US2495165A

US2495165A - Vapor-electric device

Info

Publication number: US2495165A
Application number: US54345A
Authority: US
Inventors: Norman C Fulmer
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1948-10-13
Filing date: 1948-10-13
Publication date: 1950-01-17
Anticipated expiration: 1967-01-17
Also published as: FR997090A

Description

Jan. 17, 1950 N. c. FULMER VAPOR-ELECTRIC DEVICE Filed Oct. 13, 1948 Fig.6.

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Trigger Circuit Source [0000 20000 30000 40000 50000 Resis tunce of R Fig.3.

INVENTOR Norman- C. Fulmer.

J JW ATTORNEY Patented Jan. 17, 1950 2,495,165 VAPOR-ELECTRIC DEVICE Norman C. Fulmer, Montclair, N. J

Electric Corporation, burgh, Pa., a corpora Westinghouse assignor to East Pittstion of Pennsylvania Application October 13, 1948, Serial No. 54,345

3 Claims.

My invention relates to a vapor-electric device and particularly to an impulsing system for applying periodic control impulses to the makealive electrode of an ignitron.

In the operation of vapor-electric devices provided with make-alive electrodes or so-called ignitors it has long been customary to charge a capacitor from a suitable source and to discharge the capacitor to provide an ignition or make-alive impulse to start the operation of the vapor-electric device.

In the use of such control systems there have been occasions where difficulty has been experienced in maintaining the impulses in the exact sequence or time relation desired. Heretofore, it has been customary to utilize an electric valve, particularly an electric valve of the'grid controlled discharge type for controlling the impulse.

It has heretofore been customary to provide a suitable biasing or blocking potential to the grid of the control valve to prevent premature or unscheduled discharges and to provide a triggering impulse to overcome the bias at the instant it is desired to initiate conduction.

If the biasing potential is sufficient to bias the electronic tube so as to insure adequate rapidity of cutoff or deionziation immediately following the condenser discharge, it is necessary to use a high bias potential and consequently a, high triggering potential. Since high potential requires extra insulating precautions and protection, and since a higher triggering potential requires a more complex triggering circuit, this produces an expensive and unyielding control system.

I have found that this high potential control system may be modified by providing a biasing potential proportioned to the rate of charge of the capacitor. In other words, a very high biasing potential at the initiation of the charging period which is reduced at the end of the charging period to a relatively nominal biasing potential which may be readily overcome by a reasonable triggering potential. I have found that this biasing potential may be most easily obtained from an impedance connected in series with the charging current of the capacitor and applied to the grid of the electric valve in parallel with the triggering potential.

It is accordingly an object of my invention to provide an impulsing circuit having a self-biasing component for the electric valve thereof.

A further object is to obtain grid bias voltage without the use of a separate battery or power supply.

A still further object is to obtain grid bias voltage as an inherent part of the circuit.

It is a further object of my invention to provide an impulsing circuit in which the bias is proportional to the rate of charge of a capacitor.

Other objects and advantages of my invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawing, in which:

Figure 1 is'a diagrammatic impulsing circuit;

Fig. 2 is a similar illustration of an impulsing circuit embodying my invention;

Fig. 3 is a graphical illustration of the biasing potential applied to the grid of the control valve, and

Fig. 4 is a graphical illustration of the characteristics of an impulsing system according to my invention.

In an exemplary embodiment of my invention a load device I is supplied with unidirectional po-' tential from an alternating-current circuit 2 by means of a vapor-electric device 3 of the makealive typ commonly called an ignitron. The vapor-electric device 3 comprises an evacuated container 4 having therein a liquid cathode 5 usually comprised of mercury, allium, sodium, potassium, caesium or other suitable material or materials.

Cooperating with the cathode 5 is an anode 6, usually composed of graphite or metal, in spaced insulated relation to the cathode 5. Conduction in the vapor-electric device 3 is secured by means of a make-alive electrode I, sometimes illustration of an F called an ignitor, in contact with the surface of the cathode pool 5.

My impulsing system for supplyingthe necessary control impulses to the make-alive electrode 1 comprises a source In of high voltage unidirectional potential. This may be derived from any suitable device not herein shown. In order to stabilize the high voltage potential, I prefer to connect a capacitor ll of high value across the terminals l2 and I3 of the source ill. A firing capacitor 15 connected by charging circuit In to the terminals l2 and [3 of the high voltage source In provides the actual source of potential for the impulse.

The firing capacitor 15 is charged from the high voltage source It by means of a current control impedance l6 preferably in the form of a resistor Re. The impedance I6 is of a value to determine the rate of charge and consequently the time during which the capacitor l5 will be charged from the source H3. After the firing capacitor l5 has been sufficiently charged, a triggering circuit 20 will supply a control impulse to the grid 2| of a control valve 22 in the discharge circuit 23 for the capacitor l5, which discharge circuit 23 connects the make-alive electrode 1 across the potential of the capacitor l5. Preferably an impedance 24, usually in the form of a resistor R, is supplied in the discharge circuit 23 to control the time interval during which makealive potential is applied to the make-alive electrode and to limit the peak discharge current through the control valve 22 to a safe value.

Heretofore, it has been customary to provide a constant biasing potential 25 to the grid 2| of the control valve 22. In order to be effective this biasing potential 25 must be of suflicient value to prevent accidental operating of the control valve 22 at any interval during the charging period of the capacitor |'5. Consequently, the triggering potential 20 must be sufiicient to adequately overcome this constant biasing potential 25.

In order to eliminate the necessity for a source of constant biasing potential 25 and the inconvenience connected therewith, I have obtained from the charging circuit H! a biasing potential proportional to the rate of charge of the firing capacitor 5. In order to obtain this potential, I have provided an impedance 26, usually in the form of a resistor RB, connected in the negative side of the charging circuit l4 and supplying a circuit 21 for applying the potential drop across this impedance 26 to the grid 2| of the control valve 22. Preferably, a suitable capacitor 28 is provided across the impedance 26 providing the biasing potential. The potential derived from the impedance 26 is of a relatively high value at the instant of initiation of the charge and then gradually reduces as the charge on the capacitor 5 builds up and the charging current decreases. This is shown in graphical form in Fig. 3. In the instant of the beginning of the charge a very high potential 30 appears across the impedance 26 and as the charge builds up this potential decreases according to the curves 3| of Fig. 3. Then at the instant the capacitor 5 is discharged and starts to recharge, a high potential 30 is immediately applied to the grid 2| to prevent any undesired misfire or undesirable operation of the electric valve 22.

The necessary characteristics for relation of the component parts of my circuit are best illustrated in graphical form in Fi 4. The range over which the device is operative is determined by the relative values of the resistance 24 of the discharge circuit 23 and the biasing potential source 26 in relation to the applied voltages. Assuming that the resistance R in the discharge circuit 23 has a value of ohms and the high voltage source ID a value of 3000 volts or 3 kilovolts, the resistance RB of the impedance 26 has been determined to be not less than 1500 ohms or not more than 25,000 ohms. These points were selected by decreasing the impedance of RB to a point a where the circuit misbehaved, usually by improperly firing and then increasing the impedance of RB until the circuit again misbehaved at point b, usually by failure to fire. During this intermediate period from a to b the circuit operated satisfactorily. Then with the impedance R changed to 80 ohms the circuit was again operated on the low side until it misbehaved, which was found to be at point 0 at a value of 6000 ohms. Similarly, the impedance was increased until at point d it again misbehaved at a value of approximately 19,000 ohms.

Other points on the curves of Fig. 4 were similarly obtained by changing the value of the high voltage source In and the impedance of 24. The solid line curves of Fig. 4 were the maximum and minimum impedance of RB of various potentials with a discharge impedance 24 of 10 ohms and the dotted line curves are the same characteristic with a discharge impedance 24 of ohms. Values of other components in this experimental circuit were as follows: Resistor Rc, 50,000 ohms; condenser 5, 0.02 microfarad; electric valve 22, WL677; trigger voltage 20, 140 volts peak. The frequency of operation was cycles per second.

In the operation of the system according to my invention, the high potential source 0 is applied to the firing capacitor l5 which automatically applies the bias potential to prevent discharge of the control valve 22 in series with the make-alive electrode 1. Also applied to the control grid 2| of the control valve 22 is a periodic triggering potential 20, which is in phase with and may be obtained from the potential 2 applied to the anode 6 of the make-alive device 3. As will be apparent, the biasing potential 30 of the impedance 26 at the beginning of charging of the capacitor I5 is sufiiciently high to prevent any possibility of undesirable operation. Then as the charging period is completed, the biasing potential is reduced so that the triggering potential 20 or control impulse for the control tube 22 readily overcomes the biasing potential and permits absolute control of the discharge to the make-alive electrode 1 and consequent accurate control of the current through the make-alive device 3.

While for the purposes of illustration I have shown a specific embodiment of my invention, and described my invention to the best of my present understanding, I wish it to be understood that I am not limited to the example or explanation herein given, and it is apparent that many modifications can be made therein without departing from the true spirit of my invention or the scope of the appended claims.

I claim as my invention:

1. A control system for a vapor-electric device comprising a cathode spot initiating electrode in said device, a source of substantially direct our- 4 source, impedance means connected between said source and said capacitor for controlling the rate of charge of the capacitor, circuit means including a grid controlled electric valve and a current limiting impedance for connecting said electrode across the terminals of said capacitor, circuit means energized by current flow to said capacitor for impressing a negative bias potential on the grid of said grid controlled valve and means for periodically impressing a positive trigger potential on the grid of said valve.

2. A control system for a vapor-electric device comprising a make-alive type electrode in the device, a source of unidirectional control potential, a capacitor connected across said control potential, impedance means connected in series circuit relation between said source and said capacitor at least a portion of said impedance being connected between the negative terminal of said source and said capacitor, a discharge circuit for said capacitor including in series circuit relation said make-alive type electrode, a grid controlled electric valve and a current limiting impedance means, circuit means for impressing the negative potential drop through that portion of the impedance means connected to the negative terminal of the source on the grid of said grid controlled electric valve, a source of periodic trigger potential and connections impressing the trigger potential on the grid of said valve.

3. A control system for supplying periodic control impulses to an exciting electrode comprising a source of direct current control potential, a oapacitor connected to be charged from said source, an impedance between said source and said capaoitor, a discharge circuit connecting said exciting electrode across said capacitor, a grid controlled valve in said discharge circuit, circuit means for impressing a portion of the potential drop across said impedance 0n the grid of said grid controlled valve, a source of periodic trigger potential and connections for impressing the periodic trigger potential on the grid of said valve.

NORMAN C. FULMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,889,608 Lord Nov. 29, 1932 2,008,730 Smede July 23, 1935 2,097,066 Hoover Oct. 26, 1937 2,100,700 Schlesinger Nov. 30, 1937