Патент USA US2132264код для вставки
Oct. 4, 1938. w_ R KING 2,132,264 CONTROL SYSTEM Filed Feb. 1, 1936 Fig.1. 0 JHA/fE/Q MA GA/ET 'William hing, bgg/ Hi 6‘. MM Attorney. Patented ‘0.1.4, ‘1938 ‘ ' 2,132,264 UNITED STATES PATENT OFFICE 2,132,264 ooN'raoL stem William R.,King, Schenectady, N. Y., minor- to \General Electric Company, a corporation oi.’ New York Application February 1, 1938, Serial No. 61,937 5 Claims. (01. TIL-240) This invention relates to control systems, more the following speci?cation and to the accom par'ticularly to systems for controlling the actu- panying drawing in which Fig. 1 is a simple dia ation of reciprocating loads, and it has for an grammatical illustration 01' an embodiment of the object the provision of a simple, reliable, e?lcient invention and Fig. 2 is a chart of characteristic 5 and improved system of this character. ' More speci?cally, the invention relates to control systems for vibrating screens and the like in which the coil that actuates the load is supplied with a periodically varying voltage from an elec10 tric valve which in turn is supplied from a source curves explaining the operation of the invention. 5 Referring now to the drawing, one terminal of a magnet coil‘ i0, such for example as the shaker magnet 01’ a vibrating screen, is connected to one side of a suitable source of alternating voltage represented by the supply lines ii. 12- An electric 1° of alternating voltage. In most industrial areas the frequency of the voltage supply has some fixed value, such for example as sixty cycles. In the absence of any special control apparatus, a 15 valve energized from such a source would deliver sixty current impulses per second to the coil which in turn would deliver sixty impulses to valve I3 is interposed in the connections between the opposite terminal of the magnet coil i0 and the side l2 of the supply source. As shown, the anode lit, of the valve is connected to the side H of the supply source and the cathode lac is 15 connected through conductors iii and E5 to the opposite terminal of the magnet coil ill. The the load. For certain applications, it is often de~ sirable to cause the coil to deliver a lesser num~ 20 her of impulses to the load, such for example as valve is also provided with a control electrode or grid 13b which serves to Cfmtrol the passage of current between the'eathode and the anode. 2G thirty, twenty or ?fteen impulses per second. commutator devices and, synchronous switches have previously been utilized for producing low frequency voltage, but such devices are expensive, Although the valve i3 may be of any suitable type, it is preferably of the three or four~elec~ trode type. into the Envelope Of which a Small quantity of an inert gas such for example as , g5 require costly maintenance and in general leave mercury vapor is introduced after exhaust. The 26 much to be desired. Accordingly, a further 0bject of this invention is the provision of a control system of this character for controlling an electric valve to pass the desired low ire uency 3-!) current impulses to the actuating coil and in which the control is carried out entirely by means presence of this gas within the envelope serves to ' convert the usual pure electronic discharge into an arc stream thereby constituting the valve an electrostatically or grid controlled arc recti?er. In valves of this type, current will flow between 39 the anode the electrode during that half of stationary elements and apparatus. In carrying the invention into effect in one cycle of the applied voltage in which the voltage of the anode is positive with respect to the form thereof, an electric valve having an anode, 355' cathode and control electrode is connected between a source of alternating voltage the voltage of t‘ cathode, provided the voltage of _ the grid 15 mole Positive than a l?l‘efictel‘mined 3"’ critical value necessary to initiate the current actuating coil. An energy storage device, for ex~ ample, a capacitance, is connected across the output circuit of the valve with a connection to 49 the control electrode. When the valve passes‘ current to the coil during a positive half cycle of the anode voltage, the capacitance becomes charged and applies a negative voltage to the control electrode which maintains the valve non45 conducting. Means are provided for discharging the energy storage device at a predetermined rate so that the valve is again rendered conducting after an interval of one or more positive halt flow. Once current has started to how, between the anode and cathode, the grid does not readily control the magnitude of the current flowing in the output circuit. Consequently, the current ‘10 ?ow in the output circuit can only be stopped by interrupting the anode circuit or reducing the anode voltage to zero. For the purpose of sup plying a voltage to the grid sufficiently positive _ to initiate the flow of current between the anode 4" and‘ cathode, a transformer i6 is provided, the primary winding l6; of which is connected across the supply line ii, 12. This transformer has a cycles, as desired. 50 In illustrating the invention in one form thereof, it is shown as embodied in a system for controlling the actuating coil for a vibrating screen or the like. For a better and more complete understanding 55 of the invention, reference should now be had to plurality of secondary windings I61), I60 and its. One terminal of a capacitance I1 is connected 50 through a protective resistance i8 to the grid I31; and the opposite terminal of this capacitance is connected through variable resistance i9 and re sistance 20 to the cathode '30- The terminals of the secondary winding its are connected across 55 2 2,182,264 the capacitance I1 and a resistance 2| connected in series relationship therewith so- that an al ternating voltage is introduced into the grid or input circuit of the electric valve I3. Energy for heating the cathode I30 to the required degree of incandescence is supplied from the secondary winding Hid to which the heating ?lament of the cathode is connected as illustrated. _ As thus far described, the electric valve is 10 would become conducting once during each cycle of the alternating voltage of the source ii, I 2 and would pass an impulse of current to the mag net coil Ill once during each cycle. Since it is desired to pass a lesser number of current im 15 pulses through the magnet coil than the num ber of cycles of the voltage of the source, means are provided for rendering the valve non-conduct ing during one or more subsequent positive half cycles of the applied voltage. To this end, an 20 energy storage device, illustrated as a capacitance 22, is connected from the cathode I36‘ to the side H of the supply source through a recti?er 23 and a resistor and is also connected to the com mon connection between the resistance 2| and 25 the capacitance I‘! which is connected to the grid i3b. Thus, the capacitance 22 is connected from the cathode I3c to the grid I21). When the valve I3 is conducting during a positive half cycle 3? anode voltage, the capacitance 22 becomes 30 charged and applies a negative voltage to the grid l3s so that during the following positive half cycle of anode voltage, the voltage of the grid is maintained more negative than the critical grid voltage. As a result, the valve l3 does not 35 conduct current during the following positive half cycle of anode voltage. In order to render the valve conducting after one or more positive half cycles of anode voltage, as desired, means are provided for discharging the capacitance 22 at a 40 predetermined rate. These means are illustrated as resistances I9, 20 connected in parallel with the capacitance 22. - - In order to prevent the discharge of the ca pacitance 22 by the reverse voltage across the 45 coil ID, the recti?er 23 is included in the con nections between the capacitance 22 and the side ll of the supply source. Although the recti?er 23 may be of any suitable type it is preferably a vacuum tube having anodes 23a and a~hot cath 50 ode 23b which is heated to the required degree of incandescence by means of energy supplied from ‘the secondary winding “is to which the cathode is connected as illustrated. With the foregoing understanding of the ele 55 ments and apparatus and their organization in tive than this critical grid voltage throughout the positive half cycle of anode voltage the valve l3 will not conduct. If at any instance this critical grid voltage is exceeded the valve it will become conducting and will continue to pass current dur~ ing the remainder of the positive half cycle of ap plied voltage and as long thereafter as the anode remains positive. Thus, since the grid voltage of the valve 68 becomes more positive than the critical value at 10 the beginning of the first positive half cycle of the anode voltage 24, the valve l3 becomes con ducting and a pulse of current represented by the heavy curve 27 flows through the magnet coil Hi. When the anode voltage 24 passes 15 through vzero, the current 2'8 would ordinarily tend to stop ?owing, but owing to the inductance of the coil ill the current continues to ?ow until a time '1‘; during the negative half cycle of voltage. At this point the current ?ow through the coil 20 ceases. As the current through the coil Ill builds up, the capacitance 22 becomes charged with the polarity indicated in the drawing so that a nega tive voltage represented by the curve 28 is ap- 25 plied to the grid l3». Now the actual grid volt age is the algebraic sum of the voltage represented by the curve 25 and the voltage represented by the curve 28 and is represented in Fig. 2 by the un dulating curve 29. When the capacitor 22 at 30 tains its maximum potential, the charge begins to leak oil as represented by the upward slope of the curve 28 at a rate depending upon the ohmic‘value of the resistances i9 and 20. During the second Positive half cycle of the 35 anode voltage 24, the actual grid voltage 29 at no time exceeds the critical grid voltage 26 and con sequently the valve l3 remains non-conducting during the entire second positive half cycle of anode voltage. However, during the third posi 40 tive half cycle of anode voltage, the actual grid voltage becomes more positive than the critical grid voltage and consequently the valve I3 again becomes conducting and passes a second impulse of current through the magnet coil l0 and there after the previously described operation is re peated. Thus, it will be seen that the valve l3 only becomes conducting during every other posi tive half cycle of anode voltage and therefore, if the frequency of the voltage of source il, i2 is of some commercial value such for example as sixty. cycles, the frequency of the current impulses through the coil ill will be thirty impulses per second. By varying the value of the resistance [9, the rate of discharge of the capacitance 22 can be the completed system, the operation of the sys- ' still further decreased, and the number of cur tern itself will be readily understood from the fol— lowing detailed description. In Fig. 2, the alternating voltage of the source ll, i2 is represented by the sinusoidal curve 24 in which ordinates above the axis 0-0 represent positive values of voltage and ordinates below the axis 0—O‘represent negative values of volt age. The voltage supplied to the grid circuit 65 through the secondary winding l6b of the trans former is represented by the light sinusoidal curve 25. Preferably the voltage represented by the curve 25 leads the voltage 24 by an angle de termined by the constants of the capacitance 70 I1 and the resistance 2|. However, for the pur pose of simplicity, this voltage is shown and de scribed as in phase with the anode voltage. The critical grid voltage of the electric valve I3 is rep resented by the dotted curve 26. v If the voltage 76 of the grid remains less positive, 1. c. more nega rent impulses per second still further reduced. In practice, the number of current impulses has been reduced to one impulse for every thirty posi tive half cycles of anode voltage, although there was no indication that this was the limit. When the voltage passes through zero at the end of a positive half cycle in which the valve I3 is conducting the voltage across the magnet coil i0 reverses. This voltage reversal would dis charge the capacitance 22 if it were not for the recti?er 23 which prevents passage of current in such a direction as to discharge the condenser. It will sometimes be found advantageous to ad vance the AC grid voltage represented by the 70 curve 25 a substantial phase angle ahead of the anode voltage in order to insure that the valve l3 will fire as early in the cycle as possible during those positive half cycles of anode voltage in - which the ‘valve is to conduct. As previously 75 3 amazes pointed out, this is etiected by means of the pacitance IT in the grid circuit. 08, } It will also sometimes be found advantageous to substitute for transformer secondary winding l6b a secondary winding on a separate trans former of the type commonly known as a peaking transformer. The peaked voltage wave obtained from the secondary of this transformer will fur ther insure that the valve I3 will ?re as early in 10 the cycle as possible during those half cycles of anode voltage in which the valve is to conduct. ' Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form, it will be understood 15 that the elements and apparatus are merely illustrative and that the invention is not limited to the exact arrangement shown in the drawing since alterations and modifications will readly suggest themselves to persons skilled in the art 20 without departing from the true scope of the in vention or from the scope of the annexed claims. What I claim as new and desire to secure by Letters Patent of the United States is: 1. A control system for a reciprocating load 25 comprising a coil for operating said load, means for supplying a periodically varying voltage com prising an electric valve connected between a source of periodically varying voltage and said coil, and having an anode, cathode and control 30 grid, means for supplying a voltage more positive than a predetermined critical value to said grid during a positive, halt cycle of the voltage of said source thereby to energize said valve to pass current, and means for maintaining the voltage of said grid more negative than said critical value during a succeeding positive half cycle thereby to render said valve nongconducting comprising a source to said grid so that the voltage of said grid is more positive than a predetermined critical value during a half cycle when the anode voltage is positive thereby to render said valve conduct ing, means for controlling the frequency of the voltage supplied to said coil comprising a capaci tance connected from said cathode to said grid and having a connection to the other terminal of said coil to maintain the voltage of said grid more negative than said critical value during a 10 succeeding positive half cycle of anode voltage thereby to render said valve non-conducting, and a resistance connected in parallel with said ca pacitance to control the rate of discharge thereof, and ‘a rectifier in said connection for preventing 15 the discharge of said capacitance by reversal of the voltage of said coil. 4. A control system for a reciprocating load comprising a coil for operating the load, means for supplying a periodically varying voltage to 20 said coil comprising an electric valve having an anode, a cathode and control grid, means for controlling the frequency of said voltage compris ing means for supplying an alternating voltage to said grid, an energy storage device connected 25 across said cathode and control electrode and having a connection to one terminal of said coil, and means for advancing the phase relationship of the alternating component of the grid voltage relative to the anode voltage to insure energiza 80 tion of said valve substantially at the beginning of a positive hall’ cycle of anode voltage. 5. A control system for a reciprocating load comprising a coil for operating the load, a source of alternating voltage of predetermined fre 85 quency, means for supplying a periodically vary ing voltage of reduced frequency to said coil com capacitance connected across said cathode and prising an electric valve having an anode con grid and having aoonnection to one terminal of nected to said source, a cathode connected to one terminal or said coil, and a control grid, conec 40 tions from said source for supplying an alternat ing voltage to said grid so that the grid voltage is more positive than a predetermined critical value when the anode voltage is positive thereby to energize said valve to conduct current, a ca 45 pacitance connected from said cathode to said grid and having a connection to'the opposite ter minal of said coil for maintaining the voltage oi’ said grid more negative than said predetermined said coil and a recti?er in said connection for preventing discharge of said capacitance by re versal of voltage of said coil. ’ 2. A control system for reciprocating load com prising a coil for operating the load, means for 45 supplying a periodically varying voltage to said coil comprising an electric valve connected be tween said coil and a source of voltage of pre determined irequency and having a cathode, anodeand control grid and means for controlling 50 the frequency or the voltage applied to said coil comprising a ‘capacitance connected across said cathode and‘grid and having a connection to said coil, airesistance connected in parallel with said capacitance for controlling the rate 01' discharge thereof, and, a rectifier included in said connec value during the following positive halt cycle of 50 anode voltage thereby to render said valve non conducting, a rectifier included in said connec tion for preventing discharge of said capacitance by reversal of the voltage of said coil. a resist— ance connected in parallel with said capacitance tion for preventing discharge of said capacitance for controlling the discharge of said capacitance by reversal oi.’ the voltage of said coil. ' to render said valve conducting during a subse 3. A control system for a reciprocating load quent positive halt cycle at anode voltage, and ‘a comprising a coil for operating said load, means capacitance included in circuit with said grid 80 for supplying a periodically varying voltage to for insuring energization of said valve at approx \said coil comprising an-electric valve having an imately the beginning of a positive hali cycle 0! anode connected to a source of alternating volt age, a cathode connected to one terminal 0! said coil and a control grid, connections from said said anode voltage. - WILLIAM R. KING.