eet422 emc intro-banana skins 2011-2012 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

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 Prof R T Kennedy BANANA SKINS 2011-2012

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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.


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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


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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.


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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!


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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-allAlthough 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.


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eet422 emc intro-banana skins 2011-2012 msw

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