[1]T T 3,067,617 Linited States Patent Office Patenteel Dec. 11, 1962 2 siderable non-linearity that males them extr-,mely difficult to calibrate and read. It has now been found, bowever, that a greatly improved pressure gage can be made which overcomes most of the aforementioned deficiencies in the prior art devices, yet which includes as its load-responsive element, a fi lament-supported rotatable indicator instead of a mercury-tube manometer. In the instant invention, a suitable indicator, preferably a mirror, is suspended between opposed pairs of tensioned and torsionally deflected filaments that are in turn attacbed to a Bourdon tube or other pressuresensitive element to form the load-responsive system of tl-e instrurrent. A reflectedimage-type op,ical system is operatively associated with the pressuresensitive system to produce a visual indication on a linear scale. A novel mechano-optical cam-actuated correction system is used to reorient the reflected image and correct for any nonlinearity introduced by non-uniform tensional and torsional loading of the filaments across the range of the instrument, and a photoelectricsplit-image type null indicatin.@ system is used to zero-in the corrected rep@ected image on the scale. It is, therefore, the principal object of the present invention to provide a pressure gage havin.- a sensitivity of more than twenty times that of any other instrument for the purpose. A second object is to provide a pressure-sensitive instrument of the type aforementioned that is quite rugged and portable, yet reliable. A tbird objective is the provision of a barometric device that reads substaiitially linearly over its entire range w@ 'thout being difficult to calibrate. A fourth objective of the invention is to provide a measuring instrument having an extremely accurate optical read-out system of a type adapted for either manual or auto.,natic operation. Another object is to provide a novel and improved cam-actuated mechano-optical correction system for r@ieasuring instruments. Still another object of the invention is the provision of a photo-electric split-image-type null indicator for optical read-out systems. Additional objectives are to provide a pressure-sensitive measuring device of the class described which is compact, lightweight, easy to op@-rate, simple to service, relativel@y inexpensive and decorative in appearance. Other objects will be in part apparent and in part pointed out specil@icaily hereinafter in connection with the description of the drawings that follow, ar@d in which: FIGURE I is a horizontal section taken along line 1-1 of FIGURE 2 showing the pressure gage of the pres-.nt invention, certain portions thereof having been brokei away and indicated by dotted lines; FIGURE 2 is a longitudinal section taken along line 2-2 of FIGURE I with certain portions broken away to better show the construction; FIGURE 3 is an enlarged fragmentary section showing various elements of the optical read-out system and correction systern; FIGURE 4 is a fragmentary top plan view to an enlarged scale showing the details of the cam-actuated mechano-optical correction system along with a schematic representation of the photoelectric null indicator of the optical read-out system in operative association therewith; FIGURE 5 is a fragmentary elevation to an enlarged scale shoiving the details of the coarse-adjustment mechanism of the oplical read-out system; FIGURE 6 is a fragmentary section taken along line 6-6 of FIGURE 5; FIGURE 7 is a fragmentary section taken along line 7-7 of FIGURE 6; 3,067,617 PRESSUI.ZE4 GAGE Willard E. Buck, Boulder, Colo., assi-nor, by mesne assignments, to Thomas W. Russell, Boulder, Coio. Filed Apr. 13, 1959, Ser. No. 806,OIL8 5 11 Claims. (Cl. 7,1-411) This invention relates to measuring instruments and, more specifically, to an improved pressure ga,@e of a type that includes the load-sensitive element which forms the 10 subject matter of my co-pe-nding application filed concurrently herewith together with a novel mechano-optical correction system adapted to substantiali'y eliminate aliy non-linearity in the read-out mechanism. Up to the present time the most accurate barometric 15 devices are those that include as their pre ssure-sensitive element a mercury manometer or series thereof. Instruments of this type are in widespread use and have been found adequate for a number of applications; however, recent tecbnological advances, especially in the field of 20 missile development, have proven them deficient in many important respects. Of the more significant limitations of the prior art pressure-sensitive dev@.ces, perhaps the most important is that of sensitivity. About the best that can be expected 25 of a niercury barometer under ideal conditions is a sensitivity of approximately one part in ten thousand. Unfortunately, in many specialized applications, - sensitivities of this order of rnagniti-ide are insufficient or at best marginal. Therefore, there is a definite need for a pres- 30 sure -age or the I-ike havin.- a greater sensitivity than those presefitly available. Another problem of considerable importance is the fact that mercury barorleters of the type aforementioned are extremely delicate and cannot, in any sense, be looked 35 upon as being portable. For instance, most of these barometers are mounted permanently on a fixed base in a test facil-@ty. This means, of course, that much of the complex ipstrumentation being tested must be removed from its environment, transported to the test 40 facility where the barometer is located, and returned for reipstallation. Obviously, delicate instruments are difi'icult to move from place-to-place in this manner without dama,@ing them and, if the dama,@e occtirs after they have been tested, a malfunction may occur without 45 warning. Still another difficulty arises in connection with - calibration of mercury barometers. Although instruments of this type are substantially linear, for maximum sensitivity they require that the mercury be removed and the 50 tubes cleaned at frequent intervals. Also, each reading must be corrected to compensate for both temperature and gravity. In addition to the aforementioned mercury barometers which are generally accepted as being the most sensiti,, 55 of the prior art pressure gages, there are a number of other types of pressure-responsive instruments that are suitable for use in less critical applicatiops. Of these the only ones that need be conside' I red here are those that i-,iclude as their pressure-resdonsive element, a ro- 60 ta@able ind-'@eator or mirror suspended between -oairs of ,kewed filpments. In general, pressure gages of the rotatin,@ mirror type are much less sens;tive than even a mercury barometer 6,r, due to substant;al hysteresis in the system and frictional losses found in various mechanical movements thereof. Also, these devices are somevihat sensitive to chan.-cs in temperature which renders the readings taken therefrom unreliable unless corrected. Finally, the preseice of 70 tensioned filaments, springs, etc., in the pr essure-responsive systems of most of these instruments introduces con-
[2]FIGURE 8 is a fragmentary section taken along line 8-8 of FIGURE I showing the details of the cam. forming mechanism; FIGURE 9 is a fragmentary section to an enlar,,ed scal-- taken along line 9-9 of FIGURE 3 showing the fine-adjustment mechanism of the optical read-out system; FIGURE 10 is a fragmentary front elevation of I a linear scale that can be used with the gage, portions thereof having been broken away to coilserve Space; FIGURE I 1 is a frolit elevation of the dial on the reader of the read-out system to a further enlarged scale; FIGURE 12 is a schematic representation to a flirther enlarged scale sliowing the optical reader in side elevation- and, @IGURE 13 is a view similar to FIGURE 12 showing a top plan view of the reader. Referring now to the drawings, and in p@artici-ilar to ,FIGURES 1 and 2 thereof, the pressure ga.-e of the prese@it invention has bee-ti shown housed in a case indicated in a general way by numeral 10 that includes a base 12 and adetach.able cover 14. The base is generally sect-o@--shaped and contaiiis an arcuate slot 16 that exter@ds between the, diver.-cit side edges 18 and 20 along the curved front ecige 22. The corners of the base are ipreferably s-uppoi7ted on adjustable legs 24 that form a tripod and pro,-,iide the means by which the instrument -can b-e leveled. A brac@k.-t 26 having a pin 23 projectin.- downwardly the.-efrom at the center of tiie circular are defiried by -slot 16, supports a radial a-m 3,0 for pivotal movement. The optical read-out system, null indicating system and porao-@is of the cal;brat:lon system, which have be,-n indicated broadly by numerals 32, 34 and 36, respec.tiveiy, are attached to the free end of radial arm 3,I) thi-ougl-i slot 16 for arcuate slidable movement along the top of the base in a manner that will be described in ,,-reat@-r detail, in co-rinec'io-@i witq FIC-URF-S 3, 5, 6 a-iid 7. ,@ The pressure--sensitv., iotatiiig mirror system of ti-ie pressure ga--- has been indicated in a general way by @numeral 33 and is supported on the baqe above the -pivotal co-r@n,-ctio-Ti for the radial, arrn. This system is housed within a cliai-nber d@-fined by a Dlate 40 attar-hed to the base, an inverted cup-like r@ieriiber 42 having a flang.- 44 around the lovier edge there(>f, and a collar -.-6 adapted@to re@.-cive the flarige on the cup-like member holdin- the same in s-laled relation on the Dlate to which -the collar is bolted. An 0-ring seal 43 is pref--rably locat@d between the contacting surfa-.es bf th6 plate and flange cup-like elem--nt in order to form an air-tight seal arol@.nd the bas,- of tle chambar. ne front of the cup-like element contains a window 50 located imm-.diately ahead of the mirror 52 of the rotatidg mirror system. A fused quartz Bourdon t,,ibe 54 is attach--d -- nd @seeiled vvi-Lhin registering ope-ilings thro-ugh plate 40 and base 12 by means of a two-part connector 56 containin,an 0-rin- se-al 53. Tbus a positive pressure connect--d into Bourdon tiibe S" tlirou.@h pipe 60 attached i-@ito the @iowe,r end bf fi'Ltin-@ 56, will tend to straighten out thz@ croo',-- in the Bourdon tube in a manner well Icnown in the att. A second p@'@pe 62 is also conne6ted thro,tigh the ba:se 12 and plate 40 into ihe interior of the-chamber to -provide ineans fOr measuriing differential pressures, botn a-bove and belo-,v atmospheric across the wah's of the Bour , don tube. In bther wards, when the instrument is -used to measure positivepressures, pipe 62 is cpeii to the atmosphere and the BoLirdon tube l's convected by means of pip-, 60 to the source, of positive pressure. if, on the other hand, , the instrument is to be used in -m-.asuring negative pressures, the Bourdon tt,.be is op,-ned to-the atmosphere and pipe 62 is connect@@d to the liega'tive @p'.@&ssure so-arce to pro I duce a vacuum i-iside the charnber. In differential pressure in--asuremen I ts whea neithe,r p I ressure is atmoshperic, the greater of the tw(> s,oo7,el7 4 pressures is connected into the Boufdon tube aiid the lesser into the chamber through pipe 62. Now, it will be seen that odposite ends of the crook in the Bourdon tube are provided with fused qtiat-tz filanl,-nt SUPPOTts 64 arranged in opposed relation to one another biit preferably in dir7erent planes that intersect one 9@nother along a li-iie substantially coincident with the pivot axis of radial arm 30. Two pairs of quartz filaments 66 are arran,-ed in opposed relation witli their 10 opposite ends fused to the supports 64. The adjacent ends of the filament pairs :are fused to opposite portions on the edge of the mirror 52 as shown. In accordance with tl-le teaching c-f my copending application filed co-iicurrently herewith, each filament of each pair thereof 15 is preloaded t6rsio-@ially in the same -direction approximately the sanic amount. In addition, each filament of each pair is pr,-Ioaded tensionally such that the tensicnal forces acting on the pairs of filaments in a direction to move thein from a skewed relation toward a co20 planar relation is cbunterbalanced by an equal and opposite torsional force act'@ng to,,move the filairents from a skewed relation ii-i the direction of a crossed relation. The non-linearity of the system is substantially reduced by reason of the fac@t tilat the two pairs of fila25 ments are arranged in intersecting plaies r@ither tllan a common plaiie prior tO Attachment to the mirror. This means ihat when ci-.e pair of filaments moves into co-platiar relatio-@i as the mirror turns, the other pair is becomir@.- more skewed @or moving closer to a crossed 30 rela'Lion which maii-itains a fairly Liniform force reiationsiiip in all angtilar positions of the mirror. It is also important to mention that the instant rotating mirror system contains no measurable hysteresis wha@l the severil elements thereof are formed from quartz 35 with fused joints therebetween. In addition, for all practical purposes tho system is frictionless as t'@iere are no surfaces rubbing agaiist one another, no bear;ii.-S and no sprin.-s other than the filament i)airs. Now, th-. front of the gage is provided with an areiiate 40 :face 63 that extends from side-to-side along an arc abodt the axis of rotation of the mirror as a ceiater and includes a pair of spaced substantially parallel openir. ,gs slots 70 and 72. The face is mounted on the base sli.-htly to the rear of slot 16 as shown most clearly in 4a- FIGURE 1. One end of the face 68 includes a Jai-np hoiising 74 co.@-itaii-iing a lamp 75 adapled to provide a source of illurnination. The rear face of the lamp housing is provided with a t-abular element 76 whose ax@l's iiitersects the axis c>f rotation <)f the mirror -t about tl-.e c@--@iter of the latt.-r. A plano-convex lens or the like 78 is located within the tubular eleri-.ent 76 -,nd is adapted to focus the filameiit of the lamp onto the obiective,leis 8{) po-sitioned between it and the mirror within t@,ibe 82. A bracket 84 supports tube 82 such that the axis thereof - -is substantially coincideiit with the axis of tube 76. The 00 rear end of tube 76 contains a disk having a vertical slit 85 formed tliereiii that functions to reduce the ligb, beam to an elongated narrow slit. Lens 80 is an achromat or the like adapted tb foc,,,is the slit of light on to apex of the splitting p-rism 86 in the null-indicatin(30 thportion of the reader which will be described presently. Splitting prism 86 is movable along the base along with various associated elements of the null-indicating syslem, optical read-out system and calibration syst.-m,into positioii to inter,-4pt the light beam reffected from the 65 niirror 52. With reference now to FIGURES 1-4 and 8 6f the drawings, it will be seen that the front of face 68 is provided with a scale 88 extending from side-to-side 70 th-creof above slot 70. This scale is linear and may include equal divis;ons of a 25/1000 of an inch as shown in FIGURE 10. The degree of angular d-.flection of the mirror 52 in response to different pressures appiied to ti-ic Bourdon tube is, however, @a non-linear function that.is 75 preferably correctable to read linearly. Although the,
[3]3,06@,617 5 i,on-linear@ity of the system can often be reduced below one percent by a proper selection of the range of pressures to be measured and the design of the inirror assembly, even this error must be eliminated by either correction or calibration in order to provide sensitivities of one part in two hundred thousand or better that can b-realized with this gage. Thus, the instant pressure ga.--is provided with a novel cam-actuated mechano-optical correct'on system 36 adapted to deflect the light beani between the mirror and splitting prism in a manner to compensate for any errors introduced by reason of the non-linearity of the pressure-sensitive mirror assembly 38. Accordingly, it can be seen that a plurality of fixed threaded elements 90 are attached to the base in arcuately arranged side-by-side relation. Each of these elemer@ts contains a threaded socket 92 (FIGURE 3) whose axis extends substantially radially from the axis of ro'cation of the mirror. An adjustment screw 94 having spaced abutments 96 on the shank thereof is mounted within the threaded socket in each of the clemen@s 90 for relative axial and rotational movement. An adjustable element 98 is mounted between the abulments 96 o-@i the shank of each of the screws for movcment toward and away fror@i fixed element 90 to which it is opvratively connected for radial movement relative to the mirror axis in respons@ to rotational movement of the screw. Note in connection with FIGURES 3 and 8, that the base 12 contains a plurality of radial slots ILOO loceitp-d underneath each of the adjustable eleme-@its 98 which receive the portions thereof lyin- between shoulders 102 for radial ad,;ustab,c@ movement. A friction plate 104 is attached to the underside of each element 98 by means of a pair oi- screws 106 and springs 108 which cooperate with the shoulders 102 to provide a yieldable friction co,-q,@iection betweell the base and adjustable element that allows the latt---r to slide yet maintains it in adjusted position. Of course, by tightening the screws 106 sufficiently tight agaiiist the springs and plate, the adjustable elemcnt can be held in substantially fixed position so that it cannot be moved by screw 94. Each adjustment element 98 has a pair of pins 110 projecting upwardly therefrom in spaced relation to one a,iother and arrari.@ed one behind the other, These pins retain therebet-,veen a spring band or strip 112 that extends in a generally arcuate path along behind the face of the ga.-e. It will be apparent from an examination of FIGURES 3 and 4 that this sprin,@ steel strip can b-@ bent and deflected to form an irregular cam surface by turnin.- the adjustment screws either in or out to change the relative radial positions of the adjustable elements 98 and pairs of pins 110 carried thereby. The slotted heads of these adjustment screws are re,,idily accessible through opening 114 in the face immediately above the base. Before completin.- the description an explanation of the correction system 38, it is advisable to mention briefly the manner in which the case 116 for the reader 118 and null indicator 120 is moiinted on the radial arm 30 for arcuate swingin- movement therewith and for e' limited adjustable mov ment relative thereto. For this purpose, refererce will be had to FIGURES 2, 3 a-@id 9 of the drawin,-S. The radial Frm 30 carries a block 122 near its free en'u in position to project upwardly througi arcuate open' , 'n, 16 in the base. A bedplate 124 is then mounted oi top of the block 122 extendin.@ both forwardly and rearwardly therefrom across the upper face of tt.e bas-.. T'iie bodplate 124 is provided w-ith a pair of tra-@isversely aligned and transversely extend-'@ng slots 126 adapted tO receive the shanks of screws 123 that are threaded into the unders;de of the case 1-.16 for limited relative movement. Thus, the case is connected to the arm, block and bedplate for limited transverse movement relative thereto and this feature constitutes the fine adiustment assemb]Y of the optical read-out system which will be described in detail presently. The actuating means by which this fine adjustment is accomplished comprises a generally U-shaped yoke or bracket 130 attached to the upper sur' ce of the bedplate .La a-@ld projecting into a socket 132 formed iii the underside of the case. The socket is intersected by a longitudinal bore 134 within which is mounted for rotational niovement the stem 136 of a fine adjustment control having 10 a knob 138 projectin.@ from the front face of the case 116. The stem includes an annular shoulder 140 which turns against the face of the cas-. and a screw 142 threaded into the rear end thereo'L whose head is recessed to form a rotatable retaining element. That portion of 15 the stem lying within the socket in the underside of the case is cut away to provide an eccentric portion 144 positior@ed between the spaced legs of the yoke. As the knob and stem are turned, the eccentric portion 144 engages one ol' the legs of the yoke 130 and moves the 20 case 116 fron-1 side-to-side relative to the radial arm 30, block 122 and bedp'xate. Relurning once a@aiii to that portion of the correction system 36 illustrated in FIGURES 1-4 of the drawing, it will be seen that 'Lhe reader case 116 includes an arin 25 146 projecting rearwardly therefrom through slot 7Z ir@termediate the top and bottoi-n edges of the face 68. Arrfi 146 is provided with an opening ther@pthrough within wliich ;s mounted for rotation about a substantially vertical axis, a prism mou-@it 143 on the top of which is 30' carried a prism 150 having a pair of plane p6lished faces 152 arranged in spaced parallel relation to one another and substantially perpendicular to the reflected image from the mirror. A crank arm 154 is attached to the prism mount for rotation therewith and carries a roller 35 156 journalled for rotalion on its free end in posifion to roll along the rear face of the cam strap 112 above the pins 110. Sprin.@ 158 attached between arms 146 and 154 biases the roller a.-ainst the cam strap. Now, it is, of course, obvious that the function of the 40 optical read-out system 32, yet to be described, is to provide the operator with a visual indication of the pressure being measured by the gage as shown on t.qe scale 88 viewed througli reader 118. Location of the optical read-out system at the correct position in front of the scale, however, is determined by the null-indicating sys45 tem 34 whicb is set to intercept the reflected image from the mirror and split the same on splitting prism 86. Null indicator 120 will show no deflection one way or the other when prism 86 exactly splits the light beam reflected thereon by the mirror and it is this position that 50 corresponds to the flilal pressure reading to be taken from 'Lhe reader. Were it is not for the fact that the correction system 36 is interposed between the mirror 50 and splitting prism 86 to correct for any non-linearity in the mirror system 38, scale 88 would have to be non-linear 55 and the manufacture of the instrument would involve expensive and time consuming calibration. Inclusion of the mechano-optical correctioii system, on the other hand, permits a '@inear scale 88 to be used and enables the instrument to be calibrated quite easily in accordance with 60 the procedure which will now be set forth. First of all, a known pressure is applied to the instrument and the reader 118 is positioned to read this exact pressure on the line,-r scale. In al@l probability, however, the null indicato.- will show deflection to the right or 65 left mea-qing that the splitting prism is not dividing the reflected image from the mirror into two exactly equal parts because of the non-l;nearity error in the rnirror systerr@. Such errors are usu'ally of the order of one percent or 'iess in a proper'@y designed unit and are easily 70 compensated for Nvith the correction system by merely ti-irning the adit-istment screw or screws 96 closest to the roller 156 in or out to shift the Position of adjustment elements 98 and pin pairs 110 radially, thus bending si)ring strip 112 in a inanner to turn prism 150. As 75 sbown ir@ost clearly in FIGURE 3, when prism 150 turns
