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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: Wiley - IEEE
- Sprache: Englisch
Applies basic field behavior in circuit design and demonstrates how it relates to grounding and shielding requirements and techniques in circuit design This book connects the fundamentals of electromagnetic theory to the problems of interference in all types of electronic design. The text covers power distribution in facilities, mixing of analog and digital circuitry, circuit board layout at high clock rates, and meeting radiation and susceptibility standards. The author examines the grounding and shielding requirements and techniques in circuit design and applies basic physics to circuit behavior. The sixth edition of this book has been updated with new material added throughout the chapters where appropriate. The presentation of the book has also been rearranged in order to reflect the current trends in the field. Grounding and Shielding: Circuits and Interference, Sixth Edition: * Includes new material on vias and field control, capacitors as transmission lines, first energy sources, and high speed designs using boards with only two layers * Demonstrates how circuit geometry controls performance from dc to gigahertz * Examines the use of multi-shielded transformers in clean-power installations * Provides effective techniques for handling noise problems in analog and digital circuits * Discusses how to use conductor geometry to improve performance, limit radiation, and reduce susceptibility to all types of hardware and systems Grounding and Shielding: Circuits and Interference, Sixth Edition is an updated guide for circuit design engineers and technicians. It will also serve as a reference for engineers in the semiconductor device industry.
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Veröffentlichungsjahr: 2016
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Table of Contents
Title Page
Copyright
Preface
A HISTORICAL PERSPECTIVE INTO GROUNDING AND SHIELDING
1 VOLTAGE AND CAPACITORS
1.1 INTRODUCTION
1.2 CHARGES AND ELECTRONS
1.3 THE ELECTRIC FORCE FIELD
1.4 FIELD REPRESENTATIONS
1.5 THE DEFINITION OF VOLTAGE
1.6 EQUIPOTENTIAL SURFACES
1.7 THE FORCE FIELD OR E FIELD BETWEEN TWO CONDUCTING PLATES
1.8 ELECTRIC FIELD PATTERNS
1.9 THE ENERGY STORED IN AN ELECTRIC FIELD
1.10 DIELECTRICS
1.11 THE D FIELD
1.12 CAPACITANCE
1.13 MUTUAL CAPACITANCE
1.14 DISPLACEMENT CURRENT
1.15 ENERGY STORED IN A CAPACITOR
1.16 FORCES IN THE ELECTRIC FIELD
1.17 CAPACITORS
1.18 DIELECTRIC ABSORPTION
1.19 RESISTANCE OF PLANE CONDUCTORS
2 MAGNETICS
2.1 MAGNETIC FIELDS
2.2 AMPERE'S LAW
2.3 THE SOLENOID
2.4 FARADAY'S LAW AND THE INDUCTION FIELD
2.5 THE DEFINITION OF INDUCTANCE
2.6 THE ENERGY STORED IN AN INDUCTANCE
2.7 MAGNETIC FIELD ENERGY IN SPACE
2.8 ELECTRON DRIFT
2.9 THE MAGNETIC CIRCUIT
2.10 A MAGNETIC CIRCUIT WITH A GAP
2.11 SMALL INDUCTORS
2.12 SELF- AND MUTUAL INDUCTANCE
2.13 TRANSFORMER ACTION
2.14 HYSTERESIS AND PERMEABILITY
2.15 EDDY CURRENTS
3 DIGITAL ELECTRONICS
3.1 INTRODUCTION
3.2 THE TRANSPORT OF ELECTRICAL ENERGY
3.3 TRANSMISSION LINES – INTRODUCTION
3.4 TRANSMISSION LINE OPERATIONS
3.5 TRANSMISSION LINE FIELD PATTERNS
3.6 A TERMINATED TRANSMISSION LINE
3.7 THE UNTERMINATED TRANSMISSION LINE
3.8 A SHORT CIRCUIT TERMINATION
3.9 THE REAL WORLD
3.10 SINE WAVES VERSUS STEP VOLTAGES
3.11 A BIT OF HISTORY
3.12 IDEAL CONDITIONS
3.13 REFLECTION AND TRANSMISSION COEFFICIENTS
3.14 TAKING ENERGY FROM AN IDEAL ENERGY SOURCE
3.15 A CAPACITOR AS A TRANSMISSION LINE
3.16 DECOUPLING CAPACITORS AND NATURAL FREQUENCIES
3.17 PRINTED CIRCUIT BOARDS
3.18 TWO-LAYER LOGIC BOARDS
3.19 VIAS
3.20 THE TERMINATION OF TRANSMISSION LINES
3.21 ENERGY IN THE GROUND/POWER PLANE CAPACITANCE
3.22 POYNTING'S VECTOR
3.23 SKIN EFFECT
3.24 MEASUREMENT PROBLEMS: GROUND BOUNCE
3.25 BALANCED TRANSMISSION
3.26 RIBBON CABLE AND CONNECTORS
3.27 INTERFACING ANALOG AND DIGITAL CIRCUITS
4 ANALOG CIRCUITS
4.1 INTRODUCTION
4.2 INSTRUMENTATION
4.3 HISTORY
4.4 THE BASIC SHIELD ENCLOSURE
4.5 THE ENCLOSURE AND UTILITY POWER
4.6 THE TWO-GROUND PROBLEM
4.7 INSTRUMENTATION AND THE TWO-GROUND PROBLEM
4.8 STRAIN-GAUGE INSTRUMENTATION
4.9 THE FLOATING STRAIN GAUGE
4.10 THE THERMOCOUPLE
4.11 THE BASIC LOW-GAIN DIFFERENTIAL AMPLIFIER (FORWARD REFERENCING AMPLIFER)
4.12 SHIELDING IN POWER TRANSFORMERS
4.13 CALIBRATION AND INTERFERENCE
4.14 The Guard Shield Above 100 kHz
4.15 SIGNAL FLOW PATHS IN ANALOG CIRCUITS
4.16 PARALLEL ACTIVE COMPONENTS
4.17 FEEDBACK STABILITY – INTRODUCTION
4.18 FEEDBACK THEORY
4.19 OUTPUT LOADS AND CIRCUIT STABILITY
4.20 FEEDBACK AROUND A POWER STAGE
4.21 CONSTANT CURRENT LOOPS
4.22 FILTERS AND ALIASING ERRORS
4.23 ISOLATION AND Dc-TO-DC CONVERTERS
4.24 CHARGE CONVERTER BASICS
4.25 DC POWER SUPPLIES
4.26 GUARD RINGS
4.27 THERMOCOUPLE EFFECTS
4.28 SOME THOUGHTS ON INSTRUMENTATION
5 UTILITY POWER AND FACILITY GROUNDING
5.1 INTRODUCTION
5.2 HISTORY
5.3 SEMANTICS
5.4 UTILITY POWER
5.5 THE EARTH AS A CONDUCTOR
5.6 THE
NEUTRAL
CONNECTION TO EARTH
5.7 GROUND POTENTIAL DIFFERENCES
5.8 FIELD COUPLING TO POWER CONDUCTORS
5.9
NEUTRAL
CONDUCTORS
5.10
k
Factor in Transformers
5.11 POWER FACTOR CORRECTION
5.12 UNGROUNDED POWER
5.13 A REQUEST FOR POWER
5.14 EARTH POWER CURRENTS
5.15 LINE FILTERS
5.16 ISOLATED GROUNDS
5.17 FACILITY GROUNDS – SOME MORE HISTORY
5.18 GROUND PLANES IN FACILITIES
5.19 OTHER GROUND PLANES
5.20 GROUND AT REMOTE SITES
5.21 EXTENDING GROUND PLANES
5.22 LIGHTNING
5.23 LIGHTNING AND FACILITIES
5.24 LIGHTNING PROTECTION FOR BOATS AND SHIPS
5.25 GROUNDING OF BOATS AND SHIPS AT DOCK
5.26 AIRCRAFT GROUNDING (FUELING)
5.27 GROUND FAULT INTERRUPTION (GFI)
5.28 ISOLATION TRANSFORMERS
5.29 GROUNDING AND THE PACIFIC INTERTIE
5.30 SOLAR WIND
6 RADIATION
6.1 HANDLING RADIATION AND SUSCEPTIBILITY
6.2 RADIATION
6.3 SINE WAVES AND TRANSMISSION LINES
6.4 APPROXIMATIONS FOR PULSES AND SQUARE WAVES
6.5 RADIATION FROM COMPONENTS
6.6 THE DIPOLE ANTENNA
6.7 WAVE IMPEDANCE
6.8 FIELD STRENGTH AND ANTENNA GAIN
6.9 RADIATION FROM LOOPS
6.10 E-FIELD COUPLING TO A LOOP
6.11 RADIATION FROM PRINTED CIRCUIT BOARDS
6.12 THE SNIFFER AND THE ANTENNA
6.13 MICROWAVE OVENS
7 SHIELDING FROM RADIATION
7.1 CABLES WITH SHIELDS
7.2 LOW-NOISE CABLES
7.3 TRANSFER IMPEDANCE
7.4 WAVEGUIDES
7.5 ELECTROMAGNETIC FIELDS OVER A GROUND PLANE
7.6 FIELDS AND CONDUCTORS
7.7 CONDUCTIVE ENCLOSURES – INTRODUCTION
7.8 COUPLING THROUGH ENCLOSURE WALLS BY AN INDUCTION FIELD
7.9 REFLECTION AND ABSORPTION OF FIELD ENERGY AT A CONDUCTING SURFACE
7.10 INDEPENDENT APERTURES
7.11 DEPENDENT APERTURES
7.12 HONEYCOMBS
7.13 SUMMING FIELD PENETRATIONS
7.14 POWER LINE FILTERS
7.15 BACKSHELL CONNECTORS
7.16 H-FIELD COUPLING
7.17 GASKETS
7.18 FINGER STOCK
7.19 GLASS APERTURES
7.20 GUARDING LARGE TRANSISTORS
7.21 MOUNTING COMPONENTS ON SURFACES
7.22 ZAPPERS
7.23 SHIELDED AND SCREEN ROOMS
APPENDIX A
Further Reading
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1
Figure 1.1 The force field lines around a positively charged conducting sphere
Figure 1.2 Equipotential surfaces around a charged sphere
Figure 1.3 The force field between two conducting plates with equal and opposite charges and a spacing distance
h
Figure 1.4 The electric field pattern of a circuit trace over a ground plane
Figure 1.5 The electric field pattern around two traces over a ground plane
Figure 1.6 Field configurations around a shielded conductor
Figure 1.7 The electric field pattern in the presence of a dielectric
Figure 1.8 The mutual capacitances between several traces on a ground plane
Figure 1.9 A capacitor driven from a constant current source
Figure 1.10 A typical wrap and foil capacitor
Chapter 2
Figure 2.1 The H field around a current-carrying conductor
Figure 2.2 The H field around a solenoid
Figure 2.3 A voltage induced into a moving coil
Figure 2.4 The inductance of round copper conductors
Figure 2.5 A coil wound on a toroidal core of magnetic material
Figure 2.6 A magnetic circuit with an air gap
Figure 2.7 The flux pattern for a square wave voltage applied to a transformer coil
Figure 2.8 A core with two coils that form a simple transformer. (a) Assembly, (b) symbol, and (c) winding arrangement
Figure 2.9 The equivalent circuit of a transformer
Figure 2.10 Typical hysteresis curves
Figure 2.11 Ferrite cup-core construction
Chapter 3
Figure 3.1 The electric and magnetic fields associated with a flashlight
Figure 3.2 A battery, a switch, and a transmission line
Figure 3.3 (a, b) The E and H field patterns around transmission lines
Figure 3.4 The wave associated with a transmission line terminated in its characteristic impedance
Figure 3.5 The voltage waveforms on an ideal open circuit transmission line for a step voltage
Figure 3.6 (a, b) The staircase current pattern for a short circuit termination of a transmission line
Figure 3.7 Waves that supply energy to a resistor over an impedance matching transmission line
Figure 3.8 The voltage at a termination resistor when there is a mismatch of impedances
Figure 3.9 A via geometry
Figure 3.10 Rise times and the reflections from an unterminated transmission line
Figure 3.11 Poynting's vector for parallel conductors carrying power
Figure 3.12 The termination of a balanced transmission line on a circuit board
Chapter 4
Figure 4.1 Parasitic capacitances in a simple circuit. (a) Field lines in a circuit, (b) mutual capacitance diagram, and (c) circuit representation
Figure 4.2 Grounding the shield to limit feedback
Figure 4.3 (a) The problem of bringing one lead out of a shielded region. Unwanted current circulates in the signal lead 2. (b) The E field circulates current in the shield, not in the signal conductor.
Figure 4.4 A power transformer added to the circuit enclosure
Figure 4.5 The two-circuit enclosures used to transport signals between grounds
Figure 4.6 The basic strain-gauge circuit
Figure 4.7 The low-gain differential amplifier applied to the two-ground problem
Figure 4.8 The basic low-gain differential amplifier
Figure 4.9 The single shield applied to a power transformer
Figure 4.10 The RC bypass on the input guard shield
Figure 4.11 Adding suppression resistors to parallel circuit elements
Figure 4.12 The basic feedback circuit
Figure 4.13 An LR-stabilizing network
Figure 4.14 Feedback around a power stage
Figure 4.15 Using a second transformer to isolate switching noise
Figure 4.16 A basic charge amplifier
Figure 4.17 The resistor feedback arrangement to control the low-frequency response
Chapter 5
Figure 5.1 Normal-mode and common-mode field coupling
Figure 5.2 The coupling in a transformer resulting from neutral voltage drop
Figure 5.3 Filter current flowing in signal interconnections
Figure 5.4 Typical ground plane in an electronic installation
Figure 5.5 A single-phase isolation transformer. (a) One shield, (b) two shields, and (c) three shields
Chapter 6
Figure 6.1 The harmonics that make up a square wave
Figure 6.2 The harmonics of a square wave plotted on logarithmic scales
Figure 6.3 The harmonics that make up a square wave with a finite rise time
Figure 6.4 The harmonics of a square with finite rise time plotted on logarithmic scales
Figure 6.5 The frequency spectrum for repetitive short pulses
Figure 6.6 The frequency spectrum of a single pulse with a finite rise time
Figure 6.7 A half-dipole antenna
Figure 6.8 The radiated field from a conducting loop
Figure 6.9 Electric field coupling to a pair of conductors
Figure 6.10 A sniffer and a test antenna
Chapter 7
Figure 7.1 (a, b) Characteristic impedance of a coaxial geometry
Figure 7.2 The characteristic impedance of parallel conductors
Figure 7.3 Transfer impedance test for a coaxial cable
Figure 7.4 The transfer impedance for a few standard cables
Figure 7.5 Diverting a magnetic field
Figure 7.6 The location of power conductors and a line filter
Figure 7.7 Methods of terminating the braided shield on a cable
Figure 7.8 A guard gasket applied to a transistor
List of Tables
Chapter 6
Table 6.1 A Table of common radiators
Grounding and Shielding
Circuits and Interference
SIXTH EDITION
Ralph Morrison
Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging-in-Publication data has been applied for
ISBN: 9781119183747
Preface to the Sixth Edition
Six editions of a book that spans 50 years is surely unique. I want to thank John Wiley for staying with me for all these decades. I want to thank Brett Kurzman, my new editor, for getting me a contract. I want to thank my wife Elizabeth for her continuous support. I want to thank all the readers that have supported me over the years. If it had not been for the urging of Dan Beeker of NXP Semiconductor, there would not have been a fifth edition. For this reason, I owe him a “thank you” for making a sixth edition possible. I have been puzzling how to make this edition more effective and I feel my opening statements are key. I need to tell the story so that the reader will appreciate my approach.
There are many meanings to the words grounding and shielding. To an English speaker, the nonengineering application of the word “ground” can include such diverse usage as coffee grounds, grounds for dismissal, playgrounds, ground round, or ground floor. The nonengineering use of shield can include such topics as windshield, police badge, metal armor, or protective clothing. In an electrical sense, ground can mean earth, the minus side of a battery, the conducting plane on a circuit board, the neutral power conductor, or a metal cabinet. People involved with electricity often associate these words with protection against electrical interference. The book title is intended to convey this meaning. Each reader of this book will start with a unique set of experiences associated with these words. I want to broaden that experience.
I have been involved in electrical grounding and shielding for over 50 years. My understanding comes from my experiences, my interests, and from my education. I have rewritten this book every 10 years since 1967 because the electrical world keeps changing. Also, I keep learning and the books do sell. Grounding and Shielding is an important topic as it relates to both cost and performance in about every aspect of our modern technology. The subject is difficult to present for many reasons. First, it is related more closely to conductor geometry than it is to circuit content. Next, a lot of the information that is passed on through usage is simply lore and some of it is wrong or misleading. This means that often engineers have preconceived ideas and need to do some unlearning to get things straight. In some cases, the grounding rules a user must follow are a part of a code or a regulation that leaves no choices. When the rules are printed on fancy paper, it is easy to assume they are valid. If the rules are in error, arguing against the establishment can be very frustrating. Unfortunately, not all rules are effective or practical. And finally, the subject is not taught in schools and engineers are often on their own to find answers. I have also found that quality control people will follow written rules rather than the opinion of one outside engineer or author. They respect authority, which is what they are expected to do. I have had some polite arguments that have lasted years, where my viewpoint keeps being questioned. From this fact alone, I know just how ingrained some viewpoints can become.
The subject of grounding and shielding comes up in most designs. Because it is not an exact science, there can be many opinions as to where to connect shields and reference signals. Some approaches are lore and are passed on by copying past designs or by word of mouth. In most cases, there is no simple test that tells if a viewpoint is valid. We may know how to test a piece of hardware but testing a building is another matter. There is an important question that must be asked. What measurements would you like to make? Where do I put my voltage probes? Even if tests could be made, making changes to a large system can be very expensive. In many cases, the ideas used in a design are valid but over some limited range. A person with a misconception may find it difficult to accept a different explanation. This is especially true when many different opinions have been expressed. I find that for good reason, engineers are very skeptical about an explanation that suggests a new viewpoint. They do not know what or whom to believe. Another problem is that the engineering idiom is constantly changing and sometimes valid explanations fail to communicate. The subject lies somewhere between trade practices and physics and this is a wide separation. It is a subject area that does not fit into academia. To some managers, grounding seems like a job for a technician. In reality, it is often a very sophisticated and complex issue. For these and many other reasons, it is time to write a sixth edition. I want to try to get the message across for today's designers. As much as possible, I want to keep opinions to a minimum and I want to focus on connecting this subject to basic principles. I want to use physics as the basis for explanations but without getting too mathematical.
I have taken what I feel is a unique position in discussing grounding and shielding. Circuit theory leaves the distinct impression that conductors carry signals. The fact is that conductors guide the flow of field energy and this field energy can carry signals, interference, and operate components. Nature does not distinguish between these three functions. We definitely need circuits to describe our intentions. We need circuit theory to analyze these circuits. We need to apply basic physics when circuit theory is not sufficient. We have to keep power, signals, and interference separated because nature is not going to offer any help. We need to appreciate that nearly all electrical activity takes place in the spaces between conductors. It is the intent of this book to clearly point out how this very key idea can solve problems. This field transport idea is covered in physics courses. The connection between these ideas and practical designing is usually missing in textbooks and in the classroom. The arrangement of the spaces between conductors can keep various fields separated. This control of conductor geometry is the job of the designer. This is the central theme of this book.
This book is not an introduction to circuit theory. I assume the reader is familiar with how a circuit works. It is also not an introduction to applied physics. It is about all the things that happen when an education meets the real world. The problems that are solved in a textbook are nothing like the problems that are faced by the new designer. After graduation, there are no teachers around to explain how to proceed.
I solved many problems using my intuition and my past experiences. Little by little my understanding grew. Over time, it became clear that I should have used more of my education and less of my intuition. This is easy to say and not very easy to do. In the real world, problems must be resolved not studied. Most problems are multidimensional and do not fit just one subject. Finding a way through a maze may not be very efficient but experimenting with the maze to learn more is not often done. That takes time and that means spending resources.
I was told about displacement current in college. I never appreciated the value of this concept until I began writing about digital circuits. Then I discovered this idea let me explain how current flows into the distributed capacitance of a transmission line. In reading the literature, I had never seen this explanation. I present this idea in this book and I hope it helps to explain the real world to others.
In looking back at the fifth edition, I noticed how austere Chapter 1 appeared. Reading this material seemed a little like taking medicine to get well. It is not fun. Even though I wrote it with good intentions and I was excited to tell this story, the material did not appear inviting. To correct this condition, I decided to open this sixth edition with some of my background and describe a few of my experiences to illustrate why this basic physics is critical to an understanding of grounding and shielding. So stay with me as I go back in time. I think the history is both interesting and insightful.
RALPH MORRISON
July 1, 2015
San Bruno, CA
A HISTORICAL PERSPECTIVE INTO GROUNDING AND SHIELDING
As a teenager, in 1940, I built my own crystal set. I remember connecting the circuit common (ground) to a water pipe some 20 ft away from my set. The conductor went out through a hole in a wire mesh window screen. I found out that routing the antenna made a difference, so I kept trying different approaches to receive more radio stations. Little did I know of the complex nature of coupling to a transmitted radio signal. This was my first association with grounding (making an earth connection).
My interest in electronics extended to how a radio works and before long I was spending time in the neighborhood radio repair shop, where I learned how to test vacuum tubes. I was given a discarded radio as a present because the plastic case had been smashed. I freed the speaker cone and I had my own working radio. The radio had a ground clip that suggested that a grounding wire might improve reception. As a teenager, I spent time with several classmates that had acquired the skills needed to be amateur radio operators. They were always discussing their antennas and the grounding of their transmitters. I borrowed a copy of the ARRL handbook to get some idea of their hobby and what it meant to be a ham radio operator. I was an observer as I did not have the resources to enter this hobby.
I was drafted into the army in WW2 at age 18. Eventually, I became a radio repairman in the infantry and fixed radios in Patton's third army as it crossed Germany. The radios I serviced had no connections to earth as they had to be very mobile. I never gave grounding a second thought. After I returned home, the GI bill gave me the opportunity to go to Caltech and get a BS degree in physics. I remember taking courses in electricity and magnetism, not realizing the impact this subject would have on my future. I remember solving differential equations and fumbling through systems of units. I was introduced to Maxwell's equations. At the time, I had no way of assigning significance to this information. It was as if I was reading the first paragraph of many different chapters in many different books.
After graduation in 1949, I started working as an electronics engineer at a company called Applied Physics Corporation located in Pasadena, CA. My first boss was George W. Downs, a well-respected entrepreneur. During the war, he had worked as a high-level consultant and was associated with the Atomic Energy Commission. I had a lot to learn. The company products included oscillographs, electrometers, and spectrophotometers. I was impressed with the beautiful packaging and the fact they were so well respected by their customers. All of their products used vacuum tubes and I saw “grounding” for the first time. They explained to me how they used a grounding stud that collected all the common leads used in the instrument. This included the metal case, the equipment ground, the centertap on the secondary of the power transformer, the transformer shield, and the various circuit commons. There was no explanation given to me as to why this was the best solution. I was told that the order used in placing these conductors on the stud was important, and they had found a solution that made the instrument free of noise. In later years, this star-grounding configuration would appear in very unusual places. At the time, I had no basis to be critical of star-grounding methods. The products worked well and engineers with years of experience had spoken. Do not mistake me. A grounding stud was a valid approach to building this product. It is not however a solution to grounding in general. Asking questions did not yield useful answers and I did what everyone else did – I used common sense, I copied the procedures used in other products, and I experimented when I could. I was a part of the work force.
My first assignment as an engineer was to design a dc instrumentation amplifier. This type of instrument was needed in conditioning signals from strain gages, position sensors, and thermocouples. I was shown a circuit approach that had been developed by RCA that used a mechanical chopper to correct for dc drift. I was soon immersed in regulated dc power supplies, transformers, filaments, tube type selections, and feedback. I managed a design one channel of dc amplifier including a power supply that weighed over 70 lb. Do not forget that vacuum tubes take several hundred volts to operate and these voltages had to be very carefully regulated. When I look back at those early days, I can see how far electronic instrumentation has come and in particular how much I had to learn. At the beginning, there were no shielded transformers, feedback techniques were primitive, noise and hum were problems, and there was a limited understanding of signal isolation. There were selenium rectifiers that did not work very well. Dc amplifiers and vacuum tubes are a definite mismatch. In those days, that was all there was. The techniques of differential amplification and common-mode rejection had not yet entered my understanding. My boss was learning from me. We had to start somewhere.
The period after WW2 saw the growth of the aerospace industry. I was project engineer on several analog computers that were sold to Douglas, Northrup, and Lockheed. These computers helped in the design of the first commercial jet aircraft. The computer design was based on work done at Caltech and included some dc amplifiers I had developed. After this project was completed, our instrumentation group was sold to a company in the transformer business. Our first project was to develop a high-speed recording oscillograph. The photographic paper speed in this machine was over 200 ft/s. Needless to say, Kodak appreciated our business. Getting the paper up to speed in milliseconds was no small task.1 I designed the amplifiers that drove the galvanometers. I found out about the limitations imposed by using a common power supply to power a group of single-ended instruments. It was obvious that there was a lot to be gained by using a separate power supply for each signal channel. To meet this challenge, I began working on new techniques to reduce cost and size and avoid the use of common supplies. I invented a method of using AC coupling and a parallel feedback network to make a dc instrument. The company rejected my proposals for a new product line. I recognized the relevance of my new ideas, and I talked with two other engineers to leave and form a new company. George actually helped us make the transition.
The new company was called Dynamics Instrumentation. We manufactured instrumentation amplifiers for aerospace. The product line was based on the design ideas I had proposed. I could now contact users directly and I began to understand their dilemma. In rocket test stands, vacuum tube electronics had to be mounted in a blockhouse hundreds of feet away from the rocket engines and any sensors. This meant long input cables had to carry millivolt signals between structures. This raised issues of where to connect the input and output signal cable shields. I had some ideas on how to handle these issues and wrote some articles on the subject. I passed these articles out to potential customers. I was surprised at the reception these articles received. It was obvious there was very little information available on where to connect shields on large systems. Years later, engineers would pull these articles out of their files to show them to me. Now, when I look back at that period, I too had a lot to learn. I could tell that this was a difficult problem and the size of a company had nothing to do with understanding the issues. Rocketdyne was interested in designing rocket engines not where to connect shields.
I found out that interference resulted from the flow of power current in input conductors. Remember there were hundreds of volts on the secondary coils of the power transformers. Simply put, I was the culprit. This current could be limited by the use of transformer shields. I built my own power transformers and played with the shielding until I understood what was happening. My competition built a carrier-type differential dc amplifier that used a mechanical modulator/demodulator and a multishielded input transformer. Being differential allowed input and output commons to be grounded separately without creating a ground loop. I tried to duplicate this approach, but I had problems building the input transformers. Instead, I built a postmodulator/demodulator around a postcarrier transformer using newly available transistors and managed in effect to build a wide-band differential amplifier. The mechanical modulator approach had 100 Hz bandwidth and the post-transistor modulator instrument I built had 10 kHz bandwidth. I had a new product and I had a new definition of the word differential as applied to instrument amplifier.
I needed three shields in the power transformers I used in this design. I got a company in San Diego to build them for me. I noticed one day in an electronics magazine that this company was offering what it called “isolation” transformers with four shields. On my next visit, I asked the company owner what his recommendation was for using a fourth shield. He did not know. I then asked why he offered it. The answer was simple: “They sell better.” I had aided in the formation of a new business based on adding multiple shields to distribution transformers. I had used shields to make one instrument work and the industry had decided to use these same methods to “clean up” systems. To me, they had a solution looking for a problem. To me, the multishield solution only worked for one instrument. Later, I would take a broader view of this shielding. I also saw marketing at work.
I began to feel I had something important to offer other engineers. I saw a pattern in how shields worked and how they controlled the flow of interfering current. It was all tied to the electrostatics I had studied in school. So in the days of ribbon typewriters and carbon paper I started the task of writing a book. I showed the manuscript to Dr Ernst Guilleman of MIT and he was enthusiastic. I then submitted a manuscript to George Novotny the editor at John Wiley, where, much to my surprise, it was accepted for publication. The first edition of Grounding and Shielding was published in 1967.
My first analog designs used shielded conductors to carry signals on the circuit board. I was emulating the approach used at Applied Physics. When I designed my last instrument amplifier, there was not one shielded conductor inside the package. The circuit board did not have a ground plane. I had learned how to control the layout so that shielding signal leads was unnecessary. My approach was simple. I understood how to limit the area between conductors that carried the fields of the signals. I could run signals near power transformers and avoid even 1 μV of coupling. The noise levels I attained were at the theoretical limits of the components and my instrument bandwidths were over 100 kHz. The users were still required to shield input signal cables between the transducers and the instruments.
Having a published book provided me with the opportunity to do consulting. I was now accepted by some as an expert. Selling instrumentation allowed me access to many military and aerospace facilities. This in turn allowed me to see how fairly large installations used their instrumentation. It was then that I began to see the conflicts imposed by regulations and controls. I found out that most of my recommendations were not followed. The engineers were happy because the performance was better than they had expected, and I was disappointed because things were just not very good. The engineers were constrained by rules that simply made no sense to me. As an example, I found that they had collected input and output shields in bundles and brought them to a single ground point. This was the star connection I had seen used at Applied Physics but applied in an entire building full of electronics. This is a good example of how lore can do damage when it is not controlled. In my early experiences, I expected logic to prevail and that I would be heard. I soon found out how much inertia there was and that the status quo would prevail. This was all a big disappointment. I was not heard. I was politely ignored. When I think about it, these engineers had little choice. The system was not designed to accept any step changes to approach. The bosses were from a different era and they wrote the rules. Somehow they got by and so did I.
I left Dynamics during an economic downturn and spent a few years in a company that built peripheral testing equipment for the telephone industry. The new building we were using had a so-called clean grounding conductor that was brought into the engineering area. The head of engineering had specified an approach that was a standard practice in telephone office design. Somehow the feeling that prevailed was that this was a “quiet” ground that would be used to reduce noise in testing hardware. I had a hard time accepting this strange logic, but I said nothing. This grounding rod was like the ones I had seen in aerospace. It almost seemed that engineers had invented a new physics, where noise runs downhill into a sump and never returns. This violated my understanding that current flows in loops but here again these were experienced engineers doing the facility design. I wondered if the first user would contaminate the grounding rod for any subsequent users. During my years at this company, I never once used this “quiet” ground connection.
Before the era of fiber optics and microwave transmission, telephone links relied on copper connections. The fact that the entire country was crisscrossed with hard wire was impressive. To reduce costs, the ring (bell) circuits often used the earth as one of the conductors. This made it a necessary to provide a good earth connection at each central office. The head of engineering was simply following the good practice rules he had learned in the telephone industry.
At one point in my career, I needed some additional income. I noticed a company that offered a seminar called Grounding and Shielding. I contacted Don White Associates suggesting we might be able to work together as I had a book published with this same title. Don White agreed and I attended several of his grounding seminars. In this course, he focused his attention on the treatment of high-frequency interference. He discussed topics such as ESD, lightning, radar, rf filters, radiation standards, coaxial cables, and ground planes in computer installations. Even though I had been a physics major, I had a lot to learn. Eventually, I managed to catch up with the jargon and was able to teach courses in these new topics. I began to see that there was really no separation between analog and rf. It was one continuous subject. His course gave me an understanding of the specific problems engineers encountered in grounding and shielding at high frequencies. My analog design experiences did not include radiation. Don's experience did not involve instrumentation. Don gave me many opportunities to do consulting. Obviously, I had new material for another edition to my book. I also found out that the problems of radiation were far more common in industry than the problems I encountered in amplifying signals representing stress, strain, and temperature. Radiated interference that affected radio and television reception was regulated by the FCC. Interference that affected strain gage measurement was a minor distraction by comparison. There were no agencies regulating performance in instrumentation. I needed Don's help, but he did not need mine.
Living in Southern California gave me access to the aerospace industry, which included the Jet Propulsion Laboratories, aircraft companies, Edward Air force Base as well as Goldstone. I had two close friends, Warren Lewis and Fred Kalbach that were full-time consultants. They often invited me to join them on their consulting field trips. Warren was invested in a business that sold power isolation transformers. One of these trips was to Goldstone, where lightning had knocked out a distribution transformer. This was potential business for Warren. Goldstone is where NASA located the antennas that communicated with deep space. It is located in the Mohave Desert far from habitation. This isolated location is necessary to avoid auto ignition noise as well as radio and television signals. The deep space antennas and the associated electronics are located in structures spread out over many acres of land. Just a reminder, these space antennas are nearly the size of football fields.
A single-point ground was provided for all signals and shields. This central grounding structure was a conducting rod placed in a deep well located at a point equidistant from each building. The power distribution transformers for each building were grounded locally per code. In this configuration, if lightning hit anywhere near the central grounding rod, the potential difference appearing across the windings in the distribution transformers could exceed their rated breakdown voltage. This indeed happened and they were blowing up transformers during summer thunderstorms. Here is a good example of where single-point signal grounding is not acceptable. The potential distributions in the earth that can occur during lightning activity are discussed later in the book.
The National Electric Code provides the rules used in distributing power to residences and facilities. The code was developed in the early history of power distribution under pressure from banks and insurance companies. Without controls, there were too many fires and lightning-related incidents. This code is constantly being revised to reflect best practice. In the mid-1980s, I wrote a book with Warren Lewis titled Grounding and Shielding in Facilities. I used the book as an opportunity to provide a rationale behind the code rules. In my consulting experience, I found engineers were often trying to avoid the code to solve some interference problem. If interference currents flowing in a neutral conductor were a problem, they pressured to unground the neutral. My job was to find another solution to the problem. An ungrounded neutral in a facility can be very dangerous. The code does permit this practice but only under carefully controlled conditions.
There was an economic downturn in 1991, and I decided to sell my second business. I had been involved in a small niche market. I had survived and earned a living, but I was never was able to grow as a company. After the sale, I spent my time writing and giving seminars. I received a call from Dan Beeker at Freescale2 asking me if I could give a talk
