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Nov. 19, 1946. 'r. A. COHEN. Y 2,411,247 ELECTRIC OSCILLATOR AND OSCILLATOR CONTROLLHD'RELAY- CIRCUIT ff ‘Filed Jan. '7, 1942 4 Sheets-Sheet l Z / f /7 776%‘01: RELAY (Bic/1 INVENTOR. 81%;” Z/M Arron/via’ N”. 19, 1946. 11cm,“ 2,411,247 ELECTRIC OSCILLATOR‘ AND OSCILLATOR CONTROLLED RELAY CIRCUIT Filed Jan. '7, 1942 ‘ 4 Sheets-Sheet 2 5%- 5 ‘ //? 7517416” I? [Me/1 mvmm PM 71/ .M -' ' A7702” Y Nbv. 19, 1946. T. A. COHEN 2,411,247 ELECTRIC OSCILLATOR AND OSCILLATOR CONTROLLED RELAY CIRCUIT Filed Jan. 7, "1942 4 Sheets-Sheet 3 ?j?zém i 616/? INVENTOR. BYJ4Arne/var 4:, NOV. 19, 1946. T_ A_ COHEN 2,411,247 ELECTRIC OSCILLATOR AND OSCILLATOR CONTROLLED RELAY CIRCUIT Filed Jan. '7, 1942 $1’6 4 Sheets-Sheet 4 6i!” INVENTOR. TOR/V5)’ Patented Nov. 19, 1946 I 2,411,247 ' v UNITED STATES PATENTOFFICE 2,411,247 ELECTRIC CSCILLATOR AND OSCILLATOR ' CONTROLLED RELAY CIRCUIT Theodore A. Cohen, Chicago, Ill., assignor, by memo as: ignments, to Wheelco Instruments Company, Chicago, 111., a corporation of Illi nois Application January 7, 1942, Serial No. 425,906 1 26 Claims. , (Cl. 175-320) This invention relates to'Electrical control‘ 9.9- ' paratus and its subject matter was originally in cluded in but subsequently divided from the ap plication which latter matured into United States Letters Patent 2,228,163, issued January 7, 1941, to Theodore A. Cohen, for improvements in Elec trical control apparatus. One of the objects of this invention is to pro ' vide a rugged apparatus in which the contacts of 2 ple form as at 5. This may be the pivot and Jewel structure as commonly used. A pair of induct ances 1—8 are mounted in spaced relationship to allow passage of the ?ag 2, therebetween, as the Pointer 4 moves around axis. The coils 1—8 form a portion of the resonant circuit of an electronic oscillator I, in whose output circuit is connected a relay 3, having contacts ll, l2, l0_ With the ?ag 2 withdrawn from the coil system 7-—8 the a rugged relay, may be controlled by the motion 10 oscillator is tuned to maintain the relay 3 in con of the pointer, of a sensitive measuring instru tact position as shown, with contacts Ill-ll ment, for example a sensitive .millivoltmeter closed and I ll—l2 open. Upon the ?ag 2 passing without disturbing the measuring accuracy of the within the coil system ‘l---8 the oscillator is de measuring instrument. tuned due to the change in inductance of coils A further object of this invention is to provide 15 'I--8, deresonating the oscillator I. This causes an apparatus in which microscopic motion of the the steady current through relay 3 to change to pointer or moving part oi a measuring element cause relay function and thus close relay contacts may eii‘ect dependable relay action. Ill-42 and open relay contacts ill-l l. The use A further object of the invention is to provide a split inductance such as 'l——8 is of especial operation of such relay .apparatus without dis 20 of advantage as will be pointed out more speci?cally turbing the measuring accuracy of the instru hereinafter. ment. vThe apparatus as shown is capable of operating Other and further objects of this invention will a rugged relay such as is adapted for use in fur nace control and the like: with a motion of the becomes better understood from an examination 25 ?ag 2 as small as .002". ‘become more apparent hereinafter as the same of the speci?cation and claims, in conjunction with the accompanying drawings, wherein: Fig. 1 is simpli?ed schematic drawing of the control apparatus. ‘ To prevent the possibility of charges collecting upon the ?ag which might cause disturbance of the accuracy of measurement of a sensitive in strument of which the pointer 4 is a part (by at Fig. 2 is a. modi?ed form oi.‘ the apparatus. 30 traction or repulsion thereof), a resistor 9 is in Fig. 3 is a detailed view, of a. portion of the corporated which permits grounding of the point apparatus in Fig. 1.v er 4 and at the same time, permits the placing Fig. 4 is a modi?cation. of the flag 2 and the coil system 1—-8 at the same Fig. 5 is a modi?cation. potential. This eifectively prevents disturbance Fig. 6 is a modification. -35 of the measuring function. Another method of Fig. 7 is a modi?cation. preventing possible disturbing e?ects can be ac Fig. 8 is a modi?cation. complished by the inclusion of a resistor 9a. , I Fig. 9 is a modi?ed circuit form. Referring to Fig. 2 there is shown another form Fig. 10 is a form of the apparatus assembled in pictorial and schematic form to illustrate an 40 of the apparatus and circuit wherein the pointer arm 4; ?ag 6, scale l3 and coils l-B are substan actual industrial assembly. _ tially as shown in‘ Fig. 1. 'In this apparatus the Referring to the drawings more particularly, as coils l-'-8 are part of a resonant circuit includ shown in Figure 1, reference character 4 desig nates the pointer of a measuring instrument, ' ing in addition the coil 14, condenser l5, and e. g., a pyrometer, voltmeter, thermometen'or the 46 resistor l-Sa, which is used to control the damping and therefore broadenthe tuning as desired of _ like, actuated by the moving portion of the in the circuit or which it is a part. This resonant strument, not shown for simplicity, for indicat circuit is coupled inductively to coil IS in the ing upon a scale l3, the measured quantity. Such sensitive measuring instruments, particu control circuit of the oscillator I‘l. The resonant larly of the millivoltmeter variety, have operat 50 circuit is adjustable to resonate with the oscilla ing torques of not more than 1.0 millimeter gram tor. The moving of the flag 6 within the coils per 90 degrees of rotation and usually are about '|-8 causes a change in tuning of the resonant 0.2 millimeter gram per 90 degrees of rotation. circuit and a change in the absorption of the cir The pointer 4 has attached thereto a light me cult, of coil l6, with a consequent change in the tallic ?ag 2, which may be of aluminum foil or 55 current passing through the relay 3 and a re the like. The pointer 4 is shown pivoted in sim sultant contact operation. A disturbance pre -' earner: vention means is shown at lBb and functions sub stantially as in Fig. 1. - Referring to Fig. 3 the apparatus and circuit there shown comprises the vacuum “tube I8a shown as a triode whose grid I9 is connected with a grid condenser 20, and grid leak 2! the opposite ends of which are connected to the upper end of the coil 08, the other end of the coil being con nected with the ?lament 22. In the plate circuit a conductor 23 leads to a resonant circuit includ ing the coil 24 and condenser 25 .and from this resonant circuit a conductor 26 leads to the by pass condenser 21 and'thence to the ?lament 22. From the conductor 28 the circuit leads through the choke coil 28 and relay 29 to the positive side of the battery 30'. The negative side of the bat tery leads to the ?lament 22. This type of os cillator circuit is typical of the form known as I tuned plate-tuned grid oscillator in which the coupling means for the feed back of energy from _ ' the plate circuit to the grid circuit takes the form of a coupling condenser 21. A portion of recti?ed manner as is disclosed in the aforemen tioned parent Patent #2,228,163. The inductance H3 (or 24) ‘is preferably of the dual coil form such as described in Figures 1 and 4 to 10 hereinafter described because such split coil form permits of a maximum change in in ductance with a minimum linear movement of the ?ag. ' In an automatic control problem it is desirable to sense an immediate departure from the preset control level immediately so that compensation for the departure may be provided as rapidly as possible. Therefore relay action must be ob tained with the smallest possible motion of the flag upon the measuring instrument. At the same time the relay in the oscillator apparatus should be capable of operating its contacts with the smallest possible current change. I there fore provide a relay of small differential or high throw out percentage. In this way with the sensitivity of the oscillator to ?ag position change together with the small differential relay micro scopic motions of the ?ag are translated to imme the coupling is also through the plate, grid, in diate and dependable contact operations without terelectrode capacity of the tube 98a. The choke contact between the moving measur coil prevents ?ow of oscillating energy through 25 mechanical ing system such as ?ag 6 on pointer I! and the me relay. For oscillation to take place it is necessary chanical portion of the system of which coils that the plate tank consisting of inductance 24 d'l-8 are a part. and condenser 25 be resonated to the grid tank In Fig. 4 is shown a form involving the use of consisting of inductance l8 and the circuits’ own an oscillating circuit commonly known. In this capacity. Under the condition for maximum os circuit, the coil 3| corresponds to the coil I8 of cillation, a large bias is obtained across leak 2! which makes grid is negative and thus a result ant low plate current ?ows through relay 29. Should either the plate tanker the grid tank be detuned, oscillation decreases and plate current Fig. 3. In this circuit the grid 32 of a vacuum tube 33', shown as of the triode type, is connected ‘to the grid coil 3!, a circuit leading from this coil 3i through the relay 34 and 'to the ?lament rises through the relay 29. In this apparatus, one form of detuning is shown, by means of the ?ag ’ H on pointer 66, which may be the pointer of a measuring instrument as in Fig. 1. Upon the ' metal flag ll approaching or passing within the. 40 coil l8, detuning results due to the change in inductance of i8 whereupon the plate current sharply rises to close relay contacts 30. It is obvious that the control inductance may be either the grid coil or the plate coil 24 or thevflag ll may control the amount of feed back between the grid and plate circuit as will be explained herein after in connection with Fig. 4. In the above de cribed function the grid tank and plate tank have‘ been resonated to each other in order to produce a. a low plate current to keep relay contacts 3!! open. Upon either of the tanks being deresonated, the plate current rises to close relay contacts. In some forms of commercial apparatus, it is an "ad vantage to have operation in the reverse manner, = that is, it is desired to have the relay contacts 35. A circuit leads from the plate 36 through the plate coil 31 to the condenser 38, the other side of the condenser being connected with the con ductor 40, this junction leading to the relay 34 and thence to the ?lament 35. This places the relay in the grid circuit in position to be oper ated by the: grid current. A circuit also leads from the plate coil through the choke coil M to the positive side of the plate supply battery 42. Byplacing the relay in'the plate circuit as in Fig. 3 it may be operated by plate current change. The negative side of the battery leads to the ?la ment 35. All the previous description of the oscillator. circuit in Fig. 4 corresponds with the previously described oscillator circuit with the exception ’ that the control ?ag 2 ?xed to indicating pointer 2! passes between the two inductances SLY-31 and thereby controls the feed back in the oscil lator circuit. This type 'of oscillator circuit is coupled to cause feed back by means of con 3‘ closed when ?ag is not at control point (plate current high) and then to have said contacts densor t8 and mutual inductance between coils 3i and 31. The feed back- between 3! and 31 'open when either tank is approached V-or a?ected ' is changed by'interposing control ?ag 20 to there-. by the ?ag ll. .Such manner of operation is 60 by control the steady current ?ow through relay easily obtained by deresonating plate tank ‘from 34. The coils 3ii—3'l are mounted so as to allow grid tank some prechosen amount whereupon the' '?ag 2a to pass between them such as ‘5-8 in Fig. plate current remains at an original high value l and may take the form of mutually facing coils which maintains contact as closed. Upon the ap such as in Fig. 8. 65 proach of ?ag ll within the inductance l8 (or Referring to Fig. 5 there is shown diagram 24) the tank is retuned to resonance whereupon matically a form oi apparatus for causing the plate current drops to open relay contacts 3. change in tuning of the oscillator circuit in which ' One advantage of such operation is in the case the control ?ag H9 is mounted upon a secondary where tube failure occurs relay contact 30 would pointer 62!) attached to the coil v(not shown) or 70 open to deenergize the load circuit which maybe movement system which operates the indicating ' a furnace or the like. pointer s. Such an apparatus may be desirable This oscillator, although shown energized from where it is essential that the indicating system batteries, obviously may be powered froma com mercial alternating current source either-‘by .not carry the control system. In this apparatus the movement system i2! maybe’a D'Arsonval means of the usual recti?er systemfor‘ in‘the self _ 75 _ 2,411,247 type meter, having the pointer 4 cooperating with the scale I3 and having the other pointer I20 attached to the bottom of the coil, forming a part of the movement system I 2I and carrying the control ?ag II3. Referring to Fig. 6, this ?gure shows still an other form of pick-up construction in which a small edgewise wound spiral I26 is placed in a pick-up coil circuit such as shown in the pre viously described oscillator circuits of Figures 1 to 4 inclusive and cooperates with the metal flag I 21 on the pointer 4 which with its movement will bring the metal ?ag I2'l close to and in a coil 60 and condenser 6| is connected to the grid leak ‘I0 and condenser ‘II and thence to grid 62 of the vacuum tube 63 which acts normally as a detector, the lower side of the resonant circuit‘ being connected to the negative end of the battery 61, and the positive and of the battery being con nected ‘to the plate of the tube 63 through a relay 66. The negative end of said battery is also con nected to the ?lament of said tube. 10 The oscillator system including tube 43 func tions as a tuned-plate-tuned grid oscillator as already described above for Fig. 3. The link circuit 66—6‘I-68-69—59a is adjusted to-reso nate with tank II and 62 with the ?ag 6 with plane substantially parallel to the plane of the spiral coil I26.‘ The coil I26 may be the induct drawn to a prechosen point from the cells 68 which correspond to the coils 1-8 in Fig. l or Fig. 2. When the resonant circuit 6Il--6I is reso ance I8 or 24 in Fig. 3 or the 'I—6 in Fig. 1. Referring to Fig. 7 there is shown another form of apparatus for controlling the tuning of the oscillator circuit in which the ?ag is replaced by ' a coil I22 carried by the pointer and forming part, 20 of a resonant circuit including a condenser I23 nated with the link circuit 66-5'I—68—69——63a such energy is detected by detector system 62 66—6‘I—‘I0—'II—6II—6I. Plate current through relay 66 therefore drops to cause relay action. When flag 6 is moved into coil system 63, link circuit 66-69(1, inclusive, is deresonated where also carried by the pointer. This coil I22 cooper ates with pick-up coils I24 and I25 placed in the oscillator circuit. The resonant circuit I22 and upon energy to detector 62 ceases with consequent I23 carried by the pointer 4 is normally resonant 25 change in plate current through relay 66 and to the frequency of ‘the oscillator. Upon the corresponding relay action results. Although a , approachment of the coil system I22 to the pick so-called grid bend detector is illustrated using up coils I24 and I26, energy is absorbed from the grid condenser 'II and grid leak ‘III a plate bend oscillator circuit, causing a change in plate cur detector may be used to give reverse operation rent and a consequent operation of the relay con 30 or any variety of diode detector with appropriate -. a ‘ 4 trolled thereby. bias control. The contacts for the relay 66 are Referring to Fig. 8 there is shown another form not shown but may be as illustrated in previous of pick-up coil construction involving the use of ?gures. With a resistor 59a withdrawn from the 2 spiral coils I28 and I29 lying in substantially circuit sharpest tuning results (narrow resonance parallel planes in which the flag I30 in its move 35 curve) and relay 66 is operated with smallest ment may pass between the spiral coils, the ?ag motion of ?ag 1'6. As resistor 59a increases from lying in a plane substantially parallel to the zero resonant current reduces and tuning broad planes of the spirals. These coils may replace ens requiring a larger motion of the flag 6 to 1-8 in Fig. l or I3--24 in Fig. 3 or 3I-3‘I in produce relay action. Thus the sensitivity of Fig. 4. 40 control response may be adjusted. Such opera As previously mentioned, an important func tion is useful for throttling control wherein the tion of an automatic control system is to produce relay 66 may be, for instance, a variable reactor dependable contacting with the smallest change or a positioned fuel valve since the plate current in measured quantity. It is desirable therefore change can be. made proportional to the flag to effect the greatest obtainable change in in 45 position 6 within the coils 68. ductances with the smallest increment of ?ag As shown in Fig. 10 one form of apparatus travel since it is ?ag travel which eventually. which may be used comprises a milli-voltmeter results in operating the load contacts. By lump having a movable coil 30 and a pointer 4 pivotally ing the inductance so that all portions face the mounted at 5 having an indicator ‘I5 cooperating ilag surface the largest inductance change may 50 with an arcuate scale I3 and carrying the flag 6. be obtained with minimum pointer travel. Such The flag in its travel passes between the coils ‘I. a coil structure is best exempli?ed by the spiral and 8 to ail'ect the tuning of the oscillator circuit; pancake coil in Figs. 6 and 8. These coils 1 and 8 are mounted on a setting Referring to Fig. 9 there is shown another form lever ‘I6 which is pivotally mounted at 16c co of apparatus and circuit including the oscillator 55 axially with the pointer 4. The setting lever may tube 43, whose grid 44 is connected to the grid also carry an index ?nger ‘I'I cooperating with condenser-46 and grid leak 46, the circuit from the arcuate scale I3. The setting lever ‘I6 may the other side of the grid leak leading through be set to any desired position by means of a suit the coil 41 to the ?lament 48. From the plate able adjusting mechanism 'I8. ' As indicated 43 a conductor- 56 leads to a resonant circuit, 60 above, when the ?ag 6 passes within the coils l including the coil 5| and condenser 52, the other side of the resonant circuit leading to the choke - and 8., the oscillator apparatus ‘ID will be affected causing the operation of relay ‘II. Such appa ratus is essential in automatic control problems and is shown in connection with furnace temper to said ?lament 48. A by-pass condenser “is 65 ature, control in which case the energy for con connected to the choke coil 53 and ?lament 48. trolling the positlon of the milli-voltmeter pointer This circuit functions as the oscillator described 4 is produced by thermo couple 5. in Fig. 3. Coupled to‘ the plate coil 5| is a link ,The desired temperature is set upon scale I3 coil 63 and thence to the plate supply battery 54, the other side of the plate supply battery leading circuit including coils-66, 51' and 58, condenser with pointer 11 and adjustment is. This posi 63, and resistor 53A whose function is similar to 70 tions the coils 1-8 at required point. When the resistor lid of Fig. 2. Coupled to the coil 61 is temperature is low in the furnace, insu?lcient a resonant circuit comprising the coil 60 and con energy is produced by the thermo couple 6 where denser BI'. The controlling flag 6 on the pivoted ' arm 4 cooperates with the coils 68. The upper upon the pointer 4 and indicator 16 are below the control point 11. The ?ag 6 is not fully within end of the resonant circuit, which-includes the 75 the coils 1-6 and relay 1| remains closed, con / ' an 1,247 i 7 tacts ‘it closed, energizing furnace elements 13, it electrically heated, or an electric valve if fuel ?red. - - As the temperature rises in the furnace the couple 5 is heated and .the pointer 5 moves up scale. The flag 6 enters further between coils 'I-'8 changing the tuning ‘of the oscillator and the tuning of said oscillator circuit, and means for maintaining said part and said inductive por tion at approximately the same potential to there by prevent disturbing electrical effects upon the measuring ability of said instrument, said oscil lator controlling the position of said part." 3. The combination with an instrument having I a variable position part, whose position is con thereby opening contacts 12. The furnace now trolled by variation in conditions to which the cools until flag 6 is again withdrawn below con trol point to cause a reenergization of the furnace. 10 instrument is subjected, of an oscillator circuit having an inductive portion for cooperating with This action continues giving so-called off-on or said part, said part being movable to a position two position control of the furnace. Because of in which it affects said portion to thereby affect the extreme sensitivity of the relay systemrvery close temperature control is obtainable. The . the tuning of said oscillator circuit, and means ' for preventing accumulation of electrical charges system is easily set up to produce contact opera upon said movable part to thereby prevent dis tion of 12 with a motion of the ?ag 6 within the turbing electrical effects upon the measuring cells 1-4! of less than .002". ' ' ability of said instrument, said oscillator control It is important in a control mechanism of this ling the position of said part. ' character that the control flag 6 be incapable of 4. The combination with an instrument having ' passing beyond the control coils ‘l and 8 because 20 a variable position part, whose position is con if that should take place the relay contacts 12 trolled by variation in conditions to which the would then be permanently closed and the fur instrument is subjected, of an oscillator circuit nace element 13 would be permanently energized. having an inductive portion for cooperating with The indicating pointer 15 would be de?ected to said part, said part being movable to a position the top end of the scale and all control would be 25 in which it affects said portion to thereby ailect I‘ lost, with resultant possible damage to furnace. the tuning of said oscillator circuit, and means A pointer stop 19 is therefore provided ?xed to for maintaining said part and said inductive por the lever 16 at 19A and insulated from any por tion at a predetermined potential relationship to tion of the circuit to arrest the pointer 15 before thereby prevent disturbing electrical effects upon the flag 6 can travel beyond the coil system '|—B. 30 the measuring ability of said instrument, said To prevent electrostatic charges collecting upon oscillator controlling the position of said part. the flag 6 and causing erroneous indications upon 5. The combination with a contact controlling the scale 13 of the pointer 15, the pointer and flag relay, of means for controlling the operation of 6 are metallically connected at 6A. Such con said relay comprising a detector circuit, an oscil nection is usually made at a control spring mount 35 lator circuit, a link circuit between said oscillator or leadv shown in-simpli?ed form at 6B. A leak circuit and detector circuit, and means for chang age resistor 60 places the ?ag and pointer at the ing the tuning of the link circuit to vary the same potential as the coil system ‘|—-8 at 1A. The energy transferred to the detector circuit to con line supply for the system is conventionally shown trol the operation of the relay. at Ill. The oscillator 10 shown in simpli?ed block 6. The combination with an oscillator circuit form may be any of the previous oscillator sys and a variable position control element movable tems described or one of the oscillator mecha with respect to said circuit to change the tuning nisms disclosed in the aforementioned parent thereof, of a relay controlled by said change in Patent #2,228,163. 45 tuning, said control element comprising a movable It is obvious that the control apparatus may metal plate, the circuit affected by said plate be applied to any automatic control problem such comprising a spiral coil with respect to which as voltage frequency, etc., with an appropriate said plate approaches and recedes in its move measuring element and controlled compensator ment, said plate and coil lying in substantially for the departed quantity. parallel planes when in proximity to each other. I am aware that many changes may be made 50 7- The combination with a contact controlling and details varied without departing from the relay, of means for controlling the operation of principles of my invention and I therefore do not said relay comprising a detector circuit, an oscil .wish to be limited to the details shown or de lator circuit, a link circuit between said oscillator scribed. 55 circuit and detector circuit, a portion of which I claim: _ consists of a pair of spaced inductances and means 1. The combination with an instrument having for controlling the link circuit to change its tun a variable position part‘ carrying a control ele ing to vary the energy transferred to the detector ment and whose position is controlled by varia circuit to control the operation of the relay, the tions in conditions to which the instrument is means for controlling the link circuit comprising subjected, of a, resonant circuit, a vacuum tube 60 a control element carried by a measuring instru oscillator for exciting said circuit, a second reso _ ment and movable and in spaced relationship nant circuit coupled to said ?rst resonant circuit, '7 the control elementwhose position isrcontrolled by said ‘variable position part, being movable to with said inductances. , 8. The combination with an oscillator circuit a variable position control~ element movable a position in which it a?ects the tuning of said. 65 and with respect to said circuit to‘ change the tuning second resonant circuit, and a relay controlled thereof, of a relay controlled by said change in by said oscillator, to in turn control said position tuning, ‘said control element comprising a mov of said variable position part. able metal plate, the circuit affected by said plate 2. The combination with an instrument having a variable position part, whose position is con. 70 comprising a pair of spaced spiral coil-s between which said plate approaches and recedes in its trolled by variation in conditions to which the, movement, said plate and coils lying in substan instrument is, subjected, of an oscillator circuit tially spaced parallel planes when in proximity having an inductive portion for cooperating with ' to each other. i ' said part, said part being movable to a position in which it a?ects said portion to thereby affect 75 9. The combination with an instrument having 9,411,947 a variable position part, whoseposition is con trolled by variation in conditions to which the instrument is subjected, or a resonant circuit having an inductive portion for cooperating with said part, said part being movable to a position in which it affects said portion to thereby affect the tuning of said resonant circuit and an oscil lator circuit controlled in turn by changes in tun ing of said resonant circuit, said resonant circuit being provided with adjustable means for setting a predesired damping to thereby control the sensi tivity of response for a given motion of said mov able part. " 10. In an automatic control mechanism includ ing an instrument responsive to changes in a measured quantity, said instrument motivating a movable part, a control circuit provided with inductance for cooperating with said part in 10 rated a relay, adapted to iunction in one manner at one energy level from said oscillator in accord ance with one movable part position, and in an other manner when said energy level is varied in accordance with movement of said part a prede termined distance, said resonant circuit being provided with adjustable means for setting a pre desired damping to thereby control the sensitivity of response for a given motion of said movable part. 14. In an automatic control system, a sensitive measuring instrument having a variable position part the position of which is controlled by varia tions in conditions to which the instrument is subjected, such variable position part cooperating with an inductive portion of an oscillating circuit, said inductive portion being adjustably movable over a total range of the indicating portion of the spaced relationship therewith, said inductance variable position part, said oscillator in turn con forming a portion of the grid tank of a vacuum tube oscillator, in the plate circuit of which is contained a tuned circuit adapted to be resonated 4 with said grid tank, ,in desired degree the plate trolling a relay which is in one position when said variable position part is below said inductive por tion to control the control system in one manner and in another position when said variable posi tion part is in prechosen relationship with said circuit also containing a relay adapted to be ener gized by the non-pulsating component in said plate circuit and thereby cause contact operation 25 inductive portion to control the controlled system in a second manner, said inductive portion having in another manner when said part is ‘actuated mounted in mechanically spaced relation there a predetermined distance to change the tuning with a stop element to prevent the variable posi of said grid tank. ' tion part from assuming a position with respect 11. The combination with an oscillator circuit 30 to said inductive portion whereby the controlled and a variable position control element motivated system would become non-‘operative. by a measuring instrument and movable with 15. A claim such as claim 6 with the spiral coil respect to said circuit to change the tuning there ?at. of, of a relay controlled by said change in tuning, 16. A claim such as claim 8-with the spiral coils said control element comprising a resonant cir ' 35 ?at. cuit including a condenser and coil, the circuit 1'7. The combination with an instrument hav controlled by said control element including a ing a variable position part whose position is con coil with respect to which said resonant circuit trolled by variation in conditions to which the approaches and recedes in its movement to in ‘instrument is subjected, 01' an oscillator circuit turn control the position of said variable position 40 having spaced inductances cooperating with said control element. part, said part in its motion a?ecting the induc 12’. In an automatic control apparatus, the tive relationship of said inductances whereby said . combination of a measuring instrument, having oscillator in turn controls the position of said part means for indicating or sensing departure from a prechosen level, such means including a mov able position part, cooperating in spaced relation 45 ship with an inductance forming a portion of a resonant circuit, whereby motion of said part affects the tuning of said circuit, said circuitact ing as a transmission channel for energy pro duced by a vacuum tube oscillator coupled there with, such energy being transferred in greater or less degree with motional effect or said first part on said inductance, to a coupled circuit forming a portion of a detector, in whose plate circuit is incorporated a relay, adapted to function in one and means for maintaining said part and said inductances at a’ predetermined potential rela tionship to thereby prevent disturbing electrical eil'ects upon the measuring ability of said instru ment. . ' 18. A claim such as claim 1 with the instru ment of the millivoltmeter variety with an oper ating torque of not more than 1.0 millimeter grams per 90 degrees of rotation. 19. A claim such' as claim 2 with the instru ment of the millivoltmeter variety with an oper ating torque » of not more than 1.0 millimeter grams per 90 degrees of rotation. v 20. A claim such as claim 3 with the instru ment of the millivoltmeter variety with an oper manner at one energy level from said oscillator in accordance with one movable part position, and in another manner when said energy level is varied in accordance with movement of said part 00 ating torque of not more than 1.0 millimeter grams per 90 degrees of rotation. a predetermined distance. 21. A claim such as claim 4 with the instru 13. In an automatic /control apparatus, the ment of the millivoltmeter variety with an oper mbination of a measuring instrument, having ating torque of not more than 1.0 millimeter means for indicating or sensing departure from grams per 90 degrees of rotation. a prechosen level, such means including a movable 22. A claim such as claim 9 with the instru position part, cooperating in spaced relationship with an inductance forming a portion of a reso ment of the millivoltmeter variety. nant circuit, whereby motion 01' said part affects the tuning of said circuit, said circuit acting as ment of the millivoltmeter variety. 23. A claim such as claim 10 withv the instru a transmission channel for energy produced by 70 24. A claim such as claim 12 with the instru ment oi’ the millivoltmeter variety. a vacuum tube oscillator coupled therewith, such 25. A claim such as claim 13 with the instru energy being transferred in greater or less degree ment of the millivoltmeter variety. with motional eii‘ect or said ?rst part on said in 26. A claim such as claim 14 with the instru ductance, to a coupled circuit forming a portion ment of the millivoltmeter variety. or a detector, in whose plate circuit is incorpo 76 ' THEODORE A. COHEN.