CA1227062A - Fiber optics condition sensor and method of making same - Google Patents

Abstract

FIBER OPTICS CONDITION SENSOR
AND METHOD OF MAKING SAME
ABSTRACT OF THE DISCLOSURE
A fiber optics condition sensor and a method of producing such a device is disclosed. A bundle of opti-cal fibers provides a planar termination on one end and is bifurcated to provide one group adapted to be con-nected to a light source and another group adapted to be connected to a detector. A shallow, curved, thin metal-lic diaphragm provides a central portion movable toward and away from the termination in response to the condi-tion being sensed in order to vary the light reflected to the detector and therefore produce a detector output signal which is a function of the changes in conditions being sensed. The diaphragm may be formed of bimetal for sensing temperature conditions, or of a homogeneous metal to sense pressure. The curvature formed in the diaphragm is selected to provide movement of the central portion of the diaphragm through a distance selected to match the reflective light intensity versus spacing curve so the the system provides substantially the maximum response over a predetermined range of conditions being sensed.
variations in the curvature of the diaphragm are compen-sated for in the mounting of the diaphragm with respect to the fiber optics termination so as to ensure maximum response in the total system.

Description

~ '7~

FIBER OPTICS CONDITION SENSOR
AND METHOD OF MAKI~G SAME

BACKGROUND OF THE INVENTION

Th~s lnvention rel~tes generally to condltlon sensing devlces such as temperature-responsive devtces or pressure-responsive deYices, ~nd more par~lcularly to ~
novel ~nd improved condltion sensor of such type combin-lng fiber opties And a condition sensing di~phragm or dlsc, and to a novel and i~proved method oE prsducing such devices.
.

Prlor ~rt_ It ~s known to use f1ber optlcs to ~ecurately messure the spaclng between a ~iber optics terminstlon ~nd 8 reElecSive sur~sce Ex~mples o~ such systems ~re illustr~ted ln United S~ates Le~ers Pstent ~os.
3,273,447; 4,309,618; and 4,358,g60~
It is also known to posl~on 5uch reElectiYe sur~ce with ~ pressure~respons~ve dlaphr~gm to prov~de pressure-responsive device. Ex~mples of sueh deYi~es ~re illustrated in Unlted St~tes Letters P~teneæ N~s.
3~580,082; 4~22,~7B, and 4,322,979. Su~h deY1ces tend to utllize ~lat non-me~all~c di~phr~gms which ~re ~ufFl-ciently el~stlc to provlde ~ sy~tem which is qulee sens~-tlve to low pressures. Gener~lly, such dev~ces canno~ be eEfectiYely used ln relat~vely high pres~ure ~ppllca-tions.

(3~

It ls also known to combine fiber optlcs wlth bimet~l sensors to provide ~emper~ure-responslve deYices. An ex~mple of such a device is lllustr~tecl ln United St~tes ~etters Patent No. 4 9 204,742.
It is Rlso known to produce metallic discs wlth 8 curvature to m~dify their response to temperature or pressure, or both. Usually such discs are bumped to provide them wlth two positions o F stab ility between which they move with snap ~ction. When such discs are ~ormed of blmetal, they are temper~ture-responsive. For pressure-responsive diaphragms or discs, the dl~phr~gm is gener~lly ~ormPd of a single homogeneous met~l. Examples of such bimetal snap dlsc devlces ~re illustrated in Unitecl States Letters Patents ~os. 3,500,~78; 3,573,~0V, And 3,67~,817. Examples of pressure-responslve snap discs are illustrated in United States Letters P~tents Nos. 3,378,656 and 3,720,Q90 SUMMARY OF~THE I~VE~TION

There are ~ number Df aspects to thls inYen-~o tlon. In accord~nce wlth on~e lmportant aspect~ ~ novel and lmproved combin~tlon of ~ blmet~l sn~p disc or dlaphr~gm and ~ fiber op ics bundle 1s provided. Such com~in~tlon prov~des a temper~ture-responsive opt~cal sensor ln which subst~ntlal chan~es ln optlcal ~esponse occur ~bruptly when the d~sc snaps betw~en its two pos~
: t1Ons o~ st~bility In ~ccordsnce wlth ~nother Rspect o~ thi~ inven-tion, a ~imetal d~ sc ls shaped to respond to a predeter-mined r~n~e of movement ln response to a predetermined temperature ch~nge wlthout sn~ppln~, ~nd ta provlde ~
modulated tem~erature slgnal throu~h such range of moY~-ment.

, . . . . .

()6~

In accordance wlth ~nother important aspect of this invention~ a novel ~nd improved pressure sensor com-bines fiber optics wlth a met~llic disc shaped to provlde a predetermined pressure response either wl~h or wlthout sn~p action.
In accord~nce with ~nother ~spect of the lnven-tion, novel ~nd lmproved methods ~re provided for Assem-bling temperature or pressure-responsive devices combin-ing flber optlcs ~nd curved metallic diaphragms or dlscs~
In e~ch illustrs~ed em~odiment, a re~lectiYe metallic disc ~s posltioned sd~cent to the termnin~tion 0~ 8 fiber optics bundle, whlch ls biEurc~ted to provlde a flrst group o~ optical fibers for eonnection to a light source ~nd ~ second group of optical f~bers for conduct-ing reElected l~ght to ~ detector. The met~llic dlscs are shaped ~o provlde predetermined movement in response to a predetermined r~nge of tempera~ure or pressure con-dltions SQ tha~ optlmum sign~ls are produced. The lnven-tlon however ls ~lso sppllc,~ble to ~ flber optic~ trans-mitter 5y~tem ln whlch the transmitted light is re~lected b~c~ to the de~ector ~hrough the same optic~l fiber or ~ibers through which light ls tr~nsml~ted from the light source. In such systems a beam spl~e~ is us~d ~o de-~lect the ~ght to the detector.
In on~ lllustrated embodiment, the disc i~
~ormed of bimet~l and ~s ~h~ped to snAp b~Gk ~nd orth between two posltlons o~ st~llity at predetermined tem-per~tures, When such device ls intended ~or repeat~d oper~tion, ~he fiber optics term~nation is posi~loned with respect to the disc so that the di~c does not ~mp~ct sg~inst ehe ~rmina~ion when ~t oper~tes~
Another embodimen~ provldes a non-snappin~
bimeCal dlsc whlch ~s shaped to provide ~ prede~ermined rate o~ subst~ntlally llnear movement wlth~n ~ predete mined tempeF~tur~e r~nge~ Such dlsc ls aBa~n posltloned 7(~

~d~cent to the fiber optics termln~tion so thnt such movement eEficlently provides re~lective llght v~lue changes for producin~ accurate temperature signAls by the light detector.
In ~nother embodiment, a thln, metallic dl~-phragm ls again formed wl~h ~ sh~llow curv~ture ~o th~t lt c~n respond to pressure in ~ predetermined selected manner. Such curv~ture enn ~e es~ablished so that ~he diaphragm ls either a snap acting di~phrag~ or a non-snapping diRphr~gm Two diEferent methods o~ constructing such devices ~re illustrat~d. In ~ccordRnce with one method, ~ body ls pro~lded with ~wo loc~ting surf~ces whlch establish ~ ~ixed position between the periphery of the dlaphragm and the termlnation of th~ ~lber optics bundle, ~nd ~he spacing between the loc~ting surfaces ls ad~usted to compensate for vari~tion~ of the curv~tures oF the diaphr~gms, In ~he oth~r method lllustr~ted, g~gin~ o the spaclng between the dlaphragm snd the termlnstion of the flber optics bundle ls provided by ~ method in whleh the ~iber optics bundle is mounted on ~ 1rst body memb~r ~nd the di~phr~m is suppor~ed on a second body me~ber~ a~d the two bod~ members ~re pushed together until R stand~rd v~lue of re~lected light is ~chieved ~n~ ther~ftet the ~ two body mem~ers sre loc~ed in such po~lt~on w~h respect .~ o e3ch o~her These and o~her aspecSs o~ thls in~ention are illustrated ln the ~ccompanylng drawings and ~r~ ~o~e Fully described tn the ~ollowing spectic~tlon~
i BRIEF DE CRLPTION OF THE DRA~INGS

FIG,l illustr~tes ~ flbe2 optirs sensor ln accordance with the pr~sent invention ~nd the m~nner ln which it ls connected to ~ schem~tlcally illustr~ted light source and a schem~tically lllus~rated reflective - light detector;

FI~. 2 is an enlMrged, longitudinal sectlon of one embodiment, illustrating the structllr~l detall thereof;

FIG. 3 is an enl~rged, longltudinal sectlon o~
another em~odiment, in which gaging is achie~ed by movlng f~rst and second body members un~il a predetermined re-: flective llght.v~lue is achieved;

FIG. 4 schem~tlcally lllustrates the m~nner in which light supplied through one optical fiber ls re-flected back to ~ sep~r~te optlcsl E~ber;

FI~. 5 is ~ &reatly enl~rged view o~ ~ ~iber optios terminati~n in which ~he optlcal Fibers ~re r~-domly Arran~ed "

FIG. ~ is a vlew similar to FIG. 5, illustr~ting the termin~tlorl ln whlch th~ two groups o~ optlc81 ~lbers are poslti~n~d in ~d~accnt hemispheres wi~hin the terml-n~t lon;

FIG. 7 is a grsph illustr~ting the typlc~l re~lectlve response ~or randomly snd hemlspherlcally arr~nged ~ber optics groups as ~ function o~ dls~nce of ~he reflectl~e surf~ce from the ~lber optics ter~inatlon;

71.~

FIG. B is a plot o~ a serles o~ dlsplAcement curves illustrating the manner ln whlch the cur~es can be modlfied by changing the curvature o~ a thln~ metalllc diaphra~m;

FIG. 9 ls ~ temper~ure dlsplacement curve of typical snap diaphr~m; ~nd ~ IG. 10 is an enlarged, longltudin~l section of ~n embodiment in which the diaphragm or dlsc ls respon-slve to ~ressure rather than temperQture DE~AILED DESCRIPTION OF THE DRA~INGS

A fiber optlcs condition sensor in ~ccordance wlth the present invent~on h~s many spplic~ions~ For ex~mple, such ~ devi~e ls p~rticulsrly suited f~r sensing ~ condltion withln ~ hazardous ~res, sinca the sensor portion of the devlce does not requlr~ any electric~l circuitry which could produce ~ flre hazard. I~ Is reco~nized th~t the llght source ~nd re~lectlve l~ht detector do inYo~Ye electric~l clrcultry; howe~er, such dev~ces c~n b~ remRtely loc~d ou~sld~ of ~he haz~rdous r 20 area b~ing moni~ored by ~he sensor.
FIG. 1 lllustrates s typlcal system incorpor~t-in8 a flber opt~cs sensor in sccDrdance with the present inventlon. Such system includes the sensor assembly lQ.
which is connected ~o a schematlcally illustrated li~ht source 11 ~y ~ f~rst group of optic~l flbers 1~ nnd to ~
re~lectiYe llght detector 13 by a second group o~ optlcal ~'7(~i2 fiber~ 14. The two group~ o~ cptic~l Fib~rs 12 and 1~
merge to provide a flber optics bundle 16 whlch extends to the sensor ~ssembly 10.
Although the v~rious illustr~ed embodlments provide fiber optics tr~nsmitters which include bundles of optlcRl fl~ers whlch ~re bifurc~d to provlde two - sep~r~te groups of fibers3 thls lnvention is ~lso appll-cable to fiber opt~cs tr~nsmitters ~n which the light ~ro~ the light source is delivered to ~ reFlectlve sur-~ace through the s~me flber or fibers th~t csrry the re-ftected llght back to the detector. Such systems gener-ally u~llize R beam splltter whlch sep~r~te the paths o~
the source light and the r~Flectlve light~ Further such systems may utlllze only a slngle optical fiber or ~ bun-dle oE optlcal fi~ers. The llnited St~tes l.ett~rs Pfltent No; 3,273,477 illustr~tes in Flg. 5 there!o~ ~uch a system.

The sensor ~ssembly 10 includes 8 re1ectlve diaphragm (dlscussed in dPta~l below) whlch moves tow~rd ~nd ~w~y ~rom the termlnatlon o~ the bundl~ 16 in response to changes ln the condltions being ~ens~d t~
ch~nge the valu~ oF the re~le!cted llght tran~mi~ed to ~he de~ector~ The de~ector 13 ~ csllbrAeed so th~t the output signzl genersted by the deeector i8 ~ ~unc~lon oE
the ~mount of light re~lected b8ck through the second group o~ opt~c~l 1bers 14 ~nd ls thereEore ~ ~un~tlon o~
the condltions sens~d by the sensor ass~m~ly 10.
Th~ light sourc~ 11 and ~he d~t~ctor 13 ~re schemat~cslly illustr~ted hereln, ~ince such dev~ees ~r~
known to thos~ s~illed ln th~ are, ~nd th~ ~electlon o~
the particular detector and light source from devices o such typ~ av~ ble orms no ~rt o~ thi~ invention except to the extent that the li~ht source 11 must be - cap~ble of uni~ormly producing ~ level of llght su~
cient to ~etlvate the system ~nd the det ctor must be capRble of uniformly produclng ~n output signal whlch m~intains the desired relationship between the lntenslty of ~he re~lected l~ght ~nd the output signal ~o that the detector produces an output signsl whlch ls ~ consistent function of ~he condltion be~ng sensed.
FIG. ~ illustrates, ~t fln enlarged scalel the structur~l details oE one sensor assembly 10 in sccor~
dance with ~he presen~ invent1on~ In such dev3ce, the bundle of optical flbers 16 extends into a firs~ tubular body 17 to a termln~tion 18 of the op~lcal fl~ersO At such terminatlon, the tubul~r body 1~ grips ~he bundle and m~intalns the optical fibers in a ixed posltion.
The ends of l~he ~lbers ~nd the end o~ the body 17 sre precision-finished so that the ends oF each of the optl-c~l fibers lie in ~ single plane coplanar with the ends of the remaining ~ibers. ThereFore, ~he terminatlon oE
the bundle 16 is plan~r and ~he ends o~ e~ch of the ~ibers ~re formed so that light ~ransm1tted ~long the flrst group of ~lbers 12 ls ~fficien~ly ~nd unlformly transmitted through the ends o~ the ~bers o the flrst group o~ ~ibers ~nd the li~ht reflec~ed b~ck to the ter-mlnation ls e~ficlently recelYe~ and uniFormly trans-m~tted ~ck ~long the ~lbers of the ~econd group 14v Positloned adJ~cent to the terminstlon 18 is condltlon-responsl~e dlsc or dlaphrRgm 19 provld~ng ~
rorroslon-resistant re~lectiYe surfac~ ~t le~st ~d~cent to the term~natlon 18. Such dlaphr~gm 19 ls ~ormed o~
thln metal with 8 shallow curvs~ure, discussed ln de~all ; ~elow, to provide 1~ wi~h the des~red respQnse to t~e condition belng ~ensed. In the embodiment illustr~ted ln FIG. 2, su~h dlaphragm l9 ls form~d oE bimet~l, and is responsive to temper~ture changes.

z The support for the dlaphr~gm 19 is provided by ~ second body member 21 an~ a sheet met~l up 22. The second body member 21 is formed with a sh~llow, central recess 23 extendlng ~rom ~ centr~l bore 24 sized to recelve ehe Eorw~rd end o~ the ~irst tubul~r body member 17 and the terminatlon 18. Extending from the sh~llow - recess 23 is ~ r~di~l wall 26 extendlng to ~n axl~l flange 27. The ~xl~l fl~nge 27 ends in ~ preclsion-~ormed, radial loc~ting sur~ace 2~, ~gainst which a radial seat w~sher 29 is positioned by the cup 22. The perlphery o~ the disphragm 19 ls resiliently pressed ag~inst the upper surf~ce of the ~eat washer 29 by 8 spr~ng 31. With this structure~ the se~t washer 2~, ln cooper~tlon with the r~dial wall ~6 ~nd the ~xial fl~nge 27, provides an ~nnul~r groove which receives the perlphery of the disphragm 19 and accur~tely positlons such periphery ln the plane o~ the loc~ting surface ~3.
The flrst body member 17 is ~ormed wlth ~
r~di~lly extending ~lange 32 providing a second locatlng sur~sce 33 at the lower end thereof, which is ~ormed wit~
prec i~ iorl ~o a prede t ermlned, lon~ l tud l nal spac ing f rom the plane o the termination 18.
A third loc~tlng sur~sce 34 is pr~cislon-~ormed at the upper end of the second body member 21 ~or enga~-ment ~ith the s~cs)nd loc~tlng sur~ace 33 so th~ the ter-mlnstlsn 18 is accur~qtely located axi~lly wlth respecl: to ~he second bod~ member ~1 Qnd, in turnS ~he di~phr~gm 19. A nu~ 36 h~vln~ an lnternal flange 37 ls ~hre~ded onto the second body member 21 ~nd enga~es the ~l~nge 32 to tl~htly press the two loeatin~ surf~ces 33 ~nd 34 to~ether.

71~

Because of the curv~ture ~ormed ln the dlQphrgr~
19~ and because the disphr~gm is ~ormed of blmet~l, the central portlon of the diaphragm moves ~oward and aw~y ~rom the termin~tlon `l8 ln response to chan~es ln temper-~ture. There~ore, ~he diaphr~gm c~uses a chQnge ln the reflective light vslue tr~nsmitted to the detector 13 by the second group o~ opt1c~1 ~ibers 14t ~nd thls varles the output sign~l of the detector 13 as ~ function of the temperature of the di~phr~gm lg.
~IG. 4 schematic~lly represents the manner ~n whioh light is re~lected ~rom one opt~cal ~iber to ~nother, and how u change in the sp~clng o~ ~ reflectl~e surface ~ffects the amount oF reflected llght. If it ls assumed two optlcal fl~ers 41 and 4~ are positlon2d ~d~a~
cen~ to each other and ~re provided with their termins-tlons or ends 43 and 44, respectively, in a coplansr relatlonship, ~nd lf i~ ls ~ssumed that ~ reflectlve surface 46 ls posltioned in allgnment wi~h ~he two terml-n~tlons 43 and ~4, llght delivered through the optlc31 Elber 41 ls re~lected by the surf~ce 46 b~ck to the optical ~lber 420 The light emerglng ~rom the optlc~l Elber 41 tends to disperse as ~ cone lndlc~eed by t~e dotted lines 47. The re~lective 11gh~ enter~ng the optl-c~l fiber 42 ~US~ be loc~t~d with1n ~n im~gin~ry cone indicated by the dotted llnes 48~ Thus~ the li~ht whlch ~s r~Elected fro~ the optlcal ~ber 41 to ~he opt~cal -` ~ib~r 42 is th~t llght ~hlch re~lec~ from the sur~ace 46 with~n ehe overl~pping portlon o the two cone~ repre-sented by the d~tted llnes 4~ ~nd 4B. S~nce the cur~-turs o~ t~e dlsphrag~ i5 very slight, ~h~ cen~r~l port~on of the di~phragm which ls actlve in re~leetlng the ll~h~
c~n be cons~dered ~ fl~t surf~ce~

~ 7(t~ ~

I~ the reflective surface 46 ls ~noved tow~rd ~nd away ~rom tXe termination of the optlcal ~lberst lt hfls been determined ~h~t ~ reElectlve light intenslLy curve h~ving the shape of ~he curves illustrated in FIG. 7 1~
provided. For example, if the re~lective surf~ce 46 is m~ved to the le~ so th~t lt sctu~lly engages the terml-natlons 43 and 44, the reflectlve surface acts as ~ gBte or door to prevent light from emerging from the flber 41 and no ll~ht can be reflected ~o ~he fiber 42. Thus, lF
the d~ st~nce be~ween the reflective surfaee 46 and the optlcal ~iber terminatlon is zero ~ the 2ero reflective llgh~ ls provlded and the curYes illustrated ln FI~ 7 indlc~e such ~ct.
On the other h~nd, ~s the spacing between the reflec~lve sur~aee and the fiber optics termlnation in-creases, the reElective llght lntensity increases sub-stantlally alon~ Q ~trsigh~ llne portion to ~ m~ximu~, and therehfter drops b~ck down ~rom the maxlmum alon~ a curve, as lllustrated ln FIG. ~.
The dotted curve Sl represents the response achleved when the flbers wlthln the bundle ~e randomly arranged, as lndlc~ted ~n FIG. 5. In such ~n arr~n~e-men~, the ibers connected to the light source ~re sche-matically illus~rated by the emp~y ci~cles 52 ~nd the ends of th~ ers connected to the reflectlve dstectors ~re indic~ted ~y ~he circles 53, ~hich are cross-.. h~tched. ~s lllustr~ted in FIG. S, a r~ndom arrangement ~s provided in which ~h~ ends of the optical flber~ ~2 are subst~ntial~y equally distributed across the entire 30 termina~lon~ ~nd ~he ends o~ ~he i~ers connec~ed ~o the detector ~re also substan~i~lly evenly distribu~ed over th~ term~n~t10n.

'7~6~

A response curve 54, which ls generally simllur to the response curve 51, ls provided if the optic~l fibers are hemispheric~lly arranged, as illustrsted in FIG. S. In such ~n arrangement, all of the fiber ends 56, whlch Rre connected to the ligh~ source, ~re loc~ted in one hemisphere of the termln~tlon, ~nd ~ll o~ the fibers 57 connected to the detectors, indicated as cross-h~tched, ~re locsted in ~nother he~isphere of the termlnation. It should be noted by comparin~ the two curves 51 and 54 that they both start ~t zerv origin and extend upwardly with ~ subst~nt~ally str~ight llne p~r tion 58 ~nd 5~ to ~ bre~X in the curve loca~ed at 61 and 62~ rexpectively, However, the slope o~ the curve 5~ ls not as steep ~s the slope o the curve 58~ so that the response or change ln re~lective llght intensi~y with randomly orlented fiber optics termlnatlon, ~s lllus-trated in FIG. 5, is gre~ter wlth respect to distance than the response o~ ~ hemispherlcAlly ~rr~nged termn~-tion ~s illustr~ted ln FIG~ ~ and represented by the line S9. Both types oE termlnatinn tend to provide ~bou~ t~e same pe~X intensity, and then follow æ curv~ descendlng to the right, ~s viewed in FI~ 7r slong ~he do~ed llne portion 63 ln ~he ca~e of ~h~ randomly orien~ed curve Sl and ~lon~ ~he descendlng curved port~on 64 ~n ~he c~se of the hemlspher{c~lly ~rr~nged curve 54.
In accord~nce wlth th~ prese~t inventlon~ ~he curv~tur~ ~ormed ln the dlaphragm 19 is ~elec~d so th~t : th~ central po~tlon o~ ~he d~aphr~gm moYes through ~ dl~-eance whlch i5 rel~ted to ~he r~Electlon ligh~ intensity curve of th~ ~articul~r termln~tion 1~ ln~olved ln response to a ~redetermined r~nge of ~empera~ure~. Suoh motlon o~ the centr~l port~on oE th~ dl~phr~gm ~3 m~y, ln ~ome inst~nces, move ~th snsp ~ctlon, 3r m~y mo~e wlth non-snappln8 ection.

.

'7~

Reference should now be made to FIGS ~ ~nd 9, whlch represent differen~ curves whlch msy be o~talned with a ~hln metal di~phr~gm by ad~ustlng the unstressed curvature of such dl~phragm. If the di~phrQgm ls formed o~ bime~al, the d~splacement of the center portion wlll be responsive ~o tempera~ure, and lf the di~phr~gm ls formed o~ ~ homogeneou~ metal, the diaphra~m will be responslve to pressure.
In FIG. 8, ~he curve 6~ represen~s the displ~ce-lo ment whlch would be achleved with ~ flAt m~tal diaphrsgm ln response to tempersture or pressure ch~nges, as the c~se m~y be. Such a flat diaphragm wlll provlde a curve which intersects the ordtnance of the graphs ~t their in~ersec~lon. As pressure or ~empers~ure condi~on~
increase, as the c~se mlght be, the displ~cement of the center portlon o ~he disphr~gm would b~ substantially llne~r ~long a very short portlon 67 A~ an ~ngle deter-mined by the scale of the t~v ordinances. Slmll~rly~ ~f th~ tPmperQture were decre~s~!d below ~he st~nd~rd tempe~-~ture, or the pressure were cleereased or ~pplied ln the opposite directlon, the centtal por~ion o~ the d1~phragm would be displ~ced ln a ne~ative direGt1Qn through Q
small dlstance 68 in ~ substanti~lly linear manner.
Ho~eYer, as the pressure or temper~ture is increased o~
decreased, ~he curve of the dlsplacement of the ee~ral portlon ~f th~ diaphrs~mt indi~:ated by the ~erltlcal ordl-~!, na~e h~ ~ould beg~n ~Q CUrY~ toWRrd ~ more hor~zont~l por~iun, ln~1cated ~y the curved portlons 6g ~nd 71 on the curve 5 By de~ormlng or preforming the mAt~rial formin~
the disc, ~hcther lt be bimet~l or homogeneou~ ~e~ to sh~llow curved shcpe, it is possible to change t~e slope of the central portion of the curve and to ch~n~e the displacemen~ of the centr~l portlon wlth respeet to ;2 the eonditlon being sensed, RS indic~ted by the two curves 7~ and 73. For example, in the curYe 72, 8 dlaphragm ls represented in which the displacement o~ the center portion is substsntially linear between the points 74 and 76, ~nd the slope o~ the curve b~tween such points is subst~ntially steeper than the correspondlrlg portion of the curve 66. Such diaphragm, because of its curv~
ture inltislly ~ormed ln the dlaphragm, would provide greater displacement versus change in condition being lo sensed th~n the non-curved diaphra~m represeneed by thecurve 6~. Further, the chan~e in displacement of th~
central portion, whioh ts substantlally linear ~etween the two points 74 ~nd 76, ls subst~ntiRlly greRter in the dlaphragm represented by the curYe 72 than the corre-spondlng linear displacement o~ the fl~t di~phr~gm represented by the curYe 6~.
A simil~r dlsplacement versus change in condl-tlon b~ing sensed is obtalnable by properly adJus~ing the initl~l curvature of the disc, ~s lllustr~ted by the curve 73. In such instance, th~ central portion of the curve between the points 77 and 78, alvng which the di~-placement is substanti~lly line~r wlth respect ~o condl-tion belng ~ensedJ ls further increased ~nd the slope ls ~urther tnereased. In addition, the curvature inlti31ly formed in ~h~ d i~phragm dlspl~ce~ the cur~e from the orlgin of the ordln~nce ~n a posltlve directiQn both ~l~h respect to displ~cam~nt ~nd condltlon be~ng sensed.
In pr~ctice~ lt ~5 eYen pos51ble to c~use ehe dlaphra~m to move with snap act~on wlth respect to dls-placement versus condltion bein~ ~ensed, ~ illus~rated in FIG. 9. The curve 81 represent5 the dlspl~cement versus condltlon ~eing sensed o~ the di~hragm, wh~ch Is sufficiently curved ln lts ree state to pravide R neg~-t~ve spring rate ~long a portion oÇ he cur~e. The .
,.. . ,, .. _ . ~ .... . . .

~;22'7~

Eormation of a dl~phrugm with such ~ curve ls well known ln the snap disc art, ln which a disc or dlaphragm snaps b~ck and forth between two positlons of stability ln response to predetermlned conditions being sensed. Such discs or di~phr~gms ~re sh~ped by a process, usually referred to as "bumping," to ~ shallow curv~ture so th~t the curYes provide a negatlve spring r~te between the points ~2 and 83 o~ the curve.
For ex~mple, i~ ~he diaphragm ls formed of bimet~l and ~s in the position indicated at 84~ it moves with creep ~ction untll ~he ~olnt 82 ls re~ched. Such po~nt ~s reached in the case of Q blmet~l diaphragm when the di~phra~m reaches R predetermln~d temperature deter-mlned by the sh~pe o~ the di~phragm. ~he dlaphragm then sn~ps through ~long the do~ed llne 86 to the polnt 8~, creaing an ~lmost lnstantaneous displacement of the center portion of the diaphr~gm wlthout a correspondlng change ln temper~tur~.
Subsequently, ~s ~he temper~ture oF ~he dlaphrsgm decreases. lt moves ~in ~rom Che polnt 87 w~th ~ creep acCion untll the polnt 83 is reach~d. Onc~
the poln~ 83 is re~ched3 the diaphr~gm ~gain sn~ps ~long ~he llne represented by dotted line 88 back to ~he lowe~
polnt on ~he ¢urve ~t 8~, whsre lt again assumes ~ pos1-tlon o stability. ~h~ dlfference in th~ temper~tures o~
the snsp action, known as the dlfferent~al ~e~per~tltr~ of the dlaphr~m, is repres~nted ~y ~he horizontal sp~cln~
between the two linPs ~6 and 8B. The ~ertlc~l dlspl~ce~
men~ ~long such llnes represents the d~spl~cement o~ the 0 centr~l portion of the dlsphr~gm wlth snap ~c&ion. The vert~csl dist~nce bet~en 2he polnt~ 82 and 83 represents the dlstsnce ~hrough whLch the dlaphr~gm sn~ps in both dLrectisns.

,.. ., .. ~ . , 706~

In accord~nce wlth the present invention, the curv~ture preformed lnto the dlaphr~gm ls selected ~o th~t the displ~cement of the center portlon of the di~phragm, ln response ~o & predetermlned range of cond~-~ions being sensed, m~tches the reflective llght intens~-ty curve of the termln~tion so ~s to provide ~n efficient reflective light response in ~ totAl syste~. For exam~
ple, i~ it is desired to provlde ~n ~brup~ ~hange ln the reflectiYe value at two selected temperat~res, the lo dl~phrR~m l9 is formed wl~h the proper cur~ture to produce B snap actlon ~t such two temperatures. Further, the displacement achieved durlng such snap actlon is selected to match the particul~r reflected light intensl-ty curve of the assocl~ted bundle.
For example, if a bimetal dlaphr~gm havlng ~
snap action ls intended to ~e used wlth a r~ndomly ori-ented ~lber optics terminatlon provlding the curve 5l o FIG, 7, it ~ould be deslrable ~o provide ~ diaphrsg~
h~vlng ~ dlsplacement so that whcn it sn~ps tow~rd the termin~tion~ lt wlll move to ~ positlon very closed spaced to the termin~tion. e.g., ~bout 0.001 inch there-from. Such a dlaphragm would t~nd to creep back to spacing of about 0~003 inch ~rom the termlnation snd proYlde a reflective ~lue of ~bout 0.35. Upon sn~pp~n~
through to the other position o~ seabllity, it would be desirable ~or the d~phragm to be ~rr~nged to ~nsp &round the cres~ of the curve slightly ~o th~ when lt moved wlth ~reep ~c~ion bac~ toward lts other snap po~l~ion, lt would b~ ~t ~ point of ab~ut O.OlO inch from t~e t~rmln~-tlon ~nd would proYid~ R re~lect~d li~hP lntenslty o~
8~0Ut 0. 9 .
With a snap-acting diaphr~gmJ ~t i~ desir~ble to structure the dev~ce so that tha di~phr~gm does no~
lmpact the termin~tlon wlth snhp ~ction~ I~ is for thls '7~

re~son that the minimum snap-actlng spaclng from the ter-mination should be at least about 0.001 inch. In such a devlce, the intenslty change when the diaphragm snapped away ~rom the termin3~ion would be about .6~, ~nd the change o lntensl~y when the diaphragm snapped toward the ~erminRtlon would be about .95. Such a system provldes a wide change 1n reElectiYe intensi~y, whlch can be easi1y detected to est~bl~sh that the diaphragm has reached the temperatures at whlch ~t moves wlth sn~p action.
If dl~iculty is encountered ~n producing ~
snap-acting dlsphragm having the deslred temperatures of operatlon and ~ snap range wh1ch would fit the curve 51 of a randomly oriented termln~tion~ of course, the d1Rphr~gm can be used with 8 hemlspherically a~ra~ged termin~tion of the curve 54 so th~t more sn~p trsvel can be accommodated wlthout lmpactlng the termin~tlon or extending ~round the crest o the curve too much. For example, the point 61 on the cur~e 51 QCcur5 ~t A dis-plac~ment oE abou~ 0.010 ~nch, whereas, t~e polnt ~2 on the curve 54 occurs at about O Q2U inch o~ displacement.
If it is deslred to prov~de a modula~ed response to temper~ture, 8 dlsc is foemed with curva~ure so that ~t wlll provide a substantinlly llneRr r~sponse through a displsc~ment which is agsin matchad to ~he reflectlve light intensity curve oE the assooi~ted flber optics bundl~ For example~ i~ lt is desired tQ proYlde ~
temperature~responslYe sy~tem through a temper~ure range from 80 F to 130 F. ehe precurv~ure fQrmed ln the disc should be such th~t the dlsc moY~s wlth ~ substan-! 30 tially llnear movement through ~ d~stance ln the order of .010 inch when ~ssocl~ted wlth the r~ndomly or~ented terminRtlon hav~n~ a curvc~ ustr~ted ln FIG. ?~ On the oeher h~nd, ~ such d1aphr~gm is lntend~d for u5e 1~

with a hemispher~cally ~rranged ~ermin~tion illustr~ted in the curve 54, i~ is preferable to for~ the diaphr~gm with 8 precurv~ure which will provlde a displ~cement of about 0.020 inch ln such r~nge of temper~tures-The amount o~ displacement whlch is substantially withln a glven ~emper~ure r~nge ls determlned by the size o~ the diaphragm, the materlal used to form the diaphragm, the thickness of the dLaphr~gm, and the curv~-ture ~ormed in the ~ree s~ate diaphragm. It ls therefore lo possible 1n most lnstances ~o produce 8 diaphr~gm havin~
partlcul~r desired, subst~ntially lgnear dlspl~cement through a given temperature ran~e.
Simllarly~ if ~he diaphragm is intended ~orpressure response, the thickness of ~he metal9 the si~e o the dlaphra~m~ and the type oÇ ~he metal com~ined wlth the precurvsture placed on the di~phragm, allow the pro-ductlon of ~ diaphragm having a substantl~lly line~r response through the ~esired pressure range. Although the a~orementioned dlsoussion involves the produetiQn of - ~ sensor which functlons along the portion o~ the reflect~d llgh~ intensl~y cur~e to the le~t o~ the polnts Sl and 62 ln FIG. 7, it is ~lso possible in some ln-stances to operate on the portions o~ the curve to the right of the crest. However? since the slope o~ the curve t~ the right of ~he crest is no~ as ~rai~ht a~ the por~lon of the cu~v~ to the left of ~he cres~, it ls pre~erable ln most instances ~o ~rrange ~h~ devlce so ~s to unc~ion on the steep portion of the curve ~o ~he l~t of the cres~.
FIG. 2 illustr~es an em~odiment in whioh the di~phr~gm ~n be ei~er sn~p-~c~lng or ~on-snap-aceln~
~urther, in FI~. 2, ~he curv~ture ls exa~erated ~or purpvses of lllustr~tion~

7 ( ~ ~:iZ

In order to ensure that the centrRl portlon o~
the diaphrsgm has the correct sp~cing ~rom the ter~ins-tion 18 when di~phragms havlng dlfferent curvatures ~re utiIized, it ls preferred to modi~y the sp~cing between the loc~ting sursce 28 and the locating surf~ee 34 so ~s to positlon the perlphery of the dlaphr~gm 19 in the proper position to ~chleve the required sp~cing between the centr~l portion o~ the di~phr~gm and the termtnQ-tion. For example7 ~ f ~he devices require di~phr~ms havlng a greater curvature, a corresponding gre~ter sp~cing is provided between the twv loc~t~n~ sur~aces 28 and 34, and lf the d~aphrAgms ~re provlded with ~ lesser amount of preeurv~ture, the spaclng of the locatin~ sur-faces 28 and 34 ls redueed.
FIG~ 3 illustrates ~nother embodiment whlch Is very slmllsr to the embodiment of FIG. 2~ except th~t Che g~lng to esta~llsh the prop~r spacing between the centr~ portlon of the diaphrsgm and the termln~t~on ls ~chieved in a diFferent manner. In th~s embodiment, simllar reference numeral5 ~re used to lndlcat~ ~lmllar parts to the embodiment of FIG. 2, but R prlm~ ls added to lnd~eate re~erence ~o the embodlment n~ ~IG~ 3.
Here ~gsln, R ~undle oF op~lc~l Fibers 16' ls mounted ln a ~lrst body member 171 to provlde ~ plansr termina~lon 18'. The body mem~er 17' ls ~galn provided with a ~l~n~ 32' providin~ ~ locatln~ ~ur~c~ 33' held .'~ ln ~nga~ement wlth ~ loc~tlng surFsce 34 on a second body mem~er 21' by a nut 3~i. In this ~nstsn~e, however~
the body member 21' does not p~ovide a loc~ting ~urE~ce - 30 corresponding to the locating sur~ce 2B of th~ e~odl-men~ of FI~. 2, or 8 flsnge correspondin~ t~ the fl~n~e 27 of the ~irst embodlment~ Inste~d, B was~er ~e~t 29l ls formed with ~ step 91~ whlch bo~h ~xially ~nd r~d~lly locates the diephr~m 1~'.

;z In this embodlmen~, the cup 22' is not clenched ln ~round the body 21', but ls, ins~ead~ provided wlth cylindrical wall 92' which is sized to provide ~n lnter-ference fit wlth an enlarged, eurYed portlon 93' formed on the body 21'~ G~glng is ~chieved by connect.ing the ~irst group oE optlcal 1bers to a standard light source, and ~he other group of optic~l fibers to 8 stand~rd reflectlYe llght detector. The body member 21', wlth the optical ~lber bundle mounted thereon, is pushed ln 810ng the cup while the dlaphr~gm is malntalned ~t 8 stand~rd conditlon, such as a stand~rd temperature, untll the detector indicates ~ st~nd~rd reflective light intensl-ty. Further moYement of the body member 21' ~nto the cup 22~ i5 then terminated ~nd an epoxy or sim11~r settsble m~teri~l 94' is ~pplied between the wall o~ the cup ~nd the periphery of the body to lock the sssembly in such posiCion. Wlth ~hls method of assembly, variatlons in the curvature of d~aphr~gms~ v~riations ln the reflect~ve char~cter o~ ~he di~phragms, nnd varia~lons ln the dimen-sions of ~11 o~ the other psrts are ~utoma~ic~lly compen-s~ted for and a device is marluEactured wh~ch produces ~
stand~rd vslue of re~lec~ed llgh~ in~en~lty ~t the s~n-dard temperature of the diaphr~gm It ~s pointed out th~t 1~ is known, ~s 111us-tr~ted ~n Unl~ed Sts~es Le~t~rs Psten~ No. 3,~3S,62~, ~o provl~e a press ~1~ assembl~ ~or gflging o~ bime~sl snap dlsc thermose~s~ ~nd lt i5 also known ~o ~ ize ~uc~ a method of sssem~ly ~or callbratlng SnAp dlsc ~h~rmostats.
The ~mbodlment o~ . 3 may be used wlth al~-phragms whlch ei~her ~re snap-ac~ln~ or non-sn~p-~ctln~.
FIG. 10 illustrates an embodlment whlch m~y be used Eor ~ devlce wh~ch ls pressu~e-responslve. ~ere ~aln, the structure ls qu~te sim~lar to ~he prlor embodlment oE FIG. 2. ThereEo~e, slmil~r r~Ferenoe numerRls re provlded to indicAte slmilar parts, but ~
double prime ('') ls ~dded to lndicate reEerence to the embodlment of FIG. 10.
In the embodlment of FIG. 10, the fiber opt1os bundle 16'' is ~galn mounted on a f~rst body member 17'' snd is in turn oounted on ~ second body member 21'' by nut ~not lllustrated). The termination 18'' is, there-fore, located in ~ f~xed position rel~ive to ~he b~dy - member 21' t, In this embodiment, the diaphr~gm 19'i Is normally formed of a homogeneous met~l 9 and ls responsive to pressuren The perlphery o~ the diRphrsgm is located ~gainst ~ surface 96'' on the body 21'' by a cup ~7'', which is thre~ded onto the body 21l'. In this lnst~nce, ~ thin, flexlble dlaphragm 98'' is positioned below ~he metallic dl~phr~gm 19'' to provide ~ highly flexible seal de~ining a pressure cavity ~9''. A pressure ~ittlng 101'' thre~ds lnto thc c~p 97'' to connect the davice to the pressure system belng sensed. The dl~phragm ~8'' may be formed o~ any sult~ble m~terl~l provlded 1~ ls oap~ble of wlthstandln~ the pressures to be encountered~ and lt should be su~flciently flexlble that it do~s not alter ~he respons~ of the dl~phragm lg'' to any msterlal extent. Further, slnc~ the pre~sure acelng through ~he d~aphr~gm tends to hold the perlphery of the dl~phrQgs~
Agalnst the ~houlder 96, lt is not necessary to prov~de a pos~tlonlng sprlng correspondln~: to the sprlrlg 31 o the -- f lrst embodlment .
Ag~1n, ~h~ proper spacln~ ~ætween the central portlon of the disphr~gm 15~ nd the termln~tlon 18' ' ls established ~ the proper locatlon Qf the sholllder 96' wlth respect to the sur~sce corresponding to the locatin~
sur~ace 34 o~ the Elrst ~mbodiment, and such ~paclng ls ~d3usted to eompensate For v~rlstions Ln the curvature of the dS~phr~gm.

I~ the spaclng between the termlnation 1~ und the locatlng surface 33 on the flrst body member 17 ls est~blished wlth precislon, it ls possib~e to sep~raeely assemble the dlaphr~gm on its body, and thereaEter in-st~ll the fiber optics bundle. In such lnst~nce, gaglng ls separ~tely establlshed during the manu~cture, and the subassembly, consisting of the di~phr~gm and its ~ssoci-ated body, can be supplied as A sep~r~te item for subse-quent assem31y with a standard fiber optics bundle.
With the present invention, lt ls posslble to rel1sb~y produce lmproved fiber optics condition sensing devices whlch respond ~ccuraeely to the condltion or con-dltions belng sensed. Further, ehe device and the method oE assembly descrl~ed herein lend themselves to autom~ted production so ~s to reduce ~ssembly costs~
Although the pr~Çerred embodlments of thls i~-vention have ~een shown ~nd descrlbed, lt shou~d be understood that varlous modl :Fic~tions ~nd rearr~ngements of the pAres m~y be resorted ~o without departing from the scope of th~ lnt~ention as disc~osed and claime~
herein

Claims (18)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
   PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
   l. A method of producing fiber optics condition sensors operable to sense changes in conditions through predetermined range of conditions, comprising providing fiber optics transmitter adapted to be connected to a light source and a light detector in which said transmit-ter provides a planar termination, determining the range of distance through which a reflected surface moves toward and away from said termination to produce minimum and maximum values of reflected light transmitted from said source to said detector, forming a thin metal dia-phragm with a precurvature so that the center portion thereof moves through substantially said entire range of distance in response to said predetermined range of con-ditions, mounting said termination on a body assembly, mounting the periphery of said diaphragm on said body as-sembly and positioning said termination and said periph-ery so that said center portion is positioned with re-spect to said termination so that the value of light re-flected to said detector varies from substantially said minimum value to substantially said maximum value when said center portion is exposed to said predetermined range of conditions.
2. 2. A method as set forth in claim 1, including sizing said diaphragm and selecting its thickness and the type of material forming said diaphragm so that said phragm when precurved provides a center portion which moves through substantially said predetermined range of distance in response to said predetermined range of con-ditions.
3. 3. A method as set forth in claim 2, including selecting the relative position of said mounting of said termination and said periphery of said diaphragm to com-pensate for differences in curvature preformed in said diaphragm.
4. 4. A method as set forth in claim 3, including providing said body assembly with a body member having two locating surfaces, one of said locating surfaces operating to locate said termination and the other of said locating surfaces operating to locate said periphery of said diaphragm, and compensating for the difference in curvature of said diaphragm by selecting the spacing of said locating surfaces.
5. 5. A method as set forth in claim 3, including forming said body assembly with first and second tele-scoping body members, mounting said termination on said first body member, mounting said periphery of said dia-phragm on said second body member; and while said trans-mitter is connected to a standard light source and to a standard light detector and said diaphragm is maintained at a standard sensed condition telescoping said member together until a calibrated position is reached when said detector establishes that a predetermined light intensity is reflected through said transmitter, and locking body members in said calibrated position.
6. 6. A method as set forth in claim 1, including forming said diaphragm with precurvature to cause said central portion to move with snap action in response to predetermined conditions, and positioning said diaphragm so that the center portion thereof is spaced a small dis-tance from said termination when it snaps toward said termination to prevent impacting of said center portion against said termination.
7. 7. A method as set forth in claim 1, wherein said sensor is operable to sense temperature and said diaphragm is formed of bimetal.
8. 8. A method as set forth in claim 1, wherein said sensor is operable to sense pressure and said dia-phragm is formed of a homogeneous metal.
9. 9. A method as set forth in claim 1 wherein said transmitter includes a first group of optical fibers adapted to be connected to said light source and a second group of optical fibers adapted to be connected to said light detector, said group being joined in a single bun-dle providing said planar termination.
10. 10. A method of producing fiber optics condi-tion sensors comprising forming an optical fiber trans-mitter extending to a single planar termination, forming thin metallic diaphragm with an unstressed shallow con-cave curvature selected to cause the center portion thereof to move through a predetermined range of move-ments in response to a predetermined range of sensed con-ditions, providing a reflective surface on said central portion, and mounting said diaphragm and said optical fi-ber transmitter on a body assembly with the periphery of said diaphragm in a fixed position relative to said ter-mination in which said reflective surface moves toward and away from said termination and responds to sensed conditions, and compensating for differences in curvature formed in said diaphragm by establishing said fixed posi-tion of said periphery of said diaphragm relative to said termination so that said reflective surface is spaced predetermined distance from said termination under a standard value of said sensed conditions.
11. 11. A method of producing fiber optics condi-tion sensors for sensing a range of conditions comprising providing a fiber optics transmitter having a planar ter-mination and which is adapted to be connected to a light source and a light detector, determining the spacing of reflective surface versus reflection value curve of said termination to establish a range of spacing between said termination and a reflective surface which produces sub-stantially zero reflection between said source and detec-tor and a maximum value of reflection between said source and detector, forming a thin reflective metallic dia-phragm with a shallow curvature so that the center por-tion thereof moves through a distance substantially equal to said range of spacing in response to said range of conditions to be sensed, and mounting the periphery of said diaphragm in a fixed position relative to said ter-mination determined by the amount of curvature of said diaphragm so that said center portion of said diaphragm moves through substantially said range of spacing in re-sponse to said range of conditions to be sensed.
12. 12. A method of producing fiber optics condi-tion sensors comprising providing an optical fiber trans-mitter terminating at a termination, connecting said op-tical fiber transmitter to a standard light source and to a standard light detector, forming a thin metal diaphragm with a shallow curvature to provide it with a central re-flective portion providing the desired response to the conditions being sensed, forming first and second body members so that they can be telescoped together, mounting said termination on said first body member, mounting said diaphragm at its periphery on said second body member, telescoping said body members together to move said re-flective portion towards said termination to a position in which said detector indicates a predetermined value of reflective light, and locking said members in said posi-tion.
13. 13. A method as set forth in claim 12, wherein said body members are provided with a press fit to tem-porarily maintain them in said position until said mem-bers are locked in said position.
14. 14. A fiber optics condition sensor comprising a body assembly, an optical fiber transmitter mounted on said body assembly providing a termination located at a predetermined location, said transmitter being adapted to be connected to alight source and to a light detector, a thin metallic diaphragm mounted on said body assembly, said diaphragm being preformed with a shallow concave curvature providing a central portion movable in response to a sensed condition toward and away from said termina-tion, said central portion providing a reflective surface adjacent to said termination operable to reflect light from said source to said detector, said bundle and re-flective surface providing a reflective range from a max-imum possible reflective value to a minimum possible re-lationship between the movement of said reflective sur-face and the changes of the conditions sensed being an S-curve with substantially greater slope within a second predetrmined range of movement than provided by a simi-lar flat diaphragm formed of the same metal, said shallow curvature causing said reflective surface to move through said second predetermined range of movement in response to a predetermined range of sensed conditions, said first and second predetermined ranges of movement being sub-stantially equal, said mounting of said fiber optics bun-dle and mounting of said diaphragm being selected to cause the light reflected to said termination by said reflective surface to vary through a substantial portion of said reflective range in response to movement of said reflective surface through said predetermined range of movement.
15. 15. A condition sensor as set forth in claim 14, wherein said diaphragm moves through said second predetermined range of movement with snap action, said diaphragm being positioned with respect to said termina-tion so that it moves to a position close to but spaced from said termination as it snaps toward said termination to prevent impacting of said termination by said dia-phragm.
16. 16. A condition sensor as set forth in claim 14, wherein said diaphragm moves with non-snapping move-ment through said second predetermined range of movement and at a rate which is a substantially linear function with respect to the change of conditions sensed by said diaphragm.
17. 17. A condition sensor as set forth in claim 14, wherein said diaphragm is formed of bimetal and the condition being sensed is temperature.
18. 18. A condition sensor as set forth in claim 14, wherein said diaphragm is formed of a homogeneous metal and the condition being sensed is pressure.