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.
68. Plane crash nearly caused by portable CD player
In early February a DC-10 was entering its final landing approach at New York’s JFK airport when it suddenly banked sharply to the left, nearly causing a crash. NASA and FAA experts concluded that the plane’s flight controls were upset when someone in first class turned on his portable CD player. Apparently, newer planes are more heavily computerised and vulnerable to interference. Of particular concern is interference to frequencies used by the VOR (Visual Omni-Range) network, because flight control systems use these navigation beacons for autopilot operation and instrument landing.
(Taken from Compliance Engineering Spring 1993, page 92, itself commenting on an article in Time, Feb 22, 1993, www.ce-mag.com.)
69. Use of CD players banned by some airlines
With reference to Lufthansa’s “weird” ban on CD-ROM drives (Letters, 28 March, p.64), the airline is probably extending an existing ban on personal CD players to computers. In the only documented case of interference from personal electronic equipment that I am aware of, an early CD player jammed the instrument landing system on an airliner in the mid-1980s. Because CD players are optical devices, some of the cheaper models did not include any shielding against radio-frequency (RF) interference from the logic devices in their controllers and were therefore quite noisy in the RF bands. (Allan Gibson)
In the feature “Do portable electronics endanger flight?” in IEEE Spectrum (September 1996), the reason given for the ban on equipment containing CD players is that “portable compact disc players have an internal clock of 28MHz”, which “produces harmonics at 56, 84, and 112MHz – and 112MHz is a VHF aircraft navigation channel” for aircraft. (Kevin Connolly)
(These two items both appeared on the same page (56) in New Scientist 25 April 1998, www.mewscientist.com.)
70. Airline check-in desks ban mobile phones
Earlier this year, at Paddington railway station in London, I saw this sign on the door of the airlines’ check-in area (operated by BA, American Airlines and British Midland) for customers travelling by rail (Heathrow Express) to the airport: “Please do not use mobile telephones in the area as it interferes with the equipment.” (I’d love to know more. I’d speculated — wild guess! — that it was US-built check-in equipment that had not been tested for immunity to GSM phones…).
(from Glyn Garside, Director, Engineering Services, Adept Technology Inc., San Jose, California.)
Reply from Jim Rackham of Warwickshire Trading Standards (one of Trading Standards’ four EMC Specialists): If the use of a mobile phone is likely to cause any risk to Health and Safety, then the business would have a duty to warn anyone entering the premises not to use it. On a more general note as shops are usually on ‘private property’ then the owners would have the right to lay down reasonable conditions on what actions were acceptable within the premises. If in certain circumstances mobile phones could interfere with equipment then it might be reasonable for them not to be used – some equipment could still predate the regulations. However, as installations should comply with the protection requirements and if it is reasonable that mobile phones could be used in the vicinity of CE marked equipment, that equipment should be reasonably immune from their interference.
(From Keith Armstrong of Cherry Clough Consultants): An EMC specialist from a major IT company told me that their computer systems only achieve 1V/m immunity although built from equipment that individually meets 3V/m. 1V/m is equivalent to a GSM hand-portable at around 5 metres, in a strong signal area without reflections from nearby metal structures. In weak signal areas (or standby mode) with no reflections, this would instead be around 7 metres. For this reason they generally ban the use of cellphones and walkie-talkies in the computer rooms they build.
71. Robot Wars interference problems
The robots used on the Robot Wars TV show apparently suffer terribly from interference. They are radio-controlled (R/C), often using hobbyist gear. Here are some comments extracted from the “Robot Wars: Tip Swap: weapons idea centre”, soon after a robot ran amok and injured someone. The ‘failsafes’ they are talking about are supposed to shut down all robot activity except when valid R/C is established. (From Bill Armstrong of PC Help.)
(Saturday, January 8, 2000) … Despite what the Reg’s state hardly any of the failsafes on the robots were in a working condition. Remember that an awful lot of robots were suffering from radio interference problems, this I find odd, as personally all the robots that have been built here in my workshops … have never had a problem. … As for the question of failsafes, most of them are definitely not failsafes and don’t work. …one common problem on lots of commercial units is because the unit tries to detect an output pulse from the receiver, this works well in a normal environment but in studio conditions this is not the case, interference can (and will) cause ‘spikes’ on the output and it will assume that is the correct signal and fail to shut it down. Some of the more expensive models actually measure the pulse width and if it falls outside the normal pulse width they then fail safe. …(Sunday, January 9) In my opinion, the biggest safety problem is with the failsafe system. Having run 27MHz R/C cars for years, I am used to how easily control is lost even in friendly RFI/EMI conditions. Most people use commercial RC aircraft failsafes (the little orange thing), which is fine when you are flying a plane outside, in friendly EMI conditions, and signal is completely lost (e.g. transmitter battery fails)…They are not meant to deal with conditions of huge RFI/EMI interference present at Robot Wars – indeed our electronics guy laughed at the simplicity of the circuit when he took apart the failsafe we bought. It would bypass the majority of interference, and render the robot uncontrollable (and unpredictable). …Also I have to suspect the method of testing at the auditions. According to … the test is simply to switch off the transmitter – and if nothing happens, then the robot passes. But aren’t the auditions held in a quiet warehouse, with friendly RF (i.e. little interference), making them totally unrealistic? …(Sunday, January 9) …the only problem is that a failsafe on some robots may be irrelevant. There are plenty of home-made speed controllers out there with home-rolled micros running the show that could go rogue regardless of whether they have an input at all. Even if PCM is used (for the R/C), there are some being controlled with relays and home made interface circuits that are not too stable irrespective of input. It certainly needs a more technical look at the way people are controlling their motors and weapons…(Monday, January 10) …The lack of failsafes on weapons channels scares me – I’ve been near a couple of robots when the weapons channel has fired for no reason… (Wednesday, January 12) …Just a quick note on the orange failsafes mentioned further back on this thread, I’ve done some investigating, they come in two varieties. The FS-1 (the one with undervoltage monitoring) works beautifully, the other, the FS-2 is not suitable for use on robots. As mentioned further back, it lets through most interference. There is no external difference in appearance between the two units, other than the number printed on the label…(Wednesday January 12)…The problem we have is when the receiver loses its signal, it holds its last state for 1.5 seconds before it fails safe, i.e. the robot does the last thing it was doing for 1.5 seconds after its signal was lost.
72. Trams fitted with inverter drives interfere with hospital equipment along their route
The Helsinki City Transport (HKL) rolling stock is ageing fast. The most recent trams were built 20 years ago. Hitherto, all auxiliary equipment, such as ventilator fan motors were DC and the maintenance of these units was becoming something of a nightmare. Spares were costly and it was a very labour intensive process keeping them in service.
In each HKL tram there were six ventilation fans with DC motors cooling the passenger compartment, brake resistor, and traction motor. The thinking was that one big inverter supplying six AC motors was going to be cheaper than several smaller inverters supplying one motor each, so a 15kW unit was mounted in the main electrical panel of one of the trams. The existing cabling was retained because of cost considerations and this connected the various motors in parallel. EMC problems very quickly surfaced. Not only was the vehicle’s own radio system badly affected, but –crucially – third party electrical equipment also suffered interference, including that of a hospital on the tram’s route.
The problem was solved in the end by siting individual inverters close to the motors they controlled.
(From an article by Les Hunt in dpa Magazine, March 99, Drives Supplement page 29, www.dpaonthenet.net.)
73. Solar storms black out Canada in 1989
Every 11 years violent storms on the surface of the Sun cause massive amounts of energy – in the form of protons and electrons – to be thrown out into space. After a few days, this energy reaches Earth, interferes with the planet’s magnetic field and generates huge currents – particularly in the polar regions. These induced currents can subsequently induce massive surges in (power distribution) transmission lines, damaging transformers and causing high-amplitude harmonics. In the space of just 2 minutes in March 1989, six million people in Quebec, Canada, suffered a complete blackout because of a severe storm from space. In the UK the problems were less severe, but some were experienced.
(From Electrical Review, 20 July 1999, www.electricalreview.co.uk.)
The first space weather prediction system for electric power grids has been completed in the UK. The main problem for networks is losing control of voltage regulation, but with the new system certain regions can be highlighted as being particularly at risk and necessary precautions taken. So far in Solar Cycle 23 – the name for the current bout of activity – longer-term forecasts have given two clear warnings of potential disruption.
(From Electrical Review, Vol. 233 No 5 p 10, www.electricalreview.co.uk.)
74. Walkie-talkie interferes with ship steering, causes minor collision
There was a minor collision between a supply vessel servicing a semi-submersible offshore oil and gas installation. The vessel experienced a sudden power increase brought on because of interaction between radio signals from a portable VHF radio and the joystick control. This caused the joystick to execute commands not requested by the operator and resulted in contact between the vessel and the installation. The interaction caused minor damage (though it could have been far worse).
The incident occurred outside UK waters and was reported in a safety notice issued by an offshore operator. The safety notice was seen by an HSE inspector on a bulletin board on an offshore installation, dated 30 September 1999, which referred to the incident as having happened ‘recently’.
(From Simon Brown of the HSE, 14th and 15th February 2000.)
75. EMI problems and shipping
“NOTING the growing number of problems experienced with equipment that is susceptible to electromagnetic interference, which can result in dangerous situations…”
(Extracted from IMO Resolution A.813 (19):1995, “General Requirements for EMC for all Electrical and Electronic Ship‘s Equipment”)
76. Class D amplifier launch delayed by EM emissions
National Semiconductor plans to begin shipments of Class-D audio amplifier ICs before Christmas. The delay of the launch, which was first reported by NE in June this year, has been attributed to the design of the development board. Class-D amplifiers, while efficient, require careful layout to prevent EMC problems from the internal 50kHz oscillator.
(From New Electronics magazine, 14th December 1999, p 8, www.newelectronics.co.uk.)
77. Faulty central heating thermostats can interfere with radio and TV
Faulty thermostats can cause annoying interference to radio and TV broadcast reception. They cause short bursts of interference that may recur at intervals. Thermostats in central heating systems, fridges or freezers switching on and off have all caused interference problems. Our experience shows that the thermostat found in the central heating system is most often the source of the interference. Often the offending thermostat is found in the house receiving the interference, although the agency is aware of cases where the source of the interference was some distance away.
(From the Radiocommunication Agency’s publication RA 272 (Rev3) May 1999, www.ofcom.org.uk.)
78. EMI dangers of using mobile phone handsets while driving
Millions of motorists are risking their lives every time they use mobile phones while driving. New research has revealed (that) signals sent from mobiles can disrupt sophisticated electronic control units fitted in most modern cars. And it is feared that in some instances this could scupper vehicles’ braking and engine systems. One major manufacturer has also warned that the transmissions from mobiles could trigger air bags fitted to the car.
The alert over making calls in the car was given by the AA following research into the problem. The motoring organisation is now urging drivers to ensure they stop their cars before making any calls. Last night an AA spokesman said: “It is the same as aircraft operators asking people to switch off their mobiles while on a plane. The mobile is transmitting all the time and there is the possibility of interference with electronics in the car. You might get a misfire or your braking system might not operate. The answer is to only use the phone when you are stationary or to install an outside aerial.”
(From an article by Bill Caven in the Daily Record, 10th Jan 2000, p 23. Also see an article by Ian Fletcher in the Sunday Mirror 9th Jan 2000, p 9. Both were sent in by Dai Davis, then Head of IT, Communications and New Media Group at Nabarro Nathanson, now with Brooke North LLP, Solicitors.)
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.