US2008413A

US2008413A - Electric discharge apparatus

Info

Publication number: US2008413A
Application number: US707931A
Authority: US
Inventors: John W Dawson
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1934-01-23
Filing date: 1934-01-23
Publication date: 1935-07-16
Anticipated expiration: 1952-07-16

Description

July 16, 1935. J. w. DAWSON 2,008,413

ELECTRIC DISCHARGE APPARATUS Filed Jan. 25, 1954 ATTORN Patented July 16, 1935 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE APPARATUS Pennsylvania Application January 23, 1934, Serial No. 707,931

17 Claims.

My invention relates to electric discharge apparatus and it has particular relation to apparatus for timing the operation of a work system.

It is an object of my invention to provide simple and inexpensive apparatus for timing the excitation of a work system.

Another object of my invention is to provide apparatus for controlling the state of excitation of a work system in such manner that the system may be energized when desired and will remain in energized condition when so energized for an accurately determinable interval of time.

A further object of my invention is to provide apparatus for controlling the operation of a work l5 system of a type that shall maintain the system in operating condition after the operation is initiated for intervals of time that may be predetermined at the option of the operator.

Still another object of my invention is to pro- 20 vide timing apparatus for controlling the operation of a system of a type that shall be capable of maintaining thesystem in operation for any desired length of time within the limitations of the mechanical and electrical elements of the 25 apparatus and the system.

An incidental object of my invention is to provide a simple and tractable electronic time delay relay.

Another incidentalobject of my invention is to 30 provide a time delay relay operative by electrical power the timing periods of which shall be independent of the variations of potential supplied thereto. l

More concisely stated, it is an object of my invention to provide translating apparatusfor controlling a work system in such manner that it shall be capable of being energized by a simple operation and locked in in its energized conditionY for a predetermined interval of time after which it shall be automatically deenergized and the translating apparatus reverted to a condition wherein it may again be operated.

According to my invention, I provide a translating system incorporating an electric discharge device having a control electrode and a plurality of principal electrodes. One of the principal electrodes is of such character that the electrical conductive path between it and the control electrodc has asymmetric properties. A capacitor is connected in the circuit of the last named principal electrode and the control electrode and is so charged through the conductive path between the electrodes that by reason of the resultant potential impressed between the electrodes the electric discharge device is maintained in a deenergized condition. The connections between the plates of the capacitor and the electrodes of the electric discharge device are reversed when it becomes necessary to operate thesystem. By reason of the resultant reversal of potential im- 5 pressed between the electrodes of the electric discharge device, that are associated with the capacitor the electric discharge device becomes energized and the translating system is energized.

A translating system constructed in accord- 10 ance with my invention has, of course, wide general applicability. It might for example be utilized for controlling the initiation and the timing of the steps in the processing of materials. In such apparatus contrivances may be provided l5 whereby the completion of one step in a process causes the actuation of timing apparatus, constructed in accordance with my invention, which in turn initiates and maintains a subsequent step in the process. I have found, however, that my invention has particular applicability to welding systems and in the present instance my invention will be described herein as applied to an electrical welding system.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together 4with additional objects and advantages thereof, will best be understood from the following description of Va specific embodiment when read in connection with the accompanying drawing, in which Figure 1 is a diagrammatic view showing a. system constructed in accordance with my invention,

Fig. 2 is a graph showing the initial relationship between the potentials impressed between certain of the elements of the system,

Fig. 3 is a graph showing the relationship between the potentials impressed between the same elements when the system is in deenergized condition,

Fig. 4 is a graph showing the relationship between the potentials when the system is energized, and

Fig. 5 is a graph illustrating a condition which might exist ifcertain features incorporated in the preferred embodiment of my invention were not utilized.

The apparatus shown in Fig. l comprises an electric discharge device l having an anode 3, a cathode 5 and alcontrol electrode l. The electric discharge device I may be of the high vacuum or gas iilled type. It is, however, preferably of megas oued type, and I have found. that a. grid 2 l glow tube capable of delivering continuously approximately l/2 ampere may with advantage be utilized. Again it is to be noted that the electric discharge device I may be of the hot cathode or the cold cathode type. Thus a suitable grid controlled mercury pool tube or a grid-controlled tube oi' the Ignitron type may with advantage be utilized. However, in the preferred practice of my invention a hot cathode electric discharge device is utilized.

A suitable alternating potential is impressed between the anode 3 and the cathode 5 of the electric discharge device I from a section 9 of the secondary |I of a. power supply transformer I3. The transformer I3 is provided with an additional secondary section I5, one .terminal I1 of which is connected to the cathode 5 of the electric discharge device I. The latter section I5 is so arranged with respect to thesection9, whereby alternating potential is supplied to the

principal electrodes

3 and 5 of the electric discharge device I, that the remaining terminal I9 thereof is at a potential relative to the cathode 5 which is of opposite phase to the potential of the anode 3 relative to the cathode. A potentiometer 2| is connected across a plurality of windings of the section I5. The movable tap 23 of the potentiometer is coupled to the control electrode 1 of the electric discharge device I through a movable contactor 25 of a normally deenergized relay 21, a capacitor'29, another movable contactor 3| of the relay and a resistor 33 of comparatively low magnitude (1000 ohms in the usual practice of my invention).

It will be of advantage in. the present instance to deilne the potential impressed between the control electrode 1 and the cathode 5 of the electric-dischargedevice I as the control potential and the potential impressed between the anode 3 and the cathode 5 as the principal potential. The cathode may be regarded as at zero potential.

It is to be noted that the control potential in the present instance is in opposite phase to the principal potential. 'I'his condition is illustrated graphically in Fig. 2. In this view, the principal potential is represented by a sine curve 35 and the controlv potential is represented by a second sine curve 31 displaced in phase by 180 with respect to the first sine curve. If the electric discharge device I is of the gas filled type, it has an abrupt characteristic and when the control potential is below,a..flimiting value for any particular value of principal potential, the electric dis-v charge device is deenergized. When the control potential rises above the limiting control potential value, the electric discharge device I becomes energized and remains energized in spite of further variations in the controly potential so long as the principal potential is greater than that required to maintain a discharge between the principal electrodes. The limiting values of control potential for the, principal potential represented by thef curve 35 are represented in Fig. 2 by a. 4broken line curve 39.

potential is negative while the control potential is positive. Under such circumstances the capacltor 29 in the control circuit of the electric discharge device I is charged'by the low current which flows between the control electrode 1 and the cathode 5 of the electric discharge device by reason of the potential impressed between the latter electrodes. The charging circuit extends from the movable tap 23 of the potentiometer 2| through the movable contacter 25, the capacitor 29, the movable contacter 3|, the resistor 33, the control electrode 1,. the cathode 5to the upper terminal I1 of the secondarysection I5. Since the resistor 33 in series witht'he control electrode.

1 and the cathode 5 is of low magnitude, the capacitor 29 is rate.

1,5' charged at a comparatively high f The capacitor 29 is, of course, only charged during the intervals during which positive control potential ls impressed on the electric discharge device I. However, it is to be noted that the'conductive path between the control electrode 1 and thecathode 5 of the electric discharge device is'asymmetric and for this reason the capacitor is not discharged during the subsequent half cycles when the principal potential is positive and the control potential is negative.

The capacitor 29 is charged during the negativehalf cycles of principal potential until a stable condition is attained. 'When this condition is attained a negative direct current potential is impressed on the control electrode 1 and the electric discharge device I is maintained in deenergized condition. The magnitude of the negative potential thus impressed may be varied by varying the position of the movable tap 23 of the potentiometer 2|. l

The condition of the electric discharge device as the vcapacitor is charging and in its nal charged condition is represented graphically in Fig. 3. In this view, a number of selected positive half waves of principal potential are represented by half sine curves 35 and the corresponding limiting control potential curves 39 are represented by broken line curves as in Fig. 2. The increasing negative direct-current potential of the capacitor 29 is represented by a dot-dash curve 4I and the vresultant negative control potential, which is composed of the negative direct current potential of the capacitor 29 plus the alternating potential supplied by the section I5 of the secondary I| through which the capacitor 29 is charged, is represented by full line curves 43 below the time axis 45. It is to be noted that in the third set of curves the directcurrent potential curve 4| is substantially parallel to the time axis 45. This set of curves represents the condition of the system when the capacitor 29 iscompletelycharged. By reason of the fact that the resistor 33 is of small magnitude this condition is attained in a short period of time.

The exciting coil 41 of the normally deenergized relay 21, through the

movable contactors

25 and 3| of which the vcapacitor 29 is charged, is connected in a normally open circuit including the section 9 of the secondary II whereby principal potential is supplied to the electric discharge device I and a manually operable pushbutton switch 49 which is normally in open position. When the pushbutton switch 49 is operated, the exciting coil 41 of the relay 21 be.

comes energized and the normally closed

movable contactors

25 and 3| are disengaged from their corresponding fixed contacts 5I and 53 while a plurality of normally open

movable contactors

55 and 51 engage their corresponding

xed contacts

69 and 69.

By the disengagement of the former

movable contactors

25 and 3| from the corresponding iixed contacts 5| and 53, the plate 6| of the capacitor 29 which is charged negative is disconnected from the control electrode 1 and the other plate 63 which is charged positive is disconnected from the movable tap 23 of the potential. By the engagement of the later

movable contactors

55 and 51 with their corresponding xed contacts 59 and 69, the positive plate 63 of the capacitor 29 is connected to the control electrode 1 through a high resistor 65 (preferably of the order of 10 megohms) and the above mentioned low Aresistor 33 while the negative plate 6| of the capacitor 29 is connected to a network 61 comprising an additional capacitor 69 and a rectifier 1| in series with each other at the junction Apoint 13 of the rectifier and the capacitor. The rectifier 1| may be of any available type but is preferably of the copper-oxide type. The network 61 is connected across a plurality of windings of the section I5 of the secondary |I whereby control potential is supplied.

'I'he points to which the net work 61 is connected are at a lower absolute potential relative to the cathode 5 than the movable tap 23 of the potentiometer 2|. By reason of the presence of the rectiiier 1| in the network, the capacitor 69 is charged and maintained in charged condition. The rectier 1| in the net work 61 is so connected to the capacitor 69 that the junction joint 13 to which the negative plate 6| of the capacitor 29 is connected is at a xed negative potential relative to the cathode 5 of the electric discharge device but the absolute value of this potential is less than the absolute value of the potential of the movable tap 23 of the potentiometer.

It is seen that by the excitation of the relay 21, the position of the capacitor 29 in the circuit of the control electrode 1 and the cathode 5 is reversed and a positive direct-current potential is impressed on the control electrode 1. The circuit now extends from the lower or positive plate 63 of the `capacitor 29, through the movable contactor 55, the resistor 65, the control electrode 1, the cathode 5, the biasing capacitor 69, the junction point 13, the movable contactor 51 to the upper or negative plate 6| of the capacitor 29. On this potential a negative directcurrent potential corresponding to the potential of the junction point 13 of the network 61 to which the capacitor 29 is now connected and an additional alternating potential of opposite polarity to the principal potential, corresponding to the windings of the secondary section 5 above the net work 61, are superimposed in View of the fact that the junction point 13 and the section I5 are in the above-described circuit. The points in the section |5 of the secondary to which the network 61 is connected are so selected that the positive direct-current potential applied to the control electrode 1 is considerably greater in magnitude than the negative direct-current potential and the alternating potential superimposed on the positive direct-current potential and the electric discharge device is, therefore, energized by the reversal of the position of the capacitor 29 in the circuit.

It is to be noted, moreover, that the capacitor 29 is now connected in the control circuit of the electric discharge device through a high resistor 65 and by reason of the presence of the high resistor it is neither appreciably charged nor appreclably discharged through the conductive path comprising the control electrode 1 and the cathode 5.

One of the principal advantages which arises from my invention resides in the use of the normally asymmetric conducting path between the control electrode 1 and the cathode 5 for charging the capacitor 29. Since this path has the property of asymmetric conductivity the rectifier which would otherwise be necessary in the charging circuit is eliminated.

When the electric discharge device is thus energized, the exciting coil 15 of a second relay 11 is energized. The energizing circuit for the relay extends from the upper terminal of the secondary section 9, through the anode 3, the cathode 5, the exciting coil 15 to the lower terminal of the secondary section 9. A movable contactor 19 of the relay engages a plurality of corresponding iixed contacts 8| and causes a work system 83, which may for example be a spot welding system as shown to become energized. A second movable contactor of the last mentioned relay 11 engages a plurality of xed contacts 81 ehunting the push-button switch 49 and the circuit through the exciting coil 41 of the mst-mentioned relay 21 is thus closed and the relay is energized independently of the pushbutton switch. Thus, by a single actuation of the push-button switch 49 the electric discharge device is energized and the work system 83 is locked in in energized condition regardless of the subsequent opening of the push-button switch.

The period during which the work system 83 operates may be regulated by controlling the discharge of the capacitor 29. For this purpose a plurality of resistors 89 of the grid leak type are provided. The resistors 89 are of the order of several hundred thousand ohms and are al1 of different magnitude.

The resistors 89 are each connected at one terminal to a common conductor 9| which is in turn adapted to be connected to the negative plate 6I of the capacitor 29 by the normallyopen contactor 51 of the relay 21 when the relay is energized. A movable contact element 93 is provided for the purpose of connecting the remaining terminals of each of the resistors 89 individually to the positive plate 63 of the capacitor 29. However, the contact element 93 can only be connected to the positive plate 63 through normally-open contactor 95 of the relay 11 and the remaining normally-open contactor 55 of the relay 21 both of which are in a series network with the contact element and the positive plate.

When the relay 41 is energized by the operation of the push-button switch 49, its normally-open

movable contactors

55 and 51 are closed and the electric discharge device is energized. The relay 11 is therefore, energized and a network including the normally-open movable contactor 51 of the former relay 21, one of the resistors 89, the movable Contact element 93 of the resistor system, the movable contactor 95 of the latter relay 11, the remaining normally open contactor 55 of the former relay 21 and the/capacitor 29 is closed and the capacitor is discharged at a rate depending on the magnitude of the particular resistor 89 connected across its terminals. The rate at which the capacitor is discharged is also dependent on the initial difference of potential impressed between the plates 6| and 63 of the capacitor 29 which is in turn dependent on the position of the movable tap 23 of the potentiometer 2|. It is to be observed that while finite diierences in the time of discharge of the capacitor 29 may le attained by varying the position of the movable contact element 93 from one resistor 89 to another, the adjustments of the time of discharge at values between the values attained by utilizing resistors of successive magnitudes may be attained by varying the position of the movable tap 23 of the potentiometer 2 I.

The function of the potentiometer in the system is of extreme importance for the reason that independent grid resistors must necessarily be utilized to attain appreciable times of discharge of the capacitor 29. On the -other hand it is essential for the proper operation of a system of the type involved here that the time of operation of the apparatus be capable of any desired adjustment. To attain this ilexibility in adjustment with resistors alone is out of the question since an inordinately large number of resistors would be required. The result is attained by utilizing the potentiometer in cooperation with the resistors.

Attention is also called to the fact that the capacitor 29 begins to discharge only after the relay 11 is energized. The work system 83 is also energized when this relay is energized and consequently the time required for the capacitor 29 to discharge, that is to say, the time during which the work system is energized begins to tally substantially at the instant that the work system 83 is energized.

The condition of the system during the interval during which the capacitor 29 is discharged is represented graphically in Fig. 4. In this view, the principal potential during a series of selected positive half cycles and the corresponding limiting control potential are represented as in the other views. The decay of the potential impressed on the capacitor 29 is/represented by a dot-dash curve 91 which is, for most of the half cycles 35, above the time axis 45, since the position of the capacitor 29 in the circuit has been reversed. On this potential are super-imposed the negative potential provided by the network 61 and the alternating potential provided by the windings of the section I of the secondary II which are above the network and the resultant control potential is represented by the full line curves 99.

The function of the negative direct current potential provided by the network 61 can be seen by referring to Fig. 5. In this view a half-cycle of operation of a system in which the network 61 is omitted and the negative plate SI of the capacitor 29 is directly connected to a point in the secondary section I5 through the movable contactor 5l of the relay 21, is represented.

The principal potential and limiting control potential are represented as in the other views. The decaying potential of the capacitor is represented by a dot-dash curve III I, and as it is shown it corresponds to a condition of the system in which the capacitor is substantially discharged. It is to be noted that the curve IOI approaches and is asymptotic to the time axis 45. The control potential is represented by a full line curve |03 which intersects the limiting control potential curve 39 near the end of the half cycle of potential. f

As is apparent, the electric discharge device will become energized in the actual system represented by Fig. 5 near the end of its positive half cycle of principal potential. This condition occurs near the end of period of discharge gof the capacitor and may persist for'an indefinite period of time or even recur after the electric discharge device is deenergized depending on the random condition of the apparatus whereby power is supplied to the system. Moreover, the limiting control potential curve 39 of different electric discharge devices I may vary over a comparatively wide range, and the excitation of the device I near the end of the period of discharge of the capacitor may. therefore, become a matter of uncertainty.

Careful consideration of Fig. 5 will reveal that the dimculty arises by reason of the fact that the discharge curve IUI of the capacitor is asymptotic to the time axis which is in turn above the limiting control potential curve 39 to a considerable extent. Since in the discharged condition of the capacitor the curve IIII is substantially identical with the time axis 45 the reversion of a system of the type represented in Fig. 5 to a deenergized condition must depend on the application of negative half cycles of alternating potential which are necessarily of uncertain form. For this reason the negative direct current potential of the network 81 is superimposed on the positive potential. The negative potential is of considerably greater magnitude than the most negative value of the limiting control potential and the corresponding discharge curve 91 is therefore assymptotic to the line parallel to the time axis 45 but well below the limiting control potential curve 39. In the region of the limiting control potential curve it has a marked negative slope (as shown in Fig. 4) and the half cycles during which the limiting control potential curve 39 are intersected by the control potential curve 99 are therefore sharply separated from each other.

After the electric discharge device I is deenergized, the relay 11 is deenergized, the movable contactor 85 connected across the push-button switch 69 is disengaged from its corresponding xed contacts 81 and the relay21 is deenergized. The normally-open

movable contactors

55 and 51 are, therefore, disengaged from their corresponding fixed contacts 59 and 60 and the normallyclosed movable contactors 25 and 3I are engaged with their corresponding xed contacts 5I and 53. The system is thus reverted to its initial condition.

Of particular importance in the application of my system to timing is the fact that the timing periods determined by the decay of charge on the capacitor is substantially independent of potential variations in the source of supply of energy. It is to be noted that the functioning of the system depends on the decrease of the potential impressed between the plates 6I and 63 of the capacitor 29 below the negative direct-eurrent potential provided by the network 61. If variation of a predetermined percent occurs in the potential of the power supply the potential impressed between -the platesV 6I and 63 of the capacitor 29 will be varied correspondingly and as the potential decays it will maintain the percent of variation of the value which it would have if the variation had not occurred. On the other hand the absolute value of the direct-current potential supplied by thenetwork 61 will also be varied in the same manner. The electric dis-- charge devices utilized in the preferred practice of my invention have a maximum value of limiting control potential which is of the order of two or three negative volts and for all practical purposes the electric discharge device may be regarded as being deenergized, (and the timing period may be regarded as at an end) substantially at the point at which the potential impressed on the capacitor 29 is equal to the negative potential provided by the network 61. Since, however, the per cent variation of the former in a positive sense is equal to the per cent ofv variation of the latter in the negative sense the net eiect of the variation on the timing is nil.

Since the capacitor 29 connected in the control circuit of the electric discharge device I may be charged to a dangerously high difference of potential before the system is taken out of use, a resistor |05 of comparatively large magnitude (preferably of the order of r100,000 ohms) is connected across the plates 6I and 63 of the capacitor through one of the normally-closed contactors v 25 of the relay 21. The resistor |05 discharges the capacitor when the system is disconnected from the power source. On the other hand, when the system is in use, the resistor |05 is of such large magnitude compared to the resistor 33 through which the capacitor 29 is charged that it does not disturb the charging operation. Moreover, the resistor |05 does not disturb the discharging operation when the system is in use because the relay 21 is then energized and it is disconnected from the capacitor 29.

My invention has herein been described as embodied in a particular system. It is apparent that numerous changes may be made in the system. One of the most apparent modifications which may arise involves thesection I5 of the secondary I I through which potential is supplied to the control circuit of the electric discharge device I.' In the preferred practice of my invention as it has been explained hereinabove, an electric discharge device having a so-called negative characteristic is utilized. A mercury-vapor-iilled hot-cathode grid-glow tube is an example 'of such an electric discharge device. Such a device has a limiting control potential curve which has negative values for normal values of positive principal potential.

AlthoughI have shown and described certain specic embodiments of my invention, I am fully aware that many modications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of, principal electrodes,` means for impressing alternating potentials between said principal electrodes and between said control electrode and one of said principal electrodes, a capacitor coupled between said control electrode and said last-named principal electrode, whereby said capacitor is charged by the flow of current between said control electrode and said last-named principal electrodes and a predetermined direct current potential is impressed between said control electrode and said last-named principal electrode and means for reversing the coupling between said capacitor and said control electrode and said last-named principal electrode whereby the polarity of the direct-current potential impressed between said control electrode and said last-named principal electrode is reversed.

2. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes and between said control electrode and the principal electrode with which it forms an asymmetric path, a capacitor coupled between said lastnamed electrodes, whereby said capacitor is charged by the current flow between said lastnamed electrodes and a predetermined directcurrent potential is impressed between said lastnamed electrodes and means for reversing the couplingvbetween said capacitor and said lastnamed electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed.

3. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes and between said control electrode and the principal electrode with which it forms an asymmetric path. a capacitor, means including a resistor of relatively low magnitude for connecting said capacitor between said last-named electrodes. whereby said capacitor is charged by the current iiow between said last-named electrodes and a predetermined direct-current potential is impressed between said last-named electrodes and means for reversing the connections between said capacitor and said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed.

4. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that the conductive path lbetween said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes, a capacitor, a supply of alternating potential one terminal of which is connected to the principal electrode between which and the control electrode the conductive path is asymmetric, means, including a resistor of low magnitude, for connecting said capacitor between said control electrode and the other terminal of said potential supply, whereby said capacitor is charged by the current flow between said last-named electrodes and a predetermined direct-current potential is impressed between said last-named electrodes, and means for reversing the connections between said capacitor and said control electrode said lastnamed terminal of said potential supply, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed.

5. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the prop-- erties of said control electrode and one of said principal electrodes being such that the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes, a capacitor, a supply of alternating potential one terminal of which is connected to the principal electrode between which and the control electrode `the conductive path is asymmetric, means including a resistor of low magnitude, for connecting said capacitor between said control electrode and the other terminal of said potential supply, whereby said capacitor is charged by the current ilow between said last-named electrodes and a predetermined direct-current potential is impressed between said last-named electrodes, a resistor of high magnitude and means for reversing the connections between said capacitor and said control electrode said last-named terminal of said potential supply and for connecting said last-named resistor -in series with said capacitor and the asymmetrically conductive path between said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed.

6. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes, a capacitor, a supply of alternating potential one terminal of which is connected to the principal electrode between which and the control electrode, the conductive path is asymmetric, means including a resistor of low magnitude, for connecting said capacitor between said control electrode and the other terminal ofsaid potential supply, whereby said capacitor is charged by the current flow between said last-named electrodes and a predetermined direct-current potential is impressed between said last-named electrodes, a resistor of high magnitude, means for reversing the connections between said capacitor, said control `electrode and said last named terminal of said potential supply and for connecting said l-ast-named resistongin series with said capacitor Vand the asymmetrlcally conductive path between said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed and means for discharging said capacitor at a predetermined rate after said connections have been so reversed. n

'7. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes, a

capacitor, a supply of alternating potential one' terminal of which is connected to the principal electrode between which and the control electrode, the conductive path is asymmetric, means including a resistor of low magnitude, for connecting said capacitor between said control electrode and the other terminal of said potential supply, whereby said capacitor is charged by the current ilow between said last-named electrodes and a predetermined direct-current potential is impressed between said last-named electrodes, a resistor of high magnitude, means for reversing the connections between said capacitor, said control electrode and said last-named terminal of said potential supply and for connecting said last-named resistor in series with said capacitor and the asymmetrically conductive path between said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed and means for discharging said capacitor at a predetermined rate after said connections have been so reversed, said means including a plurality of independent resistors, said last-named resistors having different magnitudes and means for connecting any one of said resistors in the circuit of said capacitor.

8. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that `the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes, a capacitor, a supply of' alternating potential one terminal of which is connected to the principal electrode between which and the control electrode the conductive path is asymmetric, means including a resistor of low magnitude, for connecting said capacitor between said control electrode and the other terminal of said potential supply, whereby said capacitor is charged by the current flow between said last-named Aelectrodes and a. predetermined direct-current potential is impressed between said last-named electrodes, a resistor of high magnitude, means for reversing the connections between said capacitor, said control electrode and said last-named terminal of said potential supply andvfor connecting said last-named resistor in series with said capacitor and the asymmetrically conductive path between said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed, means for discharging said capacitor at a predetermined rate after said connections have been so reversed, said means including a plurality of independent resistors, said last named resistors having different magnitudes, and means for connecting any one of said resistors in the circuit of said capacitor and means for lvarying the magnitude of said direct-current potential impressed between said last-named electrodes thereby to attain times of discharge of said capacitor that lie between the times attained by connecting any two of said last-named resistors in the circuit of saidJ capacitor.

9. Translating apparatus comprising an electric discharge device having an anode, a cathode and a control electrode, means for impressing an alternating potential between said anode and cathode, a capacitor, a source of alternating potential, means for connecting said capacitor in series with said control electrode and said cathode means for so connecting said source to the network including said capacitor and said control electrode and said cathode that the potentials impressed between said control electrode and said cathode are in opposite phase to the potentials impressed between said anode and said cathode, whereby said capacitor is charged and a direct-current negative potential is impressed between said control electrode and said cathode to maintain the current between said anode and said cathode low and means for reversing the connections of said capacitor in said network whereby a positive potential is impressed between Ysaid control electrode and said cathode and substantial current is transmitted between said anode and said cathode.

10. Translating apparatus comprising an electric discharge device having an anode, a cathode and a control electrode, means for impressing an alternating potential between said anode and cathode, a capacitor, a source of alternating potential, means for connecting said capacitor in series with said control electrode and said cathode, means i'or so connecting said source to the network including said capacitor and said control electrode and said cathode that potentials impressed between said control electrode and said cathode are in opposite phase to the potentials impressed between said anode and said cathode, whereby said capacitor is charged and a directcurrent negative potential is impressed between said control electrode and said cathode to maintain the current between said anode and said cathode low, means for reversing the connections of said capacitor in said network whereby a positive potential is impressed between said control electrode and said cathode and substantial current is transmitted between said anode and said cathode and. means for superimposing on said positive potential a negative potential of absolute value substantially smaller than said positive potential.

ll. Timing apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing potentials between said principal electrodes and between said control `electrode and one of said principal electrodes that are of such relative magnitudes and polarities that said electric discharge device is maintained in substantially dsenergized condition, current responsive means, for reversing the polarity of the potential impressed between said control electrode and said last-named principal electrode, whereby said electric discharge device is energized, means for providing an impulse of current to temporarily actuate said current responsive means to reverse the polarity of the potential impressed between said control electrode and said last-named principal electrode and means to be actuated by said e1ectric\discharge device when it is energized and to remain so actuated only so long as said electric discharge device remains energized for maintaining said current responsive means in actuated condition as long as said electric discharge device remains energized.

12. Timing apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, means including a capacitor to be charged to a predetermined potential diil'erence for impressing potentials between said principal electrodes and between said control electrode and one of said principal electrodes that are of such relative magnitudes and polarities that said electric discharge device is maintained in substantially deenergized condition, current responsive means for reversing the connections of said capacitor thereby to reverse the polarity of the potential impressed between said control electrode and said last-named principal electrode, whereby said electric discharge device is energized, means for providing an impulse of current to temporarily actuate said current responsive means to reverse the polarity of the potential impressed between said control electrode and said last-named principal electrode and means to be actuated 4by said electric discharge device when it is energized and to remain so actuated only so long as said electric discharge device remains energized for maintaining said current responsive means in actuated condition as long as said electric discharge device remains energized and means to be actuated by said electric discharge device after it is energized to discharge said capacitor.

13. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that the conductive path between said last-named electrodes is asymmetric, means for impressing alternating potentials between said principal electrodes, a capacitor, a supply of alternating potential one terminal of which is connected to the principal electrode between which and the control electrode,\the conductive path is asymmetric, means including a resistor of low magnitude, for connecting said capacitor between said control electrode and the other' terminal of said potential supply, whereby` said capacitor is charged by the current ilow between said last-named electrodes and a predetermined direct-current potential is impreed between said last-named electrodes, a resistor of high magnitude, means for reversing the connectionsbetween said capacitor, said control electrode and said last-named terminal of said potential supply and for connecting said last-named resistor in series with said capacitor and the asymmetrically conductive path between said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed and means for discharging said capacitor at a predetermined rate after said connections have been so reversed, said means including resistance means to be connected in the circuit of said capacitor and means for varying the magnitude of the resistance of said resistance means in finite discontinuous steps. i

14. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes, the properties of said control electrode and one of said principal electrodes being such that theconductive path between said last-named electrodes is asymmetric, means for impressing alternating Y necting said capacitor between said controlv electrode and the other terminal of said potential supply, whereby Ysaid capacitor is charged by the current flow between said last-named electrodes and a predetermined direct-current potential is impressed between said last-named electrodes, a resistor of high magnitude, means for reversing the connections between said capacitor, said control electrode and said lastnamed terminal of said potential supply and for connecting said last-named resistor in series with said capacitor and the asymmetrically conductivepath between said last-named electrodes, whereby the polarity of the direct-current potential impressed between said last-named electrodes is reversed, means for discharging said capacitor at a predetermined rate after said connections have been so reversed, said means including resistance means to be connected in the circuit of said capacitor and means for varying the magnitude of the resistance of said resistance means in finite discontinuous steps and means for varying the magnitude of said directcurrent potential impressed between said lastnamed electrodes thereby to attain times of distimes attained by varying said resistance discontinuously from one value to another.

15. Translating apparatus comprising an elec'- tric discharge device having ananode, a cathode and a control electrode, means for impressing an alternating potential between said anode and cathode, a capacitor, a source of alternating potential, means for connecting said capacitor in series with said control electrode and said cath- -ode means for so connecting said source to the network including said capacitor and said control electrode and said cathode that the potentials impressed between said control electrode and saidcathode are out of phase to the potentials impressed between said anode and said cathode, whereby said capacitor is charged and a direct-current negative potential is impressed between said control electrode and said cathode to maintain the current between said anode and said cathode low and means for reversing the- 17. Translating apparatus comprising an electric discharge device having an anode, Va cathode and a control electrode. means for impressing an alternating potential between said anode and cathode, a capacitor, a source of alternating potential, means for connecting said capacitor in series with said control electrode and said cathode, means for so connecting said source to the network including said capacitor and said control clectrode and said cathode that potentials impressed between said control electrode and said cathode are in opposite phase to the potentials impressed between said anode and said cathode, whereby said capacitor is charged and a direct-current negative potential is impressed between said control electrode and said cathode to maintain the current between said anode and said cathode low, means for reversing the connections of said capacitor in said network whereby a positive potential is impressed between said control electrode and said cathode and substantial current is transmitted between said anode and said cathode and means for superimposing on said positive potential a negative potential of absolute value substantially smaller than said positive potential but of such magnitude that the potential impressed between said control electrode and said cathode attains a value suicient to cause said electric discharge device to be deenergized while the rate of decay of the potential impressed on said capacitor has a considerable value.

JOHN W. DAWSON.