US2183412A

US2183412A - Time delay relay

Info

Publication number: US2183412A
Application number: US246181A
Authority: US
Inventors: Marvin B Sledd
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1938-12-16
Filing date: 1938-12-16
Publication date: 1939-12-12
Anticipated expiration: 1956-12-12

Description

Dec. 12, 1939. SLEDD 2,183,412

TIME DELAY RELAY Filed Dec. 16, 1938 Ir'wverwtorw Mabvin B. Sledd,

b k TJ y His Attorwwey.

Patented Dec. 12, '1939 UNITED STATES TIME DELAY RELAY Marvin B. Sledd, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 16, 1938, Serial No. 246,181

Claims.

My invention relates to time delay relays of the type wherein the delay is determined by the time required for a capacitor to lose a certain amount of charge. Such a relay has been described and 6 claimed in the copending application of Elbert D. Schneider, Serial No. 155,518, filed July 24, 1937, assigned to the same assignee as the present application. With that relay it was found that under certain conditions, such as when it was 10 used to control loads that produced considerable drop in the voltage of the line supplying the relay there was a tendency for the load controlling contacts of the relay to chatter at the end of the timing period. It is an object of my invention to provide an improved form of the relay disclosed in the' aforesaid Schneider application which will avoid any tendency toward chattering.

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

In the single figure of the drawing which is a circuit diagram showing a somewhat simplified form of the relay disclosed in the aforesaid Schneider application together with an embodiment of my invention, I and 2 represent the leads of a source of alternating current supply which, for example, may be a 60 cycle lighting circuit at 220 volts. Connected across the source is the voltage divider 3 which is shown as comprising the resistor 4 and the potentiometer 5. The electron discharge device I having the anode 8, the control grid 9 and the cathode I I] is arranged to be energized from the source I, 2, the cathode being shown connected directly with the lead 2 through the single pole, single throw switch I I and the anode being shown connected through the winding of the relay I2 with the other lead I of the source. The grid 9 connects with the movable contact 6 of the potentiometer through the capacitor 20 which is shunted by the resistor 2| forming a leakage path through which the capacitor may lose its charge at a predetermined rate. The cathode ID, in addition to its connection with the lead 2 through the switch I I, has a permanent connection with the lead I through the resistor 22. The apparatus thus far described is essentially that disclosed and claimed in the aforesaid Schneider application.

In the drawing of the present application, I

have shown the relay I2 provided with a movable contact 23 arranged when the relay is energized to close the load circuit 24 including any suitable load device represented at 25. This load 5 circuit connects with the leads I and 2 whereby the closing of the load circuit by the relay I2 may tend to produce a drop in voltage between those leads. The relayv I2 is provided with another movable contact 26 and the cooperating fixed contacts 21, which latter connect through the ll leads ,28 with the capacitor 20 and the point 29 connecting with the grid and with one side of the leak resistor 2I. The movable contact 26 is so arranged that when the relay I2 is operated the circuit controlled thereby between the capaci- 10 tor and the point 29 is opened.

Assuming the switch II to be in its open circuit position as illustrated, in which case no current flows in the anode-cathode circuit of the discharge device 'I and the relay I2 is deenergized, there will be a grid current flow during these half cycles, which for convenience will be termed the negative half cycles, at which the lead I is negative with respect to the lead 2. This grid current is that due to the potential difierence 20 between the potentiometer contact 6 and the lead I and charges the capacitor 20 in such a manner that the side thereof which connects with the 'grid is negative, it being noted that the only connection of the cathode with the source at 25 this time is that through the resistor 22 to the lead I. Thus, while the switch II is open, the negative half cycles of the supply voltage keep the capacitor 20 in a charged condition.

When the switch II is closed the anode-cathode 30 circuit of the device I is closed whereby the device may function to pass current during the positive half cycles to operate the relay I2 under the control of the grid 9. Closing of the switch II also serves effectively to transfer the connec- 35 tion of the cathode from the lead I to the lead 2, it being noted that the connection of the cathode with the lead 2 is of negligible resistance. The charge formerly given to the capacitor 20 maintains the grid 9 sufiiciently negative to prevent 40 current flow through the device 1 until the charges on the plates of the capacitor have had time to equalize through the resistor 2I, or at least to become reduced to such a value that the device I will pass current sufiicient to cause an 45 operation of the relay I2. After the operation of the relay I2, the switch II may be opened at which time the relay will move to open circuit position and the capacitor 20 will again become charged by the grid current of the device I during 50 the negative half cycles. It will thus be seen that after the closing of the switch II the relay I2 will be operated only after the'lapse of a pre determined time interval. The duration of this interval depends upon various factors such as the capacitance of the capacitor, the resistance of the resistor in shunt therewith and the setting of the potentiometer. Adjustment of the latter provides a convenient method of varying the time delay interval as desired,

In the above described operation of the apparatus I have not taken into consideration the effect of the operation of the relay l2 upon the grid circuit of the device 1 nor the effect on the line voltage of closing the load circuit 24. It has been found that in some cases the closing of the load circuit at the end of the timing interval has caused the relay I2 to chatter. This is probably due to the fact that the closing of the load circuit produced a drop in the voltage supplied to the discharge device I so that the relay 1! became deenergized sufliciently to reopen the load circuit. The load thus being removed from the supply leads the voltage supplied to the discharge device was immediately restored whence the device again passed sufficient current to re-operate the relay to reclose the load circuit. The above sequence of operation may continue to repeat itself until such time that the negative bias supplied to the grid by the capacitor 20 is-insufncient' to prevent the operation of the relay.

The

additional contacts

26 and 21 of the relay l2 being arranged to open the connection between the capacitor and the grid when the relay operates serves to reduce or to'remove the biasing effect of the capacitor on the grid of the discharge device for it will be seen that upon the first operation oi the relay l2 the connection between the capacitor and the grid is opened thus removing whatever negative bias is being supplied by the capacitor to the grid. This removal of the negative bias supplied to,the grid causes an increase in the current through the relay l2, and this increase prevents the relay l2 from becoming sufficiently deenergized by the "drop in voltage to reopen the load circuit. Chattering is thus avoided.

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

1. A time delayv relay comprising a voltage divider arranged to be .connected across a source of alternating current supply, a grid controlled electron discharge device having its anode and cathode connected with spaced points of said divider, a current responsive device in one of sad connections, a capacitor connected between said grid and a point of said divider between said spaced points, a switch in said cathode connection, a resistor connected between said cathode and said divider at a point of the divider on the opposite side of said capacitor connection from said first mentioned cathode connection and means responsive to the operation of said current responsive device for reducing the efiect of said capacitor on said grid.

2. A time delay relay comprising a source of supply of alternating current, a grid controlled electron discharge device having its anode and cathode connected to be energized irom said source, a current responsive device in one or said connections, a switch in said cathode connection, means connected with said cathode and grid and operable when said switch is open for producing 1 vider arranged to be connected across a source of alternating current supply, a grid controlled electron discharge device having its anode and cathode connected withspaced points of said divider, a relay in one of said connections, a capacitor provided with a high resistance shunt connected between said grid and a point of said divider between said spaced points, a switch in said cathode connection and a resistor connected between said cathode and said divider at a point thereof on the opposite side of said capacitor connection from said first mentioned cathode connection, said relay having cooperating contacts arranged to -remove the efie'ct oi! said capacitor on said grid.

4. A time delay relay comprising a source of supply of alternating current, a grid controlled electron discharge device having itsanode and cathode connected to be energized from said source, a relay in one of said connections, a switch in said cathode connection, means connected with said cathode and grid and operable when said switch is open for producing a grid current during the negative half cycles of the alternating current, and a capacitor having a high resistance shunt in series with said grid arranged to be charged by said grid current, said relay having cooperating contacts operative to open the connection between the capacitor and the grid.

5. A time delay relay comprising a voltage divider arranged to be connected across a source of alternating current supply, a grid controlled electron discharge device having its anode and cathode connected with spaced points of said divider, a current responsive device in one of said connections,- a capacitor connected between said grid and-a point of said divider between said spaced points, a switch in said cathode connection, a resistor connected between said cathode and said divider at a point thereof on the oppo'- site side of said capacitor connection from said first mentioned cathode connection, a relay provided with a plurality of movable contacts connected in the anode circuit, a load circuit connected to be supplied from said. source and to be controlled by one of said movable contacts and 'means whereby another of said movable contacts controls the connection between said capacitor and said grid.

- MARVIN B. SLEDD.