US2466022A - Gaseous discharge tube motor circuit - Google Patents

Description

April 1949. w. s. GORTON 2,466,022

GASEOUS'DISCHARGE TUBE MOTOR CIRCUIT 7 Filed Nov. 20, 1943 v 2 Sheets-Sheet 1 INVENTORL M112 6', k BY w. s. GORTON 2,466,022

GASEOUS DISCHARGE TUBE MOTOR CIRCUIT April 5, 1949.

Filed Nov. 20,- 1943 2 Sheets-Sheet 2 SIGNAL DC ON G ID DC-BEMF REFERRE TO-O SIGNAL VOLTS 0N CATHODE' CRITICAL GRID VOLTAGE INCREASE REFERRED TO-O 8L P H fL' H HJM a %;"I

POTENTIAL I APPLIED FOR POSITION 0F IMPULSE ADJUSTMEN IMP ULSEDISCI-LABGE DISCHARGE 0N FERRED CURVE WHEN SIGNAL GRI EEERRED VOLTS CURVE RISES TO T0-0 DOTTED LINE CRITICAL SIGNALDC 0N GRID VOLTS DECREASED REFERRED TO-O I g p L IMPULSE DISCHARGE SIGJV'AL DC 0N DC-EEM-E ON GRID REFERRED Io-o GRIDREFERRED ONCATHODE TO-"O" I REFERRED Io-o R E EEEEEF GR T T IMPULSE DISCHARGE ANDTUBENOTHRING 0N RID-REFERRED IC-D' WHEN SIGNALDC DECREASES Patented Apr. 5, 1949 GASEOUS DISCHARGE TUBE MOTOR CIRCUIT William G. Gorton, Belmont,Mass., assignor, by

mesne assignments, to Submarine Signal Company, Boston, Mass., a corporation of Delaware Application November 20, 1943, Serial No. 511,159

2 Claims The present invention relates to an electrical control circuit for a variable speed drive and in particular it may be applied to a training control system for training any rotatable gear such as may housed in submarine signaling apparatus,

in the training of Radar apparatus, in turret or which is applied to the direct current motor through gaseous conduction tubes, known by the trade name as Thyratron" tubes. Such tubes permit current to flow through them only in one direction so that by proper arrangement of the tubes current may be made to fiow through the tube is being operated, thus providing a motor drive in the forward and reverse directions, de-

.pending upon which way the current flows .through th motor. these cases for field excitation so that the direction of the .flux or current in the field need not be changed for reversing the direction of rotation A separate coil is used in of the motor. 7

In Patent No. 2,264,333 a source of alternating potential adjustable in phase angle is impressed upon the control grid of the gaseous induction tube in such a manner as to shift the instant of discharge of the thyratron tube during the alternating current cycle. w,

In Patent No. 2,147,674 the biasing. potential may be obtained either by a direct current generator Or a potentiometer, or through a phase voltage obtained through a Selsyn generator.

In the present invention the control resides in the adjustment as desired of the potential applied to the grid of a discharge tube in combination with a steadypulsedischarge'applied on the same grid directly or indirectly.

. motor in either direction, depending upon which cult employed oiIers an efllcient braking means '10: reversing the direction of rotation of the motor from one direction-to the opposite direction.

A further advantage in this circuit is that after the reversal has been accomplished, the acceleration or deceleration of the motor in the desired directionis accomplished in the same manner for both forward and reverse rotations. These and other features provide acceleration and deceleration rapidly and over a wide range without hunting or overshooting and further effect adjustments under load conditions so rapidly that little or no variation in speed is experienced with variation of load. The circuit further-is'easily ad-.

justable for operating conditions in such a way so that it may be changed to suit all demands or changes that the motor may be called upon to meet. practically no speed to over speed values for the motor.

Further advantages and merits of the present invention wili be more clearly understood from the description in the specification below showing an embodiment of the invention when read in connection with the drawings in which Fig. 1 shows a circuit diagram for the system, and Fig. 2 shows two sets of curves (2 and b illustrating operating conditions for the system.

In the arrangement shown in Fig. 1, i indicates a direct current motor armature which is provided with a magnetic field by means of the field winding 2. In the arrangement of Fig. 1

the motor armature is connected to a gear reduction system 3 which operates the load 4 which may be any type of device, as, for instance, a

' radio locator, a submarine signal sounding rang The present invention is particularly adaptable for use in the operation 01' a motor both in a foring head, a turret gun, rotating machinery or positioning devices generally used for industrial purposes. The load 4 is tied in with a Selsyn" system that is a self-synchronizing system 5 in which the portion 6 is intended to be used as the rotating element and the portion I as a stationary element. The stationary portion of the Selsyn 5 is tied in with a second Selsyn 8 which is provided with a rotor 9 adapted to be positioned through the reduction gear l0 operated by a manual control indicated by a handwheel II. If desired, this system may be tied up with a gyro compass through the Selsyn unit I 2 which is supplied by alternating current over the line I! Speed variation may be obtained irom' aceaoaa which may be of any desired frequency, 60 cycles or more, the gyro compass will rotate the rotor element l4 and vary the phase impressed upon a parallel resistance divider circuit made up of the Selsyns 5 and 8 so that the variationin voltage appearing across therotor winding 9 whichprovides the signal impulse for the operation of the system will be the differential phase voltage between the Selsyns 5 and 8 or that existing as a resultant component among all three Selsyn units 5, 8 and 12 if the unit i2 is used. In this way it will be possible to provide, for instance, on-shipboard,- an absolute directional control for the turning of a directional winding 9 is impressed between the cathode l5 sized by the same altemating' current potential applied to the Selsyn system.

The'tube 18 may be of the SN? t and is, in fact, used in the circuit described as a rectifier. Aresistance 22 may be used as a bias for the cathode and each anode-cathode circuit may be provided with similar resistances 23 and 24 which are connected in circuit with the vacuum tubes 25 and 28, respectively, to provide grid bias control for the motor circuits which will be described later. Since the grids l6 and H or the tube is are comected together, their potential is always the same and therefore unless the phase on the anodes ill and it) is ninety degrees out of phase with the grid voltage, the grid voltage can only be in the proper phase with one oi the anode= cathode circuits oi the tube it. When it is in phase, therefore, with the anode-cathode circuit l5 and iii, increased amount or current will flow through the resistor 23 in the direction of the arrow F; and when the grid potential is in phase with the anode-cathode circuit lie-95, an increased amount of current will flow through the resistor all in the direction of the arrow r". Therefore, as the potential on the grid 2? of the tube 25 becomes more negative, the grid 28 of the tube 26 will become more positive and so, therefore, the tube 26 will tend to conduct increased current through the resistor in the direction of the arrow G while the current in the resistor 36 in the direction or the arrow G will drop to zero.

' This system, therefore, provides opposite changes in two halves of a symmetrical circuit.

d becomes that or the point A. The potential from the point B to C controls the voltage drop across the resistances 31 and" which provide potentials entering as elements in the control or the grids 39 and 40 or the gaseous discharge tubes 4! and 42, respectively, which control the supply or current to the armature I or the motor in a manner which will be presently described.

The center point D between the resistances -l| and 38-is connected by an adjustable tap 43 to a potentiometer 44 which isconnected in series with a fixed resistance it across a second rectifier 4 which may also be used to supply current to the field of the winding 2. The gaseous discharge tubes 4i and 42 have cathodes ll and 48 which are connected to. each'other through resistances 49 and 50 of equal magnitude. The midpoint 0 between the resistance 49 and is tied to one side of the rectifier 48 to which the resistance 4| is connected.

It will be noted that the points B and C' are always at the same potentials as the points B and C, respectively, and it further should be'noted that the currents flowing through the resistances 31 and 38 at any instant are always in the same direction. Therefore, as the potential B approaches the potential A through the cutofl of current in the resistance 36, the potential drop from B to 0 increases, tending by this action to decreasethe negative bias on the grid 40 of the tube 42. Current may flow in either direction from B to C. If the current collapses in the resistance 36, current will flow through 38 and 31 in the direction from B to C, while if current collapses in the resistance 35, current will fiow in the opposite direction in the resistances 3|, namely from C to B. A change in direction of the flow of current in the resistances Eli and g 33 brings about a reversal of biases on the grids 39 and ill and consequently the reversal of rotation of the'armature 9. However, before a complete reversal occurs from one direction to the other, the current in the resistances ill and 38 decreases in magnitude before reversing direction.-

This has the effect, as will be noted later, oi decreasing the signal voltage below that of the generated back 33. M. since this current decrease occurs with a more rapid acceleration than the decrease in armature speed, and therefore provides, as will be seen later, reversal of current flow through the armature even before the direction of rotation of the motor is changed.

,This action, too, is sufificiently uniform and grad- The vacuum tubes 25 and 26 which may be or the applied directly to the anodes a2 and as but through the resistors 35 and 36 which are connected in series across the anodes 32 and 33. The result of this arrangement is that when the sig-=v nal voltage biases the cathode-anode current in one of the tubes 25 or 26 to a cut-off value-the potential from the point B to C is in one direction. and when the current in the other tube is biased to cut oil, the direction or the potential drop reverses. In this change the potential across the appropriate resistor 35 or 36 becomes zero and therefore the potential of the appropriate anode connected between the cathodes ll and 48 and the grids 39 and to so that a small negative bias may by this means he applied to the grids of the discharge tubes with respect to the cathodes. In the curves a and b of Fig. 2 this is indicated by the dotted lines K and. K labelled in both cases potential applied for adjustment referred to '0'," the potential being applied to the grids. This is usually a small value of the order of two or three volts. The potential drop applied between B and C in the operation of the system may vary over a great range, the range being from zero to the magnitude of the generated back E. M. F. or greater in either direction. When the tube 42 is firing during a portion of its positive half cycle, the voltage across from B to D is such as to place a positive potential on the grid 40 of the tube 42. This is shown in the curve a of Fig. 2 as the dotted line L. Under these conditions the potential drop through the resistance 30 will be such as to place the cathode 43 at a higher potential than the point in the circuit. This is 'shown in curve a of Fig. 2 as the line M. The

relative values between the signal D. C. on the I grid and the back E. M. F. on the grid will vary, depending upon the instantaneous state of opera tion. If the signal voltage has suddenly been reduced, then the back E. M. F. may be greater than that of the signal volts. In the curve shown 44 is such as to bring the negative bias on the grid 40 of the tube 42 below the critical voltage curve which is shown on a of Fig. 2 labelled "Critical grid voltage.

The discussion above does not take into consideration another important element in the The operation ofthe system will best be understood by assuming various practical conditions of operation. Assume, first, that it is desired to I accelerate the rotation of the armature I in a grid control circuit. This is the condenser discharge circuit of which thereare two, one 5| connected in series in the grid circuit 33 and one 52 connected in series inthe grid circuit 40. These circuits are energized through'selenium rectifiers 53 and I4 energized through the windings 55 and 56, respectively, through the alternating current source 51. The windings 55 and 56 are 180 degrees out of phase with each other so. that the rectifled impulses supplied across the resistances .51 and 58 are 180 degrees out of phase with each other. These rectified pulses supply a direct current pulse discharge in the grid circuits indicated by the curves N and N and curves at and b of Fig. 2. The adjustment of this discharge circuit may be such as to provide always a small amount of negative bias through proper choice of values of resistance and capacities in the discharge circuit. The pulse, however, is such as to provide a rather rapid decrease in grid potential during the critical part of operation of the tube so that the instant of discharge of the tube may be readily controlled.

In the curve a shown in Fig. 2 the negative biases on the grid 40 of the tube 42 with respect to the cathode is the sum of the instantaneous ,values on the curve N, the line K and'the line M while the positive potential on the grid is that of the line L If the absolute values at a given instant of N, K and M are greater than L by an amount equal to the critical grid voltage value. then the tube 42 will not discharge.

The tubes 4| and 42 have their anode-cathode circuits connected in reverse-direction through the armature I nd the alternating current transformer windings 60 and BI supplied through the supply line 51. These windings 60 and 6! are also 180 degrees out of phase with each other, the phase of 60 being the same as that of 55 and the phase of Bi being the same as that of ii. The

alternating potential is shown in the curves a and b of Fig. 2 as P and Q, respectively, P being applied to winding Cl and Q to the winding 60.

It may be assumed for reference that current forward direction. In this case the discharge tube 42 will, under our presumption previously made, be the tube to fire. To accomplish this the potential drop across the resistances B, C' must be in the direction from left to right inFig. l and consequently the drop from B to C will be in the same direction. This means that the current flow in the resistance 36 must decrease and that in the resistance 35 increase. This is accomplished by biasing the grid 21 of the tube 32 to cut off the cathode-anode current flow which, in turn, is accomplished through increase of current through the resistance 23 in the direction of the arrowF.

The phase and direction, therefore, of the potentie! in the grid iii of the tube I8 is positive during the positive half cycle potential between the cathode l5 and the anode l3, thus causing current to flow through the resistance 23 in the direction of the arrow F. During this moment the current in the resistance 24 in the direction of the arrow F' has decreased, meaning that the bias is in such a direction that there is a tend- =ency to decrease the current flow between the flowing through the tube 43 will ultimately bring about operation of the armature in the forward direction, and current flowing in the tube 4| will ultimately 'bring about operation in the reverse direction,-the word ultimately" being used in the sense that during the transition period, the motor may not be rotating in the direction correspond ing to the flow of current in the tube.

cathode l5 and the anode 20 in the tube l8.

Under conditions where the currents F and F are equal which is when the grid bias is at a point midway between the two positive phases on the cathodes, the currents flowing in the resistances 35 and 36 will be in equal and opposite directions, which means that the potential between the points B and C will be zero and therefore no current will be flowing in the resistors 31 and 38.

When the anode-cathode current in the tube 25 4s cut off, the potential at the point B is. greater than at C and current flows through the resistors 38 and 3'! from the left to the right as shown in Fig. i. If, however, current is cut off in the anode-cathode circuit of the tube 25, cur-- rent will flow in the resistance 38 and the potential of C will be higher than the potential or B. The reversal of direction of rotation of the motor is accomplished in this fashion. In between these points of extremity, the potential drop between B and C and therefore B and D may be decreasing to such an extent that the tube 42 will not fire while the tube M will fire. In this cas the back E. M. F. is greater than the signal voltage and as a result the tube 42 will cease discharging before the tube 4! commences to discharge because of the applied negative potential in the re- Sistances 44 and 45. The resistances 44 and 45 in this change-over have current flowing in such a direction that they aid in maintaining the negative bias on the tube 4i and oppose the positive bias of the resistance 38 on the tube 42. As the current across the resistance from B to C decreases. the positive bias on the grid 40 will be overcome by the negative drop in the resistances 44 and 45 and the back E. M. F. drop in the re- 'sistance 53. Since the drop in the resistances 38 and 31 is equal, the bias applied to the grid 49 will be the sum of both negative potentials, namely that in the resistance 31 and the resistances 44 and 45, making a larger magnitude of negative bias applies to the grid 39 than positive bias applied to the grid 40.

Following, however, this point of operation, the back E. M. F.s in the resistances 49 and 50 take over to create a suflicient bias on the tube 4| soa little greater or equal to zero, in which case the tube 4| fires for the complete cycle. The term positive bias in the above discussion is used I in the limited sense, that the direction of potential applied to the grid is positive through the element mentioned, but it may not, however, be absolutely positive because of the other negative components making up the absolute bias onthe tubes. In this connection it will be noted that most discharge tubes will discharge for the complete positive half of the cycle when the bias on the grids is zero or perhaps even slightly less than zero and that if the biases on the grids are less than zero, the discharge will occur during some point in the positive half cycle of potential applied between the anode and the cathode ofthe tube, depending upon the parameters of the tube and voltages establishing the characteristic of the critical grid voltage curves.

In the curves shown in Fig. 2 the curves R illustrate the grid voltage curves with reference to the alternating current cycles applied between the cathode and anode of the tube. The puls discharge produced across the resistances 51 and 58 creates a negative bias applied to the grids 39 and 40 of the tubes 4| and 42, which bias varies in accordance with the curves N and N previously mentioned. The instantaneous magnitude of the potential supplied by these pulse discharges is a component which must be added algebraically to the other potentials applied to the grid to determine the instantaneous potential as applied to the grid with reference to the alternating cycle between the anode and cathode of the tube and the critical grid voltage characteristic. In normal conditions when the discharge tubes are not operating, this total potential on the grid is such as to place the pulse curve below the critical grid voltage line. In curve a of Fig. 2 it willbe noted that the curve N in its full-line position intersects the critrical grid voltage characteristic. It should be noted, however, that in this set of curves the impulse discharge on the grid is referred to the point in the same way that the curves L, M and K are referred to the point 0. The net bias voltage in these curves of Fig. 1: is such that the curve N with reference to the voltage across the anode-cathode of the tube would be dropped to the dotted line position of the curve N and thus the tubes in this condition may not be firing. if, however, the signal voltage or preferably the voltage from B to C is in creased from the value L to the value of, say, L1, the curve it may be raised to thepoint N bringing about the intersection between the critical grid volt curve and the curve N at such a point to bring discharges in the cycles shown in the shaded areas H. If this is assumed to be the discharge erence line.

potential across from B to C, neither of the tubes 4! and 42 will discharge. The control of the torque characteristic on the motor I is obtained through the adjustment of values of the condensers l2 and 13: with the resistances 51 and 58 ,respectively providing the desired form for the discharge curves N and N. In place of the rectifiers 29 and 48, direct current supplies may be used.

The systemas a wholeprovides an infinite speed variation under any desired load conditions and both rapid acceleration and deceleration and also reversal of rotation with smooth accelerations and decelerations. If the motor is set for any given speed, a change in load will not substantially change the motor speed and any momentary slight change which may occur will be very rapidly restored.

,As a follow-up system the arrangement has been used with an accuracy greater than onecondenser connected in parallel with one of said resistors, means including a rectifying element for periodically charging said condenser solely from said alternating potential supply means, the charge consisting of a negative pulse occurring during each non-conductive half cycle of said gaseous discharge tube and gradually becoming. less negative during each conducting half cycle thereof, whereby the pulse potential gradlent is substantially uniformly inclined to the I critical grid voltage line during said conductive half cycle, meansfor impressing across a secand of said resistors a potential varying with motor speed, and means for impressing across a third of said resistors a control potential adjustable in magnitude.

in the tube #2, the motor will be operated in the tion L to L", thus in effect raising the impulse discharge curve to the dotted line position N which intersect-the critical grid volts curve to provide a discharge in the shaded area H. In

' this condition the motor will be running in a forward direction but current will be passed through the motor in a reverse direction, thus 2. A control circuit for operating a motor comprising a gaseous discharge tube having cathode, anode and grid electrodes and circuits, means for supplying the anode-cathode circuit with alternating potential and means for supplying a control potential to the grid-cathode circuit, said last means including a plurality of series-connected resistors between grid and cathode, a condenser connected in parallel with one of said resistors, means including a rectifying element for periodically charging said condenser solely from said alternating potential supply means, the charge consisting of a negative pulse occurring during each non-conductive half cycle of said gaseous discharge tube and gradually becoming less negative during each conducting half cycle thereof, whereby the pulse potential gradlent is substantially uniformly'in'clined to the 9,60 mm arm ltagelln'dudng no mm a "me Q 10 v0 e ,s eo e we halt Cyclamen; torlmpresslqz across a second 2 ag of said resistor-s a potential proportional to the 337831: "our 5 1942 motor-s back electromotive force. means for 1111- 2 333-393 y f""""" 1943 pressing across a third. of sald'reslstors a direct I 2:340:083 Schnan; 1:11:13. '25: 1944 menu mm 2,371,590 Brooke Jr. et a1. May 1:, 1945 in: potential supply means and means for "im- 7 pressing acros a fourth of said resistors a config g trol potential adjustable in magnitude.

r G. GORTO". I OTHER "Radio Engineering," by 1".- E. Termini. 560mm muons mm edition IDS'IJCcGnw-Hill Book 00-. pp- 468-469.

'The'tollowlnz: references are of record in the me of this netmt:

UNITED STATE PATENTS" mmber Home Beta 1,985,003 Von mm at a]. mo. 18, 1934 2,131,759 8atter1ee "flue"..- Oct. 4. 1938-

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