Editor’s Note: We regularly receive requests from readers to publish stories about real EMI/EMC problems faced by real engineers. We are pleased to bring you Banana Skins, a new monthly column in In Compliance, and a 20-year tradition that began in the pages of the EMC Journal. We hope you enjoy the column and look forward to continuing the tradition of sharing these valuable stories.
62. Copying machine interferes with CAD system
An engineering company invested heavily in a networked computer-aided design (CAD) system. However, the system’s many advantages were overshadowed by the all too regular problems it suffered. The system would crash unexpectedly, sometimes hours of work were lost or corrupted and circuit failures seemed to be almost a monthly event.
At first these were assumed to be just “teething troubles” but as time went on, and design work slipped further and further behind schedule, relations with the system’s supplier became increasingly difficult. Only when one of the engineering team read an article in a professional journal, did they realise that the problem might not be the system, but the environment. They soon observed that the system’s failures coincided with the operation of a large drawing copying machine, which was injecting switching transients onto the ring main.
(Furse Electronic Systems Protection Handbook, 1996, page 15.)
More on this topic…..
Transient faults (in computer systems) are triggered by environmental conditions such as power-line fluctuation, electro-magnetic interference, or radiation. These faults rarely do any lasting damage to the component affected, although they can induce an erroneous state in the system. According to several studies, transient faults occur far more often than permanent ones, and are also harder to detect.
Curiously, most computer failures are based on either software faults or permanent hardware faults, to the exclusion of the transient and intermittent hardware types. Yet many studies show these types are much more frequent than permanent faults. The problem is that they are much harder to track down.
(Taken from “Fault injection spot-checks computer system dependability” by J V Carriera, D Costa, and J G Silva, IEEE Spectrum, August 1999, pages 50 and 51, www.spectrum.ieee.org.)
63. Radio and radar transmitters interfere with early electronic flight control systems
Earlier analogue flight control systems have experienced malfunctions when overflying radio/radar transmitters—the new generation digital systems are very much more robust and can meet the very stringent EMC requirements.
(Taken from “Fly by Wire” by Dick Collinson of Marconi Avionics, Computing & Control Engineering Journal, IEE, August 1999 page 152, www.theiet.org.)
64. PC EMC compromised by non-compliant components
Computer manufacturers and others are finding it impossible to meet the EMC Directive because of non-compliant CE marked motherboards and power supplies, according to test house EMC Projects. The company tested 12 different motherboards for a client recently and found that every one of them failed to meet EN55022 limits, according to the company’s MD Mike Wood. Failures ranged from a few dB to 20dB over the limit line. None was accompanied by instructions about how the boards should be installed to meet EMC regulations. “I feel very sorry for companies trying to meet standards when they use these boards,” Wood said. “It is almost impossible for them to comply.” He pointed out that any manufacturer relying on CE marked components to justify compliance without testing is likely to have severe problems.
(Approval, Jan/Feb 99, page 5)
Talking to a representative of Intel Corporation (UK) of Swindon about this general issue in 1998, he said that they always tested their motherboards to make sure they were EMC compliant in a variety of different manufacturers’ PC enclosures, and that this took approximately two weeks. He claimed that this was one reason why none of the “hottest” machines reviewed in the computer trade press used Intel motherboards – given the fast pace of the computer industry, taking the time to properly qualify a motherboard meant taking second place in the performance stakes to those who were less careful of their legal and ethical obligations.
(Keith Armstrong, Cherry Clough Consultants, October 1999)
65. Investigations into possibility of cell phones interfering with implanted medical devices
According to the Cellular Tele-communications Industry Association’s web site www.wow-com.com: researchers have found that analogue phones have no effect on pacemakers, although some digital phones do. Already, doctors advice pacemaker wearers to exercise caution around electromagnetic devices such as MRI machines. Digital phones should be approached in the same way.
Wireless Technology Research Ltd conducted tests involving over a thousand pacemaker patients. They found no clinically significant interactions with the phone in the normal position at the ear. Some interference was noted in 20% of the tests with the phone 6 inches from the pacemaker. But even then, only 6% were clinically significant. Regular operation resumed once the phone was removed. The Food and Drug Administration (USA) believes pacemaker wearers should avoid placing phones next to the implant, as in shirt or jacket pockets. When using the phone, patients should hold it to the ear opposite to the side of the body where the pacemaker is located.
Other cardiac patients use implanted cardiovascular defibrillators (ICDs). The University of Oklahoma’s Wireless EMC Centre investigated the effects of all the analogue and digital wireless phone technologies operating in the US and Europe on ICDs from four manufacturers. No interactions were found between phones that operate in the 1800 and 1900MHz bands.
Only one unnamed company’s ICDs were affected, and these effects were only caused by TDMA-11 Hz which is only used in specialised operations, and even then no permanent ICD reprogramming occurred. Still, doctors say that additional research is necessary, and researchers say that ICD patients should follow the same guidelines as pacemaker wearers.
(Extracted from Electronic Design magazine, October 18th 1999, page 32H.)
66. Twenty-eight examples of interference with medical devices
During the past decade, the U.S. Food and Drug Administration (FDA) has received more than 28 medical device reporting incidents of adverse interactions between medical devices and electronic article surveillance (EAS) systems, metal detectors, and security systems. Several case reports and four peer-reviewed studies document adverse reactions between EAS systems and implanted pacemakers, implanted automatic cardiac defibrillators, implanted neurostimulators, and other ambulatory medical devices.
Anecdotal reports and newspaper articles suggest that many more device interactions have occurred and gone unreported. Each year millions of people enter establishments protected by EAS systems. Because more people are using electronic implants and ambulatory medical devices, adverse interactions with EAS systems are of increasing concern.
(Extracted from an article in Compliance Engineering magazine’s European Edition, September/October 1999, Page 32. The article does not draw any conclusions for wearers of implanted devices in the way that item 65 does.)
(Editor’s Note: The number and variety of implanted medical electronics devices is rapidly increasing. Stevie Wonder (the musician) is apparently soon to receive an artificial retina chip. Some very serious people are talking about implanted personal enhancements which are not for medical purposes. EMC takes on a whole new dimension when parts of your body or mind can suffer interference from common electronic technologies.)
67. Digital TV broadcasts interfere with critical medical telemetry
The Critical Care Telemetry Group submitted a petition document (to the USA’s FCC), ET Docket 95-177, 10/97 covering new channels from 470 to 668 MHz for powers of 200,000 µV/m at 3m at the same time as the digital TV group submission. This resulted in some confusion and a case where in March 1998 at Baylor University Hospital some medical devices failed due to the DTV broadcast. The FCC and the FDA produced a fact sheet stating that the DTV operators must co-ordinate with the regional hospitals before broadcasting. (Details can be found on the FCC web pages, http://www.fcc.gov.
(Extracted from ERA Technology’s Safety and EMC Newsletter, Supplement to Issue 47, October 1999, page 12, http://www.era.co.uk/Services/safety_and_emc.asp. This was reporting on a paper by Art Wall of the FCC presented at the IEEE’s International EMC Symposium in Seattle, August 1999)
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.
