Download EET422 EMC intro -banana skins 2008-2009 msw

EMC and COMPLIANCE ENGINEERING
1–
INTRODUCTION: BANANA SKINS
Banana Skin items briefly describe electrical/ electromagnetic interference based on
 individual’s experiences
 research
 official documents and reports
Interference incidents may relate to
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harmless or even amusing events
company downtime
financial burdens
injury or worse!
The banana skins could help identify interference problems that could affect your designs and
 help deal with them in advance as part of the normal design/development procedure.
 avoid the embarrassment and cost of trying to correct poor EMC design after products have
been shipped or systems installed.
designing EMC in from the first, saves time and cost, reduces customer returns and warranty
costs, and reduces the possibility of liability claims.
The examples and even the list in the book “The first 500 Banana Skins” probably represent just
the tip of a very large iceberg, and like the iceberg there are more EMI problems than listed.
(iceberg: the mass unseen below the water is 7 times the mass above water)
As electronic technologies continue to advance, and as more (and more complex) software is
used, interference problems can only increase and get worse. Don't slip up!
1. Fluorescent Lighting
1.i RF Emissions from Energy-Efficient Fluorescent Lighting
Conventional tungsten filament lamps are entirely without radio frequency emissions, except in
rare fault conditions. Energy efficient fluorescent lamp replacements, in support climate change
policy can however produce high levels of RF interference.
An electronic switching ballast is required for a fluorescent tube to operate at high frequency. The
typical operating frequency for a fluorescent tube electronic ballast is in the region of 20 kHz to
40 kHz and has the potential for radiofrequency interference in the same way as any switched
mode power supply.
Dimming is achieved by reducing the power applied to the fluorescent tube, however in order to
maintain the discharge the frequency of operation must increase as the light output level is
decreased. A typical electronic ballast that operates at 30 kHz for maximum light output will
supply the lamp at increasing frequencies up to 100 kHz for minimum light output.
Electronic ballasts can cause an increase in interference in long wave and medium wave bands to
portable radio receivers. Interference to AM services from dimming ballasts depends upon the
light output level of the unit.
EET422
EMC & Compliance Eng
BANANA SKINS
1
Prof R T Kennedy
2008-2009
1.ii Passive Ballasts
To fire the gases contained in a fluorescent lighting tube a ballast generates a powerful spark that
generates a strong electromagnetic wave across the radio spectrum. Nearby wires can pick up the
EM wave the same way an antenna works with a radio.
2. Consumer Electronics
Complex electronic circuitry is found in many devices used in the home and this creates a vast
interference potential that can be a source of interference or they can be susceptible to interference
from other sources of electromagnetic noise and experience reduced performance or react
unpredictably.
In addition to lighting products the hair dryer, electric drill, garage-door opener, computer, TV,
microprocessor-controlled appliance, cellphone or wireless remote control contribute to the
environmental electromagnetic noise.
2.i Thermostats Interfering with TV and Radio Reception
Thermostats switching on and off in central heating systems, refrigerators, freezers and other
automatic switching contacts can cause annoying interference to television and radio broadcast
reception. The offending thermostat may be in the house that is receiving the interference or some
distance away.
Interference is intermittent in nature and is most noticeable in analogue TV signals at 500 MHz to
850 MHz, and sometimes on FM radio at 88 MHz to108 MHz.
3. Mobile Phones
3.i ‘Twinkling’ Mobile Phones
Products are available containing one or more Light Emitting Diodes (LEDs) that 'twinkle'
(illuminate) if in close proximity to a mobile phone when the mobile is transmitting.
These devices have the potential to cause interference to the cellular networks and other users of
the radio spectrum, and the mobile phones themselves could experience loss of communications
range and the phone battery may need to be charged more frequently.
The basic problem is that the nonlinear LEDs become powered by the transmitted RF energy and
cause intermodulation and harmonic generation from the transmitted frequency. The radiated
energy contains frequencies that were not present without the LEDs and can disturb channels used
by other radio services.
3.ii Telecom Interference
The privately-owned Swedish telecommunications company, Tele2, wanted to avoid the risk of
operational breakdowns with its transmission special equipment that controls fiber optics and is
sensitive to interference from mobile phones. Tele2 use Mobile Phone Guard detectors in its
operations, to indicate the presence of mobile phones.
EET422
EMC & Compliance Eng
BANANA SKINS
2
Prof R T Kennedy
2008-2009
3.3 Banking
A bank’s Mobile Phone Guard-system alarm indicating the presence of a mobile in the middle of
the night could alert security to the presence of a mobile phone.
3.4 Fire Alarms
Mobile phones can trigger fire alarms resulting in unnecessary costs for fire services.
3.4.i Fire Rescue robots:
robots equipped with cameras and other sensors to enter dangerous environments such as
burning buildings ahead of human rescue teams
More than two-thirds of the 14 types of robot system involved in realistic training scenarios in a
large-scale USA trial lost contact with their operators due to radio interference from other
systems.
3.4.ii Anna Konda Robot
Anna Konda is a robotic fire hose moving like a snake. Developed in Norway by SINTEF, the
robot is 3 m long and weighs 70 kg and contains 20 water hydraulic motors that move the robotic
joints.
3.4.iii Altus II Robot Airplane
The Altus II robot airplane was originally designed for high-altitude, long-duration scientific
sampling missions, and is powered by a turbocharged piston engine. NASA has repurposed the
plane to help firefighters.
4. Medical
Personal digital assistants (PDAs) with wireless capabilities can affect active medical devices
when in close proximity; hence the ban on mobile phones in hospitals.
Doctors and Medical Technicians have been alerted to the possibility of interference from
intentional emitters but they are generally unaware that popular unintentional emitters can corrupt
their equipment (intravenous drips, infusion pumps, dialysis and ECG monitoring equipment).
4.i Patient Poisoning
Poisoning of a patient by an overdose of epinephrine prompted by the malfunction of an infusion
pump due to a cellular phone call received by a family member.
4.ii ECG susceptibility to Gameboy™
iPod Nano™ Cellphones
ECG machines are susceptible to emissions from
 unintentional emitters: Gameboy™ iPod
 intentional emitters: Cell Phone
EET422
EMC & Compliance Eng
BANANA SKINS
3
Prof R T Kennedy
2008-2009
Popular electronic devices can interfere with an electrocardiogram (ECG) and corrupt the
readings. Heartbeat changes ranging from 14 to 28 beats per minute were recorded due to EMI
from the devices (normal in resting mode is 70-75 beats per minute).
The results clearly illustrate the need for including both intentional and unintentional emitters in
the EMI control of hospitals, medical offices and home care environments.
5. Automobiles
Automakers perform electromagnetic compatibility testing of automobiles before their release to
customers however as the electronics content of vehicles has become greater the potential for
component or system failure caused by external sources of electromagnetic radiation has
increased.
5.i Airport Transmissions
Airport transmissions to aircraft can interfere with badly shielded car electronics due to the airport
radar systems that operate at frequencies from 1.2 GHz to 1.4 GHz and 2.7 GHz to 3.1 GHz. Cars
near runways have experienced power loss without warning lights or mechanical noises, braking
controls and airbag deployment have also been experienced.
5.ii Windscreen Wipers
Windscreen wipers {and rear-window heaters} when switched on can cause interference such that
it’s impossible to listen to the car radio.
5.iii Loss of Bus Braking
Electromagnetic Interference caused by illegally modified transceivers on trucks (in Japan) is
suspected of causing two accidents by disabling the braking system of commuter buses.
Mitsubishi Fuso Truck & Bus Corporation announced that two models of its buses were adversely
affected by high-powered EMI from short distance that resulted in the braking system not
functioning properly
5.iv Motorised Wheelchair
Taxi communications has been reported causing a motorized wheelchair to operate.
6. Aircraft and Passenger Electronic Devices (PEDs)
Radiated emissions from digital processing products (such as computers, portable video/DVD
players, etc.) occur at discrete frequencies – the harmonics of its internal ‘clock’ oscillators and
are more intense neared the product. If the emitted frequencies coincide with the frequencies used
by various navigational instruments, such as radar altimeters or the VOR (VHF Omni-directional
Ranging) beacon they could cause interference. The emissions could come directly from the
product’s printed circuit board or the devices mounted on it, but are mostly emitted by leads
attached to the product (such as headphone leads) acting as ‘unintentional antennas’.
Much of the electronic equipment for the avionics instruments is located under the floor of the
passenger compartment, which may not provide any shielding. Some seats in the passenger cabin
will therefore be closer to avionic equipment and antennas located outside the aircraft, and PEDS
used there will be more likely to cause interference.
EET422
EMC & Compliance Eng
BANANA SKINS
4
Prof R T Kennedy
2008-2009
Cellphones are an example of a Passenger Electronic Device (PED) that poses particular problems
for aircraft because of the relatively high powers of their RF emissions compared to other PEDs
(video walkman or laptop computer). The weak emissions from most PEDs are most likely to
cause interference when an emitted frequency coincides with a frequency already being used by
radio communications or navigation systems whereas the more powerful emissions from a
cellphone are capable of causing interference in electronic circuits.
Many aircraft flying use avionics navigation and communication systems designed well before
cellphones became commonplace, and as a result they may lack the necessary immunity.
6.i Trapped by Walkie-Talkie
Mobile phones on planes can lock the crew in the cockpit!
The problem was first reported in December 2003, when a Northwest Airlines mechanic
scrambled the electronic locks on the security doors of an Airbus A330 by using his walkie-talkie
in the vicinity of the flight deck.
Boeing discovered that up to June 2004 similar problems affected 1700 of its aircraft!
6.ii Baby Alarm Interferes with Aircraft Communications
A well-known make of wireless baby alarm was known to cause occasional interference to
aircraft communication when approaching UK airports. The problem was not however the
wireless technology in the baby alarm, it was the plug-top switched mode power supply. A faulty
batch of power supplies was shipped with the baby alarms, and although they function well
enough they emit on VHF radio channels used by National Air Traffic Services (NATS).
Most switch-mode power conversion technology involves power devices switching at between 50
kHz and 500 kHz. and with fast switching waveforms to maximise efficiency and minimise heat
losses. A 100 kHz switcher might give high levels of emissions at 100 kHz intervals up to 100
MHz.
Pilots approaching Luton airport in Great Britain recently picked up more than the monotone of
the air traffic controller over their radios. Authorities reportedly worked 12 hours to track down
the sound of a squealing infant that was picked up on the normal communications frequencies.
The noise was raced to a baby monitor in a home located near the airport.
6.iii Laptop Interferes with Aircraft Navigation
The pilot of a Brasilia EMB120 experienced interference with VHF navigation reception. A
passenger in seat XA was operating a laptop computer, and normal reception was restored when it
was switched it off.
6.1v Walkman Interferes with Critical Instruments
Following take-off and whilst climbing to cruising altitude a DC9’s radar altimeter gave an error
message (‘flagged’) and the traffic and ground proximity alert systems subsequently showed
‘FAIL’. The problem continued throughout the climb to 35,000 feet when it was discovered a
passenger that a Video Walkman was in use!
EET422
EMC & Compliance Eng
BANANA SKINS
5
Prof R T Kennedy
2008-2009
7. Power Systems
Electrical arcs and sparks create electromagnetic interference right throughout the radio spectrum.
Emissions tend to be at harmonics of the supply frequency with the amplitude modulated
randomly by the very same noise that one can hear them making and the natural resonant
frequencies of power lines acting as ‘accidental antennas’ result in higher levels of emissions at
some frequencies. Power system engineers often use radio receivers with very directional
antennas, sometimes when leaning out of the doors of helicopters, to help them locate bad
connections.
8. Military
8.i Patriot Missile System Interference
Military investigators are exploring the possibility that electromagnetic interference may have
been the cause of two friendly fire incidents during the Iraq war involving Patriot missiles that
resulted in downing of two allied fighters and the deaths of three airmen.
Investigators have ruled out either manual error by the operators of the Patriot missile batteries, or
mistakes by the missiles themselves, and are now focusing on whether the extremely close
positioning of multiple missile batteries on the ground resulted in elevated levels of EMI that
interfered with the systems’ high-powered radars.
9. ESD problems
An electrostatic discharge is a transfer of electrostatic charges between bodies at different
electrostatic potentials caused by direct contact or induced by an electrostatic field.
9.i Elevator Button
Static electricity is part of everyday life. At some time or another everybody gets a shock, for
example, by walking across a nylon carpet (= generation of static electricity) and then touching
the lift (elevator) button (= electrostatic discharge). Although annoying, this is not always
dangerous, but in certain areas a static spark can lead to disastrous events.
If you visit Japan don’t be surprised if you find an electrostatic discharge plate installed near
every lift button, with instructions to touch the plate to discharge any electrostatic charge before
pressing the button to call the lift.
9.ii Elevator Counterbalance
The counterweights used in elevator systems are huge blocks of metal that over time can build up
a strong magnetic charge as they move up and down the elevator shaft. A monitor against a wall
next to the elevator shaft might show strange intermittent distortions every time the elevator
counterweight passes up or down the shaft behind it. The movement of the elevator is variable
hence the distortions would appear random.
Controlled free-for-all
Although it may seem like something of a free-for-all, the electromagnetic environment is very
well controlled. If it were not, many of today’s technological advances – such as wireless internet
and mobile phones – would not be possible. The key to all this is electromagnetic compatibility
(EMC). This is the concept of ensuring that equipment does not cause or suffer excessive
interference to or from other equipment in the vicinity.
EET422
EMC & Compliance Eng
BANANA SKINS
6
Prof R T Kennedy
2008-2009