US2600317A

US2600317A - Stabilized control circuit

Info

Publication number: US2600317A
Application number: US150443A
Authority: US
Inventors: George W Nagel
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-03-18
Filing date: 1950-03-18
Publication date: 1952-06-10
Anticipated expiration: 1969-06-10

Description

June 10, 1952 5, w, NAGEL 2,600,317

STABILIZED CONTROL CIRCUIT Filed March 18, 1950' WITNESSES: INVENTOR Geor eW.Nc| el. x51 BY 9 g I ATTORNEY Patented June 10, 1952 STABILIZED CONTROL CIRCUIT George W. Nagel, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 18, 1950, Serial No. 150,443

6 Claims. 1

My invention relates to an electron discharge circuit and especially to a circuit for stabilizin an electron valve.

Conventional relay circuits frequently include a relay actuating coil connected in series with a grid-controlled gas-discharge type of electron valve. Since conduction through this type of tube cannot be interrupted by manipulation of the potential of its control grid, it is conventional to use an alternating voltage source for the anode-cathode potential. This effectively interrupts the current flow every cycle and thus restores eiiectiveness to the control grid.

This procedure necessarily means that the supple of energy to the relay circuit is intermittent. To avoid relay chattering, it is conventional to shunt a capacitor across the relay coil. The capacitor stores energy during the conductive portion of each cycle and discharges through the relay coil during the remainder of the cycle to cause the coil to remain actuated during the full cycle of the alternating current. A control voltage is impressed on the grid of the valve to cause it to become conductive. This control voltage gradually becomes more positive with respect to the cathode of the valve until a point is reached at which the control voltage causes the valve to become conductive. Current then flows through the relay coil.

In the usual arrangement, this control voltage increases gradually until, during some one positive half-cycle of the source voltage, the voltage impressed on the grid of the valve is just sufficient to cause the valve to become conductive when peak value of the source potential is impressed I from cathode to anode on the valve.

I have found that in such a control circuit the valve becomes conductive, actuating the relay for one cycle, but the valve does not become conductive during the next succeeding half cycles. This causes the relay to close momentarily and open, remaining open for a few cycles. This 0peration is referred to as chattering or the relay. Relay chattering is a highly objectionable phenomenon.

In some circuit arrangements the control circuit is capable of impressing only a limited voltage on the control grid of the thyratron. Such a control circuit may be capable of starting conduction in the thyratron when the full voltage of the source is impressed across the thyratron but may be incapable of starting the thyratron when a slightly lower voltage is impressed on it.

A similar problem arises in the use of a coldcathode gaseous-discharge valve. Conduction in such a valve is initiated by a glow discharge between the control electrode and the cathode. The magnitude of the current required in this discharge to cause the initiation of anode-cathode conduction in the valve is dependent upon the voltage impressed on the anode of the valve. A circuit may be inoperative if the current available from the control circuit is limited to a value below that required to initiate discharge in the valve.

An example of a circuit which may at times be subject to such a difficulty is shown in the application of Schultz and Nagel, No. 12 ,038, filed February 28, 1948, entitled Garage Door Opener" and which has become abandoned. The circuit shown in Fig. 3 of this application includes a cold-cathode gaseous-discharge valve 29 which is started by current flow from the photoelectric cell 4. The relay 28, connected to the valve 29, is shown symbolically as a winding. Such windings generally have a shunting capacitor to maintain the relay actuated during the negative halfcycle. The photo cell 4 must provide a current greater than a certain predetermined minimum if the valve 29 is to become conductive. After the first period of conduction, the relay circuit connected to the anode of the valve 29 impresses a back voltage on the valve and then a greater current flow is required between the grid 46 and the cathode of valve 29 to initiate conduction during the next positive half-cycle. Under some circumstances, the light which impinges on the photo cell 4 and the characteristics of the photo cell 4 may be such that the current from photo cell 4 is sufficient to initiate conduction in valve 29 for one cycle but is insufilcient to initiate conduction during succeeding positive half-cycles. Thus the current required to fire the valve 29 is dependent upon its past history of conduction, i. e. a current which will cause conduction in a cycle after a non-conductive cycle may be insufilcient to fire the valve during a cycle which follows a conductive cycle.

Accordingly, it is an object of my invention to provide a circuit for a gaseous discharge valve which allows the discharge valve to be equally responsive to a control regardless of its past history of conduction.

It is an object of my invention to provide a relay control circuit which will operate in response to a gradually changing control voltage but will not cause chattering of the relay.

It is a further object of my invention to provide a stabilizing system which maintains substantially infinite the transconductance of a gridcontrolled electron discharge device.

It is a further object of my invention to provide a circuit for a grid-controlled electron discharge device which will maintain constant its circuit response to a control voltage.

My invention arises from the realization that this chattering of the relay is due to a decrease in the voltage impressed across the valve after a first conductive period due to the presence of a residual subtractive potential across a capacitor in its anode circuit. This effect varies the control potential and/or current re'qui'red to initiate conduction of the valve during succeeding cycles and therefore changes its response to the control voltage.

The critical voltage which will cause the valve to become conductive is dependent upon the characteristics of the valve and upon the anode to cathode voltage impressed on the valve. The valve becomes conducting passing current through the relay coil and the capacitor associated with the coil. 'During the following negative half-cycle of the source voltage the capacitor partially discharges through the relay coil. During'the next positive half-cycle, the capacitor is not completely discharged and it effectively reduces the anode to cathode voltage impressed on the valve below the peak value of the source potential. If the control voltage has increased only slightly or not at all since the previous half-cycle, it is not now great enough to cause the valve to become conductive when a voltage less than the peak value f the source voltage is impressedon the'valve. Thus, in normal operations of conventional relay circuits, the control circuit may cause the valve to become conductive during part of one positive half-cycle of the source potential but be unable to cause the valve to become conductivein the next one or more positive half.- cycles. The relay may, thereforeQbe released afterhaving been actuated and a chattering of the relay may occur as it closes andopens repeatedly.

In accordance with my invention I provide a circuit in which the voltage impressed on the relay coil is derived from a resistor connected inseries with a control thyratron. A rectifier connected in series with the relay coil prevents the voltage' across the relay coil from affecting the operation of the control thyratron prior to conduction.

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 with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, the figure of which is a schematic diagram showing a preferred embodiment of my invention.

As shown in the drawing, a thyratron 3 is connected in series with a resistor 5 across a source I of alternating current. The coil 9 of a relay ii is connected from one side of the alternating current source 1 through a rectifier I3 to the anode 2! of the thyratron 3. A capacitor I5 is connected across the relay coil 9. Terminals I! are provided to impress a control voltage between the grid IQ of the thyratron and one terminal of the power source I. A source 2i of biasing voltage may be connected from the cathode 23 of the thyratron 3 through a grid resistor 25 to the grid IQ of the thyratron 3.

In operation, the thyratron 3 is initially nonconductive. The control voltage impressed on the grid i9 of the thyratron becomes gradually more positive to a point at which it is just sufficient to cause the thyratron 3 to become conductive. The thyratron 3 conducts during the remaining portion of the positive half-cycle. A positive half-cycle is defined as the time during which the source voltage causes the anode 21 of the thyratron 3 to be positive with respect to its cathode 23. When the thyratron 3 becomes conductive, current flows from one terminal or the source I .both through resistor 5 and through the relay coil Band the rectifier l3 to the anode 31 of the thyratron 3 and thence to the other terminal of the source "I. The capacitor I5 is charged during this time. During the negative half cycle no current is flowing through the thyratron 3 and the capacitor partially discharges through the relay coil. Current flowing from the capacitor causes the relay II to remain closed during the negative one-half cycle.

During the next positive half-cycle, and before the thyratron 3 becomes conductive, the voltage impressed on its anode is substantially the voltage of the upper terminal of the power source I. The residual potential across the relay shunting capacitor l5 does not reduce the impressed voltage on the anode 2'! of the thyratron 3. Thus, during the second positive half-cycle the voltage impressed across the thyratron 3 is the same as it was during the previous positive half-cycle and the control voltage is again effective during the positive half-cycle to cause the thyratron 3 to become conductive. During each positive half cycle, therefore, the voltage impressed across the thyratron 3 is the same as on all other positive half-cycles and the effect of the control voltage on the conductivity of the thyratron remains constant. If the control voltage is sufficient to cause the thyratron 3 to become conductive during one positive half-cycle, the same control voltage will be effective'to cause the thyratron 3 to become conductive during each succeeding positive half-cycle and no chattering of the relay will occur.

I have found that a circuit according to the single figure having components of the following magnitudes operates satisfactorily:

Capacitor I5, 10 ifd.

Relay ll, coil resistance 1100 ohms operates on Resistor 5, 10,000 ohms Thyratron 3, RCA type Source 1, v.

Rectifier i3, selenium rectifier with rating v.

A. 0. current 50 ma.

No bias voltage 2! was used. I have found that the resistor 5 must have a resistance small with respect to the back resistance of the rectifier H! but the resistance must be large enough not to overload thyratron 3.

Although I have shown and described certain specific embodiment of my invention, I am fully aware that many modifications thereof are possible using the principles herein disclosed. My invention, therefore, is not intended to be restricted to the specific embodiment shown and described.

I claim as my invention:

1. In combination, an electric valve having an anode and acathode, a resistor, circuit means connecting said resistor to the anode of said electrio valve, terminals for impressing across said resistor and said electric valve in series a voltage, an inductor and a capacitor connected in parallel, a rectifier connected in series with said capacitor and inductor, circuit connections between said resistor and said rectifier, capacitor and inductors such that the direction in which said rectifier allows current flow is in the direction from anode to cathode of said electric valve.

2. In combination, an electric valve having an anode and a cathode, an impedance, circuit means connecting said impedance to the anode of said electric valve, terminals for impressing across said impedance and said electric valve in series a voltage, an inductor and a capacitor connected in parallel, a rectifier connected in series with said capacitor and inductor, circuit connections between said impedance and said rectifier, capacitor and inductors such that the direction in which said rectifier allows current flow is in the direction from anode to cathode of said electric valve.

3. In combination, an electric valve having an anode and a cathode, a resistor, circuit means connecting said resistor to the anode of said electric valve, terminals for impressing across said resistor and said electric valve in series a voltage, an inductor and a capacitor connected in parallel, an element having a resistance to current flow in one direction substantially different from it resistance to current flow in the other direction connected in series with said capacitor and inductor, circuit connections between said resistor and said element, capacitor and inductors such that the direction in which said element presents the least resistance to current flow is in the direction from anode to cathode of said electric valve.

4. In combination, a coil across which is connected a capacitor, an electric valve having an anode, a cathode and a control electrode, a rectifier, series connections between said coil, rectifier and electric valve, said rectifier being oriented to conduct current in a direction from said anode to said cathode of said electric valve, an impedance connected across said rectifier and said coil, terminals for impressing pulsating voltage across said resistor and electric valve, and terminal means for impressing a control voltage on said control electrode.

5. In combination, a gaseous discharge device having an anode and a cathode, a resistor connected to said anode, connections for applying alternating current potential across said discharge device and resistor in series, an inductive load device, a capacitor shunting said load device, a rectifier, and means connecting said rectifier in series with said load device across said resistor, said rectifier being poled to conduct in the direction from the anode to cathode of said discharge device.

6. In combination, a gaseous discharge device having an anode and a cathode, an impedance connected in series with said discharge device, connections for applying alternating current potential across said impedance and said discharge device; an inductive load device, a capacitor shunting said load device, a uni-directional conducting device connected in series with said inductive load device across said impedance, said uni-directional conducting device being poled to conduct in the direction of anode to cathode of said discharge device.

GEORGE. W. NAGEL.

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

UNITED STATES PATENTS Number Name Date 1,870,064 Nickle Aug. 2, 1932 1,901,628 Brainard Mar. 14, 1933 1,966,077 Nyman July 10, 1934 2,097,578 Swart Nov. 2, 1937 FOREIGN PATENTS Number Country Date 557,653 Germany July 19, 1930 528,132 Great Britain Oct. 23, 1940