US2053016A - Controlling operating time of arc discharge devices - Google Patents

Description

H. F. WILDER Sept. l, 1936.

` CONTROLLING OPERATING TIME OF ARC DISCHARGE DEVICES Filed June 3, 1952 Brwentor Wider Patented Sept. 1, 1936 UNITED STATES PATENT GFFICE fcoNTRoLLING OPERATING TIME oF ARC DISCHARGE DEVICES Application June 3, 1932, Serial No. 615,211

3 Claims. (Cl. Z50-27) This invention pertains to the .automatic control of the operating period or duration of time that energy is supplied Vto anelectrio circuit across an arc discharge path of a. gaseous conl duction device capable of a sustained discharge after being initiated by ;a starting electrode.

The object of my invention is to provide a circuit arrangement embodying two or more ther- `mionic arc discharge tubes, one of which may isi serve asian automatic regulator or time-limit devicefor the other tube or tubes. 'The duration of operation of the energysupplylng tube being determined by the `electrical constants of the grid circuit of the time-limitingtube and which maybe varied so. that the cycle of operation that may take place is from .Olof a second to several minutes.

.In the following detailed description I shall refer tothe' accompanying drawing lin"`vvhich,-f Figure il isa schematic diagram of a circuit having two. thermion'ic arc discharge tubes arranged to function yin accordance withmyA invention, one of the tubes supplying energy to an appropriatedevice orload and the associated tube definitely controlling the duration of time that this energyl's supplied, yby automatically limiting thefunctioning vof` '.the first tube at an instant determined `by Vthe electrical constants of the secondary tube grid circuit; and Figure. 2 is a graphical representation of the several .current and voltage transients-during the initiation and at the'conclusion of these functions.

'Referring tovFigure 1,' the gaseous arc disch'argetubes T1, T2` arenof the well-known type in whichv the grid completely surrounds the cath# odean'd merely junctions to initiate a discharge betweenthe .plate and cathode, with no further control. The discharge is instantaneous upon the application of the critical voltageto the grid and the current rises abruptly to full value, which features are Aespecially applicable Ato my purpose. Both tubes are supplied from a D. vC. source indicated-as 120 volts, the regulator of, timing control tube Trbeing connected through a resistanceRrand the energy supplying tube -Tz throughgthe load. -The grid. biasis impressed by the potential drop across the resistor R1 in the common .return from the cathodes. The laments are thus at a positive potential with respect to the grid element. It will be shown that altimin'g-action may be obtained with an increase of the IR drop across'thecornmon cathode lead resistance R1, caused by'tl'ledilerence in magnitude of the respective ,anode'currents It is evident that this resistance R1 cannot be replaced by an equivalent battery.

The time-limit or control tube T1 arcs continually except during the period tube T2 is operating. The manner in which one tube may be caused to extinguish the other when capacitively coupled by a condenser C is described in U. S. Patent No. 1,855,380 granted to A. W. Breyfogel. My present invention provides a method of varying the cycle of operation with precision within wide limits determined by the electrical constants of the circuit.

The arc is struck in the energy-supply tube T2 by raising the elective grid bias, that is, the actual potential diierence between the grid element 15;

and the cathode, to nearly zero volts. At this level the few electrons attracted to the anode acquire such velocity that an arc discharge quickly cccurs. Current thus flows through the load circuit, attaining full value at once while the 2 grid loses all practical control of the current density.

Such a positive increase in the grid potential may be `eifected in a number of Ways. I have illustrated the impulse as induced in the secondary 2 coil of a transformer TR, but other devices will readily occur to engineers, for instance: the rise in E. M. F. actingin the grid resistance directly coupled to a light sensitive device; or the increase in the D. C. output level of a beat frequency oscillator, which in turn is a function of the moisture content, or the thickness of a stationary or moving web of material; or again the tube may be .triggered by direct connection to a telegraph signal amplifier. 3

y Let it be assumed that the load is to be supplied with 9 units of current vat a potentialA of volts for a period of say, 1/2 second, and at the conclusion of this interval the current is to be made zero in preparation for an additional pulse. The maximum load current depends mainly on the rating of the particular tube used.

As noted above, the tube T1 arcs continually except when the tube T2 is operating. Accordingly prior to the reception of a starting impulse 4 R1 provides the grid bias voltage Egzfor tube T2,` 55

2 v 2,053,016 f iT-fflthe bias of 5 volts. These numerical values' of voltages will, of course, change somewhat `with other circuit conditions but are suiiiciently close to those usually encountered.

The resistance RT and the condenser Cr associated with the grid of tube T1', 'constitute the' timing element of this circuit and upon the time constant RTCT depends the duration of time that tube T1 Will remain inoperative o:raijc.Y

less when once extinguished.

- Under thestatic conditions assumed, the condenser CT is charged positively-to a voltage determined by several variable quantities, butV for practical considerationmay loe-assumed to be 7 Volts. Of the -7 volts, five volts are supplied bythe drop Eg across the common resistor AR1 by the passagevof the current'(3)Ip1. The remaining two volts is produced in the tube 'and is due to the electrical position of -theV grid `in 30.A the are of the tube.y Y y It will be appreciated by those: familiar with the attempts to determine the poten'tialfgradient in an arc dischargeby means of 'an exploring element such as a grid, that theindicated voltage is a function of the physicai size ofthe grid, its position in the arc mechanicallywith respect to the other electrodes', the arc density, andthe vapor pressure,'in that the sizeof the arcrcolumn is varied in diameter and "the'ionization potenl0V tial is inuenced. In this circuit the resistance RT although of the order of several `rmegohms i enters the result. D

of the transients attendingthe starting of tube-jlbv v At the desired instantan impulsereceived by the input transformer TR induces a lsmall oscillatory pulse in the secondary coil shown in heavy lines in the diagram ofrFigure 2j and lwhich is indicated by the arrow. j Thisraises vthe voltage Egz (to be'diierentiated fromEg) to nearly `zero volts, thereby developingjanjarc in the tubeTa in approximately 10 micro-seconds. The current across theloadV rises abruptlyto (9)1152; causing a drop of 90 volts across*the"load, ap

Description proximately 15 volts in the tubeandf 15 volts across the common resistor R1'. "As' the anodes of the tubes are connected through the condenser C, the instantaneous drop at Athe anode ofthej 60, tube T2 causes the voltage at the 'anode of tube T1 to instantaneously dropfto approximately 80 volts negative with respect to its cathode, thereby extinguishing the arc. of tube T1. yDuring the short period that the condenser C is being charged at the reversed polarity, Vthe ionslin tube Tiare enabled to recombine (de-ionization). 'Asin'dicated in the diagram, the current (3)151' through the.v tube T1 was not only brought tozero but actually reversed in direction for an .instant, due to the Vscavenging effect 'in the inter-electrode space of tube T1 by the negative potential on condenser C. The current in the tube T2 not only reached itsA full value (9)1112, but, as indicated, increased slightly above this due to the 7-1 charging currentwhi'ch passed'throughresist' u cessationoffthe arc in tube Tr prevents ance R2 to the condenser C, as indicated in the diagram by the cross-hatched portion. This in'- itial heavy current momentarily decreased the potential Epz of 30 volts at the anode as indicated in the diagram by the heavy cross-hatching. Of 5 the 30 Vvolts at the anode, 15 volts constitute the drop across thearc of the tube and 15 v olts constitute the drop 'across the'common resistor R1. Also due to the soinewhat greater current during ,the charging time, the potential Egz at the grid 10 Was increased slightly in a negative direction as indicated by the crossfhatching.

Action of the timing circuit they 7 volt charge on condenser CT from escaping through thearc and as the anode potential E111 quickly reaches volts, condenser CT now charges more positively through the resistance condenser CT is:

The expression for the voltage rise on the L't'. v jt ii. VcT=KEp1 1 VRTCT 7RTCT 25 *Arma-1201 V f* Y Eg'zvllk V,1 The value of the'electro-static charge oncon-J denser CT will ultimately approach and opposev 3m the new biasing potentiallevel of 15fvolts across the resistor Rn. i i

Stopping tube T2 1. At the instant the potential Egiat the grid ofV tube T1, increasingprogressively alongthe line AB or A'B, is suii'icient to opposethe biasing volt: age Eg, an arc isV formed in the tube T1'. The condenser' C *was V'chargel-"to a potential of 90 volts by theA IR` drop V`across 'theload and hence 40 the starting of theutube T1 causes a drop at thev anode of tube T2 to minus 70 volts, that Y'is,jj90 volts minus the drop acrossthe arc in tube 'T12 The current (9)1p2 instantly dropsto'zero with a slight reversal which issomevvhat geater than 45 that previously in the tube Tilgas a greater number ofions existbetweenlthe electrodes.A The cur rent and voltage'relations' which existed Vbeforey the startingof tube Ti.' nowl return ltdtheir previous normal values. While it was vpreviously known, asin said prior patent, that two thermionic arc"dischargetubes may be arranged in a'circuit so as to be vmutually extinguishing, the" time-limitA of 'any discharge was dependent'on externally timed pulses", or other external means. VMy invention :disclosed herein provides meansV for making the 'ti'mix'ig action automaticfby introducing a'jtime constant in the grid Vcircuit of one tubewliich" mayy eV varied to suit diaerent L crbnditiona' j This autoi-j matic action is la function 'of theincrease' in voltage drop over a common resistance caused by a difference in anode 'currents and the rise in anode potential of the time-limit ftube'when extinguished.` IV have illustrated'one arrange! ment of circuits'which mayY be employed in 'car-`V rying out my invention but it willfbe-evident to engineers that various modifications canbe made Within the Vscope :of the invention. 1

Iclaim:,- j 70 1. An electricalk system,-c omprising;apairiof electrostatically controlled arc discharge, tubes connected in ,.parallel,atranslating devifcelin series with the load vr i',ube and ,a resistance element in'se'ries with'the'other tube, thelatt'r 75 A:sin v tube constituting a time-limit device for the load tube, means including circuit arrangements whereby the starting of either tube by the application of a critical voltage to its grid element causes the extinction of the discharge in the other tube, and impedance means connected to the grid of the time-limit tube, said impedance means having a time-constant which is proportioned to cause the last mentioned tube to operate at the expiration of the predetermined period of inaction.

2. In an electrical system for supplying energy to a load or translating device, a source of electrical energy, a pair of gaseous conduction devices having starting elements and capable of sustained discharge independent of the starting element after being started, and connected respectively in series with the load and in shunt thereto, circuit arrangements whereby the starting of either device causes the extinction of the arc in the other device, a starting circuit connecting the grid of said shunt tube to its anode through a resistance and to the common return from the cathodes of both tubes through a condenser, the time-constant of said interconnected resistance and condenser determining the interval between the extinction and the automatic restarting of the arc in said tube.

3. In an electrical system for supplying energy to a load or translating device, a source of electrical energy, a pair of electrostatically controlled arc discharge tubes having starting elements or grids and capable of sustained discharge after being started, and connected respectively in series with the load and in shunt thereto through a resistance, circuit arrangements whereby the starting of either tube causes the extinction of the arc of the other tube, the grid input of said shunt tube being connected respectively to its anode through a resistance and to the common return of both tubes through a capacity, and a resistance in said common return, the normal grid voltage of the shunt tube being sufcient to start a discharge therethrough, and the time constant of the circuit including said grid resistance and capacity being proportioned to cause a predetermined interval between the extinction and restarting of the arc in said shunt tube.

HAROLD F. WILDER.

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