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.
Five examples of EMI from Art Wall of the FCC. Items 79 through 83 below are taken from comments by Art Wall (Associate Chief of the Policy and Rules Division of the USA’s Federal Communications Commission) during an EMCTLA seminar on FCC requirements on the 18th May 2000.
79. Radio remote controlled garage door openers are short-range devices which use a part of the spectrum also used by the military. People got fed up with their garage doors opening every time a military jet flew over, so the manufacturers added coding to their signals.
80. Retail shops use anti-pilferage devices (the hoops that are to either side of their doors), which operate in the USA between 510 and 1705 kHz. The goods to be protected have a small label stuck on them that resonates at the appropriate frequency and disturbs the field produced by the hoops, allowing detection. It was found that heart pacemakers were susceptible to the anti-pilferage fields, so pacemaker manufacturers had to improve their designs to make them less susceptible.
81. There used to be a lot of problems with light dimmers interfering with AM broadcasts. The manufacturers added suppression to their products to satisfy customers and maintain sales levels (and not because of any regulations or standards).
82. A plywood laminating machine in Kentucky used 1.6 MW at 6 MHz to speed up the drying of the laminating glue. Operators removed a door which had a perforated metal screen so that they could see the inside of the machine better – subjecting themselves to hazardous levels of RF field. (Incidentally, Art claimed that more RF energy is used world-wide in manufacturing, for processing materials, than is used in broadcasting.)
83. Diathermic knives are electro-surgical units used by surgeons to cut tissue whilst sealing blood vessels using RF energy. Although they pass the FCC limits of 10 µV/m at 1 mile distance, they can generate 1000 V/m (1kV/m) at the surgeon’s head.
84. Mobile phones can cause interference to aircraft electronics
Evidence of interference to aircraft had been anecdotal, with many reports by pilots suggesting that mobile phones were the source of the problem. The UK’s Civil Aviation Authority (CAA) safety regulation group conducted tests on the ground on a Virgin Atlantic 747 and a British Airways 737.
The conclusion was that “transmissions made in the cabin from portable telephones can produce interference levels that exceed demonstrated susceptibility levels for aircraft equipment approved against earlier standards.” Faults attributed to mobiles included noise of the flight crew headsets and false triggering of warning signals, which could have a ‘cry wolf’ effect meaning crews might ignore a real warning.
(Electronics Weekly, May 31 2000, page 2, www.electronicsweekly.com)
85. CATV system re-radiates interference
In a recent radio interference case, a cable television (CATV) system was found to be causing radio interference. Upon investigation it was found that this was due to the CATV system picking up the interference from a buried cable in a parallel duct (and
re-radiating it).
(Peter Kerry, “EMC in the New Millennium” IEE Electronics and Communications Engineering Journal, April 2000, Page 47, www.theiet.org.)
86. Fluorescent lamps can interfere with mobile phones
People have learned to live with problems such as their mobile phone not working near the fluorescent light.
(Peter Kerry, “EMC in the New Millennium” IEE Electronics and Communications Engineering Journal, April 2000, Page 47, www.theiet.org.)
87. Spikes can cause insulation breakdown even at low levels
I was intrigued by the article by Prof. Yacamini et al. Relating to overvoltages at the terminals of downhole pumps supplied by variable speed drives (February 2000 PEJ, p.29). In the 19602 there was a series of faults on a group of cross-bonded 132 kV cables in the London area which were never satisfactorily explained, despite extensive on-site measurements using foils embedded in the joints, the last fault occurring shortly after the measuring instruments had been disconnected. These faults were located in joints at about one-quarter or half-way along the routes, successive faults occurring at the same joints, despite very careful repair by an experienced cable jointer. No serious overvoltages were measured.
Much investigation into surge voltages on cables and overhead lines has shown how steep-fronted waves can impose overvoltages, particularly at discontinuities such as exist at motor terminals. The continual overstressing of insulation by the spikes every half-cycle can lead to progressive failure, even if the overvoltage is not sufficient to cause immediate breakdown.
(H. J. Langley, Letters to the Editor, IEE Power Engineering Journal, April 2000, page 48, www.theiet.org)
88. Aluminium smelter’s underground cables interfere with power metering
Working for Ferranti in the mid 1970s, we had a problem with the power metering in a power station near Loch Lomond. Every now and again (once every few weeks) we got totally ridiculous readings. Neither the readings or their occurrence was predictable or consistent. We tried various earthing schemes and surge suppression, but then discovered that there was an aluminium smelter close by – and its huge power cables ran 3 feet underground the power station’s control room. The fields from these cables were powerful enough to magnetise wristwatches. The problem was solved by filtering the electronics of the kWh meters.
(From Dave Dunn, Senior Applications Engineer, IMI Norgren, Manchester.)
89. US$1.5 billion computer downtime caused by power quality problems
In 1994, studies revealed that the total cost of computer downtime to U.S. businesses had climbed to an all-time high of over $3 billion. “Power-related problems” was the number one cause of computer downtime, amounting to over 45% of occurrences and resulting in losses of $1.5 billion. Many of the power-related problems could be traced to the most basic element of the computer network: the wiring and grounding of the host building.
(From “Networking Equipment and Downtime: Caught in the Middle” by Tony DeSpirito, Electronic Design magazine, April 1997, pp 42-48. We wonder what the 1999 figures were.)
90. xDSL technologies could increase radio noise floor
Recent developments in broadband data access methods over existing telephone or mains wiring will cause unintentional RF emissions which may adversely affect the established radio noise floor.
(From report AY3525 produced by York EMC Services for the Radiocommunications Agency on the effects of ADSL, VDSL, and power line technology such as HomeLAN. This and many other interesting documents may be found by hunting around the (legacy) Radiocommunication Agency’s website hosted on Ofcom’s site at: http://www.ofcom.org.uk/static/archive/ra/rahome.htm.)
91. Electromagnetic ‘bombs’ – the perfect weapons?
It sounds like the perfect weapon. Without fracturing a single brick or spilling a drop of blood, it could bring a city to its knees. The few scientists who are prepared to talk about it speak of a sea change in how wars will be fought. Even in peacetime, the same technology could bring mayhem to our daily lives. This weapon is so simple to make, it wouldn’t take a criminal genius to put one together and wreak havoc. Some believe attacks have started already, but because the weapon leaves no trace it’s a suspicion that’s hard to prove.
The perfect weapon is the electromagnetic bomb. The idea behind it is simple. Produce a high-power flash of radio waves or microwaves and it will fry any circuitry it hits. At lower powers, the effects are more subtle: it can throw electronic systems into chaos, often making them crash. In an age when electronics finds its way into everything bar food and bicycles, it is a sure way to cause mass disruption.
(From “Just a Normal Town…” the cover story in New Scientist’s July 1st 200 issue, pp 20-24. The article goes on to quote a researcher who claims that modern computers and their systems are easier to crash with EM weapons than older models.)
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.
