EMC for Product Designers

Meeting the European EMC Directive

Tim Williams

• Publisher: Newnes
• Year: 2014
• Print ISBN: 9780750612647
• eBook ISBN: 9781483183886
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

EMC for Product Designers: Meeting the European EMC Directives is a six-chapter text that considers the by-product of the co-existence of all kinds of radio services, called electromagnetic compatibility (EMC). This book discusses the solution to the damaging frequency interference of EMC and the problem of EMC to electronic equipment. The opening chapter considers the effect of adapting the EMC Directives to decrease the economic damage being caused by electromagnetic interference, as well as the analysis, definition, and compliance of EMC and EMC Directives. The next chapters deal with the measurement of EMC; RF emission testing; features of circuits, layout, and grounding; digital and analogue circuit design; and description of interfaces, filtering, and shielding. These topics are followed by discussion of the equipment for mains harmonic emission, the facilities and equipment for measuring RF susceptibility, and the transient susceptibility to ESD. The concluding chapters examine the use of performance criteria in measuring EMC. These chapters describe the features and application of the Fourier spectrum. The book can provide useful information to economists, engineers, radio technicians, students, and researchers.

Chapter 1

Introduction

Publisher Summary

Electromagnetic interference (EMI) is a serious and increasing form of environmental pollution. Its effects the range from minor annoyances because of crackles on broadcast reception, to potentially fatal accidents because of the corruption of safety-critical control systems. Various forms of EMI may cause electrical and electronic malfunctions, can prevent the proper use of the radio frequency spectrum, can ignite flammable or other hazardous atmospheres, and may even have a direct effect on human tissue. The threat of EMI is controlled by adopting the practices of electromagnetic compatibility (EMC). The term EMC has two complementary aspects: (1) it describes the ability of electrical and electronic systems to operate without interfering with other systems; (2) it also describes the ability of such systems to operate as intended within a specified electromagnetic environment. Effective EMC requires that the system is designed, manufactured and tested in regard to its predicted operational electromagnetic environment, that is, the totality of electromagnetic phenomena existing at its location.

1.1 What is EMC?

Electromagnetic interference (EMI) is a serious and increasing form of environmental pollution. Its effects range from minor annoyances due to crackles on broadcast reception, to potentially fatal accidents due to corruption of safety-critical control systems. Various forms of EMI may cause electrical and electronic malfunctions, can prevent the proper use of the radio frequency spectrum, can ignite flammable or other hazardous atmospheres, and may even have a direct effect on human tissue. As electronic systems penetrate more deeply into all aspects of society, so both the potential for interference effects and the potential for serious EMI-induced incidents will increase.

Some reported examples of electromagnetic incompatibility are:

• in Germany, a particular make of car would stall on a stretch of Autobahn opposite a high power broadcast transmitter. Eventually that section of the motorway had to be screened with wire mesh;

• on another type of car, the central door locking and electric sunroof would operate when the car’s mobile transmitter was used;

• new electronic push-button telephones installed near the Brookmans Park medium wave transmitter in North London were constantly afflicted with BBC radio programmes;

• mobile phones have been found to interfere with the readings of certain types of petrol pump meter;

• in America, police departments complained that coin-operated electronic games were causing harmful interference to their highway communications system;

• interference to aeronautical safety communications at a US airport was traced to an electronic cash register a mile away;

• the instrument panel of a well known airliner was said to carry the warning “ignore all instruments while transmitting HF”;

• electronic point-of-sale units used in shoe, clothing and optician shops (where thick carpets and nylon-coated assistants were common) would experience lock up, false data and uncontrolled drawer openings;

• when a piezo-electric cigarette lighter was lit near the cabinet of a car park barrier control box, the radiated pulse caused the barrier to open and drivers were able to park free of charge;

• lowering the pantographs of electric locomotives at British Rail’s Liverpool Street station interfered with newly installed signalling control equipment, causing the signals to “fail safe” to red;

• perhaps the most tragic example was the fate of HMS Sheffield in the Falklands war, when the missile warning radar that could have detected the Exocet missile which sank the ship was turned off because it interfered with the ship’s satellite communications system.

1.1.1 Compatibility between systems

The threat of EMI is controlled by adopting the practices of electromagnetic compatibility (EMC). This is defined [98] as “the ability of a device, unit of equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment”. The term EMC has two complementary aspects:

• it describes the ability of electrical and electronic systems to operate without interfering with other systems;

• it also describes the ability of such systems to operate as intended within a specified electromagnetic environment.

Thus it is closely related to the environment within which the system operates. Effective EMC requires that the system is designed, manufactured and tested with regard to its predicted operational electromagnetic environment: that is, the totality of electromagnetic phenomena existing at its location. Although the term “electromagnetic” tends to suggest an emphasis on high frequency field-related phenomena, in practice the definition of EMC encompasses all frequencies and coupling paths, from DC to 400GHz.

1.1.1.1 Subsystems within an installation

There are two approaches to EMC. In one case the nature of the installation determines the approach. EMC is especially problematic when several electronic or electrical systems are packed in to a very compact installation, such as on board aircraft, ships, satellites or other vehicles. In these cases susceptible systems may be located very close to powerful emitters and special precautions are needed to maintain compatibility. To do this cost-effectively calls for a detailed knowledge of both the installation circumstances and the characteristics of the emitters and their potential victims. Military, aerospace and vehicle EMC specifications have evolved to meet this need and are well established in their particular industry sectors.

Since this book is concerned with product design to meet the EMC Directive, we shall not be considering this “inter-system” aspect to any great extent. The subject has a long history and there are many textbooks dealing with it.

1.1.1.2 Equipment in isolation

The second approach assumes that the system will operate in an environment which is electromagnetically benign within certain limits, and that its proximity to other sensitive equipment will also be controlled within limits. So for example, most of the time a personal computer will not be operated in the vicinity of a high power radar transmitter, nor will it be put right next to a mobile radio receiving antenna. This allows a very broad set of limits to be placed on both the permissible emissions from a device and on the levels of disturbance within which the device should reasonably be expected to continue operating. These limits are directly related to the class of environment – domestic, commercial, industrial etc. – for which the device is marketed. The limits and the methods of demonstrating that they have been met form the basis for a set of standards, some aimed at emissions and some at immunity, for the EMC performance of any given product in isolation.

Note that compliance with such standards will not guarantee electromagnetic compatibility under all conditions. Rather, it establishes a probability (hopefully very high) that equipment will not cause interference nor be susceptible to it when operated under typical conditions. There will inevitably be some special circumstances under which proper EMC will not be attained – such as operating a computer within the near field of a powerful transmitter – and extra protection measures must be accepted.

1.1.2 The scope of EMC

The principal issues which are addressed by EMC are discussed below. The use of microprocessors in particular has stimulated the upsurge of interest in EMC. These devices are widely responsible for generating radio frequency interference and are themselves susceptible to many interfering phenomena. At the same time, the widespread replacement of metal chassis and cabinets by moulded plastic enclosures has drastically reduced the degree of protection offered to circuits by their housings.

1.1.2.1 Malfunction of systems

Solid state and especially processor-based contro...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Chapter 1: Introduction
• Chapter 2: Standards
• Chapter 3: EMC Measurements
• Chapter 4: Interference coupling mechanisms
• Chapter 5: Circuits, layout and grounding
• Chapter 6: Interfaces, filtering and shielding
• Appendix A: Design checklist
• Appendix B: EMC test and control plans
• Appendix C: Useful tables and formulae
• Appendix D: CAD for EMC
• Appendix E: The EC and EFTA countries
• Glossary
• Bibliography
• Index