US2156886A - Electric discharge apparatus - Google Patents

Description

y 1939- E. H, VEDDER 2,156,886

ELECTRIC DISCHARGE APPARATUS Filed Oct. 2'7, 193'? WITNESSES: INVENTOR EO W/h /7. Veda/er.

ATTORN Patented May 2, 1939 ELECTRIC DISCHARGE APPARATUS Edwin H. Vedder, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 27, 1937, Serial No. 171,398

12 Claims.

This invention relates to the control of electrical discharge devices by means of brief impulses, such, for example, as may arise from the momentary illumination of a photo-electric cell.

It is an object of this invention to cause a brief impulse to charge a condenser and to prolong the time which will be required for the dissipation of the charge.

One particular field of utility of this invention is in connection with electrical discharge tubes supplied with current from an alternating source. In the case of such discharge devices, the tube can conduct no current during that half of each cycle of alternating voltage for which the anode is negative in potential relative to the cathode. Where such tubes are operated with a grid voltage which is normally of such value that the tube never becomes conductive during the alternating voltage cycle, but is to be made conductive by the imposition of brief control voltages, difficulty is met with in that, if such an impulse occurs during one of the half cycles of the alternating source when the anode is negative relative to the cathode, and the impulse does not last until the beginning of the following half cycle of the alternating source, the tube is never rendered conductive. In other words, to make the tube conductive, the control electrode must be positive at some time when the anode is also positive in potential relative to the cathode, and should a brief control impulse occur during a negative half cycle of voltage, the tube will remain unresponsive thereto.

It is, accordingly, a further object of my invention to provide an arrangement whereby a tube supplied with current from an alternating source would be rendered conductive by the occurrence of a brief controlimpulse, regardless of whether such impulse occurs in the half cycle of supply voltage when the anode is positive or in the half cycle when it is negative.

It is a further object of my invention to provide a system in which an electrical discharge tube intended to be controlled by photo-electric or other impulses of duration brief compared with the period of an alternating-current source may be operated by current supplied from said source without the intervention of rectifiers.

Another object of my invention is to provide an arrangement by which an electrical discharge device controlled by brief impulses may be caused to conduct load current during one, or during a predetermined number, of half cycles of an alternating voltage source, provided the control impulse occurs within a definite interval of time preceding the beginning of said half cycle.

' It is a still further object of my invention to provide an arrangement by which the length of the definite interval mentioned in the preceding sentence may be predetermined at will.

Still another object of my invention is to provide an arrangement in which light impulses enduring for a period of time less than two onethousandths of a second may be caused to initiate current flow in an electrical discharge tube of load current capacity of the order of several amperes.

Other objects of my invention will become apparent upon reading the following specifications taken in connection with the drawing in which:

Figure 1 is a diagrammatic representation of a circuit embodying one form of my invention; and

Fig. 2 is a diagrammatic representation of a difierent circuit embodying certain features of my invention.

Referring to Figure 1, an electrical discharge tube I, which may be of the high vacuum tube but is preferably a gaseous discharge tube, is provided with a cathode 2, a control electrode 3, and an anode 4. For many purposes, it will be found convenient if the cathode 2 is of the thermionically-emissive type supplied with current from the secondary 5 of an alternating-current transformer 6. Another secondary winding I may be employed to impress an alternating voltage between the cathode 2 and anode 4 through a load device 8.

The control electrode 3 may have impressed upon it normally a voltage which renders it negative relative to cathode 2 during those half cycles of the alternating source I in which the anode l is positive relative to cathode 2. Such negative potential may be impressed upon the control electrode 3 in any convenient way; for example, by connecting control electrode 3 through a resistor 9 and a condenser II to a point IE on the secondary I which is negative in potential when the anode 4 is positive. The condenser I I is preferably shunted by a variable resistor it. The potential of the point l2 relative to the cathode 2 is made such that, when the condenser H is in a discharged condition, the control electrode 3 prevents the initiation of current flow between the electrodes 4 and 2 throughout the cycle of source I.

In order to initiate current flow in response to impulses of duration which is brief compared with a cycle of the alternating-current source 6,

the condenser I I is connected in series with an electrical discharge tube I 4, which is preferably of the high vacuum type, and a source I5 of unidirectional voltage. The discharge tube I4 has a cathode I6, which may desirably be of the thermionically-emissive type supplied with current from a secondary I1, an anode I8 and a control electrode IS. A means, such as the uni-directional voltage source 2I, and a resistor 22 are provided for impressing such a voltage on the control-electrode I9 as shall render the discharge tube I4 normally non-conductive. An arrangement is further provided for impressing a control impulse of duration brief compared with a half cycle of the alternating source 6 on the control electrode I9 of such magnitude and polarity as to render the discharge tube I4 conductive of current between its electrodes I8 and I6 while such impulse persists. One convenient form of such an impulse-arrangement is the photocell 23 connected between a point on the anode circuit of tube l4 and a point on the grid circuit I9. The photo-emissive electrode of the photocell 23 should be connected to the control-electrode I9 since in this Fig. 1 species of my invention, current flow through load 8 is to be initiated by an increase of light on photo-cell 23.

An impulse of short duration, such as a flash of light incident upon the photo-cell 23 will make the control electrode I9 positive for a brief interval of time and current will flow through the tube I4 from the source I5. If the connections are as shown in Fig. 1, this will make the terminal of that condenser II which is adjacent the control electrode 3 of discharge device I more positive. If this impulse is not too short, the condenser II will charge up suificiently so that the control electrode 3 will render the tube I conductive as soon as the anode 4 thereof becomes positive in the course of its alternating cycle. If the resistor I3 had an infinite value, the charge thus imparted to the condenser II would remain on it indefinitely; and would thus insure that the control electrode 3 was sufficiently positive to initiate current fiow between electrodes 4 and 2, regardless of however long might be the time interval intervening between the brief impulse and the beginning of the succeeding half cycle of source 6 which made the anode 4 positive relative to cathode 2. In commercial practice, however, the length of the half period during which the anode 4 is negative relative to cathode 2 is of the order of one one-hundred-twentieth of a second, and it is, accordingly, desirable that the resistor I3 should have a value less than infinity. The smaller the resistor I3 is made, the more rapid will be the dissipation through it of the charge on condenser II after the termination of the brief control impulse above mentioned. It is usually suflicient to reduce the value of the resistor I3 sufiiciently so that the charge on condenser I I has fallen to say, half its value in one half cycle of the source 6. When the apparatus is so arranged, the control impulse rendering the tube I4 conductive at any time during either half cycle of source 6 will initiate current flow through load 8 during that cycle of source 6 in which said impulse occurs. Should the impulse occur during one of the half cycles in which the anode 4 is negative, current flow will continue through load 8 for an entire half cycle, provided the tube I is of the gaseous discharge type.

If the resistor I3 is made of such value as to almost completely discharge the condenser II in a time equal to one cycle of the alternating source 6, current flow through load 8 will not occur during more than one half cycle after the termination of the impulse making control electrode I9 positive. On the other hand, by adjusting the value of resistor I3 to a higher value, it is possible to make the discharge of condenser I I so slow that current flow through load 8 will be maintained for a number of half cycles after the termination of the aforesaid control impulse making grid I9 positive. The number of such half cycles may be adjusted by varying the resistance I3.

By making the resistance I3 of such a small value that the condenser II discharges in a time equal to but a small fraction of a half cycle of source 6, it may be insured that current flow through load 8 will not be initiated in any half cycle which begins more than a predetermined time after the termination of the control impulse which makes grid I9 positive. Thus control impulses on grid I9 which continue to within, say, one five-hundredth of a second of the end of a half cycle of source 6, will produce current flow through load 8 during the succeeding half cycle of source 6; and control impulses on grid I9 which would cease more than one five-hundredth of a second before the beginning of said half cycle will produce no current flow to load 8. The time one five-hundredth of a second has been used merely by way of illustration, and may be decreased by decreasing the value of resistance I3, and increased by increasing the latter.

As a specific example of my apparatus embodying my invention, the portion of the transformer winding 1 which impresses voltage between cathode 2 and anode 4 of tube I may be rated at 220 volts and 60 cycles; while that portion of said winding which impresses voltage between cathode 2 and terminal I2 may be of 40 volt rating. The tube I (KU627) may have a rating of 2500 volts and .64 ampere and require a heating current of 6 amperes. The voltage source I5 may be rated at volts and the battery 2| of 45 volts. The condenser II may be of one microfarad capacity and the resistor I3 be of such size as to comprehend one megohm within its operating scale. The resistor 22 may be of 30 megohms. The tube I4 (R3553) may be a high vacuum tube rated at volts, .02 ampere load, and requiring 1 ampere heating current.

The photo-electric cell 23 may have a rating of i 90 volts and 12 microamperes per lumen sensitivity and may be of the type SE50, sold by the Westinghouse Electric & Manufacturing Company. The resistor 9 may have a value of 10 megohms. When the resistor I3 is adjusted to one megohm, the period elapsing between the cessation of the positive impulse on grid I9 and the cessation of current fiow through tube I has been found to be of the order of six seconds with the value of circuit constants just described.

Fig. 2 illustrates a circuit which I have found to be particularly responsive to interruptions of extremely short duration in a light beam. In it, tubes I, I4 and 23 are of the type already described in connection with Fig. l, and the transformer windings 5, 6 and Il are connected to supply current to the tubes I and I4 in the same way as do similarly numbered elements in Fig. 1. The resistors 9 and I3 and the voltage source I5 are of the same type and similarly connected to the corresponding elements as in Fig 1. In Fig. 2, however, the potential of control grid I9 of tube I4 is subjected to impulse control by a network which differs from that shown in Fig.

1 and which comprises a photo-electric cell 23 1'5 and a resistor 24 serially connected with each other in shunt with a variable resistor 25. Since current flow in tube I is to be initiated in respo-nse to a decrease of light striking photo-cell 23 the anode (non-photo-emissive) electrode of the latter is connected to resistor 24. The grid electrode I9 is connected to the common junction of the photo-electric cell 23 of the resistor 24. The resistor 25 is connected between a point on the anode circuit of tube I4 and the negative terminal of a battery ill, the positive terminal of the latter being connected to the cathode circuit of tube I4.

The load 8, illustrated diagrammatically in Fig. comprises in Fig. 2 the winding 20 of a relay 2? having normally open contacts 28. A resistor 29 is connected in series with said contacts 28 in a circuit connecting the cathode 2 of tube I with a point 3i between the winding 26 and its anode 4. A resistor 32 may conveniently be connected between the point 3| and the anode 4.

When the photo-electric cell 23 is illuminated, the variable contact on resistor 25 is set at such a point as will render the tube I4 non-conductive. The condenser Ii is then uncharged and the potential. of terminal I2 relative to cathode 2 is made such that tube I is now conducting throughout the cycle of source I. When the illumination of photo-cell 23 is decreased, the potential of the control electrode I9 becomes sufficiently positive to initiate current flow between anode iii and cathode l6, thereby charging condenser II in, such a polarity as to make control-electrode 3 more positive. Should the aforesaid light impulse have occurred while anode 4 of tube I is positive relative to cathode 2, control-electrode 3 will be rendered sufliciently positive to initiate current flow from source I through relay winding 20. On the other hand, should anode 4 of tube I have been negative relative to cathode 2 at the time of said light impulse, resistor I3, having been adjusted as described in connection with Fig. 1, will dissipate the charge on condenser II slowly enough so that it will still be of substantial magnitude by the beginning of the half cycle of source I which makes anode 4 positive relative to cathode 2, and current flow through relay winding 26 will then ensue.

Current flow through winding 20 will conductively bridge the contacts 28, thereby connecting anode 4 to cathode 2 through resistors 29 and 32. By properly proportioning the relative values of resistors 29 and 32 (i. e. by making resistor 29 suiliciently small relative to the resistance of winding 20), current flow will cease between anode 4 and cathode 2 of tube I and will be transferred to the path through contacts 28 and resistor 29, source I and winding 25. Winding 26 will, accordingly, be continued in an energized condition indefinitely, regardless of the reillumination of photo-cell 23, and tube I will be relieved of current flow until source 6 is deenergized. It is obvious that by providing auxiliary contacts to be closed by the above-described movement of relay 21, any desired auxiliary or load circuit may be closed upon the interruption of a light striking photo-cell 23, and maintained closed indefinitely after the termination of said light interruption.

To give a specific illustration of a, practical embodiment of my invention, it will be stated that the portion of winding 1 which impresses voltage between the cathode 2 and anode 4 of tube I may be a 220-volt, 60 cycle source, and the portion of said winding which impresses alternating voltage between said cathode 2 and the point I2 may be of 40 volts value. The tube I may be a gaseous discharge tube (KU627) rated at 2500 volts and .64 ampere and requiring 6 amperes cathode-heating current. The resistor 9 may be of 5 megohms value, the resistor I 3 may be adjusted to a value of around 10 megohms,

and the resistor 24 may be of 30 megohms value. The condenser II may be of 0.02 microfarad capacity. The tube Hi may be a high vacuum triode rated at 150 volts and. .02 ampere and requiring a cathode-heating current of l ampere. The photo-electric cell 23 may be rated at 90 volts and 60 microamperes per timing sensitivity and be of the type sold by the Westinghouse Electric 8t Manufacturing Company under the title SE00. The batteries 2i and I5 may each be rated at 90 volts, and the resistor 25 may be of 10,000 ohms. The resistors 29 and 32 may be, respectively, 200 ohms and 500 ohms. With the foregoing, circuit constants closure of relay 2'! was produced by interrupting for only 0.002 sec ond the light intensity of 35 foot candles passing through an aperture 0.5 inch in diameter to the photo-cell 23.

While I have described the tube as being of the gaseous discharge type, it will be recognized that a high vacuum tube could be useful in its situation, although it would cease to conduct current as soon as the charge on condenser ii fell below a critical value, and its conductivity would not persist throughout the succeeding half cycle of alternating current, as would be the case when the tube I is of the gaseous discharge type.

It will also be recognized that response to light impulses of much shorter duration than two onethousandths of a second may be achieved by employing additional stages of amplification between the photo-cell 23 and the control electrode of tube 54. While I have described a photo-electric cell as the specific means of applying impulses of great duration to the grid l9, it will be recognized that other agencies for producing potential impulses of great duration are within the scope of this disclosure.

Many variations will occur to those skilled in the art, and the specific description and illustration of a single form of this invention is not to be regarded as a limitation. The only limitations which are intended are those necessitated by the prior art or expressly indicated in the accompanying claims.

I claim as my invention:

1. In combination, a source of alternating current, a gaseous electrical discharge tube having principal electrodes supplied with current by said source and also having a control-electrode, means to vary the voltage of said control-electrode comprising a direct current source and an electric discharge tube having a control-electrode, a photoelectric cell illuminated by light impulses which are of duration brief compared with the period of said alternating current, connected to control the potential of the last-mentioned control-electrode, a capacitor provided with an adjustable leakage path connected to be charged by current from the last-mentioned electrical discharge tube, and bias means in series with said capacitor between the first-mentioned control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the first-mentioned discharge tube non-conductive when said capacitor is uncharged.

2. In combination, a source of alternating current, an electrical discharge tube having principal electrodes supplied with current by said source and also having a control-electrode, means to vary the voltage of said control electrode, comprising a direct current source and an electric discharge tube having a control electrode, a photo-electric cell illuminated by light impulses which are of duration brief compared with the period of said alternating current connected to control the potential of the last-mentioned control electrode, a capacitor provided with an adjustable leakage path connected to be charged by current from the last-mentioned electrical discharge tube, and bias means in series with said capacitor between the first-mentioned control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the firstmentioned discharge tube non-conductive when said capacitor is uncharged.

3. In combination, a source of alternating current, a gaseous electrical discharge tube having principal electrodes supplied with current by said source and also having a control electrode, means to vary the voltage of said control electrode comprising a direct current source and an electric discharge tube having a control-electrode, a photo-electric cell illuminated by light impulses which are of duration brief compared with the period of said alternating current, connected to control the potential of the lastmentioned control-electrode, a capacitor provided with a leakage path connected to be charged by current from the last-mentioned electrical discharge tube, and bias means in series with said capacitor between the first-mentioned control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the first-mentioned discharge tube non-conductive when said capacitor is uncharged.

4. In combination, a source of alternating current, an electrical discharge tube having principal electrodes supplied with current by said source and also having a control electrode, means to vary the voltage of said control electrode comprising a direct current source and an electric discharge tube having a control-electrode, a photo-electric cell illuminated by light impulses which are of duration brief compared With the period of said alternating current connected to control the potential 01" the last-mentioned control-electrode, a capacitor provided with a leakage path connected to be charged by current from the last-mentioned electrical discharge tube, and bias means in series with said capacitor between the first-mentioned control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the first-mentioned discharge tube non-conductive when said capacitor is uncharged.

5. In combination, a source of alternating current, a gaseous electrical discharge tube having principal electrodes supplied with current by said source and also having a control electrode, means for supplying a control voltage to said controlelectrode and comprising direct current source and an electric discharge tube having a controlelectrode connected to have its potential varied by a control-voltage impulse which is of duration brief compared with the period of said alternating current, a capacitor provided with a leakage path connected to be charged by current from the last-mentioned electrical discharge tube, and bias means in series with said capacitor between the first-mentioned control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the first-mentioned discharge tube non-conductive when said capacitor is uncharged.

6. In combination, a source of alternating current, an electrical discharge tube having principal electrodes supplied with current by said source and also having a control electrode, means for supplying a control voltage to said control-electrode and comprising a direct current source and an electric discharge tube having a control-electrode connected to have its potential varied by a control voltage impulse which is of duration brief compared with the period of said alternating current, a capacitor provided with a leakage path connected to be charged by current from the lastmentioned electrical discharge tube, and bias means in series with said capacitor between the first-mentioned control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the first-mentioned discharge tube non-conductive when said capacitor is uncharged.

'7. In combination, a source of alternating current, an electrical discharge tube having principal electrodes supplied with current by said source and also having a control electrode, means for supplying a control voltage to said control electrode comprising a direct current voltage source in series with means rendered electrically conductive for a period which is of duration brief compared with the period of said alternating current and a capacitor provided with a leakage path connected to be charged by current from the last-mentioned means, and bias means in series with said capacitor between said control electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render said discharge tube non-conductive when said capacitor is uncharged.

8. In combination, a source of alternating current, an electrical discharge tube having principal electrodes supplied with current by said source and also having a control electrode, a source of control-voltage for varying the potential of said control electrode and comprising a direct current voltage-source and means rendered electrically conductive by an electrical impulse, a capacitor provided with a leakage path connected to be charged by current from the said electrical discharge tube, and bias means in series with said capacitor between said control electrode and the principal electrode circuit of said discharge tube, said bias means being of such value as to render said discharge tube non-conductive when said capacitor is uncharged.

9. In combination, a source of alternating current, an electrical discharge tube supplied with current from said source and having a controlelectrode, a source of voltage for controlling the potential of said control-electrode and comprising a direct current source in series with an electrical discharge tube supplied with current impulses of duration brief compared with the period of said alternating current and means for storing electric charges provided with means to adjust the rate of discharge thereof, and bias means in series with said capacitor between said control-electrode and the principal electrode circuit of the first-mentioned discharge tube, said bias means being of such value as to render the first-mentioned discharge tube non-conductive when said capacitor is uncharged.

10. In combination, a source of alternating current, an electrical discharge tube supplied with current from said source and having a control-electrode, a source of voltage for controlling the potential of said control electrode and comprising a direct current voltage source in series with means rendered conductive for periods of duration brief compared with the period of said alternating current and means for storing electric charges provided with means to adjust the rate of discharge thereof, and bias means in series with said capacitor between said control electrode and the principal electrode circuit of said disharge tube, said bias means being of such value as to render said discharge tube non-conductive when said capacitor is uncharged.

11. In combination, a source of alternating current, an electrical discharge tube supplied 25 with current from said source and having a control-electrode, a source of voltage for controlling the potential of said control-electrode and comprising a direct current voltage source and means rendered conductive by an electrical impulse supplying charge to a capacitor having a leakage path, and bias means in series with said capacitor between said control electrode and the principal electrode circuit of said discharge tube, said bias means being of such value as to render said discharge tube non-conductive when said capacitor is uncharged.

12. In combination, a source of alternating current, an electrical discharge tube supplied with current from said source and having a control-electrode, a source of voltage for controlling the potential of said control electrode and comprising a direct current voltage source and means rendered conductive by an electrical impulse supplying charge to a means for storing electric charges having means to adjust the rate of discharge thereof, and bias means in series with said capacitor between said control electrode and the principal electrode circuit of said discharge tube, said bias means being of such value as to render said discharge tube non-conductive when said capacitor is uncharged.

EDWIN H. VEDDER.

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