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Dec. 109 1946u Pf F. sHxvERs 2,412,54î ALTIMETER Filed Nov. 20, 1942 Bu 5 Sheets-Sheet l Dec. 10, 1946. P_ F,_5_H|VERS 2,412,541 ALTIMETER Filed Nov. 20, 1942 5 Sheets-Sheet 2 »EW-‘L Bu @We „4 @M5L Gitorucg Dec. l0, 1946. P. F. sHlvERs ALTIMETER Filed Nov. 20, 1942 5 Sheets-Sheet 3 mMT., Cîttorneg Dec. 10, 1946. Y P. F. sHivERs 2,412,541 ALTIMETER Filled Nov. 2o, 1942 5 Sheets-Sheet 4 È? @mi l@wìkts Gttorneg Dec. 10, 1946. P. F. sHlvERs 2,412,541 ALTIMETER Filed Nov. 2o,l 1942 //. ,YLT/Taos 500 @van 1 700 JM 400 200 /00 Bu -5 Sheets-Sheet 5 Patented Dee. 1o, e1am» l ' 2,412,541 UNITEDy y STATES PATENT OFFICE 2,412,541 -AL'rlME'rER Paul F. Shivers, Edina, Minn., asslgnor to Minne apolis-Honeywell Regulator Company, Minne apolis, Minn., a corporation of Delaware Application November 20, 1942, Serial No. 466,283 15 Claims. (Cl. 73-387) - My present invention relates to measuring instruments of the type which indicate changesy in the magnitude of a variable condition by their response to related changes in the pressure _of a means operatively connecting a pressure re .sponsive member and an indicating member, ln an. instrument such as I have described, the con~ nection being adjustable to compensate for difier gas mass. More specifically, my invention relates 5 ences, in density and temperature, between the' to the ñeld of altimeters which indicate variations standard atmosphere and the actual atmosphere in'altitude above a reference point by responding between the instrument and the reference peint. to the corresponding variations in the static air Another object of my invention is to provide pressure (that is, the barometric pressure). novel means, in an instrument such as l'. have The static pressure indicated by such an in- 10 described, for increasing or decreasing the altitude strument is influenced by the altitude of the instrument and by the density of the air mass and its temperature gradient. For the saire of unì- formity in instrument dial calibration, certain indicated by the instrument in accordance with increase or decrease of the density of the animeea phere between the instrument and the reference point arbltrary values of density and temperature have l5 A further Object or" my invention is te ¿Urol/ld@ been selected to define a "standard atmosphere." novel means, in instrument Such as' ï have rl‘his standard atmosphere is of suoli density as to described, for adjusting the instrument t@ ©0121“ give a barometric pressure at point one tout pensate L50? dîffeïâïlßës bâïJWEeü the 2li-@2m ÈGII m cury above sea 29.92 levelinches equal tohigh. that oi?‘The a column temperature of mergradient in the standard atmosphere is -sucli that at sea level the temperature is F., while te@ perature mean temperature of the standard of the atmosphere atmosphere between the instrument im@ the T’êîeï‘enß@ Swim Yet another obiect of my invention is to are» vide novelineanain aninstrurnent suoli as b describen ÍOT âäïálls'tîâ’ls the íïll‘ìißä?i‘ôïlî Gl instrument in accordance with variation in temperature at the reference point. temperature is _67° at the bottom si an 35;; thermal layer which has been found ‘to exist at a variable height of> approximately 35,@@0 m middle latitudes. .ln this standard atmosphere the barometrie pressure has ‘been :found to have an inverse logarithmic relation te the altitude, ' and pressure responsive means have been designed. to give indications'on a linear scale resp@ to logarithme elianges in pressure, ”' e altitude A still further object of my ` provide novel in en instî’urne " have described, for adjusting the ' i instrument simultaneeusl on this scale corresponding to se given static pressure is called the “pressure altitude” the point at which the pressure indication is ense-riferi, and is the altitude indicated by altimeter. The atmosphere enveloping not normally thi s but differs uncompensated craft :lT i’ tuile therefor the actual ai nie ence point. aríatiens ... llave indicated altitude @een due to extreme barometrì C may be caused. by Variations of t,M from the standard. is an object of my invention to gravide, ‘in »Ji Èîï@ îï‘lßïï‘üïïleîîî a pressure responsive instrument for measuring 5S referente altitudenovelmeans loradiusting tneinstrument met et. my invention is to nio to compensate for tite differences between the separately onerabi eentrel means for elec standard atmosphere and the actual atmosphere pressure adjusting an'aitimeter tite referente forpeint air ternperatru‘e and for responu between the instrument and a reíerence point.. It is another object of my invention to provide . .I - | - )J sltely I? ~ r. :e „ A» -`~- a. ticle rea-¿lne of the altimeter 2,412,541 4 Other objects and advantages of this inven in» accordance with the temperature and static pressure of the ambient atmosphere. tion are set forth in the following description, It is also‘an object of my invention to pro- ` vide electrical means for the transmission of the novel features thereof are pointed out in the taken with the accompanying drawings, and appended' claims. The disclosure, however, -is atmospheric pressure changes to indicating CII illustrative only and I may make changes in means whereby to eliminate insofar as possible detail, especially in matters of shape, size and meremechanical means for the amplification of arrangement of parts within the principle of the the movement of the pressure responsive means. Another object of my invention is to provide a balanced electrical bridge circuit and means for unbalancing the circuit operated by the pres invention, to the full extent indicated by the broad and Vgeneral meanings of the terms in which the appended claims are expressed. sure responsive member or aneroid of an altim eter, whereby, upon a change in .the position partsin the various ñgures, of the aneroid, the indicator means of the al- timeter may be actuated and the aneroid re 15 20 vide control means for adjusting or varying the return or zero point of a. counterbiased aneroid for aI given ambient pressure, such control means Figure l, ~` Figure 3 is an enlarged end view of the atmos- Y pheric pressure responsive control member of 'Y Figure 1. being regulated `by a temperature . responsive Figure 4 represents a _modiñed form of manu ally _operable .temperature compensating con trol - ' A perature compensating control means shown in arise. ‘ Y of my invention, Figure 2 is an enlarged end view of the tem- y ing parts through which mechanical error might means. K Figure 1 represents diagrammatically one form turned to the original or zero position so as to eliminate insofar as possible mechanical or mov - Further; it is an object of my invention to pro i In the accompanying drawings wherein like reference characters indicate corresponding ' Another object of my invention is to provide a pressure responsive altimeter and electrically . operated means for the automatic correction of means. ` » ' ' ' ' Figure 5 is a front elevational view of the ccn Vtrol panel of 'my invention shown in Figure 1 with the manually operable temperature compen sating control means of Figure 4. ^ the indication of the instrument for the -in iluence of changes in atmospheric temperature. 30 Figure 6 is a pictographical representation il lustrating the variation in indicated pressure al It is also an object of my invention to provide > _ in an altimeter a. plurality ofv photoelectric cells and a plurality of separate means for_varying_ the relative electronic emissions therefrom so as to regulate the zero or return point of a counter biased atmospheric pressure responsive member or aneroid for a given ambient pressure, one of , said means being controlled by the atmospheric pressure responsive member and the other of said means being controlled by a temperature 40 responsive means. ' Another object of my invention is to provide an instrument which will utilize an outside sourceV of power for .operating the gear train of the in dicating mechanism, instead of utilizing the ` titudes from an assumed standard altitude due to changes in atmospheric pressure caused by vari ation in the temperature of the mass or’atmos pheric air column above and below the assumed standard temperature. ‘ Y ' >Figure '1 represents a circuit diagram of a sys tem embodying a second form of my invention. Figure 8 is a front elevation of the control panel for the form of my invention shown in Fig ure'l. ' _ Figure 9 represents a circuit diagram illustrat ing a furthermodifled form of my invention. Figure 10 is a front elevation of the control panel for the form of my invention shown in Fig ure 9. relatively small movement and power of the at Figure 11 illustrates graphically the eüect on mospheric pressure responsive member or barometric pressure of variation of the actual aneroid, and in addition to so arrange the pres mean temperature from an assumed standard sure‘responsive, member Vor aneroid that it will temperature as the altitude increases and have to work through only a very small range oi 50 mean showing that the greater the rate of temperature movement. . drop per unit change in altitude the lower the Another object of my invention is to provide barometric reading for any given altitude. control means for adjusting or varying the re In each of the curves of Figure 11 the ground turn or aero point of the aneroid or atmospheric barometric pressure at sea level is assumed to be pressure responsive member of my invention, for ‘760 millimeters of mercury. Starting with this v a given ambient pressure, whereby the ratio value, the line designated by the letter A indi between barometric pressure and indicated alti cates the relationship between altitude and tude may be increased or decreased. ' barometric pressure under a hypothetical con Another object of my invention is to provide control means for varying the operative stand 60 dition wherein the temperature of the air is con stant at all levels. The line indicated by the let ard or translation factor oi an instrument such ter B indicates the relationship between altitude ` as l; have mentioned in accordance with varia and barometric pressure under a second hypo tions in atmospheric conditions. thetical condition wherein the temperature of the A further object of my invention is to provide, atmospheric air at sea level is assumed to be _15° _ in an altimeter, a plurality of photoelectric cells C. and there is a decrease in the temperature of subjected to illumination from a source of light substantially 1.13 degrees centigrade for every and control means adapted to regulate the illumi 100G-foot increase in altitude until the isothermal nation of the photoelectric cells whereby to cause layer is reached at the 35,332 foot altitude level actuation of the indicator means of the altim where the air has a. temperature of -55 degrees eter. centigrade. Under such conditions the mean An additional object oi my invention is to pro, temperature of the air column is substantially vide, in an altimeter, a balanced bridge circuit -35 degrees centigrade. The line designated by and adjustable means for unbalancing the circuit the letter C illustrates the relationship between so as to cause actuation of the- altimeter indi 75 altitude and barometrlc pressure under condi catorÀ means. ' ' 2,412,541 tions most generally assumed as standard in the calibration of the conventional altimeter: the temperature ofthe atmospheric air at sea level is _y y 6 . l winding 1 comprise the input terminals oi' the bridge circuit and a pair of, output conductors il and l1 are connected respectively to center tap assumed to be +15 degrees centigrade and for Il and to a terminal 20 on conductor H. “Center ,every 100G-foot increase in altitude the tempera 5 tap Il and terminal 20 constitute the output ter-` ture decreases substantially 2 degrees centigrade minals of bridge circuit 35, and are connected until the isothermal layer is reached at which by output conductors II and I1 with the input point the temperature of the air is -55 degrees terminals 2| and 22 of a thermionic amplifier centigrade. -Under such assumed standard con indicated generally by the numeral 39, and hav ditions the air column has a mean temperature of 10 ing output terminals 23 and 24. This bridge cir -20 degrees centigrade. The line D indicates cuit is designed so as to be balanced when the the relationship -between altitude and atmos amounts of light supplied to the cells bear a pre pheric barometric pressure under a hypothetical determined ratio to each other. Any decrease condition wherein the temperature of the atmos under the Ápredetermined ratio of the light sup pheric air at sea level is assumed -to be +145 de 15 plied to cell 5 to that to cell 6 causes a propor grees centigrade and there is a decrease in the tional increase in the resistance of cell 6, un temperature of the atmospheric air of 5.66 de balancing the bridge circuit in such fashion that grees centigrade for every 1000-foot increase in a potential diiîerence appears between termi altitude until the isothermal layer is reached with nals 20 and I8 having the same polarity and a temperature of -55 degrees centigrade. The 20 time-phase relation as the potential between ter latter air column has a mean temperature of minals Il and I 6, and of a magnitudepropor +45 degrees centlgrade. , tional to the unbaiance of the bridge. This po The computations'of the aforenoted graph are tential difference is fed through conductors I5 derived from report No. 538 of the National Ad-4 and Il to input terminals 2i and 22 of ampliiler visory Committee for Aeronautics and the alti 39.' tude pressuretablescontained therein based on Further, an increase over the predetermined the United States Standard Atmosphere. vIi’rom ratio of the light supplied to cell 5 to that to cell a study of the foregoing graph it will be seen that 6 causes a proportional decrease in the resistance the greater the rate of temperature decrease with of cell t, unbalanciiig the bridge circuit in such change in altitude the lower the barometric read 30 fashion that a potential difference appears be ing for any given altitude. Thus in an atmos tween terminals liti and ‘i6 having the same po phere where the rate of temperature decrease larity and time-phase relation as the potential with change in altitude is greater than that in cliñerence between terminals it and it, and also the standard atmosphere, the ’oarometric pres» o1? a magnitude proportional to the unbelance ol" 'the bridge. This potential cliñlerence is also fed. directly Since to terminals instantaneous 2i and 22 potential ci amplifier difference sure at any level ‘is greater’than that in thegstand arti atmosphere, and an uncorrected altimeter iri dicates too low all altitude. Similarly, in an at-= aerosols-ere where the rate oi” temperature decrease, with change :in altitude is less than iii the with between terminals between the î terminals "’eiitial and i@diiïerence is 135° ansi outimpresse itor"will ~f standard osphere, an unoorreeted altiree‘ter 40 seen. inrlieates too leigh en altitude. across resistance terminalsof cell and 22 is oi’ decreased. amplifieris39oi’t lt“ e lilly invention embodies means for automa@ loa y' eorreoting saisi erroneous iiie'hoations of an ' e phase to that impress-eel on the e " ' ait meter so that the instrument willi give »correct 'when resistanse of ne electronic ' amplifier o1 tempes@ altiti re `e ` indieetions ‘ litioos n 'or regardless diverse or" thefrom ambient of whether those et the 'oh as sie sl atmosphere. " 25, i923, " of my invention means if), and ii, ' ’ "'“ "~ of? oeil S latter ' ' 5 and. c eet impe reses to constitute two aegee-exit arms ci? a bridge circuit indicated generaliy by the ninnerai de, which the remaining two ati-ï ‘iaoent arms comprise the' halves secondary winding ’i‘erroinets it and itl ot secondary ¿ „ce secondary lne ane senses i ~ N ` y f l 'l n ,_ 2,412,541 7 oid 65 by the spring 41. Spring 41 is operatively , As described in detail in the co-pending Upton adjusted by cam 46, in response to motor 3|, so as to increase or decrease the force exerted by spring 41 upon the -aneroid 65, as .previously ex application previously referred to, ampliñer 39 is of a type >which produces in the output circuit including conductors 26 and 21 and motor wind plained. ing 33 an alternating current of the same fre 64 is adapted to be slidably ad- ` - The member -quency and phase as the potential applied to justed by a vernier adjustment knob 11 mounted input terminals 2| and 22. Since transformer on an instrument panel 54 whereby themeinber primary windings 29 and l2 are both connected 64 may be move-d linearly vwith respect to member to the same alternating current supply lines |3 _63, whereby to vary theportion of aperture 62 10 and |4, it will be understood that the potentials covered by member 63. Knob 11 has a pointer l89 appearing at the terminals 'of the secondary wind for cooperation with suitable scale markings ycar ings 30 and 1 are of the same phase. The cur ried by panel 64, and is yconnected by a shaft 86 _ rent liowing through winding 32 is, however, to vernier pinions 61 -which operatively engage shifted substantially 90 electrical- degrees with rack teeth 68 formed on the slide 64 as shown in l respect to this potential by the condenser 38, as Figure 3. The sh‘aft 68 is suitably journalled in previously explained. The winding 33, on the bearings 66 mounted on a fixed member 69. other hand, is supplied with current either in The cam 46 turns in a clockwise direction as phase or 180° out of phase, with the terminal pothe altitude increases and is so shaped as to pro tential of windings 1 and 30 depending upon the 20 gressively decrease the vertical adjustmentim direction of unbalance of the bridge circuit 35. parted to the roller 1| per unit of rotary motion In accordance with the well known character conveyed by shaft 45 as the altitude readings of istics of a split vphase motor, when the windings the indicator increase. Thus,v at ground level> 32 and 33 are supplied with currents 90° out of for example, cam 46 is positioned so that roller phase, the motor 3| is caused to rotate in a prede- ' 1| is near its closest -approach to the center of termined direction, depending on which of the shaft 45, and upon a decrease in pressure the currents lags and which leads.` The operation aneroid 65 expands upward. -Since at `this point of a split phase motor of the type described here the relative movement of cam 46 necessary to in is well .known in the art and is described` in lower lroller 1| to increase the force exerted by spring 41 to balance the circuit is relatively slight, the indicator recording for such a movement is lthe co-pending Upton application previously re ferred to. . . The motor-3| is arranged to drive -a shaft 40 ’ in a direction depending upon the sense of -the ‘ »unbalance of the bridgecircuit 35 and the re sultant phase oi the ‘current supplied from the amplifier to the motor 3|. The shaft 40 is, in turn .adapted bysuitable means such as a gear Y correspondingly slight. However, at yrelatively high altitudes, cam 46 is correspondingly ad -justed so that roller 1| is relatively widely spaced from the center of shaft 45, and considerably ' greater rotary movement of cam 1| is necessary to cause suiilcientl increase of the spring tension to return the slide 63- so as to balance the circuit. This increases the necessary rotary movement of the shaft 45 and causes a correspondingly greater - is further adapted by suitable means such_as 40 indicator recording per unit of pressure change. the shaft 40,' train of gears 4|, and a further . >'ll'his variation in the multiplication ratio of the i shaft 45 to turna cam 46 which cooperates with indicator means, as the altitude increases, is nec a roller member 1| mounted on a loading spring essary in order to approximate the true alti 41 for the adjustment` of the tension in the since, as previously explained, the vertical spring 41.V The loading spring 41 is pivoted at` tude, distance traveled for each unit of pressure fall one end on a knife edge 12 4and operably engages increases with the altitude.> » at the opposite end ananerold 65, exerting a com# The operation of this portion of my„invention pressive force on the aneroid 65 dependent in will now be apparent. In the normal position of magnitude upon the adjustment of „the tension train conventionally indicated at 4I to drive an indicator means 43, which isof a suitable type well >known in the art. Moreover, the motor 3| grêaintained in the loading spring d1 by the cam the slider 63 the amount of light passing through aperture 62 and falling upon photoelectric cell 6 is equal to the amount falling upon photoelectric cell 5, and the bridge accordingly is in balance. As shown in Figure 1, there is mounted be tween the photo-electric cells 5 and 6 an illumi Upon a decrease in atmospheric pressure, aner nating lamp 5 l, energized through a suitable elec 65 expands, causing slider 63 to move up tric circuit ëü; ‘this lamp provides the sole source 55 oid wardly to decrease the area of aperture |52 and oí’ light for the cells. Suitable means are pro thus to decrease the light falling on photoelec» vided such as lenses E32 and 53 for directing the tric cell f5. The resistance of the cell is thereby light rays from the lamp Eil to the respective increased, unbalancing the bridge circuit in a first photo-electric cells 6 and 6g. T ' direction. The unbalance potential acts through in order to control the supply> of light to the ampliner 3Q to energize winding 33 of motor di photo-electric cell 6 suitable control means are in a iirst time-phase relationship. Motor 3i op provided which, as shown in Figure 3, may com-y ' erates in such a direction as to rotate cam ¿3G in prise' an adjustable member 66 having provided a clockwise direction until the force exerted on therein an aperture 62, for the passage of the light , aneroid tä'by spring ¿l1 has been increased by an rays from the lamp 5i to the photo-electric cell 6, anda control slide 63 for regulating the supply of light passing through the aperture 62 to the photo-electric cell â. The control slide 63 is vop eratively afñxed at one end to a resilient bellows or other pressure responsive member 65 which may conveniently be referred to as an aneroid, 65 and the loading sL ing d1. The expansive force exerted by the aneroid 65 is counteracted amount equal to the decreased compressive force of the atmospheric pressure on the aneroid. lThis increase in the force of spring ¿il .is accompanied by a compression of the aneroid, and slider 63 moves downward with it, thus increasing the area of aperture 62 until equal amounts of light fall on both photoelectric cells. The bridge circuit is vnow again balanced, and operation of moto!` 3| is accordingly interrupted. actuation of the mo by the atmospheric pressure acting upon the aneroid 65 and by the force exerted on the aner 75 tor has at the same time resulted in changing the - 2,412,541 reading oi member 43 so that it indicates a higher altitude. In the same fashion, upon- an increase in vat mospheric pressure aneroid C5 contracts, caus ing slide „to move downward to increase the area of aperture 32 and thus Ato increase the light falling on photoelectrlc cell l. v'I'he resist ance of the .cell is thereby decreased, unbalanc , , lo tions varying altitude indications may result at a given altitude level depending, upon the state of the air column whether contracted or ex panded. In order to obviate inaccuracies in~ the indi-l -cation of my instrument due to the eflect of tem perature changes, Lhave provided in the form oi' my invention illustrated in Figure l (as best ing the bridge circuit in an opposite sense to that shown in Figure 2) a ñxed light control mem Just described. 'The unbalance potential actsl through4 a'mpliner It to energize winding 33 o! 10 ber 82 having an aperture 33 of a selected out line. A shutter -8| is pivotally attached by a 'motor 3| .in a second time-phase relationship suitable pivot 80 to the ñxed member 32. The which is also opposite that just described. Motor pivoted shutter 3| is operatively connected by a 3l therefore operates this time in such a direc rod 58 to a free air temperature responsive device tion as to rotate cam ‘l 1n av counterclockwise 15 ofthe ñuid illled type including a bellows mem direction, until the torce exerted on anerold 65 ber 59. The lower end of member 58 has con bysprin’g il has' beenreduced by an amount nected thereto a conduit 6G which connects equal to thel increased compressive force o! the remotely with a- free air thermometer bulb ele atmospheric pressure on the4 aneroid. ‘This re ment indicated by numeral 5 i . The thermometer duction in the force of spring 41 is accompanied 20 bulb element 6| is preferably mounted so as to by an expansion of the aneroid, and slide G3 contact the free atmospheric air so that the iiuid therein may respond volumetrically to the moves upward >with it, thus decreasing the area of aperture 62 until equal amounts of light fall on both photoelectric cells. The bridge circuit - is again in balance and operation of motor 3| is accordingly interrupted. This actuation of mo tor 3| has, however, resulted in change in the reading of member 43 so that it now indicates a temperature of the free air atmosphere. It will thus be readily seen that as the free air tem perature decreases the member 59 contracts caus- « ing the rod 58 to rotate the shutter 8| in a clock wise direction about pivot 80, so as to progres sively close the slot 83 and thereby decrease the ñow of light to the photo-electric cell 5. It will be understood that the resistance of cell 30 A manually adjusable turnbuckle 92 is pro B is determined by the area oi aperture 62 vided for regulating the length of rod 58. It will through which light from the source 5| may pass, bè realized that the iluid contained in members and that an increase of this area due to raising 59, 60, and 5| is also subject to expansion with the upper edge by operation of knob 11 produces lower altitude. I the same effect as an equal increase of the area due to lowering the lower edge by the operation of aneroid 85. If the barometric pressure at the reference point is greater than standard, the static pressure at all levels also exceeds that of the standard for that level, and the aneroid is at all levels compressed beyond the amount which is proper for an accurate reading of alti tude in the standard atmosphere for which the instrument is calibrated. Thisin turn means that aperture 62 is at all times o1' too great area. It will now be apparent that actuation of knob 1l to move member 64 in a downward direction has the effect of partially closing the‘aperture, and that by suitably calibrating the rectilinear response of aneroid 65 to changes in static pres sure, the rectilinear movement of member 84 cor responding to a unit of the scale on panel 54, the graduations on indicator 43, the outline of cam 46, and the tension in spring di (the out line of aperture .62 also being considered) the indicator may be made direct reading in altitude above an arbitrary level, regardless of changes release of pressure on bellows- 59 due to increase of altitude. The actuation of» indicator 43 due to the energization of motor 3| by amplifier 39 is dependent in magnitude on the ratio between the resistance of photocells 5 and '6, that is. on the ratio of the quantitiesof light impinging upon the anodes of the two tubes. The rectilinear response of bellows 59 to changes in pressure, its response to changes in temperature, and the outu line of aperture 83 are so selected that if the length of rod 58 is adjusted by means of ‘turnn buckle S2 to bring shutter 8| flush with the bot tom of aperture 83 when the instrument is under standard conditions at the reference point, the relative occlusion of apertures 83 and 62 with rise of the craft through a standard atmosphere 50 causes uniform increment in the indications of indicator 43. For a rise of the instrument through an atmosphere having a temperature gradient other than standard the relative oc~ clusion of aperture by shutter Si is deter« mined as before by the joint effect of temperature and pressure changes on taking place a different rate so theta factor proportional to in the density of the air. The reverse of this the departure of the temperature gradient is true if the pressure at the reíerence point is through which thecrait is rising from the standn below standard. As I have previously explained in connection 60 ard gradient is introduced into the signal elîect« ing actuation of indicator It will further be with Figure ll, the barometric pressure at any noticed that this factor occurs independent of altitude, and therefore the pressure altitude or and may occur simultaneously with change in indication of an uncorrected altimeter, is in-~ the factor iniiuenced by variation in pressure, fiuenced by the mean temperature of the air col» umn between the observer and ‘the ground. This 65 controlled by member G3 and aperture di?. The purpose of turnbuclrle t?? is to bring; the I have illustrated in Figure 6, which shows that upper surface of shutter di flush with the lower although the indicated altitude under high and low mean temperature conditions is the same as the actual altitude under the standard tem perature conditions, the actual altitude of the observer is above the indicated altitude in the case of high mean temperatures and below it in the case of low mean temperatures. lThus, it will »be seen that under such condi portion of aperture d3 in the beginning oi’ the . rise of the craft, so that there will be no period during which the shutter is moving with respect to member 82 and yet not'varylng the occlusion of aperture 83. Not only the temperature gradi ent through which a craft must rise from a given reference level, but the temperature at the start ing level may vary from the standard. The 2,412,541 12,„ traction 'of the gas mass or free atmospheric air mechanism I have just described has been pro ` column resulting from changes in the tempera vided to permit correction of the instrument for. _` ture thereof above or below an assumed standard variations in gradient, but I also provide means for correcting the indications of the instrument As is well known in the art and graphically value. for variations in the temperature at the refer ence level. For this purpose there is provided a slide 88 having mounted thereon rack teeth 8'! ' - ` shown in Figure 11,l the vertical distance traveled for each unit of barometric pressure , fall in creases with the altitude. Therefore, in order to secure a scale evenly divided in altitude units pinions 85 are' connected to a shaft 84 journalled the ratio of the movement of the indicator means 10 in bearings 44 mounted on the member 82, the 43Ito the deflection` of the pressure responsive shaft 84 projecting through a suitable control element 85 must vary continuously with the alti panel 54. Mounted at the free end of the shaft tude. For this purpose'the cam 46 is so shaped 84 is an adiustment‘knob 48 having provided a that the movement of the cam ¿it required for pointer 42 for cooperation with suitable scale unitary- increase in the tension in spring 41 in markings on the control panel 54. Thus, by ad creases as the indicated altitude increases so justing the knob 48 .the slide 88 may be raised or that the ratio between unit increase in altitude lowered with respect to the slot 83 and-the i'low indications and unit of atmospheric pressure fall of light to the cell S‘through the slot 83 thereby is properly increased with the altitude. adjusted. ’ This is specifically accomplished by construct It will be understood that the resistance of cell 20 ing the cam 46 so that the pitch of the actuating 5 is determined by the area of aperture 83 cam surface decreases in proper proportion for through which light from source 5| may pass, the assumed standard of operation as the cam is and that'an increase of this_area due to raising turned in response to a decrease in atmospheric operably engaged by a pair of pinions 85. The the-upper edge by operation of knob 48 produces pressure or rise in altitude. Thus as the altitude the same effect as an equal increase of the area 25 increases the rotary movement of the cam 48 -due to lowering the lower edge by operation of Y bellows 58. 1f the temperature at the reference pointis above the standard, bellows 59 is ex ' panded and shutter 8|, if adjusted to the lower edge of aperture 83 under standard conditions, necessary to return the aneroid to the 'starting - or zero position is increased per unit of pressure has now taken a position below the edge of aper-ture 8| in an effort to still further increase the' area for light flow. , fall. , Further, as previously explained, as the tem-_ perature of the atmosphericlair contacted by the bulb 8| decreases, the shaft -45 is rotated by the motor 3| so as to turn the "cam 46 in a counter clockwise direction decreasing the tension of the Movement of shutter 8| below the point at loading spring '41 s_o that the aneroid 85 may ex which lit coincides with the bottom ofl aperture pand upward to a position where slider 63 so 83 introduces error into the device, since it makes no actual change in the area through which light ' limits the passage of ~`light to photoelectric cell 6 that the bridge circuit 35 is balanced. ` may pass to impinge on cell >5. It is necessary Figure 11 shows that the barometric pressure that the shutter have that position of coincidence with respect to aperture 83 at the beginning of a 40 at an altitude of 25,000 feet in a standard at mosphere is 278 millimeters of mercury: in the flight. Therefore turnbuckle 92 is adjusted to atmosphere of lower mean .temperature the set shutter 8l in coincidence with the bottom- of pressure is 290 millimeters, while in that of higher \ the slot, and the area of aperture 83 is increased mean temperature the pressure is 255 millimeters. , by actuation of knob 48 to provide the necessary - An uncorrected altimeter is calibrated in terms ratio of light impinging on cell 5V and 6 respec of the standard atmosphere, and therefore reads tively. This light ratio acts through the bridge 24,250 feet in the colder atmosphere and 27,500 and amplifier to’energize motor 3| in such `fash feet in the warmer atmosphere, although the ion as to move indicator 43 to a position consist ent with the departure of temperature from the ì plane is actually at an altitude of 25,000 feet in each case. In order to bring about a correct standard, and this corrects the instrument for 50 reading of my altimeter in the warm atmosphere, temperature variations at the reference point. .my spring -46 must increase its pressure upon It will be appreciated that an increase in the illlnnination falling on photoelectric cell> 5 (which lowers its resistance) is eiïectively the same in the bridge circuit asa decrease in the illumina tion of photoelectric cell 6 (which raises its re sistance) , and that the opposite is also true. »r VAs the temperature decreases the shutter 8| pivots upward so as to progressively close a por aneroid 85 by an amount equal to the pressure differential between 27,500 feet and‘25,000 feet or, 23 millimeters of mercury. The aneroid is actually working in the 27,500 foot range while the indicator and therefore cam ¿i6 is Working in the 25,000 foot range. Similarly, in order to bring about a correct reading of my altimeter tion of the slot 83 thereby decreasing the light 60 in the colder atmosphere, my spring e5 must de crease its pressure upon aneroid 65 by an amount supplied to the cell 5. If the decrease in tem >equal to the pressure diñerential between 25,000 perature is at a rate greater than that in the feet and 24,250 feet: that is, by l2 millimeters of standard atmosphere, this decrease in light is of such magnitude as to unbalance the bridge in V mercury. Now suppose that the craft rises to an actual the same sense as motion of member 03 .down 65 elevation of 26,000 feet. In the standard at ward: that is, motor 3i is- actuated to decrease the pressure is 268 millimeters of mer the reading of the indicator and to reduce the ’ mosphere cury. -In a colder atmosphere it `is 278 mil force of 'Spring 4l on aneroid 65. A decrease in temperature thus hasv the same effect onl the bridge circuit and the motor as an increase in pressure due to a decrease in altitude.' 4An in crease in temperature has the opposite eiïect. _The 'introduction of these factorsinto the read ings of the instrument corrects the instrument Y ' for errors introduced by the expansion 0l' 09n- . limeters, and in a Warmer atmosphere it is 242 millimeters. The change in pressure in the standard- atmosphere is 10 millimeters. In a colder atmosphere the change is 12 millimeters while in the warmer atmosphere the change is 13 Vmillimeters. The indicator of my compensated altitude must'ndiove through a distance propor 13 2,412,541 ` tional to the change o! 10 millimeters, regard-_ less of the atmosphere. My temperature com pensator, therefore, alters the operative standard l» of the altimeter so that the same change in in dicated altitude takes place whether the change in barometric pressure be 10 millimeters in an atmosphere of standard temperature, 12 mil limeters in a warmer atmosphere, or 13' mil limeters in a colder atmosphere. In certain simplified applications it may not be desired to have the temperature responsive. device include both responsive and manually operable members. In such an application a modified form >of means for controlling the light 14 ing a common terminal |30. 'I'he resistance III is connected'to the impedance coil II3 by a con ductor |I8 While the resistance II2. is connected to the impedance coil |I4 by a conductor H9. A pair of terminals |32 and |33-v are located on ’ conductors H8. and IIS, and constitute the input terminals of the bridge circuit.A The bridge is energized from the secondary winding |22 of a :transformer |23, to which connection is made 10' by conductors |20 and I 2|'. Current is provided _ in secondary winding |22' by transformer action . from primary winding |24, which is supplied with alternating current from any suitable. source by I25iand I 26. . . " supplied to photo-electric cell B_may be provided 15 conductors Terminals |30 ‘and l3-I comprise the output such as shown in Figure 4, wherein-a fixed light terminals yof Abridge circuit- H0, and are con- ' control member 95 is provided having formed therein an aperture 96. Ailixed to a. shaft 91 pivotally connected to the member 95 is a shutter S8. Mounted on the shaft 91 is also a gear 99 intermeshing with a second gear 14 aiiixed to one end of a control shaft 15 which is journaled in a, bearing arm 49 projecting -from the member 95: said shaft 15 passes through a suitable aper ture formed in the control panel 54. A control knob 55 is mounted on the shaft 15 for addust ` ment of the shutter 98. A pointer 56 may be y provided on the knob 55 for cooperation with a suitable indicator scale as shown in Figure 5. The member 95 and control shutter arrangement may be readily substituted for the temperature responsive control shutter for controlling the illumination passing from light 5I to the photo electric cell 5 the amount of light passing through the aperture 96 being controlled by the position of the shutter 98. An altimeter of the type embodying manually adjustable control means such as shown in Figure 5 is readily adapted for use Where accurate cor rection factors are available. Thus, for example, if a ground operator in a commercial air line organization ñnds that in order to correct the ground altimeter so as to indicate the actual ground altitude at the ground level it is necessary to adjust the position of knob 11, such information can be conveyed by radio to the pilot of the plane. Similar information regarding the temperature at the ground station may be given to the pilot in the same way. The information supplied to the pilot enables him to operate knobs 418 and 'El so that suitable correc tion for change in the atmsopheric condition at the bottom of the column of air may be made. The altimeter then operates at an assumed stand ard based upon actual ground atmospheric con ditions rather than upon an assumed standard based upon an assumed ground atmospheric con margin dition. of lThus, erroratisrelatively the altitude slight to be measured since the in dicated altitude is in error at Ythe point of measurement only insofar as the atmospheric conditions at such. point varies from the known ground atmospheric conditions rather than from an assumed ground atmospheric condition. Further, if desired, the reading of the altimeter may be corrected for temperature conditions existing at the upper level or point of flight or for the difference between the ground temperature and the temperature at the flight level. ln a further form of my invention illustrated by Figure 7 there is provided a variable reluctance or impedance bridge circuit indicated generally by the numeral itil and including variable re sistances Hi and lili having a common ter minal I3l and impedance coils lit and ttt hav nected as by conductors I 21 and |28 with input , terminals |36 and> |35 of an amplifier I25lhav ing output terminals |36 and |31. ' ` It will be readily seen that the coils II3 and H4 form two adjacent arms of the variable im. pedance bridge circuit I|0. The variable resist ance windings l I| and I i2 form the opposite arms ~~ of the bridge circuit I I0. v Coacting with the coils II3 and II4 is a mov able core II5. The core I l5 of magnetic mate rial is operably connected by a rod IIS to an at mospheric pressure responsive member or aneroid II1. ’ The bridge circuit l I0 is so arranged that nor _mally with the core I I5 positioned substantially equally within the two coils I I3 and I I0 the vbridge circuit IIO is ìbalanced and no potential appears across output terminals I 30 and I3I. However, upon a decrease in atmospheric pres sure permitting the expansion of the aneroid II1, the core IIS moves upward. The core II5 then approaches further toward or extends fur ther into the coil I i3 and is correspondingly re moved further from or project less into the other coil I I4. The magnetic flux threading the coil I I3 therefore increases, increasing the impedance of the coil H3, and the flux through the coil llt decreases, decreasing the impedance 0i the coil IM, thus unbalancing the bridge circuit in such fashion that a potential diiîerence appears be tween terminals IM and |35 having the same polarity and time-phase relation as the potential difference between terminals i90 and lilo, and of a magnitude proportional to the unbalance of the bridge. This potential diñerence is fed through output conductors it? and lift to input terminals i3d and E35 of amplifier E Further, upon the atmospheric pressure in , creasing so as to cause the contraction of the aneroid lil and the downward movement of the core liti past the balancing point of the bridge circuit itil, the impedance of the coil ¿it? is de» creased and the impedance of the coil inn creased unbalancing the bridge circuit in such fashion that a potential difference appears be tweenterminais and iSEî having the saine polarity and til „efphase relation as the potential difference between terminals it@ and ritt, and also of a magnitude proportional to the unbal ance of the bridge. This potential difference is then reddirectly to terminals i3@ and E35» of amplifier t2@ Since the instantaneous potential diiîerence be tween conductor ital and terminal is 180° out of phase with that between conductor H9 and terminal iëlii, it Will be seen that the poten tial difference impressed across terminals ißt and S35 of ampli?ier l2@ when the impedance of coil tit is increased is that 2,412,541 shaft |50, train of gears |5| and shaft |56, to >impressed on the amplifier input when the im pedance of coil ||4 is increased. It should also turna cam |58 so as toV adjust the tension of a loading spring |59 for a purpose which will here be pointed outthat an‘increase in the impedance of c'oil'- |'f'l'3" ïëiìectively the same-as a _decrease in tneimpedäriöë ¿recu m. ' i . 'Inefajrnpriner |529 may' be any suitable type inafter be explained.` The `cam |58- cooperates ' with a roller member 4| 60Ímounted on the loading of ' electronic 7 aiñplif-i’er ` well? 'known in_ the yart _such as shown or” example îin the _previously’n'oted 4spring |59 for thé adjustment of the tension of the spring |59. ' The loading spring |59 is plvoted at one end cna ñxed knife edge |62 and engages'v the oppositefjend _theaneroid ||`| exerting PatentrNc:51586233; granted May 25.21926, to 10 aatforce 'thereon vd`ef_ae'r_i<_ìent upon the adjustment Anschut‘z-Kaeinpfe, or may be preferably an elec tronic »amplifier ofthe `type shown and 'described in the; aforenoted co-pending application- 'of Al herring-fuma, serial No. 437,561, dated Aprile; ofthe cam |58. nIt] will be seen that upon a decrease in pres sure; aston a'rise Ain altitude, the aneroid ||1 expands forcing‘the rod H6 upward against' the of the spring |59. Moreover, the upward A motory '| 45 is shown as being of the split phase 15 tension movement of the rod ||5 likewise moves the core type having a pair'of field windings |45 and |41 H5 upwardl _which as previously explained in which are mechanically 90 degrees apart in phase. the-impedance of the coil ||3 and de Winding |41 is connected bythe conductors |43 _Í creases creases the impedance of the coil ||4 and thereby and |44 to thevoutput terminals |36 and |37 of cause an unbalancing of the variable reluctance the amplifier |29,'j. " ' ` bridge circuit ||0. The unbalanced potential is A transformer |4|'is provided for continuously amplified by the Vamplifier |29 in a> manner pre energizing the motor winding |4|i,¿saidV trans viously described and the thus ampliñed electro motive force drives the motor |45 so as to rotate ondary winding |42. The primary winding |40 is connected 'through conductors |38 and .|39 to 25 the shaft |50 in a direction to-cause the actuation „former having a primary winding |40 and a sec conductors |25 and |26 which are in turn con nected to a suitable source of alternating current. of the indicator means |52 in a manner well' known in the art so as to indicate an increase in altitude. Moreover, the motor also, upon such Current is supplied to the secondary'winding unbalancing of the bridge circuit ||0, turns the ' |42 through transformer action from the primary winding |40. Motor winding |46 is continuously 30 shaftA | 56 through the shaft |50 and intermeshing gear means I5I to turn the cam- |58 in a clock energized from the secondary winding |42 of the wise _direction so as to cause downward movement transformer |4|. A condenser |48 is connected of- the roller |60 thereby increasing the tension in series between the secondary winding |42 and exerted by the spring |59 on the aneroid ||1. the motor winding |46 and causes a p_hase dis in turn causes the contraction of the aneroid placement of substantially 90° between the cur 35 This | l1 under the atmospheric pressure and the addi rent ñowing inthe winding |45 and the termi tional tension of the loading spring |59 to cause A nal voltage of the secondary winding |42. Y movement of the rod | I6 until the core As described in detail in _the co-pending Up-. ' downward ||5 is- -once' again positioned in such a manner ton application previously. referred to, the am as to balance the bridge circuit ||0, whereupon plifler £29 is of a type which produces in the the motor |45 ceases actuating caml |58 andthe ybranch of the output circuit including conduc tors |43 and |44 and motor winding |41 an alter- . indicator means |52. nating current of the same phase and frequency as the potentiall applied to input terminals |34 in the case of a decrease in altitude, the aneroid and |35. Since transformer primary windings |24 and |40 vare both connected to the same alternat ing current supply lines |25 and |26, it will be understood that the potential appearing at the « terminals of the secondary windings |22 and |42 'are of the same phase. The current liìowing through winding |46 is, howeveryshifted sub stantially 90 electrical degrees with respect to this potential by the condenser |48, as previously explained. The Winding |41, on the other hand, vis supplied with -current either in phase or 180° out of phase with the :terminal potential of wind ings |22 and |42 depending-upon the direction ` Upon an increase in atmospheric pressure, as \ ||'|l contractsv causing a downward movement of the rod | IB and causing the core I I5 to increase the impedance of coil | |4 and decrease the im peda'nce of coil | I3. The amplified unbalanced po-tential of the circuit ||0 now `causes rotation of the motor |45 in a direction opposite to that in the preceding paragraph, moves the indicator means to indicate the decrease in altitude and rotates the cam |58 ina counter-clockwise direc tion so as to decrease the tension of the loading lspring |59. The decreasing tension of the spring |59 permits expansion of the aneroid ||1 and up ward movement of the core ||5 to a position bal- A ancing the bridge circuit ||0, whereupon theun of unbalance of the bridge circuit | it. balanced potential -ceases and the flow of ampli In accordance ,with well known characteristics of a split phase motor, when the windings |48 60 fied current to the motor |45 terrr'iinates. _The movement of the motor ~|45 thus stops until the _ and |41 are supplied with currents 90° out of bridge circuit H0 is once again unbalanced. phase, the motor |45 is caused to rotate in a Cam |58 turns in a clockwise direction as the predetermined direction. The operation of a split indicated altitude increases, and the function of ' ' phase .motor of the type described herein is de this cam is the same as that of cam 46 clearly set scribed in the co-pending Uptonapplication pre forth previously. . _ » . viously referred to. _ _ In order to more accurately adjust the altimeter The motor |45 is adapted to drive a shaft |53 lby taking into account the barometric pressure in a direction depending upon the unbalancing ` at the ground and for variations from the of the bridge circuit | i0 and the resultant current standard mean temperature at the upper level, supplied from the ampliñer to the motor |45. I have provided the adjustable resistances ,i ii and The shaft |50is, in turn, adapted by suitable means H2 which under assumed standard starting or such as the gear train |5| to drive an indicator ground-level conditions are of equal resistance. means |52, which is of a suitable type well known in the art. Moreover, the motor -|45 is y . The variable resistance ||| is -adapted to be oper further adapted by suitable means such as the 75 ated by a~knob |0|, as shown in Figure _8, so 2,412,541 18 @that upon a decrease in barometric pressure separate manually operable electricalv control ' , vbelow the assumed standard for the ground or means for adjusting the altimeter for ground at mospheric pressure and for changes in the tem perature of the free atmospheric air whereby the starting level, the resistance || I may be increased in accordance with a predetermined adjustment scale and thereby cause the unbalancing of the bridge circuit IIO, and an unbalance potential return or zero point of the aneroid may be ad justed and the multiplication ratio of the indi cator means varied. Thus, the standard of op eration of the altimeter may be adjusted so as to operate accurately with’a minimum of error un 10 der conditions other than those `ol” the standard to which the instrument was calibrated. In the form of my invention disclosed in Figure 7, if the temperature gradient of the air column approxi ‘mates that of the assumed standard. and the 154 above described'adiustment is made for ground therefore appears across terminals |34 and |35. This unbalance potential ampliiied, as previously explained, then causes the motor |45 to rotate in a manner previously described so as to decrease the altitude readings and to turn the cam |58 in a counter-clockwise direction so as to decrease the Aratio between change in indicator readings andpressure change, and to decrease the force exerted by the loading spring |59 on the aneroid | I 1. The decrease in tension of spring |59 in turn temperature deviation from the standard, the causes the core- ||5 to rise- until the impedance cam arrangement I 58 and spring |59 are so con of coil II3 is increased and the impedance of structed as to increase the multiplication ratio of Y coil || 4 decreased to a point whereupon `the the indicator means as altitude increases. The bridge circuit ||0 is once again balanced. Thus, 20 instrument thereby properly reilects an increase correction is affected for altitude readings twhich in vertical distance traveled per unit of pressure if uncorrected would under an assumed indicator as the altitude increases. standard read too high duev to a decrease in the However, vunless further compensated, such a1 pressure of the air column at the ground or start titude readings may depart from the true alti ing level of the measurement. ' tude insofar as the temperature gradient or mean Further, upon an increase in the ground baro metric pressure causing the altimeter at the orig lnal standard of operation to indicate an alti- Y tude below tthe true altitude, the resistance III temperature of the actual air column diiîers from that of the assumed standard atmosphere. The extent of such error as shown in Figure 11 is sub stantially negligible at the relatively lower alti may be decreased by adjustment knob I0| in ac 30 tudes but the error increases with the altitude cordance with a predetermined adjustment scale and represents a substantial error particularly as shown in Figure 8, causing the unbalancing at the greater heights. of the previously balanced bridge circuit I I0 so In order therefore, to compensate for such that the current due to the unbalance potential errors, I have further provided in the form oi.' flows through the resistance III and coil ||4 my invention illustrated in Figure 9 automat-ic causing in turn the motor |45 to rotate so as to temperature correcting means. Thus, I have pro- turn the indicator |52 to increase the indicated vided an electric thermometer or resistor |80 of altitude. The motor |45 simultaneously turns the cam |58 in a clockwise direction so as to in crease the ratio between pressure change and -' ' change in indicator readings, and to increase the tension in spring |59 whereupon the atmospheric pressure acting upon the aneroid II'I together with the increased compressive force of spring |59 tends to force the core ||5 downward until the impedance of coil ||4 is increased and the impedance of coil | I3 decreased to a ,point where upon the bridge circuit |I0 is once again bal anced. Thus the standard of operation of the altimeter may be‘adjusted for the actual pres sure conditions existing at the ground or start ing level of the measurement. It will be obvious that the effect of varying the >resistance `of the resistor II| in this modification a metal lsuch as nickel having a positive tem perature coeflicient of resistance. The resistor |80 is mounted so as to be directly affected by the temperature of the free atmospheric air. 'Thus, upon the temperature of the free atmos pheric air decreasing the resistance of the mem ber |80 will be reduced, and similarly upon an 45 increase in the temperature of the free atmos pheric air the resistance of the member |80 will be increased. A micro or milli voltmeter IBI is shunted across the resistance |80 and is directly aiîected by the variations in the resistance there 50 of caused by the rise or fall of the temperature of the free atmospheric air. The meter |8| has a scale graduated so as to indicate degrees of temperature oi the free atmospheric air acting upon the resistor | 80. A switch |03 is provided of the device is the same as the effect of varying 55 for connecting the meter IBI in and out of the the setting of knob 'I1 in my first embodiment. circuit. ' In a similar fashion, varying the resistance of re Resistor |80 is connected in series with a var sistor I|2 in the present modification has the iable resistance |83 which may be formed of a same unbalancing effect on bridge circuit IIO as material such as manganin the electrical resist varying the setting‘of knob 48 or knob 55 in my 60 ance of which is relatively unaffected by tem ñrst embodiment.- A decrease in the resistance perature change. Resistors |80 and |83 form of the resistor ||2 unbalances bridge circuit ||0 one arm of a bridge circuit |82 which is otherwise in the same direction as an increase of the im essentially'the same as the bridge circuit ||0 pedance of winding |I4,v energizing the motor to previously shown in Figure 7 wherein like nu operate the indicator'and rebalance the bridge merals indicate similar parts. The resistance of by means of core I |5. ^ the variable resistance |83 is so arranged that A knob |02 is provided for adjusting the resist at the ground or starting level the same may be ance of resistor II'2. and the knob may have a manually varied by adjusting the knob |05, Fig pointer for cooperation with graduations suit ure 10. The knob |05 has a pointer |08 co ably calibrated in temperature units to give cor related interrelation between actuation` of knob |02 and the remainder of the device, these grad nations being carried by a suitable control panel; It will thus be seen that in the form of my invention illustrated in Figure 7, I have provided \ operating with suitable scale markings whereby the resistance |83 may be increased proportion ately as the temperature of the atmospheric air at the starting level decreases below the assumed standard causing in response thereto the re-- sistance of the resistor |80 tor‘decrease as the 2,412,541 -_ ~ 20 v ' the temperature at the lower and upper level of temperature of the free atmospheric air de Thus, the resistance |83 compensates measurement. creases. - » Although several embodiments of the inven-A,l `tion have been illustrated and described injde-f.v ¿. vention tail, it isisto’be not limited expressly thereto, understood and that that the various1 Ain-y .;- _. for `the other variable resistance |88 at the ground level. Similarly theresistance |83 may .be manually adjusted so as to decrease propor tionately as the resistance of the resistor |80 is increased in response to a temperature rise at the ground or starting level. Thus, at the changes may be made in the design and arrange- ~ . ment of the parts without departing from the - spirit and scope of the invention as the same ground level theeiîect of the one cancels the effect of the other and the _temperature com 10 Awill now be understood bythose skilled in the pensating means at the ground or starting level does not cause the altering of the indicator art. For a definition of the limits of the inven tion, reference will be had primarily to the ap-v reading. Any change in the ground reading due pended claims. v` I claim as my invention: to a variation from the standard of the atmos pheric pressure atthe ground> level is com 15 , ' 1. An altimeter comprising, in "combination, an- atmospheric pressure responsive means, an _ pensated by the adjustment of the variable re sistance |l| in the manner previously described . altitude indicatingV means, adjustable transmission means- for driving the 'indicating means in accordance with the response of the atmos ~with reference to the form of Figure 7. How ever, durlng flight the resistance |83 may be> 20 pheric pressure responsive means, and means for manually adjusted by _the knob |05 in accord adjusting the transmission means whereby the rate of change in altitude indications for unit of acce with suitable scale markings such as shown in Figure 10 for actual atmospheric tempera ture at the ground level, which information may be conveyed to the operator by radio or other atmospheric pressure change maybe varied, said adjusting ' means including a first and second 'manually operable means to regulate Said oper ' suitable means. However, upon the altimeter being raised by an airplane `or other suitable means through the air column, the resistance |83 after adjustment to ~ground temperature conditions remains constant as it is not subject to variation in the tempera 30 ture of the atmospheric free air, while the re-~ sistance of the thermometer resistor I8@ varies with the temperature of the free atmospheric air, thereby varying‘the resistanceof the arm of the bridge circuit |83 including the resistances _ - ative standard in accordance with first and sec ond atmospheric conditions existing at the vstart- v ing level of measurement and third means to regulate vsaid operative standard in accordance with the variation, from an assumed standard, of an atmospheric condition existing at the level oi measurement. ' ` 2. An altimeter- comprising, in combination, an atmospheric pressure responsive means, an altitude indicating means, adjustable transmis sion means for driving the indicating means in |83 and |80. However, since the resistance |83 remains constant after adjustment to ground accordance with the response of the atmospheric pressure responsive means, and means for ad atmospheric temperature and the resistor l|8il changes in accordance with the temperature oi , justing the transmission'means whereby the rate the atmospheric free air, it will be readily seen 40 of change in altitude indications for unit of at mospheric pressure change may be varied, said » that the eiïect of such arrangement is to con adjusting means including a manually operable tinuously adjust the operative standard of the -means to regulate said operative standard inac altimeter while passing through the column of cordance with atmospheric pressure conditions air for an average temperature between that existing at a starting level-of measurement and existing at the lower end of the column of.' air further means to regulate said operative standard and at the point of measurement. It will be ap in accordance with temperatures of the free at parent that the function performed by resistor mospheric air existing at the starting level and |80 in the present modification of my invention at the level of measurement. is strictly analogous so that performed by mem 3. An altimeter comprising, in combination, an ` ber 8| and so forth in the modification disclosed 50 atmospheric pressure responsive means, an alti by Figure 1, and that members 8| and 86 of Fig vtude indicating means, transmission means for ure 1 together are the equivalent of members |85 and |83 in the present modiñcation. driving the indicating means, adjustable in' ac ~ In summary, it Will be seen that I have pro vided novel compensating means for an alti cordance with- the response of the atmospheric 55 pressure responsive means, and means for adjust meter whereby the-calibration of the instrument may be adjusted at any time to accord with the atmosphere through which the craft is iiying. ing the transmission means whereby the rate or change in -altitude indications for unit of atmos pheric pressure change may be varied, said ad justing‘means including first manually operable ' '_I'he device operates Without adjustment in a means to regulate said operative standard in ac , Vstandard atmosphere, and is adjustable, in part 60 >automatically and in part manually, `to accord with the deviating conditions of any other at mosphere. Manual adjustment is provided for both pressure and temperature at the ground level, and automatic adjustments maintain the instrument in constant calibration ‘with regard to the pressure and temperature of the ambient atmosphere. _ . There is thus provided a novel altitude gaug ing apparatus which provides a continuous auto cordance with atmospheric pressure conditions existing at a starting level of measurement, sec ond manually adjustable means to regulate said operative standard in accordance with the tem perature of the free atmospheric air existing at the starting level of the altitude measurement, and third -means for iniluencing said operative standard in accordance with the temperature ,of the free atmospheric air existing at the level-of the altitude measurement, said second and third _means arranged in such a manner as to regulate tude in accordance with the vertical mean tem perature distribution in the column of airv said operative standard in accordance with the arithmetic mean of the temperatures oi’ the free atmospheric air at the starting level and at the through which the apparatus passes based 119011 75 level of the altitude measurement. ' matic means for` correcting the indicated alti ' 2,412,541 «2l y4. An altimeter comprising in combination an atmospheric. pressure responsive means movable a bridge- circuit, a plurality of adjustable mem pressure responsive means, a resetting mecha ' ybers for controlling the electrical balance o! said circuit, a first condition responsive means and a second- condition responsive means,> operating nism actuable to varyl the force of the counter biasing means in such a manner as to return the atmospheric pressure responsive means from the second position to the ñrst position, means op-- to unbalance the circuit, indicator means, means actuating said indicator means upon the unbal ancing of the circuit, biasing means effective upon from a ?lrst position to a second position, a coun »ter biasing means acting upon the atmospheric the said adjustable members in such a manner as actuation to alter the response of one of said con- eratively connecting said responsive means with 10 dition responsive means, and means actuatingsaid said resetting mechanism in controlling relation biasing means, upon unbalancing of Ithe circuit, thereto, said last named means including first in such fashion as to alter the responseof the and second manually operable means for actuat last named condition responsive means> to rebal ing the resetting mechanism so as to vary the said return position of the measuring member, iirst 15 visual- indicating means whereby the position of ' ance the circuit. 8.' An instrument comprising in combination a measuring member movable from a iirst posi tion under influence oi’ the forces to be meas related With specific values of atmospheric pres ured, a biasing >means acting upon the meas sure, and second visual indicating means where uring member, a sourceof light, a plurality of by the position of said second manually operable 20 photo-electric cells arranged yto be equivalently means may be correlated with specific values of illuminated from said source, whereby to induce atmospheric temperature. equivalent electrical responses from said cells, 5. An altitude measuring device comprising in control means actuated upon movement of said combination, a plurality of electrical resistors measuring member for varying the ratio of light forming an electrical bridge circuit, two of said said first manually operable means may be cor supplied> to said cells in such a manner as to dif resistors being adjustable for atmospheric tem ferentially affect said responses of said cells, mo perature and atmospheric pressure conditions at .tor means controlling the actuation of said bias the starting level of the altitude measurement, ing means, and means causing energization of another of said resistors responsive to atmos pheric temperature and having electrical charac 30 said motor means in accordance with differential responses of said cells, whereby to actuate said teristics variableby changes in atmospheric tem biasing means in such a. manner as to cause the p'erature, a slidably mounted magnetic core sur return of ~the measuring member to the iirst po rounded by inductors in opposed legs oi’ said bridge circuit, an atmospheric pressure respon 9. An instrument comprising in combination a sive member operatively `.connected to said> core measuring member movable from a ñrst position >whereby upon movement of said atmospheric under influence of the ¿forces to be measured, a pressure responsive member movement is impart biasing means acting Jupon the measuring mem ed to said core in such a manner as to vary the ber, a source of light, a plurality of photo-electric impedance in said inductors in the opposed legs of said bridge circuit, a spring means biasing the 40 cells arranged to be equivalently illuminated from said source, whereby yto induce equivalent elec pressure responsive member, adjustment means trical responses from said cells, iìrst control for varying the tension of the said spring means, means actuated upon movement of said measur motor means energized upon the unbalancing of ing member for varying the ratio of light sup said bridge circuit for adjusting the said adjust sition. ment means so as to vary the tension of the spring means so as to cause thereby -the move ment of the said member adjusting the core for rebalancing the bridge circuit, andan altitude indicating device actuated by the said motor means in response to the movement thereof, . whereby the altitude indicating device is posi tioned in response to the atmospheric pressure existing at the point of measurement and the po sition of said indicating device corrected for the temperature to which said atmospheric temper ature responsive resistor is subjected at the time of measurement and for atmospheric pressure and temperature conditionsexisting at the start ing level ofsaid measurement. „ _ , f plied .to said cells in such a manner as to differ entially aiîect said responses of said cells, motor means controlling the actuation of said biasing means, means causing energization of said motor means in accordance with differential responses of _ said cells, whereby .to actuate said biasing means in such a manner as to cause the return of the measuring member .to the iirst position and sec ond control means for varying the ratio of light supplied to said cells so as to cause said motor means to change 4the return position of the meas uring member. l0. An altimeter comprising in combination, a normally electrically balanced bridge circuit, a single source of light, a iirst photo-electric cell, a‘second photo-electric cell, said photo-electric 6. A pressure responsive instrument, compris 60 cells forming adjacent counter balancing arms ing, in combination, a balanced bridge circuit, a of said bridge circuit, said cells of the electron pair of adjustable members for unbalancing said emissive type arranged to receive iight from said circuit, a motor means energized upon the'unbal source, a ilrst apertured control slide for regu ancing of said circuit, an atmospheric-pressure lating the intensity of the light supplied to the condition responsive means operatively connected ñrst cell from said source. a second apertured con to one of said members and a ltemperature condi trol slide for regulating the intensity of the light tion responsive means operatively connected .to supplied to the second cell from said source, said the other of said members, both said condition re control slides thereby regulating the electron sponsive means jointly controlling Ithe unbal emissions from said cells and thus the balance of ancing of said circuit, indicator means actuated said bridge circuit, an aneroid for movably actu by said motor means upon the unbalancing of ating said ilrst slide upon a change in atmospheric said circuit, and biasing means actuated by said pressure, a spring exerting a tension upon said 'motor means for moving at least one of said mem aneroid, a mechanism controlling the tension of bers so as to rebalance said circuit. said spring, an altitude- indicating device, a free 7. An instrument comprising, in combination, air atmospheric temperature responsive ther 1 , i 2,412,541 Y 23 mometer bulb of the distant type for movably actuating the second slide upon a change in tem perature, and a reversible electronic drive motor controlled by the unbalanced potential oi said bridge circuit and mechanically connected to said . tension control mechanism and said indicating device, and upon movement of either of said slides causing the unbalancing of said bridge circuit energizationof said motor is effected in such a 2t ment of said measuring member for varying the ratio of light supplied to said cells in such a man ner as to differentially aiîect said responses of said cells, motor means controlling the actuation of said biasing means, and means causing energize. tion of said motor means in accordance with dif-V ferential responses of said cells, whereby to actu ate said biasing means in such a manner as to cause the return of the measuring member to the manner as to adjust said indicating device and 10 first position, said motor means adjusting said in.. dicator means during such return movement of actuate _said tension control mechanism so as to said measuring member, and second control vary the tension of said spring causing the move means for varying the ratio of light supplied to ment oi' said aneroid and movement of the ñrst said cells in such a manner as to cause said motor sllde'so as to balance the said bridge circuit, whereby the altitude indicating device is posi tioned in response to the atmospheric pressure means' to change said return positionfof the meas uring member and cause said motor to change the adjustment of said indicator means. existing at the point of measurement and the po 14. In an altimeter the combination with a re sitionl of said indicating device corrected for the silient diaphragm movable from a i'lrst position in temperature to which said temperature respon sive device is subjected at the timeof measure 20 response to'a change in atmospheric pressure act- ' ment. ` ing thereon; of a tension _spring acting upon said diaphragm,`a source of light, a plurality of photo l1. An instrument comprising in combination: an atmospheric pressure responsive member mov electric cells arranged to be equivalently illumi nated from said source, whereby to induce equiv able from a ñrst position under the influence of the forces to be measured; a counter-biasing 25 alent electrical responses from said cells, an indi means acting upon said member; a normally bal eating device, a ñrst control device actuated upon movement oí-said diaphragm for varying the in anced electrical bridge circuit; means associating tensity of thelight supplied to said cells in such said member with said bridge circuit, whereby , movement of said member from said ñrst position -a manner as> to differentially ail‘ect the electrical ' añects the balance of said bridge circuit; a reset -30 responses of said cells,- a motor controlling the force exerted by said tension spring, and means ting mechanism operatively associated with'sai'd bridge circuit for actuation upon unbalance ofv causing energization of said motor means in ac_ said bridge> circuit to vary the force -exerted by- « cordance with differential responses of said cells, ` said counter-biasing means for _returning said whereby to actuate said spring to cause the re- ` member to said first positionçindicator means - turn of the diaphragm to the ñrst position, and said motor adjusting said indicating-device dur ing such return movement of said diaphragm, a second control device for varying the intensity of the light supplied to said cells so as to diii‘eren tially aiîect the electrical Vresponses from said movably positioned by said resetting mechanism; and manually operable -means for unbalancing Y I said bridge circuit to bring about actuation of said resetting mechanism so as to vary the re .turn position of said member andthereby adjust the position of sai-d indicator means. , ` 12. In an altimeter the combination with a re silient diaphragm movable from a ñrst position in response to a change in >atmospheric pressure act ing thereon, 'of atension spring acting upon said diaphragm, a source of light, a plurality of photo electric cells arranged to be equivalently illumi-- cells- in such a manner as to canse said motor to change said ñrst position of the diaphragm and ' cause said motor to change the adjustment of '. said indicating device, and a free air atmos pheric temperature responsive device for actuat ing the second control device. l5. An altimeter comprising .in combination: movable means -"-whose position is related to at ’nated from said source whereby to induce equiv mospheric pressure; movable means whose posi alent electrical responses from said cells, a iirst .control device actuated upon movement of said 50 tion is related to altitude indications on a .ñxed scale; adjustable' means -operatively connecting -‘ diaphragm forvarying the intensity of the light said first named movable means and said second ‘ supplied to said cells in such a manner‘as to dii named movable means, whereby movement of said ferentially affect the electrical «responses of said cells, `a motor controlling the force exerted byÀ ñrst named lmovable means may cause movement of said second named movable means, said ad said tension spring, and means causing energiza justable means comprising means for varying the tion of said motor means in accordance with dif ratio between movements of said connecting ferential responses of said cells, whereby to actu Ä means and of said second named movable means, ate said spring to cause the return of the dia said ratio varying means comprising ñrst manu phragm to the iirst position, a second control de vice for varying the intensity of the light supplied 60 ally operable control méanseffective to alter the rate of change of said altitude indications withto said cells so as to diñ`erentially affect‘the elec-" changes in atmospheric pressure, and a second trical responses from said cells in such a manner manually operable control~ means eñective to al as to cause said motor to change said ñrst posi ter the rate of change of said altitude indications tion of the diaphragm, and a free air atmospheric temperature responsive device for actuating the , with changes in atmospheric temperature; iirst second control device. calibrated means whereby actuation of said ñrst‘ i I . 118. An instrument, comprising in combination, a measuring member movable from a ñrst posi tion under influence of the forces to be measured, an additional biasing means acting upon the measuring member, a plurality of photoelectric cells arranged to be equivalently illuminated from said source, whereby to induce equivalent elec trical responses from said cells, an indicator means, first control means actuated upon move control means may be interpreted in terms of deviation of actual atmospheric pressure at a reference level from a standardyand second cali brated means whereby actuation of said second control means may be interpreted in terms of the difference between the temperature ambient to said ñrst named movable means andthe temper ature at said reference level. i PAUL F. SHIVERS.