CONTENTS

SECTION 1 BASIC THEORY

Two Basic Types of Measurement-Indirect Method: Advantages and Disadvantages-Direct Method: Advantages and Disadvantages-The Null Method-Null Circuit With Voltage Dividers-Basic D-c Bridge: Configuration-Basic AC Bridge: Configuration Bridge Generator and Detector Requirements

SECTION 2 RESISTANCE BRIDGES

Basic Slide-Wire Bridge--Carey-Foster Resistance Bridge-Potentiometer-Type Slide-Wire Bridge-Practical Multirange Slide-Wire Resistance Bridge--Slide-Wire Bridge With Extension Arms-Basic Wheatstone Bridge-Practical Wheatstone Bridge-Kelvin Double Bridge-Murray Loop-Varley Loop-Universal Galvanometer Shunt-Megohm Bridge-AC Bridge Measurement of Resistance-Measurement of Negative Resistance

SECTION 3 CAPACITANCE BRIDGES

Basic Slide-Wire Capacitance Bridge-Potentiometer-Type Slide Wire Capacitance Bridge-Practical Potentiometer-Type Slide-Wire Capacitance Bridge-The Need for Power-Factor Balance-- Capacitance Comparison Bridge--Schering Bridge-Wagner Ground Bridge Operation With DC Polarizing Voltage- Wien Bridge Capacitance Bridge With Transformer Ratio Arms-Three Terminal Capacitance Measurements-Substitution Method

SECTION 4 INDUCTANCE BRIDGES

Basic Slide-Wire Inductance Bridge-Potentiometer-Type Slide-Wire Inductance Bridge-Practical Potentiometer-Type Slide-Wire Inductance Bridge-The Need for Q Balance-Inductance Comparison Bridge-Wagner Ground-Inductance Bridges With Capacitance Standards-Hay Bridge-Maxwell Bridge-Anderson Bridge-Owen Bridge-Inductance Bridge With DC Polarization-Mutual-Inductance Measurement-Substitution Method of Inductance Measurement

SECTION 5 COMBINATION BRIDGES

Universal Bridge-Resistance-Capacitance Bridge-Combination Inductance Bridge-Impedance Bridge

SECTION 6 RADIO-FREQUENCY BRIDGES

Reactance/Resistance Radio-Frequency Bridge-Swr Bridges-RF Impedance Bridge-Bridge-Type Uhf Admittance Meter

SECTION 7 FREQUENCY-MEASURING DEVICES

Series-Type Resonance Bridge-Shunt-Type Resonance Bridge Wien Bridge-Supplementary Uses of Frequency Bridges

SECTION 8 BRIDGE MEASUREMENTS OF TUBE AND TRANSISTOR PARAMETERS

Vacuum-Tube Bridge-Tube Plate Resistance-Tube Amplification Factor (DC)-Tube Amplification Factor (A-e)-Tube Transconductance-Transistor Bridge-DC Amplification Factor of Transistor-AC Amplification Factor of Transistor

SECTION 9 NON-BRIDGE NULL DEVICES

DC Potentiometer-Potentiometric Voltmeter-Felici Mutual-Inductance Balance-Bridged-T RC Network-Bridged-T LC Network-Twin-T (Parallel-T) Network-Hall Network

SECTION 10 SUPPLEMENTARY USES OF BRIDGE AND NULL CIRCUITS

Meter or Relay Zero-Set-Bridge-Type Meter or Relay-Phase Shifter-Balanced Modulator-Dc-Ac Converters-RC-Tuned Oscillators-RC-Tuned A-f Amplifiers-Distortion Meters Thermistor Bridge-Strain-Gauge Bridge-Photocell Bridge-Pressure Measurement-Gas Sniffer-Temperature Measurement With Potentiometer-Crystal Filter-Magnetic-Flux Measurement-Neutralization of Rf Amplifier-Bridge Rectifier-Voltage-Sensitive Bridges-Bridge as Simple Analog Computer

INDEX

The bridge type circuit is found with increasing frequency in modern electronic apparatus and test equipment. This is due basically to certain unique properties which make it particularly useful, but which are not always clearly understood by the technician. Chief among these properties is the null principle. it, in general, makes accurately calibrated indicating instruments unnecessary in the bridge-type measuring circuit (except in a few cases where such instruments play an accessory role) Bridges and Other Null Devices is intended to fill the "information gap" on bridge-type instruments by presenting, in concise form, the essential data on every significant bridge design being manufactured. It is not intended in any way to be a detailed operating manual for any instrument. However, any reader interested in bridge-type instruments will be much better equipped, after reading this bock, to choose the correct bridge instruments for his needs before considering a purchase. In addition, the guide will expand his knowledge of the capabilities of bridge instruments in general.

The first Section discusses the basic theory of bridge circuits. Subsequent Sections cover different general types of bridges. The final Section shows how bridge design is applied to specific instruments serving widely varied purposes.

ABOUT THE AUTHOR: Rufus P. Turner is the author of Over 2500 articles and 20 books. He earned his B.A. degree from California State College at Los Angeles, and his MA and Ph.D. degrees from the University of Southern California. He is licensed as a registered professional engineer in California and Massachusetts and has had wide experience in the semiconductor field. Other SAMS books by Dr. Turner are Diode Circuits Handbook, Technical Writer's & Editors Stylebook, and abc of Varactors.

Preface

Bridge circuits find widespread usage in modern electronics. Introduced in 1833 as a precision resistance-measuring device, the bridge gradually encompassed measurement of other properties: capacitance, self-inductance, mutual inductance, reactance, impedance, frequency, distortion, and tube and transistor coefficients. Today, bridges--in one form or another--are as familiar in the repair shop as they are in the research laboratory.

Supplementary to bridges, a family of bridge-like null devices also emerged concurrently with the growth of electronics. Like bridges, some of these devices enable measurement of resistance, capacitance, inductance, or frequency; but they find use principally as selective circuits-alone or in amplifiers and test instruments.

Bridges and non-bridge null circuits alike have uses other than the original one of checking components. For example, they are essential parts of modern industrial, military, and communications equipment.

Here they provide automatic response or precise control in such roles as voltage regulation; power measurement; frequency control ; filtering; phase shifting; sensing of temperature, pressure, strain, humidity, and magnetic fields ; carrier suppression; and modulation.

This guide describes principal members of the numerous classes of bridges and non-bridge null circuits, bringing the explanations together in this one place for convenient study or reference. The arrangement and development of the material favor either a consecutive study of the text or spot reference to parts of it. Our intended reader is the practical man, whether technician or engineer.

by RUFUS P. TURNER

Also see:

Gas Tubes (1958)