* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Measuring instrument of the potentiometer type
Fault tolerance wikipedia , lookup
Ground (electricity) wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Current source wikipedia , lookup
Electric machine wikipedia , lookup
Stray voltage wikipedia , lookup
Commutator (electric) wikipedia , lookup
Opto-isolator wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Electrical substation wikipedia , lookup
Alternating current wikipedia , lookup
Induction motor wikipedia , lookup
Buck converter wikipedia , lookup
Flexible electronics wikipedia , lookup
Integrated circuit wikipedia , lookup
Stepper motor wikipedia , lookup
Circuit breaker wikipedia , lookup
Loading coil wikipedia , lookup
Rectiverter wikipedia , lookup
Crossbar switch wikipedia , lookup
Earthing system wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Capacitor discharge ignition wikipedia , lookup
Light switch wikipedia , lookup
Ignition system wikipedia , lookup
Feb. 10, 1942. E. A. ‘KEELER 2,272,914 MEASURING‘ INSTRUMENT OF THE POTENTIOMETER TYPE I Filed Sept. 30, 1938 , ' 2 Sheets-Sheet 1 FIG. I. INVENTOR. EARL A. KEELER BY ATTORNEY ' Feb. 10, 1942. 2,272,914 E_ A_ KEELER MEASURING INSTRUMENT OF THE POTENTIOMETER TYPE Filed Sept. 30, 1938 2 Sheets-Sheet 2 A.C. LINE INVENTOR. EARL A. KEELER A TTORNEY Patented Feb. 10, 1942 2,272,914 UNITED STATES PATENT OFFICE 2.272,914_ MEASURING INSTRUMENT OF THE POTENTIOMETER TYPE Earl A. Keeler, Norristown, Pa., assignor to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Application September 30, 1938, Serial No. 232,586 13 Claims. The present invention relates to measuringin strum'ents, and more particularly to an instru (CI. 17145) drawings and descriptive matter in which I have illustrated and described a preferred embodiment ment that is both sensitive and rugged for meas of the invention. uring the value of a condition. In the drawings: At the present time it is customary to measure CR Fig. 1 is a wiring diagram of one form of my high temperatures by means of a potentiometer invention showing diagrammatically recording I circuit in which deflection of a galvanometer in response to variations in the voltage of a ther mocouple, subjected to the temperature, is~used provisions and a furnace; . Fig. 2 is a side view of my novel galvanometer; Fig. 3 is a view on line 3--3 of Fig. 2; to position a relay which in turn rebalances the 10 Fig. 4 is,a fragmentary sectional view through potentiometer and adjusts a pen with respect to one side of the galvanometer coils; a chart. The di?iculty with such an arrange Figs. 5 to 7 are wiring diagrams of other em ment is that the relay mechanism is ordinarily both cyclic inoperation and cumbersome. It is bodiments, of my invention; an object of my invention to do away with the tion in which the galvanometer pointer does not necessity of a complicated relay system and the. necessity of depending upon any cyclically op ' Figs. 8 to 10 are wiring diagrams of my inven directly detect the measuring circuit unbalance; and erating mechanism in order to rebalance a po Fig. 11 is a wiring diagram of my invention in tentiometer circuit and ‘obtain a reading. To this which the galvanometer pointer serves only to end de?ection of the galvanometer is directly 20 limit the de?ection of the coil. used to disclose a circuit and operate a series of Referring ?rst to Fig. 1, a galvanometer i hav electrical relays to cause rebalancing of the po ing a pointer 2 is adapted to ‘respond to unbal tentiometer circuit. I also provide a mechanism ance in a null point potentiometric circuit, the that is free from any cyclic mechanism and is latter of which may be of any suitable type, such substantially ‘instantaneous in its response to 25 as the Brown potentiometer circuit disclosed in any variation of the value of the thermocouple 'Harrison Patent 1,898,124, issued February '21, voltage. 1933. Such circuits are well-known and it is su?i It is a further object of my invention to provide cient for the present purpose to note that the a measuring instrument which is rapid in action' potentiometer circuit includes a circuit branch and one that is inherently stable in operation. 30 including a source of variable potential to be Such an operation is accomplished with the addi-‘ measured ‘such for example, as the thermocouple tional feature of obtaining an accelerating action 3 inserted in a furnace 4 whose temperature is to in the instrument by using a second coil in the be measured. An opposing circuit branch in galvanometer which upon energization thereof, cluding a source of known potential such as the is used to add an additional biasing force to the .35 cell 5, and resistors 8, a variable portion of the galvanometer. Upon the completion of a rebal latter of which may be connected» into the op ancing operation a circuit through the additional posed branches by means of a sliding contact 1 or‘auxiliary coil is broken and a recoil action is whereby the respective effects of the variable and produced which quickly returns the galvanometer known sources are made equal and opposite, and toward its neutral position. It is a further ob 40 the galvanometer is thus rendered undeilected ject of my invention to provide a galvanometer when the circuit is balanced for a given value of which has two movable coils, one of which is in a the E. M. F. of the thermocouple 3- with contact measuring circuit to cause a de?ection thereof, ‘I in a corresponding position along the resistors and the other of‘ which is in an auxiliary or 6. The position of contact ‘I is then a measure biasing circuit and is used to add an additional 45 of the value of the thermocouple E. M. F. and force to that-of the ?rst coil and toy provide a may then‘serve as a measure of thevv temperature means that produces'a recoil action upon break _ to which it is exposed. ing of the circuit. ' . . In the form of Figure 1 my invention is ‘con The various features of novelty which charac cerned with the manner in which the contact ‘I terize my invention are pointed out with particu 50 is moved along the resistances 6 to rebalance a larity in the claims annexed to and forming a potentiometer circuit. The contact ‘I is mounted part of this speci?cation. For a better under on and movable with a carriage 8 that is shifted ‘standing of the invention, however. its advan in response to rotations of a threaded shaft 9 tages and speci?c objects obtained with its use, uponpwhich the carriageis mounted. Also fas reference, should be had to the accompanying 55 tened to the carriage 8 is a marking‘element i0 2 8,272,914 that is adapted to move across a chart II. This through the circuit which includes contacts 2| chart is provided with calibration marks in and 2|, coil 2|, battery 2|, conductor 21, coil terms of the temperature to which the thermo couple is exposed and is driven past the marker 2|, contacts 25 and 24, conductor 22, coil H and pointer 2, regardless of its low magnitude will III by a motor I2 and a driving drum l2. produce‘a torque which is additive to that pro The construction of the galvanometer l ‘which I use is novel and tormsa highly important fea duced by the current in the coil II to thereby cause additional pressure between contacts 2| and 2|, to permit a greater current ?ow there through. Thus the current builds up until it is ture of my invention. The galvanometer em ployed may desirably be heavily damped and con sists of a frame H of usual form upon which is 10 suilicient to energize the relays Ill and 2| and open their respective switches 22 and 24. As wound‘a coil || whose terminals I511 and ||b the switch 22 opens, the motor 24 will rotate are connected in the potentiometer circuit. A second coil I8 is also wound upon the frame I4 '- shaft 9 and adjust contact ‘I along resistance | in a direction to restore potentiometer balance. and this coil has one lead connected to the pointer ’ 2 while the other lead extends to a relay circuit 15 Switch 24 is an interrupter switch which pref erably is not opened until the motor N has per to be described below. These two coils l5 and formed a rebalancing operation. The time de I8 do not have any electrical connection with lay between the opening of switch 22 and the each other. Extending from each end of the opening of switch 24 is due to the fact that a frame M are the usual bearing shafts that are greater flow of current is required to actuate pivoted in any suitable manner in frame members that relay to move contact 2| out of engage l1 and ||. The pointer 2 is attached to the ment with contact 2| and break the holding cir lower supporting shaft and is in the form of a cross, three arms of which are threaded and re ceive balancing weights || that are adjustable to insure free turning of frame l4. The fourth arm is the pointer proper and has contact element 2| formed on its tip, which contact is adapted to cooperate with either of the adjustable contacts 2| and 22 depending upon the direction of de?ec tion of the galvanometer coils. , Referring now to Figure 1 it will be seen that, as above described, one end of coil l| is con nected to pointer 2 while the other end'is con nected by a conductor 22 to a movable contact 24 that forms part of a switch. The other con tact 2| of the switch is connected to one end of a relay 2| that is connected by line 21 to the mid point between two batteries 2| and 2|. The other cuit. Opening of switch 24 permits relay 2| to again close switch 22 to stall motor 24 and relay 2| to close contacts 24 and 2|. If the movement of contact I along the resistances 6 was suiii— cient to rebalance the potentiometer circuit the contacts 2| and 2| will now be open. If not, the same cycle of operations will occur and the motor will be rotated in a series of short, rapid steps until the potentiometer circuit is re balanced. Upon the occurrence of a de?ection of pointer 2 in a clockwise direction the opposite of the above operations will take place and relay 2| will open switch 22 to permit motor 34 to rotate in a reverse direction from that in which it pre- I viously rotated. It is noted that the battery 2| is of such a polarity that the current ?ow, in terminal of battery 2| is connected to one end of a relay coil 2| whose other end is connected to ll) this case, through the coil || will increase the pressure between contacts 2| and 22 until the the contact 2|. In a like manner the second ter current flow is suillcient to energize the relay minal of battery 2| is connected to one end of 2|. a relay coil || whose second end is connectedto The embodiment of the invention disclosed in the contact 22. The relays 2| and 2| are adapted, when energized under control of the galvanome 45 ll'lgureoisverysimilartothatinli'ig. 1,the ter, to open the normally closed switches 22 and - diilerence being in the manner that relay 2| is connected in the circuit. In this embodiment 22, respectively, to which switches are connected the relay 2| is of the ‘time delay type and is nor on one side to the line and on the other side to mally energized to hold contacts 24 and 2| closed. the ?elds of a standard reversible induction mo Each of the relays 2| and 2| when energized in tor 2| and from there to the other side of the addition to actuating vthe motor switches, also a line. In a circuit of this type when one of the open respectively switch 2| and switch 2| in the switches is opened, one field of the motor is con circuit of the relay 2|. The switches 2| and 2| nected directly to the line and the other is con are shown connected at each end of the relay nected to the line through a condenser 2|a. In such a case the energizing current for one of the 55 2| so that when either is opened, switch 2| by relay 2| or switch 2| by relay 2|, the connec rotating ?elds lags the other to set up a rotating ileld in the rotatable element of the motor, the direction of rotation depending upon which is leading. Upon energization of one of the relays 2| or 2| by the galvanometer a switch is opened in one field circuit and the motor is energised to rotate shaft | to shift carriage | in the proper direction for contact ‘I to rebalance the poten tiometer circuit. In the operation of this embodiment of the invention if the thermocouple voltage varies in tion between the batteries” and 2| and ‘the ‘relay 2| will be broken. - In the operation of this embodiment a varia tion in the thermocouple voltage will cause a de?ection of the galvanometer pointer 2 to bring contact 2| into engagement witheither contact 2| or contact 22. If, for example. the contacts 2| and 2| engage, a circuit will be completed from‘ contact 2| through relay”, battery a. line 21a switch 2|, 2|, line 22 coil ||, pointer 2 a direction to cause coil II to move counter ‘ clockwise in Figure 1 the contact 2| will be and contact 2| to energize relay 2| in a manner pressure between the contacts 2| and 2| to cause direction,. while opening switch 2| deenergises su?icient current to now through the circuit to operate relay 2|, though a very small current the relay 2|. previously described. When the current flow has built up sufficiently the relay 2| will open moved into engagement with contact 2|. In the ordinary form of galvanometer, a slight poten 70 switches 22 and ||. Opening switch 22 permits motor?torotatetodriveshaftlintheproper t‘ometric unbalance will not result in suiilcient may‘ ilow between the contacts. This ?ow when the relay 2| 7 is deenergised an interval of time will occur before contacts 2| and2lareseparatedanditisduringtmsin 2,272,914 terval that motor, 34 rotates. When contacts 24 and 25 open they break the holding circuit for relay 36 to deenergize that relay and close switches 32 and 35. The closing of the former stops the motor and the closing of the latter energizes relay 26 to close contacts 24 and 25 and places the circuits in condition for another 3 use of a recti?ervin a source of A. C. voltage to produce the D. C. for the relays instead of the batteries previously disclosed. It is of course to be understood that the batteries may be used if desired in this case just as the recti?er can be used instead of the batteries in the previously described embodiments. One end of relay 36 is connected as usual to As in the embodiment of Figure 1, if the con contact 2| and the other end is connected at tact ‘I was not moved enough to rebalance the 10 33 to a voltage divider 46. The other relay 3| potentiometer circuit the operation will be suc is connected at 4| to the other end of the voltage cessively repeated until potentiometerrebalance divider 46 and to the contact 22. A center 'tap is obtained. Upon the occurrence of an opposite 42 of the voltage divider is connected through galvanometer de?ection, where contacts 26 and the switches 35 and 36 .to the conductor 23 and 22 are brought into engagement, the relay 3| 15 from there to the coil l6 to complete the circuit will be energized and it will open switches 33 and for the relays 36 and 3| respectively when pointer 36 to respectively cause an opposite rotation of 2 is de?ected to bring contact 26 into engage motor 34 from that previously obtained and to ment with either contact 2i or contact 22. deenergize the relay 26. Shunted across the switches 35 and 36 is a vari ‘The embodiment of the invention disclosed in 20 able resistance 43 and a condenser 44 in series, Figure 6 differs from those previously described which upon opening of either switch 35 or 36 in that only two relays are used with a condenser is placed in circuit with the relays 36 or‘ 3|. in each relay circuit serving to permit the neces The voltage divider 46 is supplied from an A. C. sary time delay during which the motor 34 is ‘source through a copper oxide recti?er 45 of energized for rotation. 25 usual type and a transformer 46. In this embodiment one end of relay 36 is con In the operation of this embodiment of the nected, as previously, to the contact 2| while invention a de?ection of the galvanometer pointer the other end is connected both to one contact 2 will move contact 26 into engagement with, of the switch 35 and one terminal of a condenser for example, contact 2|. A circuit will thus be 31 of suitable capacity. The other terminal of 36 completed from contact 2|, relay 36, the upper the condenser and the other contact of the switch é' half of voltage divider 46, through center tap are both connected to one terminal of the bat 42, switch 35, switch 36, conductor 23, coil l6, tery 28. In a like manner one end of relay 3| pointer 2 to contact 26. When the current is is connected to contact 22 while the other end su?icient the relay 36 will be energized to open is connected to one contact of switch 36 and 35 switches 32 and 35. As in the previously de one terminal of a second condenser 36. The scribed embodiments of the invention the open ing of switch 32 will permit the motor 34 to rotate second contact of switch 36 and the second terminal of condenser 38 are connected to one shaft 3 and move contact 1 across resistances 6 terminal of battery 29. The conductor 23 in to rebalance or tend to rebalance the potenti this case extends from coil l6 to a connection be 40 ometer circuit. The opening of switch 35 breaks the circuit for relay 36, but deenergization of tween the batteries. operation. > ‘ ' In the operation of this embodiment a varia- ' tion of the thermocouple voltage will cause a de?ection of the pointer 2 to bring, for example, contacts 26 and 2| into engagement. Thus, in a manner described in connection with Figure 1, a flow of current is set up through contact 2|, coil 36, switch 35, battery'26, conductor 23, coil i6, pointer 2 and contact 26. When sufficient current has been built up in the circuit the relay the relay is delayed due to the subsequent charg ing of condenser 44. The time interval during which the charging of the condenser takes place determines the lengths of time that the motor 34 is rotating and this interval can, be varied by adjusting the value of resistance 43. In a similar manner a de?ection of the gal vanometer to bring contact 26 into engagement with contact 22 would cause energization of relay 36 will become energized to open switches 32 and '35. The opening of switch 32 permits the motor 3|, this time using the lowerhalf of the voltage divider 46 between point 4| and center tap 42 to rotate shaft 3 to shift contact ‘I along re in order to reverse the direction of ?ow of the current in the circuit. This is necessary in order sistances 6 in a direction to rebalance,‘ or tend to rebalance, the potentiometer circuit. The .55 that the coil |6 will bias the pointer toward opening of switch 35 breaks the circuit for relay contact 22 instead‘ of‘ toward contact 2| as it formerly did. ’ 36, but the relay is not instantly deenergized due to the charging of condenser 31. The in In each of the above described embodiments terval of time during which the condenser is of the invention, the additional torque on the charging after switches 32 and 35 have been 60 galvanometer that is derived from the secondary opened and before the relay 36 is deenergized is coil I6 is used to add to the unbalance of the the time during which the motor 34 is rotating galvanometer. I have discovered that if this shaft 9. This operation is, as in the previously force, with relation to the galvanometer design described forms of the invention, rapid enough is such that it tends to slightly bend the pointer so that a substantally continuous rotation of 55 2 between its point of support and contact 26 the motor is obtained until the potentiometer or to shift the coil in its pivots, or both, a rapid circuit is rebalanced. For an opposite de?ection recoil takes place when the circuit is broken. of the galvanometer the same operation would The eifect secured is quite valuable and sub take place through relay 3| and condenser 36 to stantial in that it gives an acceleration feature‘ energize the motor 34 for rotation in the oppo 70 to the operation of the device. site direction. In a self-balancing instrument of the general . The embodiment of the invention disclosed, in type shown in Fig. 1, “hunting” or oscillation Figure '7 is similar to that of Figure 6 except of the device may occur by virtue of the time that only one condenser is used instead of two. lags-and particularly the mechanical time lags Also there is disclosed in this embodiment the 76 involved. For example, the, time ‘necessary to 4 2,272,914 galvanometer pointer is so great compared to the speed of the electrical changes in the potenti ometer system that nothwithstanding the rota ever of relays 25 or 3| was energized. If the ro tation of the motor 54 was su?icient to rebal ance the measuring circuit the galvanometer coil will remain in its neutral position, if not the tion or motor 34 into a position which the con tact should occupy to rebalance the system under a stabilized. condition, the galvanometer will et same cycle of operations will be repeated until the measuring circuit is rebalancr‘d. Another, type of relay mechanism is shown in iect further motor rotation before such rotation is interrupted. While for a slow motor opera connection with my invention in Figure 9, which relay uses a so-called “A. C.-D. C." galvanometer. overcome the inertia of even a light and delicate tion, the system may be suitably damped with 10 As shown the moving coil I! of the galvanometer is connected by means of pigtails or slip rings 52 auxiliary means, it is essential for high-speed and 53 with the leads lid and I5!) while the recorder operation to insure that motor 24 will auxiliary coil |l is connected at one end by slip come to rest exactly at its balance point. The ring 54 with the conductor 22. A iclr-up coil recoil action referred to above following deen ergization of the galvanometer coil II, it prop 15 55, which is positioned in an alte ating mag nétic ?eld, is connected to the pivot of the gal erly predetermined in magnitude, as it can be vanometer coils l5 and I6 and is arranged to be by adjustment of the biasing force of coil II. rotated therewith. The pick-up coil is connect in a manner hereinafter described, will restore ed between the poles of a suitable ?eld structure the galvanometer to its neutral position, thereby interrupting the action of the rebalancing motor. 20 55 on which is wound a ?eld winding 51 that is energized from a suitable A. C. supply line, and is Another type of relay mechanism with which so arranged with respect to the poles of the ?eld my invention may be used is shown in Fig. 8. structure 56 that when the coil I5 is in its un In the previously described embodiment the de?ected position the pick-up coil is in zero in pointer 2 was used both to detect the unbalance oi the measuring circuit and to close the circuit 25 ductive relation to the alternating magnetic ?eld set up in the ?eld structure. When the galva through coil It. That this double function of nometer moving coil i5 de?ects in one direction the pointer is not necessary is shown in the or the other the pick-up coil de?ects accordingly embodiment now to be described. and, as a result, an alternating voltage in phase In Figure 8 the galvanometer coil i5 is respon sive to variations in the measuring circuit as 30 with or 180° out of phase with the line voltage will be induced in the pick-up coil. . in the previously described embodiment. ~The In the operation of this embodiment, when the cell has attached to it for movement therewith, thermocouple voltage changes the galvanometer in addition to the pointer 2, a mirror 41 that moving coil l5 will be de?ected in one direction is adapted to reflect a beam of light from some or the other and thereby the pick-up coil 55 will suitable source, such as from the lamp 4!, to be rotated into inductive relation with the alter a photocell 49. A mask 50 is provided in front of cell 4! so that if the galvanometer de?ects in nating magnetic ?eld set up by the ?eld struc one direction the beam falls on the cell and it it de?ects in the other direction the beam is on the mask. The current from cell 49 goes to an ampli?er 5| that is used to _energize one or the other of the relays III or 5| depending upon whether the light beam is on the cell 49 or the ture 56, resulting in the induction of an alter nating voltage in the pick-up coil. The phase and amplitude of the alternating current so in duced is determined by the direction and extent oi’ de?ection, respectively. The induced alter~ mask 50. If the galvanometer is in its neutral position the beam falls equally on the cell and mask and neither of the relays is energized. Various forms of ampli?er relays are available which would be suitable for use as ampli?er 5|, tails or slip rings 58 and 59 to the input terminal, of an electronic ampli?er 60. The output of nating voltage is connected through suitable pig~ ' ampli?er O0 is connected to one winding of a ro tating ?eld motor 8|, the other ?eld of which is connected to line. As is well known, motor 5| is and in particular the device 5| may include a re energized for rotation in one direction or the lay for a coil responsive to the ampli?ed photo cell current and a pair. of contacts adapted to control the energization of coils 3|! and II ex cept for the normal current condition of the other depending upon the phase of the current supplied from ampli?er 60. As in the preceding embodiments motor 8| is adapted to effect an adjustment in the rebalancing direction of the contact ‘I along the resistances 6. photo-cell circuit existing when the galvanometer is in its neutral position. See, for example,_the ampli?er disclosed below in connection with Figure ll. The function of coil I8 is the same in this em bodiment as it was in the embodiment of Fig. 8, When either of the relays 20 or 3| is energized. it opens its switch 32 or 22, respectively, to per mit rotation of the motor 34. As the galva nometer deflects it brings contact 20 on pointer 2 into engagement with either contact 2| or 22 engagement with either contact 2| or 22 to com plete a circuit from one of those contacts through namely to e?ect rapid mechanical rebalance of the galvanometer. Upon de?ection of the v gal-' vanometer, pointer 2 will bring contact 20 into either battery 28 or 29, switch contacts 25, 24, coil 28, line 23, slip ring 54, coll I8 to the pointer 2. When the current ?ow through the relay 2| tacts, battery 22 or 2!, switch contacts 24 and H25, coil 24, line 22, coil I‘ back to pointer 2. The 65 has increased to a large enough value the relay will be energized to open‘ contacts 24 and 25 to battery brought into ‘the circuit is of such a p0 break the circuit._ If the potentiometer[circuit is larity that the current v?ow through coil l6 in-v not rebalanced the cycle will be repeated until creases the bias of pointer 2 in its initial direction to complete a circuit through one of the con ' to increase the pressure between-contact 2|! and suchtime as it is. contacts 2| or 22. As the current in the relay 25 70 My invention is shown in Figure 10 in use with a capacitance type relay. In this embodiment increases it will movecontact 24 away from con a condenser plate 62 is carried by and insulated tact 25' to the circuit and the galvanometer Winter" 2:,willspring back to its neutral position; thiQiIsOImQves ‘the beam of’ light until it is equal from the pointer 2. This plate moves relative to a second stationary condenser plate 83, the plates ly_ on the cell 45 and-mask ‘I to deenergize which 75 being connected to an oscillator 54 the output cur 2,272,914 rent of which varies in response to the relative positions or the plates 62 and 63. As the output current of the oscillator varies the energization of a relay coil 66 varies in accordance therewith to shift its armature 66 that is used to control the position of a switch member 61, which is pivoted at its left end. An adjustable spring 61a urges member 61 toward contact 69 from which it is normally held in the neutral position of the galvanometer by the normal current value in coil 65. t . 5 balanced the‘ cycle will be repeated until such . is the case. From the above description it will be seen that by providing a second coil in the galvanometer I am able to use the galvanometer pointer direct ly to actuate the rebalancing system of a po tentiometer circuit. By having the two coils on the galvanometer frame separate from each other no disturbing in?uence is introduced into the thermocouple circuit and its initial sensitivity can be retained. The motor 34 is caused to rotate In the operation of this embodiment of the in in a series of steps that are short enough to vention when the pointer 2 is in its neutral po give small movements to the contact ‘I and thus sition the plates 62 and 63 are in such relative the possibility of moving the contact too positions that the oscillator output current 15 render far negligible. On the other hand the steps fol through relay 65 is su?lcient to keep the switch low each other in quick enough succession that member 61 out of engagement with contact 69. for larger unbalances of the potentiometer cir When, however, the galvanometer de?ects due to cult the rotation of the motor 34 is substantially .a change in the thermocouple voltage the relative positions of the plates 62 and 63 are changed to 20 continuous so that the contact -‘I may move smoothly across the resistances 6. ' vary oscillator output current and thereby " In cases where the pointer does not form either increase or decrease the energizing force part of the electrical relay system it still serves of relay 65 and bring switch member 61 into an important part by acting as an element in engagement respectively with contact member 68 or 69. Contacts 68 and 69 are connected to the fields of an ordinary reversible series motor 34A which is adapted to serve the same pur the circuit of the auxiliary coil l6 or acting as a stop to limit the de?ection of the galvanometer coils. In any event the use of the pointer in a manner above disclosed and the auxiliary coil on the galvanometer produces a quick acting and The coil I6 has the same function in, this em bodiment of the invention as it has in the pre 30 inherently stable device which has an anticipat ing effect. The latter is true because after each viously-described ones and operates here in a rebalancing step of the motor the recoil action manner identical to Figures 8 and 9. produced by deenergization of the coil I6 always The embodiment of the invention disclosed in pose as motor 34 of Fig. 1. Figure 11 is very similar to that disclosed in Fig returns the galvanometertoward its neutral po electrical circuit for the coil l6. In this form tion. The introduction of the relays in the sys ure 8, but differs from that embodiment and from 35 sition to immediately stop the motor 34 and‘pre vent any overrun or hunting of the system it the other embodiments previously disclosed in the potentiometer has reached balanced condi that the pointer 2 does not form part of the tem permits the use of a motor which is suf and ‘II to limit its movement and that of the 40 ?ciently powerful to move the contact ‘I and pen l0 and to actuate any desired controls that may mirror 41.‘ be used in connection with the system. The circuit for the coil l6 extends from one the pointer cooperates with adjustable stops ‘I6 end of the coil through conductor 23, normally I have thus provided a measuring instrument closed contacts 24, 25, relay 2'6‘, normally open which is free to instantaneously respond to any ~ variation in the condition which it is being used switches 12 or 13, actuated by relays 30 or II,‘ batteries 28 or 29, respectively, and conductor 45 to measure, without the necessity of relying on the cyclic operation of any relay mechanism and 14 to the coil I6. In this case the contact mem without the necessity of introducing the result ber 24 is shown provided with an adjustable ing complications of such a relay mechanism spring 24a that tends to hold it in closed po ' sition. In this manner more current has to be 50 into the instrument. ' It should be noted in connection with the re built up in the coil 26 before it can break the coil or acceleration effect, particularly in com circuit through contacts 24 and 25 and an ad nection with Fig. 9 which does not employ a justable time delay is provided. It is obvious contacting relay for rebalancing motor control, that a similar spring may be used if desired, in this relay in the other embodiments of the in 65 that advantage may be taken of this effect in a device which does not include a step-by-step mo vention. 1 tor action, which step-by-step action in itself In the operation of this embodiment, a varia tends to decrease thenecessity for anti-hunting tion of the measuring E. M. F. through the coil I! will cause a de?ection thereof to move point or acceleration features. ‘ ‘ While in accordance with the provisions of the er 2 into engagement with one of the stops 10 ' or ‘II and move mirror 41 so that it will re 60 statutes, I have illustrated and described the ?ect the beam or light either completely on the photocell 49 or the mask 66. In either case one of the relays 30 or 3| will be energized. Assum ing that relay 30 is ‘energized, the switch 22 best form of my invention now known to‘ me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the will be opened to permit motor 24 to run and 65 spirit of my invention as set forth in the ap shift the contact 1 along resistances 6. At the pended claims and that in some cases certain "same time the switch ‘I2 will be closed to com features of my invention may sometimes be used plete the circuit between'it, battery 26, coil l6, to advantage without a corresponding use of switch 24, 26 and the relay 26. vWhen sutncient~ 70 other features. ‘ a _. , current has been built up in the relay 26 to over Having now described my invention, what I come the force of spring 24a it will open switch clog: as new and desire to secure by Letters Pat 24, 26 to deenergize the coil I6 and permit the galvanometer to move to its neutral position. If en : 1. In'a self-balancing measuring instrument, the measuring; circuit has not been completely 75 a galvanometer having a pair of coils associated 6 2,272,914 therewith and a pointer, one of said coils being in the measuring circuit which includes a varia ble to be measured and to which said coil is re sponsive, a motor for rebalancing said circuit, control circuits for said motor, the other oi’ said coils being selectively connected in one or the other of said control circuits in accordance with the direction of de?ection of said galvanometer pointer in response to changes in said variable. 2. In a measuring instrument a gaivanometer responsive to variations in a measurable condi tion, a control circuit comprising a relay coil, a switch actuated thereby and a source or current, means to energize said second coil and means ‘ to deenergize said second coil a predetermined time later. 8. In a sell-balancing measuring instrument, a galvanometer having a pair of coils associated therewith one or which is in a measuring circuit that includes a variable to be measured and to which said coil is responsive, a motor to rebal ance said circuit, control circuits ior said motor responsive, respectively, to said galvanometer de ?ections in one sense or the other, an additional biasing force for said galvanometer including said second coil, means to energize said coil in opposite directions in response to de?ection 01' responsive to de?ections of said galvanometer to 15 said galvanometer in one direction or in the op posite direction from a neutral position, and close said circuit and energize said relay coil to means operative in response to energiaztion oi’ open said switch, charging of said condenser pre said second coil to complete one of said motor cir venting immediate deenergization of said relay a condenser shunted across said switch, means coil. cuits. . - . .3. In a measuring instrument a galvanometer 20 9. In a measuring instrument, the combination de?ecting in response to variations in a measur with a galvanometer having two coils associated able condition, a circuit comprising a normally therewith one 01 which is connected in a meas deenergized relay coil, a normally closed switch uring circuit that has a variable to be measured operated thereby, and a source of current, a sec .to which said coil is responsive, a pair of biasing ond switch in said circuit closed in response to 25 circuits each including said second coil, means de?ections of said galvanometer to thereby close responsive to de?ection of said galvanometer in said circuit to energize the relay coil and open either direction to close one or the other of said the ?rst switch, a‘ condenser shunted across said biasing circuits to add an additional force to the ?rst switch, the condenser charging through the galvanometer in one direction or the other, 30 means forming part 0! each circuit to break said relay coil when the ?rst switch is opened. 4. In a measuring instrument, a galvanometer biasing circuit and suddenly release said iorce de?ecting in response to variations in a measur whereby the galvanometer will spring back to able condition, a ?rst circuit comprising a ?rst ward its neutral position. relay coil, a source of current, a second relay coil 10. In a measuring instrument, a galvanometer and a switch operated thereby, a second circuit as adapted to de?ect in both directions from a mid comprising a third relay coil, a source of current, position and having two coils, one 0! said coils said second relay coil and said switch, means re ‘ being in a measuring circuit and being respon sponsive to de?ections 01' said galvanometer to sive to variations thereof to cause de?ections of close one of said circuits to energize said ?rst or said galvanometer, a pair of control circuits each third and second relay coils, said second relay 40 comprising a relay coil and a source of current, coil opening the said switch to deenergize said means responsive to de?ection 01.’ said galvanome relay coils, and control apparatus operated by ‘’ iter to place the second coil thereof into one of said ?rst and third relay coils. said control circuits and to close the said circuit 5. In a device of the class described, control whereby to energize said relay coil, means re circuits each comprising a relay coil, a switch 45 sponsive to said energization to break said cir operated thereby to open the circuit and a source cuit and time delay means to retard deenergiza of current supply, a condenser shunted across tion ot‘said relay coil. said switches. a device responsive to variations in 11. In a measuring instrument the combina a condition adapted to complete one or the other tion with a measuring circuit, a galvanometer 50 of said circuits to cause energization of one or having two independent coils one of which is in the other of said relay coils to open its respec said measuring circuit, a pointer for said gal tive switch in response to the direction oi the vanometer, the second of said coils being con variation, and control apparatus operated in re nected at one end to said pointer, a pair 0! con t:Kionse to the energization 0! one of said relay is. v trol circuits each including said second coil, said 55 pointer, an individual source of current and an 6. In a measuring instrument the combination with a potentiometer circuit, a galvanometer having a pointer and a pair of unconnected coils, individual relay coil, means responsive to de?ec one of said coils being in the potentiometer cir cuit, a pair of alternate control circuits, means including said pointer to connect the second gal vanometer coil in one or said control circuits de pending upon the direction 01 movement of said in the opposite direction to close the other of pointer and control apparatus operated by said tion 0! the pointer in one direction to close one of said circuits and to de?ection of the pointer said circuits and thereby energize one 01’ said re lay coils, means operative upon closure of the circuit to open the circuit and means to inject a " time delay into‘ the opening means. 12. In a measuring instrument, a galvanometer 65 responsive to a variable condition, a coil carried control circuits. 7. In a self-balancing measuring instrument, a by said galvanometer, a motor, a pair‘ 0! control galvanometer having a pair of coils, one of said circuits therefore each including said coil, means coils being in the measuring circuit which in responsive to de?ection of said galvanometer in either direction to energize one 0! said pair of cludes a variable to be measured and to which said coil is responsive, a motor for rebalancing control circuits for said motor depending upon said circuit, control circuits for said motor re the direction 0! de?ection, adjustable mechani sponsive, respectively, to the direction 01 de-. cal stops to limit the de?ection of said galvanom lie'ction oi the galvanometer, means to quickly eter, completion oi either of said control circuits open either of said control circuits upon comple through said coil operating to bias said galvation thereof comprising the second or said coils, 75 nometer‘ for further rotation in‘themdirectlen of 7 2,272,914 the stop limiting the movement thereof, ‘and means operated following completion of either 01' said control circuits to break said control cir cuit, discontinue said biasing means, and stop said motor. 13. In a measuring instrument the combina .tion with a measuring circuit, of a galvanometer having a pair of coils associated therewith one of which is in said measuring circuit, a pointer for said galvanometer having a contact on the end thereof, a pair of cooperating contacts, the second of said coils being electrically connected to said pointer, a pair of control circuits each including said second coil, said pointer and its contact, a source of current, a relay coil and one of said cooperating contacts, de?ection of‘ the pointer in one direction into engagement with one of said cooperating contacts operating to close one control circuit, and de?ection of the pointer in the opposite direction into engagement with the other of said pair of contacts operating to close the other control circuit, completion of either of said control‘circuits through said sec ond coil operating to bias said pointer for fur ther rotation in the direction of the cooperating contact it is engaging, and means operating fol lowing the completion of either control circuit to break said control circuit and discontinue said biasing means._ " EARL A. KEELER.