Jan. 14, 1947. ' _ ‘ w. an. CLARK . 2,414,190 CIRCUIT’ ARRARGEHENT :FOR RATIO ESTER; Filed Jami. 22.‘ 1944 ' M. ‘ i240 I ‘ WmsLow B.M'. CLARK. ‘ 3" £4...” attorney 2,414,190 Patented Jan.v 151947 UNITED '1 STATES ' “PATENT OFFICE I I cmomranaalféésiigalmronmno Winslow s. M. can, West 0range,'N. 1., alslznor Orange, N._J., a corporation of New Jersey Application January 22', 1944, Serial No. 519,373 _' to Thomas A. Edison, Incorporated, West 4 Claims. (01. 111-95) 1l e _ My invention relates 2 to improved means and‘ cooperating ‘circuit elements in accordance with Q methods for e?ecting adjustments in circuit ar rangements, especially in circuit arrangements for electrical measuring instruments, and has for a primary object to provide‘ novel and improved. . my invention; - Figure 3 is another elevational view of this ra tlometer assembly, taken at right angles to the line of view in‘Figure 2; means and methods for calibrating electrical measuring instruments. My invention has particular commercial util ity, and is‘ herein illustrated and described, in , Figure 4 is a perspective view of the coil ar rangement of the present ratiometer; and Figure 5 is a diagrammatic view of the ra tiometer' circuit in accordance with my inven terms of a circuit arrangement for ratiometer 10 In the illustration of my invention, I show a instruments. These instruments, as is well type of ratiometer instrument, purely by way of known, are arranged to measure the ratio of two example, such as is described and claimed in the currents and the circuits into which they are pending application of Frederick G. Kelly, Se connected, which are typically bridge circuits, are tion. . > adapted for producing ,changes in the ratio of 15 rial No. 450,222, ?led July 8, 1942 (now Patent No. 2.362.562), and having a common assignee with the present application. This ratiometer in dition to be measured. It is an object or my in strument comprises a permanent bar magnet I vention to provide a simpli?ed and economical carried pivotally by a shaft‘ 2 which pivots in top means and method for adjusting such circuits whereby such instruments may be readily cali 20 and bottom jewel serews‘2a and 2b. The mag: net has a generally symmetrical shape relative to brated in production. the shaft 2 and has its magnetic axis- at right My invention has useful application to temper angles to the shaft. Surrounding the magnet are ature-compensated electrical ‘measuring systems, two sets of ?eld coils 3 and 4 of which each set particularly to remote indicating systems such as telemeters and ratiometer systems or. the char 25 consists of two serially connected coils positioned at diametrically opposite sides of the shaft 2 acter above explained. By way of illustration, with their medial planes parallel to the shaft; ratiometer systems are. commonly used for re These sets of coils are positioned at angles to mote temperature-indicating purposes,‘ in which case an element- variable with temperature is 30 each-other about the shaft 2, one set oft coils passing through the other. Surrounding the coils immersed in the medium whose temperature is 1 and magnet is a cylindrical shield cup 5 held in to be measured and is connected into a ratiometer concentric relation to the-shaft 2. The shield circuit the other elements of which are placed at cup is preferably made of a- highly permeable and a remote indicating point. Frequently, it is re non-permanent magnetic material such as that I quired that the ratiometer circuit be compen known commercially. as “Mumetal” or “Perm sated for changes in the ambient temperature at alloyi? andthe magnet is preferably made of a the remote indicating point. It is‘ another ob permanentand highly efficient material such as a ject of my invention to provide a novel and im one of the. socalled "Alnicos'.” In response to two currents in. response to variations in a con proved means‘ and method for adjusting and calibrating such temperature-compensated cir-v cuits. ’ " ' ‘ changes in the relative current energization of 40 the coil sets, the magnet will de?ect to different ‘ ' positions according to the ratio of the currents in the coil sets, and the positions of the magnet will be indicated by readingsoi' a pointer 6 carried A further object of my invention is to provide can electrical measuring system incorporating an improved form of rheostat .for adjusting and/or calibrating the system. ‘_ ‘ Yet i'urther'and allied objects and features of my invention are more fully pointed out in the ‘following description and the "appended claims. In the description of my invention reference is had to the accompanying drawing, of which: Figure l‘is an axial view of a ratiometer, largely ‘ ‘ “ ' ‘ ' Figure 2 is an elevational view‘ of an assembled unit comprising the ratiometer oiv Figure 1 and I by tlae'shaft 2relative to a scale I provided on a Moreparticularly, the operation or the ratiom dial ,. ‘ . ' .. , . ‘ . V - eter is as follows: Upon considering the mag netic ‘axis of the magnet to correspond to its 50 diagrammatically shown, with which‘ my inven tion is herein illustrated; “ 45 central‘ ‘longitudinal ' axis,- it ‘ will ‘be understood that upon passing a current through only the coil ,set 3 (the two ‘coilsvot the set being of course polarized in the same direction) the magnet will assume ‘a position wherein its magnetic axis is aligned withthe axis of that coil set, and upon proper relative polarization of the coils and mag 2,414,190 3 > . ' Y 4 ». tions will be unaiiected by material changes in the voltage of the battery 9, for variations in bat tery voltage produce like variations in the cur rents of both coils without changing the ratio of . net the pointer ‘ will register with the low end of the scale ‘I. Similarly, upon passing a current through only the coil set’ 4, and in the proper direction, the magnet will assume a position wherein the pointer 6 will register with the high 'end of the scale. When current is passedthrough both coil sets, in proper relative directions as above explained, the coil sets will exert torques on the magnet in opposite directions and the those-currents. » > While the ratiometer system here shown is basically a resistance-measuring system, it will be understood that the resistance in may be varied according to variations in any condition to be magnet will assume intermediate positions where 10 measured‘ and that the meter may be calibrated , in these torques are in balance, the pointer then directly in terms of that condition._ One such reading at intermediate positions of the scale. common application'oi the present ratiometer is These intermediate positions are determined by the ratio of the currents in the coil sets. as a temperature-measuring device on aircraft, In this application the resistance [0 comprises For effecting changes in the ratio of the cure . rents in the coil sets in response to changes in a _ I the active element of a resistor bulb l6 that is immersed in the medium whose temperature is to condition to be measured, I preferably employ a be measured and whose resistance varies accord bridge circuit such as is shown in Figure 5. this ing to that temperature, a preferred example of being a type of bridge circuit generally described such bulb being that disclosed in the pending ap and claimed in the Kelly application abovemen 20 plication of Frederick G. Kelly, Serial No. 493,9i7, tioned. This bridge circuit has two branches con ?led July 8,1943, and assigned to the assignee of nected in parallel across a source of direct cur the ‘present invention. rent such as a battery 9,. One branch serially in cludes a variable resistance Ill to be measured and In such applications the resistor bulb is located remote from the ratiometer instrument and its a?xed resistance I I, and the other branch serially includes three ?xed resistances l2, l3 and M. The other associated elements, and the instrument two coil sets of the ratiometer are connected from a junction l5 between resistances l0 and I I of one sembled unit such as is shown in Figures 2 and 3. This unit comprises a case only the base ll of which is shown. ‘Secured to this base is an up ~ and those other elements are provided as an as branch to the respective extremities of the, middle resistance IS in the other branch. 30 standing bracket "! comprising two spaced-apart As the resistance I0 is varied, the absolute po- ‘ upright members I8a having top and bottom legs tential oi the junction point I5 is varied relative l8b and lac, the members |8a being joined by a to the absolute potentials present at the extremi cross member "id. The bottom legs I80 seat on ties of the resistance l3, and so long as the po tential of junction I5 is between that of the ex 35 tremities of resistance I3, the voltage drop across one coil set will increasehwhile that across the . other coil set will decrease. Accordingly, for a the base I‘! and are secured thereto by screws IS; .the top legs support a cross arm 20, held thereto . by screws 2|, which carries the top jewel screws ‘in and the dial 8; and the cross member 18d car ries the ratiometer per se by way ‘of an L-bracket prescribed lower value for the resistance Ill, the 22 onto which the shield cup 5 is seated and held potential of junction 15 will correspond with that 40 by a screw v23. The side members |8a of the of the junction between resistances i2 and I3. bracket [8 serve to support the resistances of the leaving zero voltage drop across one. coil set and bridge circuit of Figure 5, these resistances being maximum voltage drop across the other. Simi respectively wound on spools 24 and held in place larly, for a prescribed higher value of resistance ‘by screws 25. The ‘necessaryleads from the as III, the potential of junction l5 will correspond 45 sembled unit to the resistor bulb l6 and battery with that of the junction between resistances l3 9 are led through‘ the base II by way of a de and 14, leaving only the other coil energized; and pending tubular portion Ila. thereof and may for intermediate values of the resistance l0,'cur therein be connected to respective pins of a con rents will pass through both coils in ratios ac nector plug not shown. cording to the values of that resistance. Thus, 50 - It will be understood that the currents which the pointer 5 will register with one end of the ?ow through the respective coil sets 3 and 4 are scale for one prescribed valueoiI resistance l0 - determined, among other things, by the ‘re and with the other end of the scale for another ‘sistances of the respective coils. Since these coils I prescribed value of resistance Ill, and for inter are preferably wound with copper wire, and copper mediate values, oi that resistance the pointer will 55 has asubstantial temperature coe?icient, changes assume intermediate positions, each position of ' in the ambient temperature of the meter unit the pointer being one wherein the torques exerted above described tend to produce errors in the by the respective coil sets‘on the magnet are in indications of the meter. Particularly in aircraft balance. In order, however, that the pointer will applications the meter unit is subjected to large register with the low end of the scale-the left end changes in the ambient temperature, and it is of the scale as it appears in Figure 1—for low important that the unit he therefore compen values of the resistance Ill, and at the high end sated so as to be substantially free of in?uence of the scale for high values of the resistance It, . by those changes. This compensation has been ‘the coil sets 3 and 4 are directed axially ‘toward ‘ provided satisfactorily, in accordance with ‘the the low and high end portions of the scale, and teachings of the abovementioned Kelly applicae the coil sets are connected respectively to the tion Serial No. 450,222, by'making the resistances right and left extremities of resistance It in the II and I2 wholly of a material having a negligible bridge circuit of Figure 5, Also, for a scale length ' temperature coe?icient,‘ a predominant portion of 120° the axes of the coils are typically sepa No of resistance l4 of such material and the rated by this angle, or, in other words, the medial. 70 remaining portion Nb of copper and comparable planes of the coils are separated by an angle of 60‘? portions I31; and 13b of resistance I: of such as shown. ‘ » material and copper respectively. Satisfactory materials havingnegligible temperature coeiii» It will be understood that with proper calibra tion or the scale, the pointer will read directly cients for this purpose are those known commer vthe values of the resistance l0, and the indica 75 cially as "Manganin” and "Advance.” 2,414,190 . I 5 . For the case where the voltage of battery 9 ranges from 11 to 14 volts, the maximum per missible current through the bulb I8 is approxi—_ mately 1'! ma., the resistance of the bulb is‘ ap proximately 68 ohms at minus 70° (2., 108 ohms at 50° C. and 152 ohms at 150°~C., and the re sistances of the outer and inner coil sets 3 ‘and 4 are 290 and 230 ohms respectively (the inner coils having less resistance for the same number of been accomplished by a simple means without materially compromising the compensation of the meter unit‘ for changes in ambient tempera ture. This simpli?cation has been made possible by the observation that the variable portion of the resistance [3 may wholly comprise a material of negligible temperaturev coe?icient-i. e., totally comprise the resistance IMP-and that, upon pro viding this variable portion directly adjacent the turns because of their smaller mean ‘length of 10 Junction of resistance II with resistance l2, it turn), it has been found satisfactory to employ and the variable portion of resistance l2, herein resistances in thevbridgehaving average values termed resistance He, may comprise a single and as follows: resistance II, '700 ohms Manganin; integral resistance element 26. By providing such resistance I2, 91 ohms Manganin; resistance Ila, resistance element with two movable contacts in 615, ohms Manganin; resistance 14b, 85 ohms 15 the form of _a simple rheostat, and electrically copper; resistance Ba, 11 ohms Manganin; and interconnecting the contacts to provide .a single resistance I313, 24 ohms copper. ‘ , Typically, resistor'bulbs do not have a truly linear characteristic for their resistance change, junction for connection with the coil set 4, then the resistances I2 and I3 may be varied inde pendently of each other to permit a direct and in response to‘ a given incremental temperature 20 easy calibration of the instrument. Also, by mak change, is greater at high temperatures than it is ing the total value of the resistance element 26 at low temperatures. The tendency of this non . at least as great as the sum of the maximum linearity of the bulb is thus to expand the high values of the variable ranges required for the re end portion of the scale. It however occurs that sistances i2 and 13 in calibrating any one of a the bridge circuit arrangement illustrated and. 25 group of instruments, the rheostat can be’stand described has itself a non-linear response char ardized since one such form of rheostat can be , acteristic which counteracts the non-linearity of __ used for calibrating each of the instruments. 1 the bulb and tends itself to contract the high In Figures 2 and 3 I show a rheostat 21 for the end portion of the scale. The non-linearity of abovementioned purpose, comprising an in the bridge. increaseswith increase in the range 30 sulating frame 28 made for example of Bakelite of temperature to be measured, and for tempera and having a base portion 28a seating on the ture ranges greater than 100° it will generally base I‘! and held thereto by a screw 29 to form a over-counteract the non-linearity of the bulb to permanent part of the meter unit. The frame give a resultant contraction of the upper end por has a cylindrical head 28b provided with an tion of, the scale. Additionally, there are the 35 arcuate groove 30. The resistance element 26 is factors that the inner coils I have closer magnetic wound in the form of a helix of wire having a coupling to the magnet I and have less resistance negligible temperature coefficient, preferably of than do the coils 3, the eifect of which is further “Advance,” and this helix is ?tted into the groove to accentuate the non-linearity of the bridge. To 30 and held therein by cement. Leads 3! from correct for these effects which tend to over 40 the ends of the helix make connection to a pair counteract the non-linearity of the bulb; and so of terminals 32 mounted on the frame 28, and to that there may be obtained a scale symmetrical these respective terminals are connected the fixed relative to its central point, there is placed a component of resistance l2, indicated in Figure 5 resistance 25, typically about 115 ohms, in series as Rb, and the ?xed component 13b of resistance with the 0011s 4. This resistance is preferably 4.5 l3. Slidably engaging the‘ helix- are two in made of copper so that the two cross arms of the dependently adjustable spring contact arms 33 bridge will each have the same temperature and 34. These contact arms have separate aper tured hub portions which overlie one another and Individual calibration of each ratiometer is are pivoted to the central portion of the head 280. required because in production variations occur 50 by a screw 35. Clamped against these hub-por in the respective elements which make up the tions also by the ‘screw 35 is a soldering lug 36 coef?cient. ' ’ ratiometer system. It is found, however, that‘ which is held against turning about the screw 35 ‘ when resistances H and Il are held within suit by a rivet 31. This lug constitutes a common able tolerances, and the resistance 25 is properly Junction for connection in the bridge to the coil selectedas above explained, the calibration of 55 set E. , each ratiometer requires only a proper adjust - It will be understood that the central portion ment of the values of resistances l2 and i 3. This of the resistance element 26 is shunted by the is because the resistance 13 controls the angular two contact arms and that it is only the end por length of scale obtained in response to a given ' tions of the resistance element, beyond the re range in temperature of the resistance l0—i. e., 60 spective contact arms, which are the active re the distance of separation of the scale divisions sistance portions comprised within the respective and the resistance l2 controls the positioning of resistances l2 and I3. Merely by way of ex the temperature indications or of the scale rela ample, it may be noted-that the 'total resistance tive to the dial 8. These calibrating adjustment-s of the element 26 may be 34 ohms, that in prac have been heretofore carried out by determining 65 tice the range of variation for resistance 12a is with decade boxes the proper values of the re from 9 to 15 ohms and that of resistance 13a sistances I2‘and I3, and then taking resistance from 10 to 12 ohms, and that therefore, on the spools having an excess number of turns and re average,_the contact arms 33 and 34 will shunt moving, by trial and error, enough turns until out approximately 11 ohms of the resistance ele the correct values of the resistances are obtained. 70 ment '26., it may, moreover, be noted that while Obviously, this calibrating procedure was very the resistances i2a and 'llc have to be critically‘ laborious and time-consuming, and materially in creased the cost of the instruments. By the present invention, the calibration pro cedure has been vastly simplified and this has determined, the adjustment of the arms 33 and 34 is however not critical in view of the resistance element 28 being spread over a large diameter . through nearly a complete circle. Moreover, _ ‘2,414,100 . , ‘7 while in the present invention all-oi the vari ation of resistance 13 is con?ned to its portion of negligible temperature coei?cient, this does not have any material adverse e?‘ect on the tempera ture compensation oi the bridge since the range of variation of that portion is only approximately dial for a given range of said variable element and Y the other oisaid resistances controlling the posi tioning of said de?ection range in relation to the ,scale on said dial; and a rheostat comprising a single resistance element including portions of said two resistances, and having two independent A _ l ly movable contacts associated with said re I have herein shown and particularly described sistance element for varying the values of said my invention in terms of apreferred embodi resistances respectively. ment, but it will be understood that this embodi~ 10 3. In an electrical measuring system including ment is subject to changes ‘and modi?cations an electrical bridge having two branches con without departure from the scope of my inven nected in parallel, one of said branches including tion, which I endeavor to express according to two serially-connected resistances, and an elec the following claims. ' trical indicating instrument adapted to be ‘elec I claim: ‘ trically connected across said branches to meas 1; In an electrical circuit system including a ure the unbalance or said bridge, said instrument ' ratiometer, a bridge having a ?rst branch serially including a coil adapted to be connected to the including ‘a variable resistance to be measured Junction 0! said two resistances: a device con and a ?xed resistance and a second branch serial necting said coil to said Junction, and adapted 2‘ohms, ly including three ?xed resistances, the middle 20 for adjusting said resistances independently of resistance or said second branch comprising one > component having a‘s'ubstantially neglible tem perature co?lcient and another component hav ing a positive temperature coe?lcient and one of the ?xed resistances of said second branch having one another, comprising a unitary resistance element including at: least portions of said two resistances, and a pair of electrically intercon , nected contacts associated with said resistance element, said contacts being connected to said coil and ‘independently adjustable along said re sistance element. and adapted‘ to be connected from a common 4. In an electricalmeasuring system compris point in said ?rst branch to the respective ex ing an electrical bridge having two branches in tremities of the middle resistance of said second 30 parallel, said bridge including a variable resist branch: means for connecting one or said coils to ance to be measured and one of the branches of one of said extremities and for varying said said bridge including two serially-connected con middle resistance and said one ?iled resistance, trol resistances, an electrical indicating instru comprising a resistance element having-a sub. ment ‘for measuring the unbalance of said bridge, stanti'ally negligible temperature coeillcient and said instrument comprising a pointer and co including a portion at said one component of said operating scale, and an impedance element middle resistance and a portion of said one ?xed adapted to be connected across said bridge from resistance; a pair of movable contacts associated the junction of said two control resistances, one with said resistance element; and electrical con of said control resistances controlling the de?ec a substantially neglible temperature coemcient, and a pair of coils comprised in said ratiometer nections from said one coil to both said contacts. 40 tion range or said pointer in response to a given 2. In an electrical meter system comprising an range of variation of said variable resistance and electrical indicating instrument having a pivoted the other controlling the. position of said de pointer and a dial, said dial bearing a scale with ?ection range relative to said scale: a rheostat which said pointer cooperates: the combination of an electrical bridge including a variable ele ment to be measured and having a branch serially including two resistances, a coil included in said instrument and connected between the branches of said bridge and having a connection to the junction between said resistances, one of said resistances controlling the range of de?ection of said pointer in relation to the scale on said connecting said impedance element to said junc tion and adapted for adjusting said control re sistances independently of one another, compris ing two contacts associated with said control resistances respectively, each of said contacts being connected‘to said impedance element, and said contacts being independently adjustable relative to said respectively associated resistances. WINSLOW B. M ‘CLARK.