Read other posts in the “Elephant in the Test Room” series here.
It is looking good for using 3D software to diagnose the performance of the radiated emissions test fixture. Should get the go ahead any day now. Meantime, let’s explore this year’s hot topic.
The Annual IEEE EMC Show – Why Dresden?
It is no surprise that some USA residents in the EMC industry are wondering why the 2015 symposium is being held in Germany. Here is my take.
I learned long ago in history class that the first duty of the State (Monarch, Oligarchy, elected Government, Dictator) is to protect the State’s borders. Other duties may be of the utmost importance, but are always secondary to this first duty.
Likewise, when it comes to the board presiding over an engineering society symposium, the board’s first duty is to ensure the survival of the symposium.
With this in mind, let’s examine the decision to hold the 2015 symposium in Dresden.
History on a Postage Stamp
The symposium really took off with the explosive growth in interest caused by European legislation stating that Electrical/Electronic goods must be stamped with the CE mark.
Before being stamped with the CE mark the goods had to comply with regulations on electromagnetic compatibility. No CE mark, no sales into the European Common Market.
This got the attention of US companies intent on selling into Europe, many of whom were completely ignorant of European EMC regulations. Employer backed symposium attendees hungry for knowledge went through the roof. Subsequently, so did the number of fee paying vendors buying booth space. A happy time in the history of the symposium, and a time of plenty for the vendors.
The powerhouse behind the regulation was Germany, so to me it is quite fitting that if the event is to be held outside the USA, then it should be in Germany. I have been to the annual EMV show many times in Munich and in Dresden (the cities take turns). Good shows when I used to go, but at the time not as ‘grand’ as the US show. To me, and I dare say many others, the IEEE EMC symposium was and always will be ‘the greatest show on earth’.
At the time (1980s) I saw the European regulation as protectionist, and simply a market barrier erected against low-price / low-quality products flooding in from third world countries. However, since then, EMC has become a world-wide concern in its own right, whether covertly protectionist or not.
All good things come to an end and like most industries, the EMC industry matured and saturated. The hunger for knowledge long since satisfied, symposium attendance has declined with a corresponding shrinkage in the number of vendors. Year on year the show seems to get smaller. This is the current situation faced by the IEEE EMC board.
[Somewhat off topic here, but it is widely acknowledged that the car industry is a key bellwether of looming economic recessions. The first thing people do as times harden is put off buying that new car. Well, guess what? There is another. Sales in the entire EMC industry fell by 75% overnight during the lead up to the last recession (the near financial meltdown, auto-manufacturer bankruptcies, etc). I suppose companies can put off buying that new piece of test equipment just as we can put off buying that new car.]
I heard long ago that the types of attendees at the show were basically made up of one third, one third, one third. That is, one third was made up of vendor booth-staff, one third came from the surrounding area, and one third came from ‘out of state’.
In my view, this will translate across the Atlantic Ocean, with any shortfalls due to the European location made up by local vendors and attendees.
Next time we will look at current incentives / disincentives to attend the show, and why attendees bother to attend at all. Meantime, a heads up on where this is leading – the Dresden decision was a hard-nosed business-style decision, completely in line with the first duty of the board.
Proof of the Arbitrary Nature in the Selection of Automotive Harmonic Limits
When we first questioned the automotive edict stating power amplifiers used in RF immunity testing must have -20dBc harmonics or better, we wanted to know ‘just how sensitive is the test field integrity to amplifier harmonic performance?’ Is it a lot or a little? Is -20dBc a great deal better than -19dBc?
On the way to the answer, we derived the simple equation that determines the integrity of the test field itself,
E2dBc = P2dBc + G2dBc
Where E2dBc is the harmonic field level compared to the fundamental field level in the test field itself (in dBs), P2dBc is the harmonic power level compared to the fundamental from the amplifier (in dBs), and G2dBc is the gain the antenna presents to the harmonic compared to the gain it presents to the fundamental (in dBs).
For our purposes, our 1-18 GHz horn antenna has a fixed worst-case G2dBc of 4dB (fundamental gain to harmonic gain ratio).
Calculating the Percentage of the Intended Field
E2dBc doesn’t give much of a feel for how pure a test field is, other than we know the bigger the magnitude of the number, the better the field (-11dBc is better than -10dBc). Fine, but how much better? To get a true feel for test field integrity, it is best expressed as the percentage of the total test field created by the intended test frequency.
The following example shows how the percentage is calculated: –
For no particular reason we choose E2dBc = -10
E2dBc = 20 log10 [E2/E1]
where E2/E1 is the ratio of the harmonic field to the fundamental field.
20 log10 [E2/E1] = -10
E2/E1 = antilog10 -10/20
E2/E1 = antilog10 -0.5 = 0.316
E2 = 0.316E1
Substituting this into Total field E = E1 + E2
Total Test Field E = E1 + 0.316E1
E = E1 (1 + 0.316)
E = 1.316E1
E1 = E/1.316
E1 = 0.76*E
That is E1 is 76% of the total field
As a demonstration of the diminished return from improving the harmonic performance of the power amplifier by 1dB, look at the table showing the percentage of the intended test field making up the total test field.
As can be seen, an amplifier with worst-case harmonics of -19dBc will result in 85% test field integrity, whereas one with -20dBc results in 86%. One percentage point difference seems tiny, is barely measurable due to uncertainties, and seems unreasonable. Maybe the automotive technical committee that deemed this arbitrary number lacked the engineering grounding that would have allowed them to see just how ridiculous the edict is.
It is down to you as a blog audience to draw your own conclusions, but let me state mine – the responsible automotive technical committee was duped. Look, there is a lot to be said for having industry representatives on committees, they are a ‘calming’ influence on what can, and what cannot be done in terms of the feasibility/affordability of a proposed solution. But how do you stop those supplier influencers from skewing decisions that give the supplier company paying their salary a market advantage?
-Tom Mullineaux
