EMC York 2004

The Racecourse, Knavesmire, York, England, 1st-2nd July 2004.

  

EMC York was moved from the University to York Racecourse for the first time this year. The exhibition was retained and exhibitors appeared to express a preference for the new venue, giving them easier access for setting up. Certainly parking was easier than last years conference at the University and the facilities and catering were an improvement on some previous York conferences. I have to confess to a personal liking for York University campus and when they provided on-campus accommodation for delegates the overall conference package was the best value conference I have attended (it is still one of the best value EMC conferences).  The University appear to have "shot themselves in the foot" by making it more difficult for York EMC Services Ltd (YES) to organise this event at the University than to use an external service provider for this conference.  

  

The Grandstand at York Racecourse,

 the venue for EMC York 2004

Credit must go to YES for organising a seamless transition from the University to the Racecourse and at the same time expanding the conference from 1 to 2 days (this reviewer attended the first day only but has reviewed the content of the second day from the conference proceedings for completeness).   Attendance figures were up by approximately 25% on last years 1-day event, with over 150 registered attendees proving the event is maintaining its' popularity.

  

Session 1A: Introduction to EMC Workshop

(not attended by reviewer)

 

The "Introduction to EMC" workshop has become a well respected feature of EMC York and this year was no exception.  The morning of the first day covered the basic introduction with some practical demonstrations by Andrew Rowell.  This was followed by an introduction to the European EMC directive (86/336/EEC) by Les McCormack and an EMC update by Darren Hayes.  All the presenters of the "Introduction to EMC" workshop were from YES and the presentation thumbnails only were included in the proceedings.

 

Session 1B: Measurement Techniques Workshop

 

Proposed CISPR Method of EMC Testing Above 1GHz in an Anechoic Room

Martin Alexander,  National Physical Laboratory (NPL)

The presentation looked at the newer standards to cover testing (radiated emissions and immunity) above the present 1GHz upper limit for the majority of commercial EMC test standards.  It was commented that the CISPR committees are dominated by US and more recently Japanese representatives, delegates were encouraged to get involved via their trade organisation or BSi. The presentation looked at some of the standards for OATS and Semi-Anechoic Chamber (SAC), concentrating on field uniformity, statistical methods and limit modelling. With the exception of the Reverberation Chamber standard (61000-4-21) all other standards covered appear to be at the committee draft (CD) stage and are not yet released standards.  It was acknowledged that more work is required by practitioners before these standards and methods can be agreed and released. This has the knock-on implication that obtaining these draft standards can be difficult unless you "know" someone on the standards committee.

 

Alternative field uniformity methods to the standard volumetric Normalised Site Attenuation (NSA) were mentioned to reduce measurement costs by reducing the number of measurements and the number of positions (eliminating side position measurements).  Also included was using "Site VSWR" method with omni-directional radiators and fixed receiver, however, this appeared to offer little benefit over volumetric NSA without removing some positional test points.  Some discussion on measuring the Equipment Under Test (EUT) in 3-dimensions as well as rotating (above and below EUT) were provided.

 

Martin Alexander is still promoting the Fully Anechoic Chamber (FAC), including now for tests above 1GHz. The presentation was somewhat staccato, almost as if Mr Alexander was viewing the slides for the first time. There was no formal paper given with the presentation, only thumbnails of the slides.

 

Radiated Emissions and Immunity Measurements with TEM Waveguides

Prof. Michael Koch, University of Hanover

Again there was no paper given in the proceedings, a great shame as this was an excellent presentation, even though Mr Koch advised the presentation was prepared by his colleague and co-author Prof. Henyo Garbe (although you couldn't tell as Prof. Koch was clearly very familiar with the topic and the presentation).

   

It was suggested that the TEM cell methods are used due to relatively low cost, small size and ability to enable transient testing to be conducted (transient radiated immunity). I would also add that TEM cells also permit high field strength generation at relatively low power amplification, a major reason why these methods are used for automotive immunity testing.  

  

A problem highlighted for small TEM cells is field homogeneity, the use of statistical methods was proposed to overcome the problem of small volume measurements and better than +/-3dB can be achieved.  Keeping the end-plate depolarisation angle under 20 degrees also helps maintain field content in X-Y-Z planes (higher modes being difficult to generate and maintain in some TEM structures).  Another problem for open TEM structures (e.g. striplines) is the emissions from the equipment limiting their use to shielded rooms and onset of mode dispersion.  Closed TEM cells (e.g. Crawford, GTEM) can reduce emissions and standing waves within the cell can be avoided by use of internal absorber material and shallow angles (less than 30 degrees).  In general it was stated that above the 400MHz-500MHz frequency range field homogeneity is poor for TEM cells.

  

Emissions were skipped quite quickly as time was running out, but TEM cells are less commonly used for emissions measurements than they are immunity.

   

An Introduction to Reverberation Chambers

Dr. John Dawson, University of York

 

Although (again) no paper was included in the proceedings, the presentation is based around the EMC and Compliance Journal article by the presenter (et. al.) that is available on-line. This was one of the best presentations on Reverberation Chambers I have heard (and I've heard a few) covering some of the basic arguments for use of these test chambers, aspects of their design and a look at the costs.

   

The presentation looked at the reasons for the use of reverberation chambers, including versatility for immunity and emissions testing, viability for high frequencies, especially above 1GHz, and omni-directional reception/transmission results in total radiated/received power rather than the more usual dBuV.  Consequently some of the perceived problems are due to a change in the method of testing in comparison to other methods rather than any genuine problem of the reverberation chamber method itself.  Measurements need to be averaged over the mode stirring paddle positions and this adds some complication.

  

Dr John Dawson explains the finer points 

of Reverberation Chamber Design 

(".. and the paddle was this big...")

Relatively compact chambers can be built with useful frequency ranges (200MHz up to the leakage limit of the chamber construction) and requiring no absorber makes the total cost relatively low, estimated at 26k including mode stirring paddle.  As with TEM cells, field uniformity (homogeneity) is determined using statistical methods (although not for the size limitation reasons) and chamber quality factor can influence the field strength achievable for immunity testing as well as field uniformity.  The final parts of the presentation looked at standards that already call up reverberation chamber methods (including a mention of the GM and SAE specifications) and paddle design, the latter being a very useful piece of work that I had not seen elsewhere and suggesting folded paddles as the best low-cost, high-performance design.

  

Session 1C: EMC Design and Simulation

 

Simulation of Coupling Phenomena Between Radiating Antenna and a Cable

Jacek Skrzypczynski, Wroclaw University of Technology

 

Mr Skrzypczynski was ill so no presentation was provided, however, there is a technical paper in the proceedings. The paper describes the simulation of a voltage induced in a wire above a ground plane when using a dipole antenna source at 900MHz. The project is intended to enable simulation of the voltage induction into the cabling harness of public service vehicles from use of GSM phones, however, at this stage the results are a comparative study of two simulation tools; NEC and CONCEPT.

 

The Impact of Grounding Design on the Radiated Emissions from Interface Cards

Stuart Charles, E-Mead Consulting

 

This paper and presentation examined the coupling between signal pins and ground for interface cards in a telecommunications rack. In particular problems that had been experienced in radiated emissions results when a "paddle card" had been added to a backplane of the rack.  The problem was broken down by considering the partial self inductance and mutual inductance of the pins in the paddle card interface, for a limited number of pins.  Manual calculation and simulation of the ground voltage offset and the effect of multiple ground connections on this offset value as a function of frequency was performed for a small number of pins, however, as the pin count was increased the problem was transferred to FLO/EMC simulation tool for further analysis.

 

I'm not certain that the results are a great surprise; the more ground pins the lower the voltage offset and hence the lower predicted radiated noise levels. However if, when measurements are made, the differences simulated prove similar to the measured differences the technique will have proved a useful representation of interface card grounding schemes and should enable better designs to be simulated prior to build.  Mr Charles expects hardware to confirm (or otherwise) the simulation results for the later half of this year, currently delayed by software problems. 

 

This was a very interesting presentation of the problem of grounding interface cards and I hope Mr Charles returns next year to EMC York 2005 to present test results for comparison to these simulations.

 

Review of Progress on Intermediate Circuit Level Modelling Techniques

Tad Konefal, University of York

 

ICLM is an simplified method of modelling EM systems using electrical circuit analogy.  Consequently electrical circuit simulation techniques are used that are significantly faster and less computationally and financially limiting.  This paper and presentation was an update on some of the problems that have been successfully simulated using this simplified modelling method, including monopole and dipole coupling, apertures in shielded enclosures, coupling to loop antennas on a circuit board (stripline and microstrip constructions) and wire penetration though an enclosure. 

 

The presentation was a summary of the technique and its successes rather than giving any great detail on how the models are derived.  It is an encouraging technique for those of us with limited budget for simulation software and the paper included references where more detailed analysis of model derivation may be obtained.

 

Wired or Chassis Ground: The Best Solution for Automotive Emissions

Martin O'Hara, Telematica Systems

 

This was my paper and as such I can not give a fair review.  As expected there were few delegates at this conference with an interest in Automotive EMC and I did at times feel like I was talking to myself (as usual according to my wife).  The relevance of some of the results to telecommunications systems were not lost on those non-automotive delegates who did attend and I thank them for the interest they showed.

 

On LCL Filter Design

Wolfgang Kampfer, Schaffner EMV

 

One of the most interesting aspects of this paper and presentation was the optimisation of these filters based on cost and size rather than the usual performance parameter.  The designs are intended for the usual PWM inverter suppression of switching noise for medium current (8A) devices with switching frequency around 10kHz at 600VDC and 50Hz AC mains.

 

The usual combinations of choke inductances were examined, however, the 3:1 ratio of inverter side inductor was abandoned for a 1:3 ratio with a higher load side inductor.  Materials other than the usual Silicon-Steel compound were examined although the material choice was kept a secret. Values for damping resistance were given for all configurations of damping, and their relative loss values.

 

Filter performance from the cost optimised devices appeared to be good, meeting the requirements for this type of product with low loss and low ripple voltage.

   

Sessions 1D and 2A: Railway EMC Workshops

  

YES have made a good niche for themselves with Railway EMC and these 2 workshops proved how successful they have been in attracting the largest players in the Railway industries to EMC York for this topic.  Unfortunately there are only 3 technical papers in the proceedings and 2 presentations had no written information at all.  Given there were 10 papers in total this was quite a poor showing by the rail industry and makes assessing the content of these workshops impossible for anyone who did not attend.  It also devalues the proceedings as a record of the conference.

  

Note: some presentation copies were made available on the day to those attending these sessions.

   

Catering facilities were an improvement 

on the University.

Session 2B: Electromagnetic Measurements

   

Measurements of Protection Properties of Closed Shields in Time Domain

Despite the relatively convoluted title of this paper it is an interesting look at the ability of electrically conductive packaging to protect sensitive electronic equipment and components.  Definitely worth a look if you are having handling problems or are a conductive materials supplier, not the usual shielded box paper I expected.

  

Time Domain Measurements to Detect Defects on OATS

This paper looks beyond NSA measurements to identify physical limitations in an OATS, limiting field distribution and hence error location and repeatability (between sites and on the same site).  The results examined ground plane and reflections as the main source of discrepancies not necessarily observed in an NSA assessment.

  

Influence of EUT's vertical Cable Terminations to Different Results of Radiated Emissions in Fully and Semi-Anechoic Chamber

The paper develops an end-driven wire (EDW) model of the effect of terminating a cable with an absorbing clamp or leaving unterminated and suffering some resonance effects.  The conclusion seems to be that the EDW model allows easy comparison of SAC, OATS and FAC test methods and SAC can be made equivalent to FAC with limited floor absorber placement.

  

EMI Receiver plus Digitizer RF Transient Measurements

Presentation only, no paper.

  

Reduction in Test Effort for Emissions Measurements Above 1GHz by Using Statistical Analysis

An examination of the testing of an EUT over 1GHz to 4GHz and comparison with TLM modelling of the test resulted in some similar qualitative results (noticeably different quantitively).  The physical influence of the EUT effected the near-field pattern resulting in increasing complexity that the model had difficulty replicating.  Overall the statistical values (maximum, mean etc.) can be relatively close between model and measurement, but at the end of the day tests will still need to be perfromed.

  

Session 2C: Directive Update

  

EMCD 2007

Presentation only, no paper.

  

General Product Safety Directive

The notes in the proceedings indicate this should effect all products on the EU market and goes beyond just "CE" and electrical products and includes aspects of product recall and the sanction of criminal law.  It is worth trying to get hold of this paper alone and is probably available directly from the presenter; Dai Davis (daidavis@iee.org).

  

Sustainable Development

No papers or thumbnails of the WEEE/RoHS and Eco-design presentations were available from the DTi.

  

Session 2D: Electromagnetic Measurements and Safety

    

Detecting Faulty Electric Installations in Railway Systems and Engines Using Computer Logging of GPS Positions and Currents in Railway Cars

The method has been implemented in Sweden and proved to be a successful technique for automated fault detection for long stretches of track, particularly where these are in remote access areas.  There is still a lot of "interpretation" required and the method is being continually improved to get to a situation where it can be fully automatic and unmanned.

  

Personal Safety in High Frequency Electromagnetic Fields, Protective Clothing, Standards and Measurement Procedure

Effectively a study of the shielding effectiveness of conductive suits as used by telecommunications service and installation engineers when operating on "live" communications equipment.  The lack of suitable permeable materials for integration into fabric means that these suits have limited protection against magnetic field and are susceptible to arcing from live equipment.  Glad I don't work in this field of operation!

  

Human Body Magnetic Exposure and Magnetic Interference with a Track Circuit in Proximity of Rail Thermo-Electric Regulation System

An investigation into the amount of magnetic field rail workers get exposed to while working on long welded rail installations. The results suggest the welding system does not exceed the regulatory requirements for the workers, I hope this was assessed before the installation method was approved?

   

A Reduction Method of the Magnetic Human Exposure in Proximity of High-Voltage Overhead Power Lines

A look at the field exposure from 380kV, 220kV and 150kV lines and a simple rectangular inductive ring shield suggested that effective shielding could be achieved close to the lines at relatively low cost.

  

Field Nose, A Frequency Selective and Isotropic System for Long Term EMF Measurements and Monitoring

The spelling is correct, it's a measurement system for long and short term EMF detection.  Applied to areas of public concern such as mobile base stations and microwave relays the results were impressive for what looks like a low cost compact measurement system.

  

Exhibition

  

The exhibition was relatively well supported with 18 exhibitors.  Delegates were virtually absent during conference sessions, as might be expected, but gave the exhibition a "buzz" during conference intervals.  The exhibitors I spoke to all thought the new venue was better, especially for access, space and parking, although some expressed a little disappointment in attendance figures.  It was good to see them supporting the event although the low number of test service providers in attendance was a disappointment.

  

Summary

  

Overall I thought the event was successful, with a good mix of topics and a nice venue with easy parking access.  

  

The exhibition was quiet during conference 

sessions but busy in the intervals.

There were still too many submissions in the proceedings that did not have a formal paper, but fewer overtly commercial presentations than last year.  The lack of formal paper submission is not the fault of the organisers per se as they did request papers, however, many of the presenters appear to have taken the easy option of not writing a paper and submitting their presentation only.  It has since been pointed out to me that only 3 sessions (1C, 2B and 2D) were refereed conference streams and that the others were workshops and as such no formal paper was necessary for the 5 workshop sessions (although speakers were invited to submit a paper).  I would certainly be very unhappy if I bought the proceeding for the sessions on the Rail Transport EMC papers as some of these did not even have presentations in the proceedings (some were available on the day and YES have advised they will be making some available on-line for downloading).  However, at 25 the proceedings are still good value compared to other EMC conferences.

    

I was genuinely surprised and pleased with the good mix of relevant papers for the Automotive EMC engineer such as myself.  You had to dig below the surface of the paper title to find them, but the topics on testing above 1GHz, TEM waveguides and Reverberation Chambers were all relevant.   I expect I will be back again next year and as an event in which to network with other EMC professionals, as well as hear some very good papers, it is worth the effort of travelling to York.

  

Martin O'Hara

Telematica Systems Ltd

July 2004

 

 


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