Banana Skins – March 2020 (#258-264)

The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column. The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans of the column. All of the EMC Journal columns are available at: https://www.emcstandards.co.uk/emi-stories, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community. We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.


258.  Immunity issues with pacemakers

Pacemakers have always been designed with interference in mind. When they sense signals outside of the normal signal range of 10 to 300 beats per minute they go into an ‘interference mode’ and pace in a backup safety mode. This will keep the patient alive but will make them feel very unwell. All modern pacemakers have bi-directional radio telemetry systems that allow the cardiology technician to send instructions to the pacemaker. The digital coding is robust, but it is an obvious point of entry for interference signals.

In general mains signals do not cause problems with pacemakers. Surgical diathermy can be a problem. There have been some reports of pacemakers being damaged and some currents being conducted down the lead and causing myocardial tissue fibrosis, with consequent loss of pacing function, but these are extremely rare. Arc welding has long been known to be contraindicated for patients who have pacemakers. The problem is mainly with spot welding as the interference generated can appear at roughly cardiac frequencies. There have been isolated reported cases of ventricular standstill when a therapeutic ultrasound unit’s lithtripter is synchronised to the P wave of the ECG. RF physiotherapy equipment using pulsed and CW at 27MHz can cause interference problems – care needs to be taken and an expert involved in any discussion about patient treatment.

GSM mobile phones can be a problem when held very close to the pacemaker site. This is due to the 2.2Hz bursts of 900MHz signal at switch on and switch off, and 8.3Hz bursts during the ring phase. Patients are told to use the phone with the ear opposite the pacemaker site and not to keep it in their breast pocket. Otherwise there are no problems. Transcutaneous nerve stimulators (TENS) (such as are used in slimming and muscle toning devices – Editor), are common sources of interference. They can cause complete inhibition of pacing and potential death. Patients who require TENS above the waist should be individually evaluated by the pacemaker clinic and safe levels of operation established.

A number of recent reports have indicated that Electronic Article Surveillance (EAS) systems in shops can be a problem. These normally only occur when pacemaker patients linger close to the security gates. Under some extreme circumstances the field can be sufficient to cause the pacemaker to revert to its emergency reset conditions. This is not life-threatening but can make the patient feel very unwell.

External pacemakers are particularly prone to interference because they have a much longer lead and the system is not entirely screened within the body Such systems carry a high risk in the hospital environment and patients need to be kept well away from physiotherapy departments which have potentially life threatening sources of interference. Mobile phones and hospital radios can also cause problems that may initiate dangerous cardiac arrhythmias.

(Taken from “Electromagnetic interference and cardiac pacemakers”, by Lindsay Grant, Medical Physics Department, Royal United Hospital, Bath, IPEM conference “Practical Methods for Mitigation of EMI and EMF Hazards within Hospitals”, York, 28th January 2003. IPEM is the Institute of Physics and Engineering in Medicine, at: http://www.ipem.org.uk.)

259.  Most medical devices fail EMC tests at first attempt

It is quite staggering to discover that over 90% of medical electrical devices that we have tested have failed to comply with the standards applied for on the first attempt.

(Taken from: “Why 90% of medical devices fail conformity assessment the first time around”, by Donald J. Sherratt, Medical Stream Director, Intertek Testing Services, IEEE 2002 International EMC Symposium, Minneapolis August 19-23 2002, Workshops and Tutorial Sessions. Note that his graphs show 97% failing EMC tests to IEC 60601-1-2:1993 – which is easier to meet than the current versions of the generics – and 90% failing safety standards.)

260.  EMC efforts are needed to save lives with wireless  informatics in hospitals

Healthcare need wireless informatics to reduce the numbers of patients dying from medical errors (such as lack of patient medical records). The electromagnetic environment in a hospital is very low, if no portable radio-frequency sources are near by. (But see Banana Skin No. 257 – Editor.)

But the EMI patient-injury risk is hard to calculate because the immunity of medical devices is largely unknown. The potential for EMI malfunction is very high, but these don’t necessarily injure patients. Even though the patient-injury risk is small, it needs minimisation. Soon, wireless usage in top hospitals will not be optional, it will be essential. EMC efforts are needed to make it happen.

(Taken from “Wireless Informatics in Healthcare: Making it work” by Bernard Segal, McGill University, SMBD Jewish Hospital, Montreal, speaking in the “Current EMC issues in healthcare” workshop session of the IEEE 2002 International EMC Symposium, Minneapolis, August 19-23 2002.)

261.  Under-reporting of medical EMI incidents considered likely

In the USA, the Food and Drug Administration (FDA) collects reports of medical equipment failure. Jeffrey Silberberg of the FDA’s Centre for Devices and Radiological Health (CDRH) states that between 1979 and 1993 there were over 100 reports attributed to EMI. These include interference to a wide range of devices, including ECG, ventilators, infusion pumps and apnoea monitors, from a variety of sources including electrosurgery, fluorescent lights and radio transmitters.

The EMI reports form only a small portion of the 95,000 incidents reported to the FDA each year, but Silberberg and others believe there is widespread under-reporting of EMI incidents.

(Taken from “EMC of Medical Equipment”, Dr Martin P Robinson, University of York, N. J. Wainwright York EMC Services Ltd., EMV’99 Dusseldorf, Germany. Also, see – “Performance degradation of electronic medical devices due to electromagnetic interference”, Jeffrey L Silberberg, Compliance Engineering vol. 10 p. 25 1993. An updated version was published in Compliance Engineering’s European Edition’s 1995 Annual Reference Guide as: “Electronic medical devices and EMI”, pages F-10 – F-15.)

Editor’s note: Other useful sources of information on medical EMC issues include the IPEM seminar mentioned in Banana Skin numbers 254-258, plus: “Electromagnetic compatibility for medical devices: Issues and solutions”, FDA/AAMI Conference 1995, conference report edited by Stephen Sykes of the U.S. Food and Drug Administration, 1996, ISBN 1-57020-054-8;  Electromagnetic compatibility/ electromagnetic interference: Solutions for medical devices”, FDA/AAMI Conference 1997; “Technical Information Report TIR-18 – 1997: Guidance on electromagnetic compatibility of medical devices for clinical/biomedical engineers – Part 1: Radiated radio-frequency electromagnetic energy” – all published by the Association for the Advancement of Medical Instrumentation, http://www.aami.org.

For FDA’s Centre for Devices and Radiological Health (CDRH) “Safety Alerts”, public health Advisories and Notices, go to: http://www.fda.gov/cdrh/safety.html. For the FDA’s “Med Watch” safety information and adverse event reporting program, go to http://www.fda.gov/medwatch.

262.  Tilting train interference problems

The high-speed tilting train project on the West Coast  Main Line has been hit by more problems after tests revealed it can interfere with signals. The hitch was discovered during a non-passenger run of the Virgin Trains Pendolino train between Crewe and Liverpool. It was discovered that electromagnetic interference from the controls driving the motors on the trains can change the lights on the signals.

The roll-out of the service, which is planned to run between London and Scotland, has already been subject to delays. Network Rail – the company that has taken over from the Railtrack –  said it was now discussing the problem with Virgin, the Strategic Rail Authority and the Alstom company, which is building the Pendolinos. There is speculation that train’s traction motors might have to be redesigned and that special filters will need to be fitted to the signals.

But a Virgin spokesman insisted on Friday that the company did not anticipate having to put back the autumn 2004 date for the Pendolinos to switch from 110mph to a full tilting mode of 125mph.

The trains were due to be introduced in full 125mph tilt mode on the West Coast line in May 2002. But a series of delays have seen the cost of the West Coast upgrade reach £9.8bn and have meant the Pendolino project timetable has slipped. Virgin has so far received 15 of its 53 Pendolinos.

But they are only running at 110mph in non-tilt mode and only on Tuesdays between London and Wolverhampton and on Wednesdays and Thursdays between London and Manchester. Virgin hopes to run Pendolinos on five days a week by the end of the summer and, by 2006, reduce journey times between London and Scotland by about an hour to four hours 33 minutes.

(BBC News World Edition, Friday 2 May 2003, http://news.bbc.co.uk/2/hi/uk_news/england/2995355.stm. A similar item appears on Erik’s Rail News for May 2003, at http://www.eriksrailnews.com/archive/may03.php, and we understand that another report on this interference problem appeared in the Daily Mail around the same time.)

A rail industry insider, who wishes to remain anonymous, brought the above news item to our attention – and adds the following comments…

The fact that interference is taking place at a number of different sites raises the issue of general safety procedures associated with the installation of new equipment within the railway.

It is likely that the interference is probably due to the introduction of new rolling stock using motor drive systems based upon fast switching power converters (refer to Tim Williams’ article “EMC Threat to Broadcast Bands”, Approval, Nov/Dec 2001, pages 26-30).

As well as the threat to radiocommunications at 150kHz and above, interference is produced by these switching converters in the frequency range 10kHz to 150kHz. Unfortunately, this is outside the range covered by the present family of railway EMC standards, EN 50121-1 to -5.

However EN 50121 (and the Protection Requirements of the EMC Directive) does require that all EMC phenomena be addressed in the EMC control process, i.e. all interference sources and levels are to be identified and only equipment with sufficient immunity to them should be installed.

In new railway projects this process works well with equipment being designed installed and tested to the requirements of meeting the emission and immunity requirements of the EN 50121 family of standards.

The problem is that much of the equipment installed in the UK railway is based upon so called ‘grandfather rights’, meaning that equipment that has been in use within the railway for many years with no EMC problems being reported, can be used in new projects without having to meet EN 50121.

Clearly, if the electromagnetic environment of the railway network remains the same, the use of ‘grandfather rights’ is justifiable. But if the EM environment is significantly changed by the introduction of a new major source of interference (such as the Pendolino? or the Eurostar – see Banana Skin No. 41) the use of the ‘grandfather rights’ approach must be questionable in any part of the railway where the new interference source is to be employed.

263.  Railtrack did not know the electromagnetic susceptibility of much of its rail network

The following excerpts are taken from a hearing into complaints from rolling stock suppliers Adtranz and Alstom against the infrastructure operator (Railtrack) – regarding the inability of Railtrack to provide technical data (including EMC data) for acceptance of new rolling stock onto the UK rail network.

Adtranz/Alstom: Railtrack still does not know where its infrastructure is or how it performs. Nor does Railtrack know where its own infrastructure is non compliant with its own norms. The result has been that Railway Group Standards fail to define in key respects, mainly electromagnetic interference and gauging, the actual requirements that Railtrack will demand compliance to when trains are presented for approval.

Railtrack’s fundamental failure to know where its infrastructure is, how it performs and the condition that it is in, continues to produce extraordinary turbulence in the requirements for safety acceptance.

We have £500 million vehicles parked in the sidings. All those vehicles are built within existing gauges. They are built with lower interference levels than any of the vehicles in service and we are trying to get those vehicles approved against criteria which are spiralling towards the impossible and left to individuals and subjective appraisal.

Railtrack: Railtrack’s inherited infrastructure is 57,000 track circuits of a variety of different types. Many of them have been introduced over a number of years, tens of years, thirty years plus. Many of those track circuits were never designed for the concept of modern traction packages that we currently have being used today.

Most of them were originally designed for something like very statically controlled EMUs etc. A lot of those track circuits are susceptible to certain generated interferences that will come off these new trains. It is an inherent factor of the new train design. The track circuits which were installed and in many cases installed by BR do not necessarily meet
today’s standards.

Certainly the manufacturing requirement from Westinghouse or Alstom or previous companies that designed these track circuits would have designed it for work at a certain length. For reasons of fitting it to the infrastructure, the infrastructure will sometimes be of varying lengths, sometimes they are much longer in length because clearly if you could just increase it by 50% you can reduce the number of track circuits being fitted to the railway, has a nasty effect of making it far more susceptible to the EMC.

At the time the BR engineers did that, there was perfectly reasonable reason for doing it. They could make the track circuits work, they could make them reliable to operate the railway in a safe manner to detect trains. Unfortunately that same design criteria has made them more susceptible to the design of traction packages today.

Chairman: Sitting where we are if 15 years ago the British Railways Board had mandated that track circuit design ought to be a fairly limited range of track circuits that appeared to be roughly right in terms of emerging traction packages for the next ten years then we might not be sitting here now talking about electro-magnetic interference.

(Taken from “Hearing RE Adtranz/Alstom complaint about vehicle and route acceptance”, held on Tuesday 9th May 2000 at the Office of the Rail Regulator, London. Document reference 14419 Version 2 – Final. From: http://www.rail-reg.gov.uk/filestore/docs/adtranz-alstom.pdf or else go to the Rail Regulator’s home page at http://www.rail-reg.gov.uk and enter 14419 into the search window.

Note that the Eurostar trains are still not permitted to travel north of London because they can interfere with track circuits. This problem became public in 1996 – see Banana Skin No. 41 – but seven years later the problem still has not been fixed.

Other examples of railway interference problems can be found in the “Banana Skins compendium” via a link from http://www.compliance-club.com, especially (at the time of writing) numbers: 12, 42, 94 and 115.)

264.  Potential for interference from railways

A report from York EMC Services for the Radiocommunications Agency has looked at the potential for interference from the various parts of the railway system. The following quotes summarise their conclusions:

“It is well known that the railway electromagnetic environment is much more severe than that found in most commercial and domestic premises. However, in many instances the railway runs very close to such premises. In fact, in the example of an inner city light rail scheme the railway effectively runs along public roads, which brings it into close proximity to non-railway premises and potential victim systems.

There are concerns about radio frequency emissions from railways and their potential to interfere with the operation of commercial radio services and other equipment, such as information technology equipment.

There is concern amongst CISPR and the radio community that the emission levels and measurement techniques set out in EN 50121 [the railways emissions standard] do not provide adequate protection to radio services. Some evidence has been found showing that such emissions are capable of interfering with electrical or electronic equipment and radio services operating adjacent to the railway lines. The findings of this study have implications for planned or existing buildings in which IT equipment will be used, where the buildings are situated very close (i.e. less than 10m) to electrified railway lines. There is a significant probability that the passing trains will interfere with PC monitors that are only a few metres away from the lines.”

(Taken from the Radiocommunication Agency’s very helpful  EMC Awareness” website. When the RA was absorbed into OFCOM, this site was included in the ‘Archives’ section of their website, at: http://www.ofcom.org.uk/static/archive/ra/topics/research/RAwebPages/Radiocomms/index.htm.

OFCOM have also made a link from their ‘active’ site to the EMC Awareness site as follows: On their homepage http://www.ofcom.org.uk, click on ‘Legacy Regulator Archives’. Then click on ‘Technology Research’. Then click on ‘RA’ (Radiocommunications Agency), which takes you to what was the RA’s home page. Find the “EMC Awareness” box and click on it. The website is also hosted at: http://www.emcuk.co.uk/awareness.)

About The Author

Keith Armstrong

After working as an electronic designer, then project manager and design department manager, Keith started Cherry Clough Consultants in 1990 to help companies reduce financial risks and project timescales through the use of proven good EMC engineering practices. Over the last 20 years, Keith has presented many papers, demonstrations, and training courses on good EMC engineering techniques and on EMC for Functional Safety, worldwide, and also written very many articles on these topics. He chairs the IET’s Working Group on EMC for Functional Safety, and is the UK Government’s appointed expert to the IEC committees working on 61000-1-2 (EMC & Functional Safety), 60601-1-2 (EMC for Medical Devices), and 61000-6-7 (Generic standard on EMC & Functional Safety).

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