product compatibility all of a sudden is disconcerting. Often due to an ad-hoc internal transfer or promotion, it is not uncommon for say a digital-electronics engineer to be saddled with the responsibility. The employer and new appointee both know they need to fill vast knowledge gaps quickly, either directly by way of attending ‘introductory’ technical presentations and workshops, or indirectly through making the acquaintance of experienced attendees at the show (so they can tap their brains later).

For the guy with mid-level EMC experience, keeping knowledge current is the chief motivator, and they will seek out and attend papers that update EMC personnel on standards changes, new technology, etc.

For the highly experienced guy, one pertinent topic can be enough to entice. They like to keep ahead of the curve with theoretical sessions, and during question time, can give vital input to leading-edge papers.

For both the mid and high level attendee, networking can be seen as important for job security

De-Motivators

Pressure at Work and No Travel Budget

Sadly, it is harder for staff to attend shows nowadays. Sometimes due to project pressures (everything seems to be project based these days), and sometimes due to increased pressure at work due to previous payroll cuts. It can be impossible for key staff to be ‘lost’ for a week, or even for a day. And in the rare situation where they can be spared, travel is often the first victim of budget cuts.

Regarding payroll cuts, I can state from first-hand observation that that the disappearance of support staff results in highly paid design engineers being reduced to busying themselves with jammed photocopiers, when they should be pressing ahead with the design of next year’s world leading product. Corporate madness prevails sometimes.


Types of Paper Delivered

Papers seem to range from the outlandish (university staff doing the ‘publish or die’ thing), to the same-old, same-old revamping of old topics. ‘Introduction to EMC’ type papers are always of use to a newbie, but to the more experienced engineers, I think perhaps the papers are less of a draw. Possibly as a result of the maturing of the industry.


To be continued.........



Elephant in the Test Room #4 - The Zip Code Lottery


The room: Whether a manufacturer’s product passes the relevant emissions test can be a matter of where in the Country their premises are located

The culprit: The seemingly EMC industry wide acceptance that a 10dB variance in emissions measurements made on the self-same ‘golden’ emitter test-piece is OK

The consequence: This opens up the prospect of the unfair situation where one manufacturer’s design with comparatively superior emissions performance fails, while a second manufacturer’s design with inferior emissions performance (compared to the first) passes at another location

NOTE: Be sure to listen in on the EMC-LIVE webinar event  October 16 as this topic will be one of the roundtable discussions ( EMClive2014 ). This is sure to be fun because in truth I am simply a bystander with a pretty good understanding of the physics behind EMC tests, and the event is a chance for the experts on the panel to put me in my place.

 Continuing with the elephant at hand, in my view, the ‘root cause’ blame for its existence, and likely continuing existence, lies with the accepted design of open area test sites (OATS). The OATS test methodology involves the inclusion in the measurement of a deliberately created second field, routed via a deliberately created indirect path.

Here is the history of emissions testing as I see it. In the early days it made sense to build an open area test site (OATS) at a rural green-field site far from urban turmoil and its associated ambient RF noise. The trouble was it did not take long to realize that inter-site measurements varied enormously and there was no repeatability worthy of the name.

Figure 1 shows a key reason why these first failures of the method occurred. The figure depicts an unintentional path allowing a second field to be presented to the measurement antenna. The strength of this second field varied depending on the reflectivity of the substrate between the EUT and the antenna. Pavements and soil types at different sites would vary in reflectivity, and one site’s reflectivity could change depending on when it last rained.


Therein lay the problem, and it was decided not to attenuate or divert the second field, but rather to make it consistent in strength (site to site) by installing a fully reflective ground plane as shown in Figure 2. 


 This presented a problem in that the maximum combined field might not occur in direct vertical alignment with the EUT. So to rectify this, a further decision was made to add complexity by searching the vertical space at the measurement plane.

Once accepted as a method, chamber manufacturers wishing to claim equivalence had to replicate the second path (simple and cheap) and also had to increase the chamber volume to allow for the 4m height scan (simple, but far from cheap).

I wonder if the founding fathers of EMC realized the ramifications this method would have later on in the design and cost of semi-anechoic chambers.

Question - Could they have come up with another solution? Easy for me to say since I wasn’t there to face their constraints, but I wonder if they gave serious consideration to diverting the second field away from the antenna as shown in Figure 3.


 If you are going to search for a rural green-field site, why not choose one with a natural slope such as a hill? The hill slope might need to be graded to the best angle and access roads and unobtrusive scaffolding for the antenna mount would be an issue, but the impact on chamber designs would have been a lot kinder.

To be continued....

-Tom Mullineaux

Monday, September 8, 2014

The Annual IEEE EMC Show in Dresden (continued) Plus Elephant #4 ‘The Zip Code Lottery in Achieving Product Compliance’

Great news, borrowing 3D EM software to diagnose the performance of the automotive radiated emissions test fixture is a go! I have been given a contact at the 3D EM software house and things should pick up quickly after the contact returns from the EMC Europe show in Sweden. I am excited. Meantime ....

The Annual IEEE EMC Show - Why Dresden?

Leaving aside the European location for the time being, why does anyone, whether presenting a paper, attending the technical presentations, or exhibiting, bother to go at all?

Let’s hear it from the exhibit floor first.

The Vendor’s Tale

Motives enticing the vendor to attend are varied and complex. They include but are not limited to:

• It is a place to display application-specific wares to a highly-targeted audience

• It is an economical way of catching up with a lot of key people all in the one place, all at one time, saving the expense of flitting all around the country to meet each in turn.

• It is a low-cost opportunity to provide Rep product training, and a place to meet, interview and recruit reps. This situation is symbiotic as Reps are often touring the hall looking to add lines to their line card too.

• You can arrange to meet local customers either at the show, or visit them just before, or just after the show.

• You get a chance to meet your competitor’s customers. I have seen booth staff look on in abject horror as their best customers wander off in the direction of a competitor’s booth.

• You can check out what is new with the competition – new products, new hires, etc.

• It is a chance to get to know and recruit a competitor’s best staff (recruitment activities such as advertising positions at the booth is banned, but this does not prevent poaching).

• Strangely, it can be seen as dangerous not to exhibit – rumours of solvency issues can spread, prospects may read into it that you are reducing your market presence in this sector, and there is always the concern that a competitor choosing to attend may gain from what turns out to be a ‘good’ show after all.

The main de-motivators to signing up for a trade show include:

• Disappointment with the number and quality of sales leads at last year’s show.
Many vendors go in with unrealistic expectations. In their dreams they would like orders to be placed at the show, or very soon afterwards. More savvy companies know exhibition attendance plants the seeds of future sales by reinforcing market presence.

• It is hard to measure the return on the dollars invested
The problem of how to measure return on dollars spent is not limited to exhibiting. If that full page advertisement in a magazine resulted in a major sale 18 months later – how would you know? If not attending a show or looking small (you decided to reduce the booth size) at a show cost you the opportunity of a major sale, how would you know?

• Other marketing opportunities competing for scarce marketing dollars
With little hard measurement data to compare the return on investment types, adding an exhibition to the marketing mix will always be a dilemma for companies.

• Opportunity costs
These are all the other things the sales and marketing staff twiddling their thumbs at the booth could be devoting their time to (sales presentations, customer visits, etc). The saving grace of emailing from the booth or the hotel room is only ever fire-fighting, or trying to hold things until you get back. It is never as efficient as being at the office.


Before we leave the vendor’s tale, there is a personal reason booth-staff like exhibitions. Depending on the attractiveness of the location, it can mean a cheap vacation of sorts. Your flight and hotel room are already paid for by the company, so you only need to find the airfare for the wife and kids and ‘wham’, you have a vacation. The better shows have tours to amuse family members while you are away working the booth.

Next time we will hear from the attendee principally at the show to learn from the technical presentations. Here is a ‘heads up’. It is in the nature of vendors to complain, and some of the big ones truly believe the show exists because they fund it with their exhibition hall floor-space fees. Nothing could be further from the truth – no technical presentation attendees, no show.

The Linearization of EMC Amplifiers

This topic has not been forgotten, it has just been on hold while Elephant #2 ‘Disharmony in Harmonic Limits’ was explored to the full. The previously proposed minus 13dBc giving 75% field purity may not be good enough. However we haven’t factored in the cable loss (higher for the harmonic), so let’s do a few more calculations.

Meanwhile – as another way of looking at how the linearization is achieved, think of the noise cancelling headsets as used by airplane passengers.

The principle of operation for the headset is to sample the ambient repetitive noise (aircraft engine hum), invert it, and add it to the signal feeding the speakers. The result is cancellation of the hum. The blurb on the box says you can still hear announcements etc, as if this was a designed in feature, but this is a trick. The headsets can only cancel repetitive deterministic noise, they cannot cancel stochastic noise.

For our EMC application things are even simpler. We know the noise frequency in advance and have a PC that has the necessary cancellation signal attributes stored and ready for use.

Elephant in the Test Room #4 - The Zip Code Lottery

Elephant #4, like the other elephants we pretend not to see, is one where many already know about it, but few mention it.

With this particular elephant, whether a company’s product passes RF emission tests can depend on which test house it is taken to. Most companies prefer to use a local test house for ease of transport of the product, and for the ease of having one of their engineers at the site to try and fix problems as they arise.

Some years ago, a round robin study showed that for the self-same test-piece sent out to several test houses, the measured emissions levels varied by many dBs. The word around the water cooler was it was up to 10dB difference between the labs.

So if a company is unfortunate enough to be in the ‘capture’ area of a test house that measured high emission levels from the round robin test-piece, then their new product may fail the test. Conversely, and somewhat ironically, a second company’s product, with worse emissions than the first one’s, could pass at a test house that measured lower emissions during the round robin exercise.

You may argue that there could be myriad reasons as to why this situation exists, including operator error, the stacking of uncertainties in one direction, etc. But to my mind it is because we are using an unevenly damped reverberation chamber to try to contain and control the fields within the overall test space.

To put this in context, we will start next time by looking at the layout and equipment arrangement of open area test sites.

To be continued

-Tom Mullineaux

Thursday, August 28, 2014

Ta DAH!

At long last, Department of Defense Instruction 3222.01, the DoD Electromagnetic Environmental Effects Program, has been signed and released. For those of you following along, its been a long road! See the post from Dec 2013.

So, we have a new DoD E3 Instruction…what does that mean? First of all, as the title indicates, it's an Instruction, not a Directive – the difference is that directives tend to be very broad brush with a lot of “thou shalt” but not a lot of “how shalt I?” That is, the Directive has no procedures in it, while the Instruction does. While the new Instruction isn’t chock full of new procedures, it does strengthen the requirements to consider E3 in military procurements and to assign various responsibilities to DoD organizations at every level.

So, what’s new and exciting in DoD Instruction 3222.01?

  1. The policy section is a lot more specific in the new document. There is reference to operations without degradation due to EMI, the operational EME and Joint Service control through DoD –wide techniques and procedures. Definitely trying to get the Services to play as a team, E3-wise.
  2.  It formalizes the DoD E3 Integrated Product Team, which holds monthly meeting to discuss E3-related topics and issues relevant to all military services.
  3. It provides a more formal and expanded description of the DoE E3 Program details of which are managed by the Defense Spectrum Office under DISA. It details many of the requirements for E3 control through the life cycle of a military system.
  4. It incorporates the criteria for the installation and operation of systems and equipment in the vicinity of designated DoD sites, which was previously the topic of a separate Directive.
  5. It provides greater references and procedures for controlling electromagnetic hazards.
  6. And finally, it greatly emphasizes the need for E3 related awareness and training. This includes several references in the Responsibilities section requiring DoD organizations to develop and provide such training to both operational personnel as well as the acquisition corps.

OK, maybe its not as exciting as running a full threat lightning test on an aircraft you’re sure is going to fail, but it's great news for those us of in the E3 business. The Instruction strengthens the requirements to implement E3 control and to make sure that everyone involved in military systems acquisition is aware of the importance of E3 control. And at the end of the day, it's to make sure that our soldiers, sailors, marines and airmen have equipment and systems they can count on in today’s operational electromagnetic environment.

Download the Instruction from acc.dau.mil/library….go to Policy and Instructions!

-Brian Farmer