Патент USA US2404894код для вставки
July 30, 1946. w, p_ WILLS 2,404,894 MEASURING APPARATUS Original Filed Nov. 15, 1938 FIG. 1. "\46 T 50 5 ZNVENTOR. WALTER P. WILLS . 31/ * KMW: / TO Patented July 30, 1946 2,404,894 UNITED STATES PATENT OFFICE 2,404,894 MEASURING APPARATUS Walter P. Wills, Philadelphia, Pa., assignor to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Original application November 15, 1938, Serial No. 240,594. ‘Divided and this application Septem ber 25, 1942, Serial No. 459,638 12 Claims. (Cl. 172-239) 1 2 A prior application Serial No. 240,594, ?led November 15, 1938, by Thomas R. Harrison and myself as joint inventors and issued into Patent 2,300,742 on November 3, 1942, discloses certain improvements in methods of and apparatus for preventing hunting in automatic recording and controlling systems. Said prior application dis unidirectional potential or current under meas urement. When the source of minute unidirectional po tential or current under measurement is derived from a thermocouple which is located in a fur nace, the temperature of which it is desired to ascertain, additional problems in the measure closes certain improvements in methods of and apparatus for the measurement of minute elec trical currents or potentials and their utilization for control and analogous purposes which were ment of the minute unidirectional potential or current are encountered because of the introduc tion of extraneous alternating currents into the measuring circuit from leakage paths in the fur nace between the thermocouple and ground. By way of example, when the furnace whose tem not the joint invention of the applicants who made said prior application and are my sole in vention and are disclosed and claimed by me in the present application, which under the circum stances is to be regarded as a division of said prior application. ' perature under measurement is an electric fur 15 nace which has heating resistance elements dis \ A general object of the invention is to provide an improved method of measuring and/or re cording potential or current variations of minute posed in its walls, alternating currents frequent ly flow from the furnace heating elements to ground through leakage paths in the furnace walls. The thermocouple extends through the 20 furnace walls and even though it is provided with a protecting tube some of the alternating A more speci?c object of the invention is to or ?uctuating currents which ?ow in the furnace provide a. method of employing current or po Wall leakage paths tend to ?ow through the magnitude. tential variations of' minute magnitude to con thermocouple and the measuring circuit to trol the operation of electro-mechanical appa 25 ground. The thermocouple and measuring cir ratus. cuit provide a shunt path for such leakage cur A still more speci?c object of the invention is rents to ground since va portion of the apparatus to provide an improved method of and apparatus utilized for measuring the potential or current for eliminating the e?ects of spurious electrical variations of the thermocouple, generally the eifects upon the operation of apparatus employed 30 electronic ampli?er is grounded. It is noted that for measuring the magnitude and changes in ?uctuating currents will also tend to be estab magnitude of minute electrical currents or po lished in the thermocouple and measuring circuit tentials. due to electrolytic action between the thermo It is a particular object of the invention to couple and ground. The alternating or ?uc provide a method of and apparatus for prevent 35 tuating currents introduced into the thermo ing the introduction of extraneous alternating couple and measuring circuit produce inac currents into the measuring circuit of apparatus curacies in the measurements obtained and utilized for making measurements of minute uni render the operation of the apparatus un directional currents or potentials in low resistance stable. More speci?cally, when a potenti circuits. ometric measuring arrangement of the self A serious problem in the measurement of mi balancing type is employed in conjunction with nute unidirectional potential or current varia the thermocouple and electronic ampli?er, such tions in low resistance circuits, particularly in po extraneous alternating currents in the thermo tentiometric measuring circuits wherein the couple and potentiometer circuit introduce false source of minute unidirectional potential or cur 45 balance points into- the potentiometer and also rent is derived from a thermocouple, is the chili cause erratic operation of the potentiometric re culty of electrically amplifying such potential or balancing motive structure. current variations. The direct ampli?cation of It is accordingly a primary object of the pres— minute unidirectional or current variations in sent invention to provide an improved method low resistance circuits by means of conventional 50 of and apparatus for measuring minute unidi electronic amplifying circuits is difficult because changes in the spacing and relative positions of the electrodes of the amplifying tubes produce effects which are similar to and are. of the same order of magnitude as the. changes inthe. minute. 55 rectional potential or current variations pro duced by a thermocouple in which the di?iculties pointed out above have been wholly eliminated or materially minimized. This advantageous result is obtainedin accord 2,404,894. 3 ance with the present invention by isolating the thermocouple from the potentiometric measur ing network and the associated electronic ampli fying apparatus. To that end the thermocouple is periodically connected to the terminals of a condenser of suitable value which is insulated from ground, and during alternate intervals the condenser is disconnected from the thermocouple and is connected to the input terminals of the potentiometric measuring network and the asso ciated electronic ampli?er. By this means any extraneous alternating or ?uctuating currents which may exist in any leakage paths from the thermocouple to ground are prevented from ?ow ing through the potentiometric measuring net work and associated electronic ampli?er, and 4 9 adapted to ride on a screw threaded rod Iii which is rotated in one direction or the other under control of the thermocouple 3. A suitable reversible electrical motor H is provided and is coupled in any convenient manner to the screw threaded rod ii! to rotate the latter at the de~ sired speed and in the desired direction and there by to move the contact 8 along the slidewire re sistance ‘l to rebalance the potentiometer 6 when the latter is unbalanced. The terminals of the thermocouple 3 are con nected by the conductors 13 and 5 to the input terminals [2 and 13 respectively of a double con tact interrupter M which is illustrated in Figs. 15 2 and 3. When in one position, the interrupter it operates to apply the potential developed by the thermocouple 3 to the terminals of a con therefore, are rendered incapable of affecting the denser l5 which is suitably insulated from ground. operation of the measuring apparatus. Since the To this end, the interrupter I4 is provided with a condenser is insulated from ground, no leakage movable pair of contacts l6 and ll which are 20 currents tend to ?ow to the condenser from the insulated from each other and from contacts l2 furnace leakage paths, and i3 and are adapted to be moved into engage The various features of novelty which charac ment with the contacts 52 and 113, respectively, terize my invention are pointed out with par when the interrupter i4 is in said one position. ticularity in the claims annexed to and forming a part of this speci?cation. For a better under 25 When the interrupter is in its other position the movable contacts l6 and H are in engagement standing of the invention, however, its advan with a pair of insulated contacts l8 and !9, respec tages and speci?c objects obtained with its use, tively, and in this position of the interrupter the reference should be had to the accompanying potential which was impressed on the condenser drawing and descriptive matter in which I have l5 by the thermocouple 3 is connected in opposi illustrated and described a preferred embodiment tion to the potentiometric potential between the of the invention. left end terminal of the slidewire resistance 1 Of the drawing: and the contact 3. It should be noted that in the ’ Fig. l is a diagrammatic representation of the last mentioned position of the interrupter M the use of the invention in a potentiometric record " thermocouple 3 is totally disconnected from the ing and controlling system; Figs. 2 and 3 illustrate in detail a form of interrupter that may be employed in the arrange ment of Fig. 1; and Fig. 4 illustrates schematically a form of elec remainder of the measuring apparatus, and there fore, is eii‘ectively isolated from the remainder of the apparatus. In this manner the introduction of any extraneous ?uctuating or alternating cur— tronic ampli?er that may be employed in the 40 rents in the thermocouple circuit due to leakage paths which may be established between the thermocouple and ground through the walls of the furnace due to electrolytic action between drawing, there is illustrated in schematic form the thermocouple and ground is eifectively pre an arrangement including an electronic device l shown in detail in Fig. 4 for producing effects 45 vented from affecting the operation of the meas uring apparatus. In addition, since the con in accordance with the extent of unbalance of a denser !5 is insulated from ground, n0 extraneous potentiometric measuring network which controls ?uctuating or alternating currents will flow to the electronic device and is unbalanced in acthe condenser from leakage paths between the cordance with the variations in a quantity to be thermocouple and ground. . 50 measured and in which because of the small mag The form of interrupter l4 shown in Figs. 2 nitude of the unbalance electromotive forces, it and 3 includes a continuously rotating shaft 28 is not practical nor desirable to have the said which may be driven by any suitable form of motor effects produced directly by the potentiometric such as a synchronous electric motor 2! which measuring network. More speci?cally, an arrangement is illustrated 55 receives energizing current from supply conduc tors not shown and on which shaft are insulat in Fig. l for recording and controlling the tem ingly mounted two pairs of slip rings 22, 23 and perature of a furnace 2 in the interior of which a 24, 25 and a four segment commutator 26 each thermocouple 3 is arranged in heat transfer rela segment being of the same arcuate length and tion therewith and is responsive to slight changes in furnace temperature. The thermocouple 60 all insulated from each other. Brushes l6 and I‘! are provided for the commutator 2'5 and corre which may be located at a distance from the re sponding brushes l2, l3, l8 and 19 are provided mainder of the measuring apparatus has its ter for the slip rings 22, 23, 24 and '25, respectively. minals connected by a pair of conductors ll and 3 Brushes l6 and H are connected to opposite ter~ to the terminals of a null point potentiometric ‘ minals of the condenser 15 while the brushes [2 measuring network 5. The potentiometric meas 85 and i3 are connected to conductors 4 and 5, uring network 5 includes a slidewire resistance '7 respectively, and the brushes l8 and is are con and an associated contact 8 which is capable of nected to one end terminal of the slidewire re being moved along the length of the slidewire and sistance l and to contact 8, respectively. One may be of any suitable type for example such as opposite pair of segments On the commutator 25 the Brown potentiometric measuring network are connected to the slip rings 22 and 23 and the disclosed in Patent 1,898,124 issued to Thomas R, other opposite pair of segments are connected to Harrison on February 21, 1933. the slip rings 24 and 25. Thus, during each cycle The movable contact 8 of the potentiometer of rotation of the shaft 20, one pair of segments is attached to a suitable carrier which for example may be in the form of an internally threaded nut 7,5 on the commutator will be in engagement with Fig. 1 arrangement. > Referring more particularly to Fig. 1 of the 2,404,894 the brushes [6 and I1 for one half cycle and dur ing'that time will close the circuit from the ther mocouple leads 4 and 5 to the condenser l5. Dur ing the remaining half cycle the other pair of commutatorsegments will be in engagement with the‘ said brushes to connect the potentiometer slidewire resistance ‘I in circuit with the condenser 15. The speed of the motor 21 which drives ‘6 be a strip chart as shown and is adapted to be driven in any convenient manner as for example / by'a undirectional motor 33 through suitable gear ing (not shown), so that a record of the tempera ture to which the thermocouple v3 is subjected will be recorded as a continuous line on the chart. The electronic ampli?er i as noted hereinbefore is illustrated in detail in Fig. 4 and as shown in the shaft 29- is so adjusted that the time for one cludes an electronic valve 34 which is preferably cycle of rotation of the shaft is identical with the 10 a heater type high mu triode having an anode, time of one cycle of the alternating current sup cathode and a control electrode and having its plied by the conductors L1 and L2 in Fig. 1. The input circuit connected by conductors 35 and 36 reason for so relating the speed of rotation of the to the terminals of the resistance 2?. Anode volt motor 2! and the time of one cycle of the alter age is supplied the valve 34 from the terminals of natin-g‘current supplied by lines L1 and L2 is made 15 a suitable ?lter 3'! which is connected in circuit apparent hereinafter. between the valve 34 and a. recti?er 38. The rec The periodic connection of the potential pro ti?er 38 is a conventional full wave recti?er em duced on the condenser H3 in opposition to the ploying a recti?er valve 39 including two heater potential tapped on the potentiometer slidewire type diodes in one envelope. Energizing current resistance 1 produces a pulsating drop‘ across a 20 is supplied the heater ?laments of the diodes from resistance 2‘! connected in the potentiometer cir the low voltage secondary winding 40 of a trans cuit, which potential drop is either in phase with former (‘it which also includes a line voltage pri the voltage of the supply lines L1 and L2 or is mary winding 42, a high voltage secondary wind displaced 180° in phase therefrom. This pulsat ing 43 and an additional low voltage secondary ing potential drop is impressed on the input ter 25 Winding 44. The line voltage primary winding minals of the ampli?er I wherein it is ampli?ed :22 is connected to the alternating current supply and the ampli?ed quantity is applied to the ter lines L1 and L2. The anode of the one diode of minals of one winding '28 or 29 01" the reversible valve 35 is connected to one terminal of the wind ‘ electrical motor H which as illustrated in detail ing- 43 and the anode of the second diode is con in Fig. 4 also includes a winding 39 which is con 30 nected to the other terminal of the winding 43. nected to the alternating current supply lines L1 The cathodes of the diodes are connected together and L2 through a suitable condenser 3|, and through a resistance 45 to the positive ter The reversible electrical motor H is of the in minal of the ?lter 31 and the negative terminal duction variety and includes a squirrel cage. rotor of the latter is connected to a center-tap on the and two pairs of oppositely disposed ?eld poles 35 winding 43 and to a center-tap on the winding 4%). on which the windings 28, 29 and 39 are wound. The negative terminal of the ?lter is desirably Winding 28 is wound on one ?eld pole of one of connected to ground potential as shown. said pairs and winding 29 is wound on the other The ?lter 3‘! includes a condenser 46 which ?eld pole of that pair. Winding 3B is wound on shunts its positive and negative terminals and the other pair of ?eld poles and due to the ac 40 has its positive terminal connected to the anode tion of condenser 3| the current which flows of valve 34 through resistances 41, 48 and 49, and through the winding 39 will lead the line voltage has its negative terminal connected directly to the by approximately 90°. The current supplied the cathode of said valve. As illustrated, the point of winding 28 by the ampli?er l is in phase with the engagement of resistances 4i’ and 48 is connected supply line voltage and establishes a ?eld in the 45 by a condenser 50 to the negative terminal of the rotor which is displaced 90° in the forward direc ?lter and the point of engagement of resistances tion with respect to that established therein by 48 and 49 is connected by a condenser 5| thereto. the winding 30. Similarly, the current supplied Energizing current is supplied the heater ?la winding 28 by ampli?er l is in phase with the ment of valve 34 from the low voltage transformer supply line voltage, but since the winding 29 is 50 secondary winding 44 which also supplies energiz wound on an opposite ?eld pole from that on ing current to the heater ?laments of a twin type which the winding 28 is wound, winding 29 estab electronic valve 52. The flow ofv current through lishes a ?eld in the rotor which lags by 90° that valve 34 is normally maintained at a mean value established by winding 3|]. Reaction between the since the resistance 21 is connected directly across ?eld set up by winding 28 or 29 with that set up 55 the input circuit thereof, but when a pulsating ' by winding 30 establishes a rotating ?eld in the potential appears across the terminals of resist rotor which rotates in one direction or the other ance 21, the conductivity of valve 34 is alternately dependent upon whether winding 28 or 29 is ener increased and decreased resulting in a pulsating gized and thus on the direction of potentiom potential drop appearing across the resistance 49 etric unbalance. The motor rotor is connected 60 in the output circuit of the valve 34. through suitable gearing or couplings to the screw The output circuit of valve 34 is resistance ca threaded shaft [9 so that the contact 8 is.ad— pacity coupled to the input circuit of valve 52 justed along the slidewire resistance 1 in accord through a condenser 53 and a resistance 54 con ance with the direction of rotation of the rotor. nected across the input circuit of valve 52. Valve The direction and duration of rotation of the ro 65 52 is a heater type valve including two triodes in tor is controlled by the direction and extent of one envelope. Each triode includes anode, cath unbalance of the potentiometer so that on motor ode and control electrode elements. For conven rotation, the contact 8 is adjusted in the proper ience, the triode having the resistance 54 con direction to reduce the potentiometer unbalance. nected ‘across its input circuit will be referred to If desired, a pen may be mounted on the car riage 9 which carries the potentiometer contact 8 as the triode A and the second triode will be re ferred to as the triode B. and arranged in cooperative relation with a re Anode voltage is supplied the triodes A and corder chart 32 to thereby provide a continuous B from the terminals of the ?lter 31, and as record of the temperature of the furnace in which shown, the anode of triode A is connected the thermocouple 3 is inserted. The‘ chart 32' may 75 through a resistance 55 to the point of engage 2,404,894 ing 56 of a transformer 5‘I to the minal of the ?lter. The cathodes and B are connected together and tive terminal of the ?lter. The output circuit of triode A capacity coupled by a condenser 58 ance 59’ to the input circuit of the condenser I5 and resistance 65 in eliminating overshooting and consequent hunting of the po tentiometric system is described in detail in the positive ter of triodes A to the nega prior application, Serial No. 240,594 ?led by Thomas R. Harrison and myself and referred to hereinbefore and therefore will only be brie?y described herein. With the resistance 55 and condenser I5 ar ranged as shown, it will be apparent that when is resistance and a resist triode B and the output circuit of the latter is coupled by transformer 51 to the input circuit of a pair of electronic valves 59 and 65 which are connected in push-pull. The transformer 51 includes a center tapped secondary winding 5|, the termi nals of which are connected to a respective con 8 The operation or this arrangement including ment Of resistances 41 and 48, and the anode of trio-de B is connected through the primary wind the interrupter contacts I5 and I? are in en gagement with the contacts I? and I3, the ther mocouple 3 operates to charge the condenser I5 through the resistance 55 and the electromotive 15 force thus developed between the condenser ter trol electrode of the valves 59 and 60 and the center tap of which is connected through a bias ing resistance 62 to the cathodes of the valves, which, as shown, are connected together. As illustrated, a condenser 63 may desirably be con 20 nected across the terminals of the transformer minals is thereafter compared with the poten tiometer electromotive force at the then position of the contact 8 along the slidewire resistance 1 when the interrupter contacts I6 and H are moved into engagement with the contacts I8 and I9, respectively. With the temperature of the furnace to which secondary winding 5| for tuning the latter to the thermocouple is responsive at a predeter the frequency it is desired to amplify. Valves 59 mined value, the condenser I5 will tend to be and 60 are heater type tetrodes and include anode, cathode, heater ?lament, control elec 25 charged through the resistance 65 until the con denser electromotive force is equal to that of the trode, and screen grid elements. The heater ?l thermocouple. The contact 8 would then be in aments of the valves 59 and 59 are energized from a position along the slidewire resistance ‘I such the Winding 44. that the electromotive force tapped off the slide Anode voltage may be supplied the valves 59 and 60 directly from the supply conductors L1 30 wire ‘I is exactly equal and opposite to the con denser electromotive force. For convenience, and L2, as shown, or may be supplied thereto when the slidewire electromotive force is referred from a suitable transformer energized by the sup to hereinafter, that portion tapped off resist ply line current, if desired. Winding 28 of mo ance ‘I and opposed to the condenser electromo tor II is connected in the anode circuit of valve 59 and winding 29 of the motor is connected in 35 tive force is the electromotive force intended. On a change in the temperature of the furnace, the anode circuit of valve 60. for example on an increase in temperature, the In operation, when a pulsating potential drop thermal electromotive force will increase the is produced across resistance Z‘I as a result of potentiometer unbalance, the resulting ampli?ed electromotive force developed across the con an alternating voltage across the terminals of duce a potential drop across the latter, and as appears across the terminals of the transformer til the current through resistance 65 is reduced to zero or in other words until the system is again balanced. Thus, until the slidewire electromo tive force is adjusted to the new value of the pulsating current flows through the transformer 40 denser terminals. The ?ow of charging current to the condenser through resistance 65 will pro primary winding 55 will cause the induction of a result, the electromotive force developed across the transformer secondary winding 6| Which the condenser terminals will not assume the ? voltage is impressed on the input circuit of valves 59 and 68. The alternating voltage which 45 nal value of the thermal electromotive force un secondary winding 6| swings the potentials of the control electrodes of the valves 59 and 50 in opposite phase at a frequency corresponding to the supply line frequency and thereby renders 50 thermocouple electromotive force, the condenser electromotive force will tend to assume a value one valve or the other non-conductive depending intermediate the thermocouple and slidewire upon the phase of the voltage of the transfermer electromotive forces. The flow of current secondary winding 6| with respect to the supply through resistance 2‘! on unbalance of the con line voltage. The resulting deenergization of one motor winding 28 Or 29 and the increased ener 55 denser and potentiometer electromotive forces will operate substantially immediately to pro duce energization of motor II for rotation to ef gization of the other operates to produce rota tion of the motor in one direction or the other fect adjustment of the contact 8 in the proper direction to reduce the unbalance between the depending upon the phase of the pulsating po tential drop produced across resistance Z‘I and thereby the direction of potentiometer unbal ance. As illustrated, a condenser 64 may be de sirably connected between the anodes of valves 59 and 69 to increase the available torque of the motor I I. 60 condenser and potentiometer electromotive forces. It is noted that there is no delaying means in the circuit through which the condenser and slidewire electromotive forces are opposed so In order that the speed of the motor I I may be 65 that the ampli?er I responds substantially im mediately to unbalance in said electromotive as great as possible without overshooting of the forces to energize the motor II for rotation in new balance point of the potentiometric network one direction or the other to adjust the slide 6 and consequent hunting taking place, means wire electromotive force as required to reduce have been provided to insure that the motor the unbalance and reduce the motor energization speed is reduced to zero as the balance point is to zero at the instant the balance between said reached. This end is obtained by the arrange electromotive force is restored. Due to the in ment including the condenser I5 and a resistance ertia of the motor, however, the speed of the 65 which is inserted in the conductor 5 leading latter will not fall off as quickly as the energiza from the interrupter contact I3 to the thermo 75 tion thereof and consequently, the slidewise elec couple 3, as shown. 2,404,894 tromotive force will tend to overshoot the value of the condenser electromotive force. As a re sult, the potentiometric network will be momen tarily unbalanced in the opposite direction, vice to charge the latter, opposing the E. M. F. on said device to a known E. M. F. during each interval when said ?rst mentioned E. M. F. is not impressed on said device whereby the resultant which unbalance will produce an effect energiz b of said opposed E. M. F.’s creates a- current of a ing the motor for rotation in the reverse direction regular frequency which can be readily ampli to thereby quickly decelerate the latter. Inas ?ed, amplifying said current, and applying said much as the condenser electromotive force differs ampli?ed current to effect a balance between said from the thermocouple electromotive force by an amount equal to the potential drop produced across resistance 65 by the ?ow of current there through, the contact 8 will not have reached the position along slidewire resistance 1 correspond» ing to the new value of thermocouple electromo tive force at the instant when the condenser and slidewire electromotive forces were exactly bal anced. After the condenser and slidewire elec tromotive forces are balanced, the condenser will not assume‘the thermocouple electromotive force until after the lapse of a predetermined interval required to charge the condenser to the thermo couple potential and by making this interval of the proper duration, the motor will be decelerated and ease the contact 8 ~gradually into its true balanced position without overshooting. The proper adjustment of the duration of the lag be tween the condenser and thermocouple elec tromotive forces may be readily effected by prop erly proportioning resistance 65 and condenser H5 in relation to the effective resistance of the cir cuit including the slidewire resistance 1 and re sistance 21. When the circuit components are properly proportioned, the motor may be ex tremely fast in its rebalancing effect and is capa— ble of moving the contact 8 completely along the length of the slidewire resistance 1, a distance of approximately 12" in some cases, in a fraction of a second without overshooting and consequent hunting taking place. It will be apparent that the motor H may be employed to operate a control valve or rheostat for controlling the supply of heating agent to the furnace 2 to the temperature of which the ther mocouple 3 is responsive, or another motor de opposited E. M. F.’s. 2. The method which comprses producing an M. F. to be measured, periodically impressing said E. M. F. on an electrical capacitive react ance to charge the latter, opposing the E. M. F. on said reactance to a known E. M. F. during , each interval when said first mentioned E. M. F. is not impressed on said device whereby the re— sultant of said opposed E. M. F.’s creates a current of regular frequency which can be readily ampli ?ed, amplifying said current at said frequency, _ and applying said ampli?ed currents to effect a balance between said opposed E. M. F.’s. 3. In measuring apparatus, a circuit including in potentiometer resistance, a standard source of i I. for said resistance, an electrical energy ..tcring device, means to periodically connect a scurc of E. M. F. to be measured to said device to charge the latter and to connect said device‘ in said circuit to oppose the E. M. F. on said device to said standard E. M. F. during each interval when said E. M. F. to be measured is not con nected to said device to thereby create a pulsat ing current ?ow of regular frequency in said cir cuit, means to amplify said pulsating current, and means energized by said ampli?ed quantity to eifect a balance between said opposed E. M. F.’s. 4. In measuring apparatus, a circuit including a potentiometer resistance, a standard source of E. M. F. for said resistance, an electrical capaci tive reactance, means to periodically connect a source of E. M. F. to be measured to said react ance to charge the latter and to connect said re actance in said circuit to oppose the E. M. F. on said reactance to said standard E. M. F. during each interval when said E. M. F. to be measured sirably operated together with the motor I I may 45 is not connected to said ‘reactance to thereby be so employed. For example, as shown in Fig. create a pulsating current flow of regular fre— I, the furnace 2 may be heated by a resistance quency in said circuit, means to amplify said pul 66 which is connected to electric supply conduc sating current, and means energized by said am tors L3 and L4 through a rheostat 61 the adjust pli?ed quantity to adjust said potentiometer re ment of which may be effected by a motor 68. 50 sistance to effect a. balance between said opposed The motor 68 may be exactly like motorll and E. M. F.’s. is connected in parallel therewith. The mechan 5. In measuring apparatus, a circuit including ical connection of the rheostat 67 to the motor 68 a potentiometer resistance, a, standard source of is such as to increase and decrease the supply of E. M. F‘. for said resistance, an electrical capaci electric current to the resistance 66 as the tem as tive reactance, means to periodically connect a perature to which the thermocouple 3 is respon source of E. M. F. to be measured to said react sive drops below and rises above a predetermined ance to charge the latter and to connect said re level. actance in said circuit to oppose the E. M. F. While in accordance with the provisions of the on said reactance to said standard E. M. F. dur statutes, I have illustrated and described the best ing each interval when said E. M. F. to be meas forms of embodiment of my invention now known ured is not ‘connected to said reactance to thereby to me, it will be apparent to those skilled in the create a pulsating current ?ow of regular fre art that changes may be made in the forms of quency in said circuit, means to amplify said pul the apparatus disclosed without departing from sating current at said frequency, a source of alter the spirit of my invention, as set forth in the nating current of said frequency, a two phase appended claims and that in some cases certain rotating ?eld moto; connected to said potentiom features of my invention may be used to advan eter resistance for adjustment of the latter and tage without a corresponding use of other having one phase energized from said source, features. ' and means to apply said ampli?ed quantity to the Having‘now described my invention, what I 70 other phase of said motor to control the operation claim as new and desire to secure by Letters of the latter and thereby the adjustment of said Patent ‘is: potentiometer resistance as required to effect a 1. The method which comprises producing an balance between said opposed E. M. F.’s. E. M. F. to be measured, periodically impressing 6. In measuring apparatus, a circuit including said E. M. F. on an electrical energy storing de a potentiometer resistance, a standard source of 2,404,894 11 E. M. F. for said resistance, an electrical capaci tive reactance, means to periodically connect a source of E. M. F. to be measured to said react ance to charge the latter and to connect said re actance in said circuit to oppose the E. M. F. on said reactance to said standard E. M. F. during each interval when said E. M. F. to be measured 18 tity to said motor to control the operation of the latter, said resistance and reactance cooper ating to automatically control the E. M. F. on said reactance in a predetermined manner with respect to time on a change in said ?rst men tioned E. M. F. so as to cause a balance of the opposed E. M. F.’s in said circuit when the dif ference between said ?rst mentioned E. M. F. and not connected to said reactance to thereby create said standard E. M. F. is equal to the E. M. F. a pulsating current flow of regular frequency in by said device under control of said said circuit, means to amplify said pulsating cur 10 produced motor following deenergization of the latter. rent, and means to utilize said ampli?ed quantity 10. In measuring apparatus, a circuit includ to effect a balance between said standard E. M. F. ing a potentiometer resistance, a standard source and the E. M. F. on said reactance. of E. M. F. for said resistance, an electrical en 7. In measuring apparatus, a circuit including ergy storing device, a double pole-double throw 15 a standard source of E. M. F., an electrical energy switch to periodically connect a source of E. M. F. storing device, means to periodically connect a to be measured to said device to charge the latter source of E. M. F. to be measured to said device to charge the latter and to connect said device and to totally disconnect said device from said rent, and means to apply the amplified quantity to said device to control the operation of the lat ter, said resistance and reactance cooperating to quency, a source of alternating current ‘of said E. M. F. to be measured and to connect said de in said circuit to oppose the E. M. F. on said de vice to said standard E. M. F. during each inter 20 vice in said circuit to oppose the E. M. F. on said device to said standard E. M. F. during each val when said E. M. F. to be measured is not con interval when said E. M. F. to be measured is nected to said device to thereby create a pulsat not connected to said device to thereby create ing current flow of regular frequency in said cir a pulsating current flow of regular frequency in cuit, means to amplify said pulsating current, and said circuit, means to amplify said pulsating curmeans to utilize said ampli?ed quantity to effect rent, and means energized by said ampli?ed a balance between said standard E. M. F. and the quantity to effect a balance between said op E. M. F. on said device. posed E. M. F.’s. 8. Measuring apparatus including means for 11. In a measuring apparatus, a circuit in producing a variable E. M. F. to be measured, means for producing a standard E. M. F., a de 30 cluding a potentiometer resistance, a standard source of E. M. F. for said resistance, an elec vice having inertia for varying said standard trical capacitive reactance, a double pole-double E. M. F., a circuit in which said standard throw switch to periodically connect a source of E. M. F. is permanently‘connected, an electrical E. M. F. to be measured to said reactance to capacitive reactance, a resistance, means to charge the latter and to totally disconnect said‘ 35 periodically connect said ?rst mentioned E. M. F.,v reactance from said E. M. F. to be measured and‘ said resistance and said reactance in series to to connect said reactance in said circuit to op~ charge the latter and to connect said reactance pose the E. M. F. on said reactance to said stand in said circuit to oppose the E. M. F. on said re ard E. M. F. during each interval when said actance to said standard E. M. F. during each interval when the E. M. F. to be measured is not 40 E. M. F. to be measured is not connected to said reactance to thereby create a pulsating current connected to said reactance to thereby create a ?ow of regular frequency in said circuit, means pulsating current flow of regular frequency in to amplify said pulsating current at said fre said circuit, means to amplify said pulsating cur frequency, a two phase rotating ?eld motor con nected to said potentiometer resistance for ad justment of the latter and having one phase energized from said source, and means to apply automatically control the E. M. F. on said react ance in a predetermined manner with respect to said ampli?ed quantity to the other phase of time on a change in said ?rst mentioned E. M. F. so as to cause a balance of the opposed E. M. F.‘s 50 said motor to control the operation of the latter and thereby the adjustment of said potentiometer in said circuit when the difference between said resistance as required to effect a balance between ?rst mentioned E. M. F. and said standard said opposed E. M. F’s. E. M. F. is equal to the E. M. F. produced by said 12. Measuring apparatus including means for‘ device due to its inertia following deenergization producing a variable E. M. F. to be measured. of the latter. 65 means'for producing a standard E. M. F., a device 9. Measuring apparatus including means for for varying said standard E. M. F., a motor ar~ producing a variable E. M. F. to be measured, ranged to adjust said device when energized and means for producing a standard E. M. F., a device having the inertia characteristic which produces for varying said standard E. M. F., a motor ar ranged to adjust said device when energized and 60 further adjustment of said device following dc energization, a circuit in which said standard having the inertia characteristic which produces E. M. F. is permanently connected, an electrical further adjustment of said device following de capacitive reactance, a resistance, a double pole energization, a circuit in which said standard throw switch to periodically connect said ?rst E. M. F. is permanently connected, an electrical capacitive reactance, a resistance, means to peri 65 mentioned E. M. F., said resistance and said re‘ actance in series to charge the latter and to odically connect said ?rst mentioned E. M. F., totally disconnect said reactance from said ?rst said resistance and said reactance in series to mentioned E. M. F. and to connect said reaccharge the latter and to connect said reactance. tance in said circuit to oppose the E .M. F. on reactance to said standard E. M. F. during each 70 said reactance to said standard E. M. F. during each interval when the E. M. F. to be measured‘ interval when the E. M. F. to be measured is is not connected to said reactance to thereby not connected to said reactance to thereby cre create a pulsating current 'flow of regular fre-, ate a pulsating current ?ow of regular frequency quency in said circuit, means to amplify said pul in said circuit, means to amplify said pulsating in said circuit to oppose the E. M. F. on said current, and means to apply the ampli?ed quan 1; eating current, and means to apply the ampli 2,404,894 13 ?ed quantity to said motor to control the opera tion of the latter, said resistance and reactance cooperating to automatically control the E. M. F. the opposed E. M. F.’s in said circuit when the difference between said ?rst mentioned E. M. F. and said standard E. M. F. is equal to the E. M. F. produced by said device under control of said with respect to time on a. change in said ?rst 5 motor following deenergization of the latter. on said reactance in a predetermined manner mentioned E. M. F. so as to cause a balance of WALTER P. WILLS.