The Design of a Remote Reading Extensometer Citation Serrell, Peter Van Horne (1939) The Design of a Remote Reading Extensometer. Master's thesis, California Institute of Technology. doi:10.7907/FDWF-JQ52. https://resolver.caltech.edu/CaltechETD:etd-10282005-144806 Abstract No abstract submitted. Item Type: Thesis (Master's thesis) Subject Keywords: Mechanical Engineering Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Mechanical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1939 Record Number: CaltechETD:etd-10282005-144806 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-10282005-144806 DOI: 10.7907/FDWF-JQ52 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 4286 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 01 Nov 2005 Last Modified: 23 Feb 2023 00:51 Thesis Files Preview PDF - Final Version See Usage Policy. 615kB Repository Staff Only: item control page

In I ' ~ r t 1 : l . l S u l P i l n e n t o ;' the Rcqulrencntr-'f o r the Decree o f f;as"uer o f Sclence in S n f ~ l n c e r ' l n g S r ~ 1 S f o ~ n .I fn~s t i t u t e of %echficlo~;r Pasadena, C n l 1 f o ~ n l . n1939 ~ THE DG3TGN O F A WLAOT2 HEADING E ~ X T D ~ S O ~ i f U T ~ R The problem o f a.n a c c u r a t e s t r a i n gage f o r use i n the e x p e r i m e n t a l d e t e r m i n a t i o n o f s t r s s e e s l a one o f g r e a t i m portance. Desirable c h a r a c t e r i s t i c s of B U C ~an instrument are : 1, Accuraoy 2. Wide r a n g e 3. hlaintenanoe o f c a l i b ~ a t i o n 4. Lightness 5. Compactness 6. Simplicity 7. P o o s f b ; t l l t y o f remote r e a d t n g M o c h a n i c d , optical , and e l e o t r i a a l means, and cornbinat i o n s t h e r e o f have been enployed t o f i l f i l a l l o r p a r b f the eabove r e q u i r e m e n t s . Urzder t h e h e a d i n g o f meohanioal i n s t r u m e n t s , come t h e v a r i o u s l c v e r and d i a l gage i n s t r u m e n t s , u a u a l l y r e s t ri c t e d t o rather l a r g e s i z e , and uoZng d i v e r s e methods o f a t t a c h t h e C I O B ~ ~ ~ ~ c e a s off u euch l ment t o t h e ~ ~ e c i m e n Among . l n s t rument s i s t h a t developed by Huggenberger. R. 2 cm. p q e l e n g t h , and ;;ives It eraploys n.n a c c u r a c y o f 1;; o r b e t t e r at u n i t s1ora~;ntlons o f 0 . 0 5 'LO 0 . 0 7 , about t h e s l a s t i o I f n ~ l l t of "chc heat t r e a t a b l e aktxminur;l a l l o y s , A t G A L C I T , as we14. a s e l s e v ~ l l e r e , t h e s e % n s t y u ~ e n 2 ;have s been u s e d w i t 1 1 c o n ~ i d e r h h l e success in s t r u c t u r a l I n v e s t 1 ~ ; n t i o n a . t h e Tuckem8n t r i p l e m i r r o r s t r a i n gage used by t h e Burow o f Standards. It i s o f t h e s e l f columnating t y p e , t h e mix- r o r s being i n t h e measuring head, and t h e reading b e i n g clone t e l e s c o p e o f f i x e d foca.1 l e n g t h c o n t a i n i n g both t h e l i g h t source and t h e s c a l e . The t e l e a c o p e may be s e t up and t h e instrument rend fmm any p o s i t i o n I n t h e p l a n e o f symmetry o f t h e n e a ~ u r l n ghead f r o m whfch a l l t h r e e m i r r o r s may be Been a t once. P r o p e r alignment o f t h e t e l e s c o p e 1s i n d i c a t e d by t h e appearance o f a secondary image o f t h e l i g h t eource i n t h e f i e l d o f view. The measuring head i a q u i t e corn- p ~ c t ,and t h e s e n s i b i l i t y claimed f o r t h e Instrument i s l/250,O0Ot~, (1). The disadvantage of" mechanical and o p t i c a l i n s t r u m e n t s i s t h a t they must be seen, and u e u a l l y from a d e f i n i t e dlr s o t i o n , t o be read. Furthermore, t h e i r s e n s i t i v i t y i s n o t r e a d i l y s u b j e c t t o change. i f i G @lilEttiG ~ ~fA A iC wn Ar , im , a, u nifw l4An 7 nn p l a s t i o region. An instrument a d ~ p t e dt o measurp- 3.e p r ; ; z t l c a l l y werthless i n t h e The e l e c t r i c a l i n s t runlent, on t h e o t h o r hnnd, may be read wherever i t i s oonvenient t o s e t up t h e output meter. m r t h e r , by c1lanf;inl;. t h e s e n s i t i v i t y o f t h i s meter, t h e s e n e i t i v i t y o f t h e instrument a6 a av?iole i s chaneed, and t h e same measuring head clay be u s e d In t h e e l a s t i c region and i n at l e a s t t h e f i r s t p a r t o f t h e p l a s t l c r e g i o n . A l l i n all, t h e e l e c t r i c a l instrument may have a n advantage o v e r t h e mechanf c a l o r o p t i c a l sy~ter!lsu n d e r any c o n d i t i o n e , and cert a i n l y i t e x c e l l s f o r remote reading. E l c c t r i c c t l i n s t r u m e n t s i n g e n e r a l may be c l a s s i f i e d a s (1) s e e T r a n s , o f A . S . T . I . , . , Vol. 23, P a r t 11, p . 6 0 2 , 1923 resistive, capacative, o r inductive. The r e s i s t i v e t y p e depends on t h e defbrmntilon o f t h e s e n s i t i v e element pmduc- i n g a measurable change i n t h e r e s i s t a n c e o f t h e element. For t h i s element carbon s t r i p s o r r e s i s t a n c e w i r e a r e u ~ u a l l yemployed. F o r example, carbon 8 t r i p s cemented t o t h e b l a d e and connected t h r o u g h an oscilloscope have been u s e d t o d i s c o v e r v i b r a t i o n p a t t e r n s i n metal a i r p l a n e prog e l l e p s , ( z ) , and n w i r e wound t e n s i o n dynamometer, a l s o conn e c t e d t o a n o s c i l l o s c o p e , l e u s e d i n irnpaoe r e s e a r c h a t t h e California Inntitute. F o r r e a s o n a b l e a c c u r a c y , however, t h e s e elements r e q u i r e c o n s i d e r a b l e f o r c e t o make thern o p e r a t e , and the setup becomes q u i t e b u l k y , Furthemiore, t h e carbon s t r i p s a r e s u b j e c t t o creep which r e n d c r s them undesf r a b l e f o r s t a t i c inventigttt ions. In t h e caprtcitLve t y p e o f inst-rwnerlt, t h e strain? o f t h e specimen i s rnctcle t o o p e r a t e a v a r i a b l e condenses on xvhich i s impressed a n n l t e ~ n a tnf g voltaiye o f r a d i o f r e q u e n c y . The chp.n[';e I n c u r r e n t due t o chance i n c a p a c i t y ~1nybe rieasured. v~lth sultable i n s t ~ ~ u - ~s e. n tIn c c n e r n l , however, t h e s e i n s t r u m e n t s a r e higl-llyv s e n s i t i v e t o anytlsirli; i n their 1r:lclediate o r even rcrnote nei,n$lborl?ood, anit maintenance o f c n l - i h r a tI o n The i n d u c t i v e t y p e o f i n s t n ~ r : ~ e n salsa, t, Ir; e x c i t e d by a. 0 0 : l r c ~ ?a.ltel-n:-itinj.; cur;-ent , u s u a l l y o f a u d i o f r e q ~ . e n c y ~ lire s e n s i t , i l v e eleni:rit 1:11, the ;7l7.. ? . :lip n l i is i n c. i!!~i;:;nct 201-1 ~ ~ i iltl1h f r ~ nc o r e , ;,;ap o f s;-iich I s v a r l e i i 1:jr the stx'nin o f the op$c:nen. ilh;~n(;e i i . 1 %lie :.:.I 1 ;-::sp ~!.ra..ni:c: s inciv.ctanc e 311i: F n t ul-n ?;he j,r;-il;,e&:ini:e o f t : ~ e@oil, ivhich. i s ciezr;urad by r,, ;;.1l.~:lj;o;::et::3: i n a ' r ~ r i d ~netrwork c o n t a i n i n g t h e c o i l s o f t h e r n e a s u r i n f ~ The c o i l s a r e , o f c o u r s e , s u b j e c t t o t o n p e r a t u r e c h a n g e s head. i n r e s i s t a . n c e , h u t o t h e r w i s e tlne i n s t r u m e n t i R s e l f s h i e l d i n g a n d q u i t e stable. A s mentioned l a t e r , t h e t e n p e r a t u r e v a r i a - t i o n s i n r e s i s t a n c e c a n lie lninirnized b y u s e o f t h e p r o p e r c i r cuits. 3 y nild bar;;e, for s t a t i c t e s t s , <and f o r d y n a i i c t e s t s o f low f r e q u e n c y , t h e i n d u c t i v e t y p e o f i n s t r u m e n t seen:s to be * Ithe a u t h o r has h:>ci some e x p e r i e n c e 1,~ci.tha s e t o f s u ~ hi n - s t v l ~ u l e nst ?:evelopad by t h e E : a t e r i a l P r u e f u n ~ sA n s t a l t o f t h e 'L'echnische Ho o b s c h u l e D a ~ m s t a d t . T h e s e p a r t i c u l a r i n s t r u m e n t s vbrere cieveloped .to , u o s s e s s v e r y s h o r t :;n:;e 5 mm. ) 1en;;ths (from {j- t o t o be a 6 a p t e d t o measu.rin;: s t r a i n s i n T L ~ ISO ~ s~iall Ff,?. 1 1s a p h o t o g r a p h o f reentraiit cornel-P, f i l l e t s , e t c . o n e o f t h e i n s 2 ; r ~ r i ? l c n t s , a b o u t 2;: tiinen %oi-.r;l~le i z e , i n ? l a c e o n the cnlihi.;i",n~; F i y . 2 s l z o ~ st h e r:lethod o f a t t a c h - 11,nr. to 3 ?clip3 f i a n c e riioi-;.ei. ,.,. ,, ,.., G& T-, A sc:'nc:nntl.c diacrnrri an6 e x ~ l ; ~ n a - tinn 12f tl-.!e cls7culit used is s?lov!n in Fb;.:. 3 , 1iv11ile ? 1 ~ .4 ~ ' ; ~ > ~ . r?. ! a~ c - : , ~ t 4 c?;llrou:*-l-i r? t h e r;;ensurln:-: l-lea<-. - ,.,<:* 1.-. ,,-., 7 & . Cun(j ,"i r . 2 t & , - (.....,,n;~ - ~ - ,j c ,>t~ ~ *-- s -.>>,~,!(3. 4 (, d-7. I ~ ~ ~ !.,:LC : ~ : ::j.:> 9-11 " ; o.'incper.i:s, ~;!flil~. i;]~:ito f J..otlctn of' the nr;:!ri- 1 tlis !-:.~.*-~,i.~st-j..c ::ircufl; 0:; o n e "chi?~ ' ~ 1 7 . 3 3 r1113~y~?r.s?:'. tlin ::gIl A;i-rfi coils foyi:: t ~ c ;o f t h e f o ~ . ~c=or.~pcn~?ents r of r~ 'brltl;,-e r~:::?;i~:.:-:II .. .. , t h e ~:r:;ls9;;ivj.ty of the ii.~.strur!;s?ltis i?o!:hl.@c? eve;.. t,l:n.'i o-r 2 ~i~~i',le c o i l in:;tsaiuVie;-lt. A l s o , i f l;liLs hrld.i;e z.!??;!:jo:-l: is ;.::~CC? ;;.g nc::-l>lg g;rr;l! ieh71i:21- a:: po ~ ~ 1 1 - , l m c ~q ; i ~ . ' S n t l oin n ? e s i st,.;l?c= 3.~10 to l,yl.c?.yc, ...,. ,., . -? - p p i, -?-<. t ~ : r - r ~ ~S:!~O~I.IC'~ i . t ~1.e t h e :,l.ii(.:: for I m t h s i d e s of the ~ i ~ ! i f ? - sl~ouic'i..c n u F e onl:,:. n srtcond o sc1t.r u n b a l n n c i ~ z : ~ &,r.cI ; i : P l e c t i o n o f th~: [;:~lv;tnor!cto;-- I P ;!LL~OS~; dlrnc?;- F1, ~ z n l - 0 d - iui ~ j l c :.re:-.c?i~~;;e5 cr t h c t lo ad rii~~y,:ev??iich ~?ntuz?r%ll:r ~P(~c~u.c> us.J:17;.: . c : the l l i ~ t ~ ! , ~ ~ - ol,~t~ic?.e ~i?nt thin load ran;;e, C,:JOVC tllc p,l::.stic li;yi't. ~ o P B ~ T o h~oI~~r e~v:e,r , do The or n o t np- perir to ;-.)e -)r!~~~~~o\li?titlj~i? 6.iPf j-cult l e s , o r charncterist ics 7;;.'rll c!i cc-!nnot l.c elir.ij.n;;tcc? bg p o d deo1;n. A goricsl>.nt l:~r;-,~:.. i n s t r~menl;I s bel.ni; de~~elopeti 21; present; ; : t GALCIT. n : ~ c!;iven 113. FE;;;s. Rlte:.r:n'i;ive 5 :!.nc?, 6. c!.osi[;ns of the i i l e a s ~ . ~ r . fhen6 n~ It . c j i l l l~cnoted tliat t i l e ~ 0 1 1 s nni?. t!lciy i:-oi? c o p e s :me asser!ll-)led, and. 1?rl.t.4~ tile bf:?i?inr:. /_ posts r'olil t h ~ e~.ciso f t h o c o i l , a1.e mouldeci I n a t r m s p n r c l ~ t 'Tl?: s p~*ovider;a n c > ; o e l l e n t r~ethoc?o f iz..aulc..tin~;the ~ l r . si tc . c o i l s nn?. l.:olclilij,; the pa:-ts f i m n l y i n p l n c e n i ' ~ h P ~ , ~ - I R tc o~ or.? f-moLlle:-. To d a t e , t h o c o r e l a ~ f i i n n t i o n shcve h e r ? ;?Po- C~i.cec?-Cro!n 'iwa d.iffcr.ont n.llo:r::; L7 t h e hi;ii:e flwn ~ 1 1 3 - c o n,ste?J., ai:d ao f l c x i i ~ l eas p o ~ s i i ~ l et h, e nechnnism ::!:is b r a k c n . Another l?in[fe mcchnnisr,~13 tunde~-c o n s t i'uction o n t i l e p r i ? - c i y l e a o f Fi;;. GI, onc1 n i l 1 be ~roectt o s t u d y t i l e ef f c c t o f t h e v a r i a b l e s , x;'l~chn s f r e q u e n c y , c u r r e n t , co 19e a l l o y , a i r p p , e t c . o n t h e I-onpor se o f t h e i n s t r u m e n t . FIu-ch t i r n s mas s p e n t i n tr*yfi?c; t o a d ~ l p t alunl.num viire t o t h e vindiny; o f t h e cc ile by nn~;li.y,,inc, it; i r r ~ l ; c ? . d ~of e n n r ~ e l i n gi t f o r i n s u l n . t i o n , i 2nd a f t e r cevcrr.1 unr;uocessful a t t e m p t s , I t mas docided t o r z s e r v e .';his ,4017 tile Sutu17e. It i s h o p e d that by usin;; n vncuur.1 t u b e c i y c u . i t i t n i l 1 he p o s ~ i h l ct o use (z 11033 i'lug;ed instr-urgent i n t h e b r i d ~ enetwork t h a n t h e oerisit Pve i;nlvnnorileter usecl. 9 n Dnirnotadt . A t PI-eocnt, no Ct';Pinitc precllctions a s t o the p e r f o m nnce o f t h e i n s t r u n c n t can l ~ erlade, save on t h c h a s i s of t h e c x p e r f e n c c o f othe:-.s. It i n ~ z n d e r s t o o i lby t h e a u t h o r t h a t t h e P r n t t & VJllitney Comy,nny Ilas d e v e l o p e d an i n ~ t r u m e n tt o t,ake the pl:ace of a ' y o - no ;;o" ;;age ~ u c c c ~ l a f i ~ ol lny t l i o uatlc p r i n c i p l e ~!Ilichoperrl.tes q u i t e . Furtherno re , hf s ex- perieizca ~ i l t ht h e D n r ~ a t a d tf n s t m ~ n e n tl e a d s him t o b e l f c v c Zlnt 1;" 2 r e : : s o n t h ~ l e ,r:,cly;e leiz,c:tll i s u s e d , m c i care. is tnlien to c e c t h a t t l i o supposedly const:-lnt f r c t o r s in t h e s ; r ~ t e r r.re ~ : ? c t ' ~ ~ a lcl oy n s t a n t , t h e I n s t n ~ m e n t should effect ti r e n s o n a b l e cornproclf se o f t h e d e s i r a b l e cklamc- t e r i ~ t i c ss e t f o ~ t hi n t h e f i r s t paragraph. p n i n t e d l?~ftl-I.n i r y l a n e dope t o p r e v e n t unravel1i n c , c o p p e r :'!l-c n.~l!i fox*c~:?(i onto tile c o r e n o v e r s u i t a h ~ l e111~ul;:"l;ion. To tile b r ~ 4 . si ~ n a c - ! r t s ~ l i f c h2.1n.ve been draillni"., b u t n o t tappec3, a,re solcieretl thc: ends of' t i l e c o i l 7:?indi.n;.-;s0 The rtcr,er:l'l)l;r fs then p l a c e d in the X O U ~ ~ ?tlie , c o r e f i t t i n [ ; i n t o t h e s l o t s 111 dr;~:;!il~i;. $:C-25'7-4/a, f t e n s 4 a n d 5 r)lmviil!cd an6 the e x t r a l e n g t h o f I n s e r t o projectin,:;. Lnto t h e api3l~>p~-~i:ntt? h o l e s i n items q1e ~ i l o u l di s t h e n ~ i l t i . ~ di n. the j iy, t l i c ponciured 3 2nd 6. zsbnst f c is i n t r ~ ? ~ u c e i n l froi?t o f t h e plux~c;ea , and tl~ec a s t - F :znd n o t L ~ . s Gt11m T:,!IOC) p . !:. i. --in;-'. in poi:Ponnei! :it 315' T11.c r:\o~xI,i! is coolct'. u.nciein grac-?naul*e. m ihe Y:irtx7d" ?;r1nc1e o f L~!ci."i; ~tsrci.for. 'LILB no?rl(?f!l;: ~ ~ : i t e l ~ l ;,i . l : . illc ~ r i u$2; @fi.st:n;; I7 :j~-;.i?- ?:t; 2.2 cht!cli.cC1 f n t!?a ~ i o u l dw i t h t h e t o y tl;or~ ~rlei ;o'vcil m12 tyl..!.~p 1.m (r: su x'f ;i.cr:-fi :: r e i';:cec?. in t h e Li1,_ . r : .;i:,:;!.l. ~;?:.?r;it'i.nn.::3:-e 1 1 'tli~: i i > ~ , ~ - p ' ! ~:;j?i? , c.:-~:ll.lfr::* ~ : j ' tl:c:: "i!-;i? t;i.?l>il~;; 0 2 tile 7>z7~,,o3 lo:: i~ i;?:~.r; on?:)oaite . - ?- y'),(+ j - ? ,;..,--: A. :,I;- :; (-&.\. . .. " j.j.1 t l l j . :; t]j.:? j., ;:, ,:irp j.13 t : 2 . ~ ; (.:..Aid< 13' fi 3.c Fig. 1 Dnrrnstndt I n s t m n c n t on Calibration Ear. About 2.:: T i m e o Actunl S i z e i 2 r)nl.r.~~to.tit l;nstmir9cnt 3 e t up t o 1Jenslxre T a n - e i ~ t i a l S t r a i n i n t h e F i l l e t o f a P i p e man;-;e i:odel -P -7 A- :.t ~ SECTION CF eOU~C iRGl,_ e W! I C E .~2!3.&~-~ ~ CALIFORNIA I N S T I T U T E OC TECHNOLOGY .... ~.. ~ ~ a CASr!NG JIG 4 PNRr MOULD - BRASS ~ ~ ~ ...