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.
54. TETRA radio system interferes with car keyfobs
Ken Yard of the Radiocommunication Agency described the problems it had recently faced with the introduction of the TETRA services to the UK. Interference to car alarms and immobilisers had caused over 12,000 call-outs on roadside recovery services in the last year alone. He said that the problem was partly caused by TETRA base stations but the main cause was poor quality receivers (in the car system) with insufficient rejection of out-of-band transmitters. He hoped that this situation could be avoided with the new 868MHz band for car keyfobs.
(From the article “Compromise on 868 MHz”, page 14 of Low Power Radio Association News May 1999, describing a meeting on March 23rd 1999, www.lpra.org/news/index.php. If your present car keyfob uses 418MHz, you could easily suffer from TETRA during the coming months and afterwards. If it uses 433MHz you may escape – if your receiver is of good quality.)
55. New kidney dialysis machines very susceptible to power quality issues
Power quality is especially critical in hospitals, where life-sustaining processes demand clean reliable electrical supplies. This was recently highlighted at Glan Clwyd Hospital in North Wales where a problem became apparent on the renal dialysis unit during the testing of emergency generators. The switch from mains power to generator power was causing the newer, computer-controlled dialysis machines to close down and generate an alarm. This caused distress to patients and problems for staff who needed to reset several machines quickly before their blood began to coagulate.
Resets were generally successful, though occasionally a unit would not respond so a patient would need to be moved onto a spare machine. The problem was solved with uninterruptible power supplies to provide continuity of operation at the hospital during generator testing. Ten 2.5kVA UPSs are now used in the dialysis unit and one on a treadmill in the cardiovascular unit to safeguard patients from injury should power failure cause the treadmill to stop suddenly.
(Extracted from page 121 of IEE Review, May 1999, www.theiet.org. Take care: not all UPSs appear to be as reliable as we might wish!)
56. Aircraft carrier interferes with garage doors in Hobart, Tasmania
Hobart in Tasmania suffered an unusual blight earlier this month. Residents all over town found themselves trapped in their garages when the remote controls that operate the garage doors suddenly failed to function. Roll-a-door companies were flooded with calls from angry garage owners and were at first completely nonplussed by the problem.
Then the explanation emerged: the aircraft carrier USS Carl Vinson had just cruised majestically into the town’s docks, equipped with navigational radar employing the same frequency as the remote controls for the town’s garage doors. According to the local newspaper The Advocate, an apologetic Lieutenant Dave Waterman, the ship’s public affairs officer, said that the problem would only occur when the ship was arriving and leaving.
(New Scientist, 24th April 1999, page 100, www.newscientist.com.)
57. Screening cable helps engine run smoothly
A control cable to the engine management system of a motor car was damaged, and repaired with a terminal block. But the engine ran rough. Wrapping the repair all over with EMC copper tape (conductive adhesive) made the engine run smooth again.
(Arthur Harrup, Chief Engineer, William Tatham Ltd, Rochdale, 16th Feb 1999)
58. Three examples of interference from UK Trading Standards
Some robotic toys interfere with TVs. Some touch-controlled lamps interfere with long-wave radio, even when their light is turned off. An illuminated (battery powered) yo-yo interfered with a Porsche.
(Jim Rackham, Principal Trading Standards Officer, 23rd February 1999)
59. Chart recorder runs at double speed on Saturdays
During the 1980s we used a French make of chart recorder, which often ran at double speed on Saturdays. This turned out to be due to the increased numbers of TVs and radios in use on a Saturday, whose power supplies injected second harmonic currents into the mains supply. The synchronous motors in the chart recorders were able to latch up to the resulting 100Hz voltage distortion, and consequently ran twice as fast.
(Stan Lomax of RTM Group Ltd, Altincham, March 99)
60. Cable TV interferes with aircraft navigation and radio comms
The German economics ministry is considering restricting cable TV networks because of mounting concerns about their possible impact on air traffic safety. Frank Krueger, an economics ministry spokesman, says that the possibility that interference from household cabling will interfere with aircraft navigation and ground communication systems has prompted the government to propose regulations. “It is possible that, in individual cases, certain stations will have to be closed down after a review of the dangers posed by their frequencies.” said Krueger. According to the European Cable Communications Association, the discussion about cable broadcasting and air traffic safety is not confined to Germany.
Similar safety issues are currently being discussed by the Benelux states and the Nordic countries. The UK Radiocommunications Agency says that, as far as it is concerned, the only debate surrounding clashing transmissions relates to avoiding potential interference with other European broadcasters. (From the lead article on page 1 of Electronics Times, April 1999, www.eetuk.com.)
EMC consultant Diethard Hansen has written: “In spite of using coaxial cables in the TV distribution systems there is a lot of shield leakage, based on technical imperfections and ageing. Catastrophic emissions in the aeronautical security bands are jamming Germany.”
(From: “Megabits per second on 50Hz power lines”, Diethard Hansen, IEEE EMC Society Newsletter, January 2001, http://www.ewh.ieee.org/soc/emcs.)
61. Millennium Wheel installation delayed by interference from microwave comms
The Millennium Wheel on the Embankment in London was supposed to be lifted on September 12th 1999. One of the delays was caused by an EMC problem. The Daily Telegraph, Saturday September 11th 1999 (page 6) said: “The operation had fallen victim of the publicity that it had generated because the satellite dishes on the fleet of television vans covering the event interfered with the laser signals monitoring the cables pulling the wheel upright.”
The Guardian, September 11th 1999 said: “Work was initially delayed when satellite dishes on media vehicles interfered with electronic equipment used to monitor the lift, and further hampered when a stabilising cable had to be re-routed.”
The Engineer, 17th September 1999 (page 2) chose to ignore the EMC issues altogether and focussed instead on the problems with the stabilising cable and its wheels, brackets, and lateral pins.
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.
