March/April 2001 EXPERIMENTAL TECHNIQUES 15

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STRAIN GAGES Back to Basics by Peter K. Stein

STRAIN GAGE HISTORY AND THE END OF THETWENTIETH CENTURY

There could not be any two things more basic tostrain gages than their bonded wire and bonded foilversions. In this year, 2000, the last of the 20thCentury, we mourn not only Dr. Arthur C. Ruge

whose obituary appeared recently among these pages, andwho passed away peacefully on April 3, 2000, but also PeterScott Jackson who died June 27 in Del Mar, California.

Prof Ruge had discovered the bonded wire strain gage in1938 and perfected it to commercialization in 1939. Its in-ventor, Edward E. Simmons, Jr., still lives in Pasadena, Cal-ifornia where his invemntion occurred. Peter Scott-Jacksoninvented the bonded foil strain gage in 1952 in England. Itis today the dominant form of strain gage especially fortransducer applications. Below is the story of Peter G. ScottJackson.

INVENTOR OF THE COMMERCIALIZED BONDEDFOIL STRAIN GAGEPercy George Scott-Jackson, better know as Peter Jacksondied of a stroke at his Del Mar, California home at the ageof 84, on June 27, 2000. He was born in 1916, the eldest sonof 7 children of Percy George and Kathleen Scott-jackson,Peter was born in Ryde, on the Isle of Wight and educatedon the Island. He is survived by two sons, Nigel in Californiaand Ian in Texas. Peter’s brother, Mick, 15 years his junior,lives in England and was kind enough to provide some of thepersonal details of this euology.

Peter joined the RAF in 1933 as a 28 entry Halton appren-tice and was commissioned soon after. He was attached tothe Czechoslovakian 311 squadron and had a number ofother special assignments during World War II such as radarresearch for the Air Ministry. It was during this period thathe developed a keen interest in electronics and made a num-ber of significant developments in the audio field.

After the war he took up an appointed with Saunders Roeon the Isle of Wight and was instrumental in setting up theirelectronics division. He worked on strain gaging, especiallyon the Princess, a very large flying boat under developmentat the time.

In 1952 Saunders-Roe bought a helicopter company and ac-quired two developmental programs with it, the smaller oneof which was the stimulus for the invention of the foil gage.This program, called the Skeeter, was to develop a verysmall, agile machine. The Electronics Division, which I had

ET is pleased to feature ‘‘Strain Gages—Back to Basics,’’ a series on strain gages,thanks to veteran SEM member, Peter K. Stein. This series is intended for thenovice, and as a refresher for all others. Each article in the series will address aspecific topic. If you have any comments about the series, or questions for Peter toaddress in this series, please contact met at abstractesem1.com.TB.

Peter K. Stein (SEM Fellow and 48-year member) is President of Stein EngineeringServices, Inc. In Phoenix, AZ.

founded and of which I was then Chief Engineer, was calledin to execute strain measurements.

Peter ran into great difficulties with the then available wirestrain gages because of fatigue failures, slipring noise prob-lems and lack of sensitivity. I became convinced that the wirestrain gage was a total waste of time and funds on that par-ticular project. I also discovered that necessity is not themother of invention. Invention needs two parents: one anger;the other frustration. A certain amount of screwing aroundis also required.

The foil gage was born on the Southampton–Isle of Wightferry, returning home from yet another series of disasters.There had to be a better way! I was traveling with one ofmy engineers who had come to me from a guided missileprogram. He talked about making amplifiers on a copper-clad Bakelite on which the circuitry is etched. This is it! Isaid to myself. If we combine the etching process with thelacquer another part of my division was making from Aral-dite epoxy, we’ve got it! The rest is history. In my wildestdreams I could not have imagined what has happened to thefoil strain gage!

It took about two weeks to get it done. The day after I gotthis flash, I went to Johnston Matthey to get some high-resistance foil made. They had just bought a Szendzimir millfrom Germany and I got some 0.8 mil copper-nickel foil toplay with. I went to Technograph who were the people whohad done this Bakelite-backed foil etching process to get agage made, and within a couple of weeks we had the firstspecimens in our hands.

I shall never forget the first day we put a bridge down on analuminium bar, clamped it in a vice, connected the batterypower very cautiously, and the current burst sent the gal-vanometer off scale when we pushed on the bar. We wereable to drive a 0–1 ma meter very easily!

Apparently a part of a model railway bridge was instru-mented with the new gage, and son, Ian Scott Jackson ofTexas writes: ‘‘The only memories I have of all this is a visitto the Farnborough Air Show when I was about eight yearsold. I can still see the model train repeatedly crossing thebridge and repeatedly sending that needle swinging acrossthe meter. They had it set up behind a glass window. I haveno idea why that made such an impression on me, but Iremained transfixed for hours, waiting for the next bridgecrossing to cause the next needle swing.’’

Peter approached Dr. Paul Eisler who developed the printedcircuit to commercial success and who insisted that OffsetLitho would be a suitable method of production. This wasnot the case. Peter was not happy with his dealings withTechnograph. Kodak came to the rescue with their metaletch resist KMER which made the foil gage a success.

16 EXPERIMENTAL TECHNIQUES March/April 2001

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STRAIN GAGE HISTORY ANDEND OF TWENTIETH CENTURY

Peter Scott Jackson continues: ‘‘Technograph made such foilstrain gages for Saunders-Roe and Tinsley under a Saun-ders-Roe license.’’ Note the importance of this statement andalso of Jackson’s ignorance of the patents for which Tech-nograph had applied in the U.S., as a later section will elab-orate.

I have been asked how come 55 ohms were chosen. Two rea-sons: that was the best we could do with the Cu-Ni foil roll-ing capabilities of those days, and it fed a solution into an-other helicopter-generated problem—measuring systemsensitivity. The gage was impedance-matched to the 55-ohmgalvanometer coils of our 8-channel recorder which we drovedirectly from the strain gages giving the maximum possibleoutput from the system. The greater surface area of the foilover the wire permitted better heat transfer to the specimenand hence higher currents and output.

The anger and frustration of the mechanical failure of thewire gages and the slipring problems sent Jackson, the Elec-trical Engineer to look for a new solution. A new inventionresulted which put the bonded resistance strain gage fieldon a new plateau of performance, especially in transducerapplications such as load cells.

I left England in 1955 to join Canadair in Montreal for 3years and then went with Convair /Astronautics with re-sponsibility for the Atlas /Centaur test and checkout equip-ment development and design. The last job before I becameself-employed was as Manager of Engineering Research andDevelopment for Zenith Radio.

He also had a number of top executive appointments withCorporations such as Monsanto (St. Louis) and Non-LinearSystems (Del Mar). As vice President of Non-Linear heworked on the development of helical scanning heads forportable color video Tape Recorders for the U. S. Army.

Peter was always full of Fun but had a deep mistrust ofpoliticians as do most of us. His brother Dennis said, ‘‘Peteronce soaked the Prime Minister of Canada and his entouragewith a water pistol! He loved good literature, and the modernclassics. He also loved good music, especially the jazzgreats,’’ wrote brother Mick.

Peter would visit the Isle of Wight regularly until his wifebecame ill. It was always in September, when, he insistedthe local Bembridge Crabs were at there best

Peter attended the June 1988 Fifty-Year Golden AnniversaryCelebrations of the commercialization of the bonded wirestrain at the Sixth International Congress of the Society forExperimental Mechanics in Portland, Oregon. He was hor-rified and speechless to find that the Plenary Speaker at-tributed his invention to Dr-Ing. Paul Eisler, also of England.Eisler, who re-discovered the printed circuit was instrumen-

tal in commercializing Peter’s invention, an application ofthe printed circuit, made by Technograph. He also effectivelywas given credit for the strain gage part of printed circuitsand Peter’s name did not appear in any of the historical writ-ings about foil strain gages. Since Peter left the U. K. beforethat event, he did not even know about that part of straingage history and how popular and widespread his inventionhad become!

I have tried to rectify this error and have given due creditto Peter for his invaluable contribution to strain gage historyin my many publications.

At the January 27, 1990 Strain Gage Jubilee Celebration inPasadena, California at California Institute of Technology,he was our star performer, telling his story much as it isrecounted above.

We will miss this unorthodox, free-roaming spirit whose in-vention we meet every day of our lives since foil-gage-basedtransducers are ubiquitous.Rest well, friend.

A FOIL STRAIN GAGE EARLY HISTORYCHRONOLOGY

Early 1952Peter Scott Jackson totally frustrated with unsuccessful wiregage application on a helicopter with sliprings invents foilstrain gage in England.

May 29, 1952Peter Scott Jackson applies for foil gage patent, granted May27, 1953 in England, granted as No. 720,325 on May 27,1953 and assigned it to Saunders-Roe Ltd.

August 28, 1952Dr. Paul Eisler’s patent application on printed circuit appli-cations also covering foil gages, granted April 20, 1955 inEngland as British Patent No. 728,606. Eisler’s patent wasentitled Electric Resistance Devices, illustrating straingages amongst other applications. This is the patent mostoften, but erroneously, cited as the basic foil strain gage pat-ent.

August 1953Peter Scott Jackson’s paper His first publication: The FoilStrain Gauge, Instrument Practice, August 1953, pp. 775–786.

October 21, 1953Dr. Eisler’s first publication: Printed Circuits: Some GeneralPrinciples and Applications of Foil Techniques, Journal ofthe British Institute of Radio Engineers, Oct. 21, 1953, pp.523–538. �