Accurate Clock Pendulums

by Matthys, Robert James

• ISBN13: 9780198529712
• ISBN10: 0198529716
• Format: Hardcover
• Copyright: 2004-08-05
• Publisher: Oxford University Press

Summary

The Shortt clock, made in the 1920s, is the most famous accurate clock pendulum ever known, having an accuracy of one second per year when kept at nearly constant temperature. Almost all of a pendulum clock's accuracy resides in its pendulum. If the pendulum is accurate, the clock will beaccurate. In this book, the author describes many scientific aspects of pendulum design and operation in simple terms with experimental data, and little mathematics. It has been written, looking at all the different parts and aspects of the pendulum in great detail, chapter by chapter, reflectingthe degree of attention necessary for making a pendulum run accurately. The topics covered include the dimensional stability of different pendulum materials, good and poor suspension spring designs, the design of mechanical joints and clamps, effect of quartz on accuracy, temperature compensation,air drag of different bob shapes and making a sinusoidal electromagnetic drive. One whole chapter is devoted to simple ways of improving the accuracy of ordinary low-cost pendulum clocks, which have a different construction compared to the more expensive designs of substantially well-made ones.This book will prove invaluable to anyone who wants to know how to make a more accurate pendulum or pendulum clock.

Author Biography

Robert J. Matthys was a Senior Research Engineer at Honeywell, Inc., from 1952 to 1987. He has spent thirty-seven years designing a wide variety of hardware and instrumentation in the fields of electronics, optics, acoustics, mechanics, and photography. In addition, he has spent nine years designing and testing pendulums of various kinds, along with their electronic drive systems and servos, both pulsed and continuous sine wave. He lives in Minneapolis, Minnesota.

Table of Contents

Preface	vii
Introduction	ix
Part I: General	1	(94)
Better accuracy from simple pendulums	3	(4)
A short history of temperature compensation	7	(6)
Scaling the size of a pendulum	13	(6)
Finding a pendulum's axis of rotation	19	(2)
Does a pendulum's axis of rotation shift with amplitude?	21	(2)
Some practical properties of quartz	23	(4)
Putting Q in perspective	27	(10)
The Allan variance and the rms time error	37	(6)
Transient temperature effects in a pendulum	43	(4)
Transient response of a pendulum to temperature change	47	(10)
Dimensional stability of pendulum materials	57	(22)
Variations on a Riefler bob shape	79	(8)
Bob shape	87	(4)
Rate adjustment mechanisms	91	(4)
Part II: Suspension spring	95	(58)
Spring suspensions for accurate pendulums	97	(24)
James' suspension spring equations	121	(6)
Barometric compensation with a crossed spring suspension?	127	(4)
Solid one-piece suspension springs	131	(8)
Stable connections to a pendulum's suspension spring	139	(4)
Stability of suspension spring materials	143	(10)
Part III: Pendulum rod	153	(30)
Pendulum rod materials	155	(4)
The heat treatment of invar	159	(4)
The instability of invar	163	(4)
Position sensitivity along the pendulum rod	167	(4)
Fasteners for quartz pendulum rods	171	(8)
Effect of the pendulum rod on Q	179	(4)
Part IV: Air and clock case effects	183	(38)
Correcting the pendulum's air pressure error	185	(6)
Pendulum air movement: A failed experiment	191	(4)
Pendulum air movement: A second try	195	(10)
Time error due to air pressure variations	205	(6)
Effect of the clock case walls on a pendulum	211	(10)
Part V: Electronics	221	(40)
An electronically driven pendulum	223	(4)
Sinusoidal drive of a pendulum	227	(14)
Photoelectronics for pendulums	241	(8)
Check your clock against WWV	249	(6)
Electronic correction for air pressure variations	255	(6)
Conversion Table	261	(2)
Index	263