US2366060A - Electric valve time-delay relay - Google Patents

Description

Dec. 26, 1944.

E. D. SCHNEIDER 2,366,060

ELECTRIC VALVE TIME-DELAY RELAY Filed Nov. 24, 1942 Inventor: Elbehb D. Schneider,

|-lis Attorney.

Patented Dec. 26, 1944 2,366,060 ELECTRIC VALVE TIME-DELAY RELAY Elbert D. Schneider, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application November 24, 1942, Serial No. 466,754

8 Claims.

My invention relates to time-delay relays of the type employing electric valves and more particularly to an improved circuit of this type which provides uniform operation for a given time setting.

Time-delay relays employing electric valves and some energy-storage means for controlling the conductivity thereof have been widely used in industrial applications. It has frequently occurred that these relays have functioned erratically when included in a particular installation. I have found that much of this erratic operation is due to transient voltages which are impressed on the control member of the electric valve. In accordance with the teachings of my invention, I provide an improved electric valve time-delay circuit which is characterized by the uniformity of its operation for a given time setting.

It is an objectof my invention to provide a new and improved time-delay circuit.

It is another object of my invention to provide a new and improved electric valve timeclelay relay circuit.v

It is a still further object of my invention to provide a new and improved time-delay relay employing an electric valve in which erratic operation resulting from transient voltages introduced into the circuit of the control member is substantially eliminated.

In accordance with the illustrated embodiment of my invention, I provide an improved circuit for controlling the energization of a load circuit for a predetermined time interval after the closure of an initiating switch by means including an electric valve which is rendered conductive at the end of the time interval. The circuit is, in general, similar to the time-delay circuits described and claimed in my Patents 2,171,347 and 2,171,348, dated August 29, 1939, and assigned to the assignee of the present application. An energy-storage means, such as a capacitor, is connected across the conductors leading to the initiating switch which is often located remotely with respect to the remainder of the relay cirout. This capacitor has been found very effective in eliminating erratic operation of the relay which is believed to result from transient voltages appearing across the conductors connected with the initiating switch. It will be noted that the initiating switch is included in the cathodeto-control-member circuit of the electric valve and that the load current flows through the initiating switch immediately upon closure thereof. If there is momentary bouncing of the switch contacts to cause further charge of the timing capacitor and thereby change the operating time of the relay circuit. In applications where the initiating switch is remote from the v remainder of the relay circuit, I have found that transient voltages may be induced in the conductors leading to the initiating switch which are of sufficient magnitude to cause erratic operation of the relay. These voltages are substantially eliminated by the use of the capacitor connected as shown in the illustrated embodiment.

My invention will be better understood by reference to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. .In the drawing, the single figure is a schematic representation of one embodiment of my invention.

In the single figure of the drawing, there is diagrammatically illustrated a time-delay circuit for effecting the energization of a load circuit, which, as illustrated, may comprise the coil ID of an electromagnetic relay II, from an alternating-current supply I2 for a predetermined interval of time after the closure of an initiating switch l3 which may be operated either manually or automatically. The initiating switch I3 and the operating coil ID are connected in series relation with the contacts I4 of an electromagnetic relay I5 and across the alternating-current supply circuit I2. An operating coil I6 is provided for actuating the contacts I4. The energization of the coil I6 is controlled by an electric discharge device I! which is preferably of the type employing an ionizable medium, such as a gas or a vapor, and which comprises an anode I8, a cathode I9, a control member 01 grid 20, a shield grid 2|, and a cathode heater element 22. The midtapped secondary winding 23 of a transformer 24 energized from the supply circuit I2 provides means for energizing the heater element 22.

The anode-cathode circuit of the discharge device I! is connected to the supply circuit in the following manner. The anode I8 thereof is connected to one side of the alternating-current circuit I2 through the operating coil I6 of the relay I5 which is parallelled by a series-connected capacitor 25 and resistor ZB. The capacitor 25 provides means for energizing the coil l6 during the half cycles of the supply that the anode I8 is negative and the resistor 26 limits the half cycles of supply voltage that valve II conducts current. A resistance 21 of a relatively high ohmic value is connected between the anode and cathode of the electric valve I1 and provides a path for energizing the winding IE with an alternating-current of small magnitude after switch I3 is closed and before electric valve I1 is rendered conductive. The cathode of the electric valve is connected to one side or the alternating-current supply circuit through a resistor 28 and to the other side of the supply circuit through the initiating switch I3. The control member 20 of the electric valve is connected to an adjustable tap 29 on a voltage divider including resistance elements 30, 3|, and 32, which are connected in series across the alternatingcurrent supply circuit I2. Connected in series between the tap 29 and control member 20 is a biasing circuit including parallel connected resistor 33 and a capacitor 34. As illustrated in the drawing, the shield grid 2I is connected directly with the cathode by conductor 35 and a conventional transient-suppressing capacitor 33 is connected between the control member and cathode.

In installations causing th most trouble, from the standpoint of erratic operation, th initiating switch I3 is located remotely from the remainder of the relay and this has been illustrated in the drawing by interrupting the conductors 31 and 33 which lead to the initiating switch I3 by the dotted portions. The capacitor 39, which I have found substantially eliminates erratic operation of the timer, is connected across the conductors 31 and 33 close to the electronic relay.

In one timing circuit constructed in accordance with the teachings of the present application, resistor 28 is 500 ohms; resistor 30, 10,000 ohms; capacitor 34, .5 microiarad; capacitor 33, .002 .microfarad, and capacitor 39, .05 microfarad. This timer was designed for operation from a 115 volt alternating current supply circuit.

A brief consideration of the operation of the illustrated embodiment of my invention will provide a better understanding of the objects and advantages thereof. When the initiating switch I3 is open, the capacitor 34 charges to a predetermined voltage by grid rectification. The voltage is determined by the position of the tap 29 on the voltag divider and is or a polarity to maintain the control member 20 negative. From an inspection of the drawing, it is seen that the charging circuit starts with the lower conductor of the alternating-current circuit I2 and includes resistor 30, a portion of resistor 3|, tap 29, the gridto-cathode circuit of the valve I1, and resistor 23 to the upper line of the alternating-current supply circuit. When it is desired to initiate energization of the load circuit I II, the switch I3 is closed and current immediately starts to flow through the coil I and normally closed contacts I4 of the relay I5. After the expiration of a predetermined time, the charge on the capacitor 34 is reduced sufliciently by discharg resistor 33 so that the aitemating-current component of voltage appearing between the lower conductor I2 of the supply circuit and th tap 29 is sufllcient to overcome the negative voltage the capacitor to render the electric valve II condu e which, in turn, operates the relay I to terminate the energization of the load circuit. The relay may be reset by opening the initiating switch.

From a consideration of the drawing and the foregoing description of the operation of the illustrated embodiment, it will be apparent that the initiating switch I3 is connected in the cathode-to-control-member circuit of the electric valve I1 and also in series with load circuit In which, as illustrated, is inductive. When the switch I3 is closed, current immediately begins to flow through the load circuit III and any bouncing or momentary opening of the contact of switch I3 may cause transient voltages of considerable magnitude to appear across the contacts thereof. The introduction of this voltage in the circuit of the capacitor 34 causes it to charge to a voltage of different magnitude than would ordinarly be established by the position of the slider 29 and, therefore, cause erratic operation of the timer for a given setting of the slider. This tendency is substantially eliminated by the use of capacitor 39. In installations where conductors 31 and 33 are relatively long and are in proximity to other equipments such as relay contactors, the voltage induced in the cathode-to-control-member circuit oi the electric valve I1 is sometimes sumcient to charge the capacitor 34 negatively and of a magnitud which resets th relay after the valve IT has been rendered conductive or, expressed in another way, after the relay is timed out. These voltages are also substantially eliminated by the capacitor 39.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my-invention in its broader aspects, 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.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating-current supply circuit, a load circuit, a relay including an actuating coil and a normally closed contact for controlling the energization of said load circuit, an electric valve including an anode, a cathode, and a control member, means for establishing a predetermined negative bias on said control member, means connecting the actuating coil of said relay to one side of said alternating-current circuit and to the anod of said electric valve, means including an initiating switch for connecting said cathode with the other side of said alternatingcurrent supply circuit and for completing a circuit between the cathode and control member of said electric valve, and capacitance means connected across said initiating switch to eliminate from said cathode-to-control-member circuit transient voltages appearing across said initiating switch.

2. In combination, an alternating-current supply circuit, a load circuit, an electric valve including an anode, a cathode, and a control member, means connecting said anode for energize.- tion in accordance with the voltage or one side of said alternating-current circuit, means for connecting said cathode to the same side of said alternating-current circuit, a capacitor, means connecting said control member through said capacitor to a voltage intermediate the voltage of the lines of said alternating-current circuit to establish a predetermined negative voltage on said control member, an initiating switch connected between said cathode and the other line of said alternating-current supply circuit for completing the anode-cathode circuit of said electric valve for energization from said supply circuit and for completing an external circuit between the cathode and control member of said electric valve to include the voltage of said capacitance and an alternating-current component of voltage dependent upon the voltage at said intermediate point, a discharge circuit for said capacitor, and capacitance means connected across the contacts of said initiating switch for eliminating the effect of transient voltages on the charge of said capacitor.

3. In combination, a supply circuit, an electric valve including an anode, a cathode, and a control member, a voltage divider connected across said supply circuit, a timing capacitor, means connecting said capacitor between a point on said voltage divider and said control member, means connecting said anode for energization from one side of said alternating-current circuit, means connecting said cathode through an impedance element to said one side of said alternating-current circuit to establish a charging circuit for said capacitor including the internal cathode-tocontrol-member circuit of said electric valve, a discharge circuit parallelling said capacitor, an initiating switch for connecting said cathode to the other side of said alternating-current supply circuit and thereby preventing further charge of said capacitor, said initiating switch also completing the external cathode-to-control-member circuit of said electric valve to impress thereon an alternating-current component of voltage and the voltage of said capacitor, the discharge of said capacitance determining the time after closure of said initiating switch that said electric valve is rendered conductive, means responsive to conduction of said valve for terminating the energization of said load circuit, and energy-storage means connected across said initiating switch for rendering the operation of said electric valve independent of transient voltages induced in the leads to said initiating switch or caused by closure of said initiating switch.

4. In combination, an alternating-current supply circuit, a relay having an actuating coil, an electric valve having an anode, a cathode, and a control member, an initiating switch, means connecting said initiating switch, the operating coil of said relay, and the anode-cathode circuit of said electric valve in series relation and for energization from said supply circuit, a voltage divider energized from said supply circuit, a timing capacitor connected between a point on said voltage divider and the control member of said electric valve, means connected with said cathode for completing a circuit from said point on said voltage divider through the internal cathode-tocontrol-member circuit of said valve to one side of said supply circuit to charge said capacitor to a predetermined value when said initiating switch is in the open position, said initiating switch being located to connect saidcathode to the other side of said alternating-current circuit so that the contacts thereof are in the external cathode-to-control-member circuit of said electric valve, and capacitance means connected across said initiating switch to suppress transient voltages appearing across saidswitch and thereby eliminate erratic operation of said electric valve resulting from the effect of said transient voltages on said control member.

5. In combination, a supply circuit, a load circuit, an electric valve including an anode, a cathode, and a control member, an initiating switch, means for impressing a predetermined negative voltage on the control member of said electric valve when said initiating switch is open, a source of turn-on voltage, closure of said initiating switch being eiiectiveto connect said load circuit for energization from said supply circuit and said tum-on voltage in circuit with said control member, means for effecting reduction of said negative voltage at a predetermined rate so that said turn-on voltage renders said electric valve conductive after a predetermined interval of time, means responsive to conduction of said electric valve for interrupting the supply of energy to said load circuit, and capacitive means connected across the contacts of said initiating switch for suppressing transient voltages in the cathode-to-control-member circuit of said electric valve.

6. A control circuit for rendering an electric valve conductive after a predetermined interval of time comprising an electric valve having an anode, a cathode, and a control member, a supply circuit, a capacitor, means connecting said capacitor with said supply circuit and with said control member, means for connecting the cathode of said electric valve with said supply circuit so that said capacitor is charged to a predetermined voltage through the discharge path from control member to cathode of said electric valve, a source of turn on voltage, an initiating switch operable when closed to alter the connection of said cathode with said supply circuit and for impressing said turn-on voltage on said control member so that said electric valve is rendered conductive when said capacitance has discharged a predetermined amount, and capacitance means connected across the contacts of said initiating switch to suppress transient voltages in the cathode-to-control-member circuit of said electric valve.

7. In combination, a supply circuit, an electric valve including an anode, a cathode, and a control member, an initiating switch for connecting the anode-cathode circuit of said valve for enerization from said supply circuit, means for impressing a predetermined negative voltage on the control member of said electric valve when said initiating switch is open. a source of turn-on voltage, closure of said initiating switch being effective to connect said turn-on voltage in circuit with said control member, means for effecting reduction of said negative voltage at a predetermined rate so that said turn-on voltage renders said electric valve conductive to perform a controlling function a predetermined interval of time after closure of said initiating switch, and capacitance means connected between the cathode of said electric valve means and a point on the external cathode-to-control-member circuit connecting said cathode to the same side of said alternating-current circuit, a capacitor, means connecting said control member through said capacitor to a voltage intermediate the voltage of the lines of said alternating-current circuit to establish a predetermined negative voltage on said control member, an initiating switch connected between said cathode and th other line of said alternating-current supply circuit for completing the anode-cathode circuit of said electric valve for energization from said supply circuit and for completing the external cathode-to-controi-member circuit of said electric valve to in-- clude the voltage oi said capacitance and an alternating-current component of voltage dependent upon th voltage of said intermediate point,

a discharge circuit for said capacitor, and capacitance means connected between said cathode and a point on the external cathode-to-control-member circuit of said electric valve more remote from said control member than said capacitor.

ELBERT D. SCHNEIDER.

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