US1847893A

US1847893A - Electrical control circuits

Info

Publication number: US1847893A
Application number: US512103A
Authority: US
Inventors: Harry L Palmer
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1931-01-29
Filing date: 1931-01-29
Publication date: 1932-03-01
Anticipated expiration: 1949-03-01

Description

Match 1, 1932. H. L. PALMER ELECTRICAL CONTROL CIRCUITS Filed Jan. 29, 1931 Inventor" Hart-g LPalmer His Attorney.

Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE HARRY L. PALMER, F SCO'IIA, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COM.- PANY, A, CORPORATION OF NEW YORK ELECTRICAL CONTROL CIRCUITS Application filed January 29, 1881. Serial No. 512,103,

My invention relates to electrical control circuits and particularly to automatic control circuits for electric valves.

Control circuits of the bridge type for electric valves are well known in the art. Such circuits usually comprise four impedances connected in the form of a \Vheatstone bridge, at least two non-adjacent arms of which have different thermal, voltage or current resistance characteristics. Stated more broadly the non-adjacent arms have corresponding electrical properties whlch change relatively to each other with similar changes in their electrical or physical condition.

Such an arrangement is, in effect, a reversing switch, with an off position when all four arms have equal impedances, and reversing on positions depending upon which air of non-ad'acent arms have the reater impedance. y connecting the ano e circuit of an electric valve to the same source as supplies the input to the bridge, the operation of the bridge may be made to secure a reversal of polarity, or a 180 degree phase shift, in the grid potential of the valve with respect to its anode potential.

In accordance with my invention I provide a novel and simplified combination of a bridge control circuit and a hot cathode electrio valve, or valves, in that at least one valve filament is connected to form one of the arms of the bridge circuit. As these valves have filaments, or heater elements, of tungsten, which has a comparatively high positive temperature coefiicient. of resistance, they are readily ada tablefor use as the arms of bridge circuits. ucli use results in a distinct saving in that the cost of at least one of the usual bridge arms is eliminated while at the same time the steady power loss in this element is saved.

An object of my invention is to provide a novel static control circuit arrangement for an electric valve or valves.

My invention will be better understood from the following description taken in con nection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring now to the single figure of the positive temperature coefiicient of resistance.-

00 versing means by the reference character 2,

and the reversible motor by the character 3.

The control circuit is in a form of a \Vheatstone bridge having a pair of non-adjacent arms 4 and 5 composed of ordinary resistance material, such as iron, and a second pair of non-adjacent arms 6 and 7 com rising the heater elements, or filaments, 8 an 9 of a pair of electricvalves. These heater elements are preferably connected to the bridge circuit by means of small filament transformers 10 and 11 as shown. The filaments, or heater elements, 8 and 9 are usually made of tun sten and consequently they have a relatively iigh The input terminals ofthis bridge circuit are connected across one of the phases of a three phase power supply circuit-12, while the output terminals of the bridge are connected to the primary winding of a grid transformer 13.

When the voltageof circuit 12 is normal the arms of the bridge circuit are so adjusted that the two parallel paths between its input terminals, comprising respectively resistance 4 and filament 8 on the one hand and resistance 5 and filament 9 on the other hand, are equal in magnitude so that no voltage appears across the primary winding of the grid transformer 13. If now the voltage of circuit 12 should increase the increased current flowing to the arms of the bridge will increase the resistance of the filaments 8 and 9 with the result that the bridge will be unbalanced and an alternating voltage will appear across the primary winding of transformer 13. Also, if the voltage of circuit 12 should fall the decrease in current in the bridge arms will decrease the resistance of the filaments 8 and 9 with the result that an alternating voltage of 100 opposite polarity, or a voltage shifted 180 de grees in phase will appear across the terminals of the primary winding of transformer 13. It will thus be seen that when the voltage in circuit 12 is normal no voltage is aplied to transformer 13 while increases and 'ecreases of volta on circuit 12 cause alternating voltages 0 reverse polarity to be applied to this transformer.

The anode circuits of the valves are supplied with current from a supply transformer 14, which is also connected across one of the phases of su ply circuit 12. As shown, the electrical mi point of the secondary winding of transformer 14 is connected to the filaments while the terminals of the secondary winding are connected res ctively to the

anodes

15 and 16 of these va ves through actuating coils 17 and 18 respectively of a air of reversing

relays

19 and 20. I The secon ary winding of grid transformer 13 has one of its terminals connected to the

grids

21 and 22 of the electric valve through current limiting

resistors

23 and 24, while the other terminal of this secondary windin is connected to the filaments through a grid bias battery 25.

Motor 3 is connected to be energized from supply circuit 12 through the reversing contactors, or relays, 19 and 20. As shown these contactors are so connected that they reverse one of the phases of the power supply circuit which is connected to this motor whenever one or the other of the relays is energized. This causes a reversal of motor 3 in a manner which is well understood by those skilled in the art.

The electric valves may be either of the A high vacuum pure electron-discharge type or the gas-filled type. I prefer, however, to use the gas-filled type because of their larger current-carrying capacity.

The operation of the system illustrated in the drawing is as follows: Assume that sup ply circuit 12 is energized and that its voltage is normal. Under these conditions the bridge circuit will be balanced, as pointed out above, no voltage will be applied to the grid transformer 13 and both electric valves will be non-conducting because their grids are at the negative potential produced by the grid bias source 25.

If now the voltage of circuit 12 should decrease, an alternating volta e will be produced by the secondary winc ing of trans-- former 13, as explained above, and this voltage will be transmitted to the

grids

21 and 22 of the electric valves. This voltage will be in phase with the anode potential of one of the valves and will be 180 degrees out of phase with the anode potential of the other valve because of the fact that the anode potentials of the two halves are themselves 180 degrees out of phase due to the way they are connected to the secondary winding of transformer 14. As a result the valve in which the grid potential is in phase with its anode potential will become conducting with the result that an anode current will flow through the operating coil of one of the

contactors

19 or 20. The result will be that motor 3 will be connected to circuit 12 and the motor will then start to operate. If new, the voltage of circuit 12 should rise above normal the potential of the secondary winding of grid transformer 13 will reverse with the result that the other valve will become conducting, and the valve which has been conducting will become non-conducting, thereby energizing the operating coil of the other contactor and deencrgizing the operating coil of the first contactor with the result that the phase connections to motor 3 are reversed and the motor operates in a reverse direction.

Thus, for example, if the voltage of circuit 12 rises, the right-hand valve. may, for example, be made conducting with the result that contactor 19 operates and motor 3 runs in one direction, while if the voltage in circuit 12 falls the left-hand electric valve be comes conducting and the .right-hand valve becomes non-conducting with the result that contactor 20 will be energized thereby to reverse motor 3.

It should be understood that while I have shown my novel and simplified control scheme as applied to a pair of valves which control contactors for reversin an electric motor, my invention is not so limited and that the scheme may be used in connection with any pair of valves which are to be selectively energized.

\Vhile I have shown and described a preferred embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made with out departing from my invention and I therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

.Vhat I claim as new and desire to secure by Letters Patent of the lnited States is,

1. In combination, an electric valve having a plurality of electrodes and means "for fchanging an electrical condition of one of said electrodes in accordance with changes in an electrical property of one of said electrodes.

2. In combination, an electric valve having a plurality of electrodes. means responsive to an electrical condition of an electric circuit for controlling an electrical condition of one of said electrodes, said means having at least two elements whose corresponding electrical properties change relatively to each other, at least one of said elements being an electrode of said valve.

3. In combination, a hot cathode electric valve and means for controlling the opera tion of said valve including a bridge circuit,

one of whose arms comprises the cathode of said valve.

4. In combination, a pair of hot filament electric valves and means for controlling I said valves including a voltage bridge, two of whose arms are composed of the filaments of said valves.

5. In combination, a voltage balance control device of the type having two pairs of 10 impedances having diflerent temperature coefficients of resistance, all connected in the form of a Wheat-stone bridge, a pair of hot cathode electric valves connected to be controlled by said bridge, said cathodes formin one pair of impedance elements of sai bridge.

6. In combination, a device for producing a control voltage to be applied to the control electrode of a three element electric 10 valve com risin d a balance circuit including two impe ances aving dilferent temperature coeflicients of resistance, a three element electric valve, and means connectin the filament of said valve as one of the impedances of said 2! balance circuit.

7. In combination, a bridge circuit for controllin the operation of a hot cathode electric va ve, a hot cathode electric valve and a filament transformer connecting the cath- {0 ode of said valve into said bridge circuit as one of the arms thereof.

8. In combination, a supply circuit, a load circuit, an electric valve including a cathode havin a variable coefiicient of resistance for I! contro lin the energization of said load circuit, a bridge circuit including the cathode of said valve and connected to be responsive to an electrical condition of said supply circuit for controlling said valve.

40 9. In combination, an electric circuit, an

electric motor, circuit controlling means connecting said motor to said circuit so as to be operable in reverse directions, hot cathode e ectric valves for controlling said circuit 48 controlling means, a. voltage responsive bridge connected to control said valves in response to variations in the voltage of said circuit, the cathodes of said valves being connected to form two of the arms of said bridge. 60 In witness whereof I have hereunto set my hand.

HARRY L. PALMER.