US1957247A - Photo-electric relay - Google Patents

Description

May 1, 1934.

w. D. COCKRELL 1,957,247

PHOTO-ELECTRIC RELAY Filed Jan. 21, 1932 Inventor: William D. Cockrell. b Mam H is Attorne g.

Patented May 1, 1934 UNITED, STATES PATENT OFFICE PHOTO-ELECTRIC RELAY New York Application January 21, 1932, Serial No. 587,925

3 Claims.

for limiting the voltage applied thereto to a prescribed value. A further object is the provision in a relay of this type including a vapor electric discharge device and a circuit interrupter therefor of means for preventing the loss of control due to failure of the interrupter completely to open the circuit which it controls.

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 illustrates one embodiment of my invention, I have shown at 1 and 2 the positive and negative sides respectively of a direct current source which for example may be a 250 volt source. Connected between the sides 1 and 2 is a voltage divider comprising the adjustable resistor 3 and resistors 4, 5, 6, and 7. In order that the fiow of current through resistors 5, 6, and 7 may be reversed for purposes to be hereinafter described I provide the reversing switch 8. When this switch is shifted to a position to reverse the current through resistors 5, 6, and 7, it cuts off resistor and substitutes resistor 9 therefor, which resistor connects at the point 10 with the divider as above described. Resistors 5 and 9 are approximately equal in resistance, the value of which as well as that of resistors 6 and 7 may for example be a few thousand ohms each. The photo-electric tube 12 connects through the reversing switch 13, which is provided for the purpose of reversing the polarity on the tube when reversing switch 8 is operated, with the contact 14 of switch 8 and through resistor 15 whose resistance preferably is of the order of 10 to 50 megohms with the adjustable contact 16 on resistor 7. Electron discharge amplifier 18 has its'plate 19 connected through resistor 20 with the positive side of the supply circuit, its cathode 21 connected with the divider at the point 22 and its control grid 23 connected with resistor 15 and phototube at the point 24. This amplifier is shown provided with the screen grid 25 also connected with the divider but the use of a screen grid tube is not essential to my invention.

With the reversing switches 8 and 13 each in the position illustrated, the phototube is adapted to cause the operation of the amplifier in response to an increase in light while with these switches shifted to their opposite positions the tube is adapted to cause the operation of the amplifier in response to a decrease in light. With little or no light falling upon the tube 12 the potential of the grid 23 of amplifier 18 is negative with respect to its cathode since the point 16 on the divider is more negative than the point 22. When light is thrown upon the tube 12 or the illumination thereof isincreased to a predetermined amount the resulting lowered resistance of the tube causes the grid 23 to become positive with respect to its cathode since tube 12 connects through resistor 9 with the divider at the point 10 which is positive with respect to point 22. Thus the amplifier 18 becomes operative. It will be noted that the potential applied to the phototube in this case and when it is dark is substantially that which exists on the divider between the points 10 and 16, the effect of resistors 9 and 15 which are in series with the phototube being so small that it may be neglected. Inas- 30 much as the phototubes of the gas-filled type which are the most sensitive thus far developed operate with the greatest efiiciency when supplied with the maximum voltage for which they are designed but which may be ruined if the ap- 35 plied voltage exceeds a certain amount, for example, volts, the voltage divider is so constructed that the voltage supplied to the tube 12, namely that between the points 10 and 16, is approximately the maximum which may be safely used on the 90 tube.

When it is desired to have the phototube cause the amplifier to operate in response to a decreasing light, the switch 8 is thrown to its down position and switch 13 thrown to the left, thus reversing the direction of current fiow through the resistors 6 and '7. Resistor 9 is now included in the divider instead of resistor 5, the two resistors being approximately equal. With no light on the phototube the charge on the grid 23 of the amplifier is positive with respect to the cathode since now the point 16 is positive with respect to the point 22. However, since grid 23 is positive with respect to its cathode a small grid current will pass and there will be a resulting small IR drop across the resistor 15. Hence the voltage applied to the phototube 12 will equal that produced by the divider between the point 16 and the point 14, instead of point 10 as before, minus the Voltage drop due to the grid current in resistor 15.

By a proper proportioning of the resistors this net voltage which is now applied tothe phototube may be made approximately equal to that which was applied when the reversing switch was in its original or upper pwition. Thus it will be seen that although the IR drop in resistor 15 of the grid current in the lowered position of switch 8 subtracts from the voltage applied to the tube, the circuit connections of the tube have been changed to include resistor 9, whereas formerly it excluded the equal resistor 5. It hardly needs to be explained that when tube 12 is illuminated with the switch 8 in its lower position the grid 23 is charged negatively with respect to its cathode and the amplifier 18 is rendered inoperative until the light on the tube 12 is cut off or reduced to a predetermined value. As a result of this arrangement the single phototube 12 may cause the operation of the amplifier 18 either in response to an increase in light when the switch is in its upper position or in response to a decrease in light when the switch is in its lower position, the phototube in either case operating with a maximum efficiency and without danger of its being subjected to an injuriously high voltage. Amplifier 18 may be used to control any desired apparatus such, for example, as the vapor electric discharge device 30.

In the foregoing it has been assumed that the load current passed by the vapor device 30 does not appreciably affect the voltage distribution in the divider. Should the conditions in any particular case be such that this is not true and there be a material increase in the IR drop in the resistors 5, 6, '7 and 9 due to the load current then a suitable change in the resistors should be made in order that the phototube may not be subjected to a voltage in excess of the maximum allowable voltage therefor when the largest current flows in the resistors. This feature of my invention is described and claimed in my copending divisional application Serial No. 658,566 filed February 25, 1933 and assigned to the same assignee as the present application.

Another feature of my invention relates to the combination of the amplifier 18 and the vapor device 30 whereby the amplifier may be operated with the highest allowable voltage on its plate yet without danger of that voltage exceeding the maximum voltage rating of the amplifier when the amplifier is inoperative. As illustrated the plate 31 of vapor device 30 connects through the winding of relay 32 with the positive side of the supply circuit, the cathode 33 connects with the voltage divider between resistors 3 and 4 and the control grid 34 connects through the resistor 35 with the connection 36 between plate 19 and resistor 20. Inasmuch as the amplifier 18 has its greatest voltage amplification when the resistor 20 connected therewith is a maximum it becomes desirable to have this resistor connect with the highest positive potential available, namely directly with the positive side of the supply circuit. The amplifier 18, however, has a maximum plate voltage rating which must not be exceeded.

When amplifier 18 is inoperative and no current flows through the resistor 20, the voltage applied to the plate 19 may be in excess of the maximum rating of this amplifier. This difficulty I have avoided by connecting the control grid 34 of device 30 through the resistor 35 with the connection 36 so that when amplifier 13 is inoperative, at which time grid 34 is positive and device 30 operative, there will be a small grid current in device 30 traversing resistors 20 and 35. The IR drop or this grid current in resistor 20 is sufllcient to prevent the voltage applied to plate. 19 of amplifier 18 from reaching an excessive value.

It will be noted that when amplifier 18 is operative the vapor device '30 is inoperative to pass current since its grid 34 at that time is negative with respect to the cathode 33 thereof. However, as soon as amplifier 18 becomes inoperative the grid 34 becomes positive and the vapor device 30 conducts. Inasmuch as the vapor device is operated with direct current, I employ a suitable switching device for opening the plate circuit. By way of example I have illustrated such a switching device as the rotatable interrupter 37 which may for example be driven by the apparatus controlled by relay 32. It sometimes happens that the interrupting switch in the plate circuit of the vapor device becomes coated with grease or dirt particularly when the switch is of the rotary type having brush or roller contacts so that the switch fails to completely break the plate circuit and as a result the vapor device remains ionized until the switch again closes the plate circuit. In such a case the vapor device may continue to operate without grid control. In order to prevent such an occurrence I have provided the resistor 38 whose resistance may, for example, be from 100 to 100,000 ohms connected between the cathode and the plate of the vapor device 30. With this resistor 38, whose resistance is small in comparison with the leakage circuit across the contacts of the switch 3'7 when the same is in open circuit position, the potential difference between the plate and the cathode of the device is reduced to a value which is less than the ionization voltage thereof, and the device will cease to conduct.

It will be noted that I have shown the resistor 3, which is the most positive resistor in the voltage divider, as a variable resistance. This resistor preferably is composed of some material having a non-linear characteristic, such, for example, as that known as Thyrite. Such material will tend to maintain a more constant IR drop across its terminals than will ordinary resistance material with variations in current and will permit a larger load current to be drawn through the vapor device for a given increase in current in that part of the divider which is negative to the cathode of the vapor device. Likewise resistors 4, 5, 6, '7 and 9 also may be made advantageously of such material. In shunt with the resistor 3 I have shown the capacitor 39 whose purpose is to supply additional current to the relay 32 at the instant the vapor device 30 becomes operative to assist in closing the relay, the current flowing in the relay winding thereafter being only that which is necessary to hold the relay in closed position.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and scope of my invention, which modifications I aim to cover by the appended claims.

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

1. In combination, a source of direct current, a vapor electron discharge device having an anode and a cathode connected therewith, an interrupter in the anode connection subject to an incomplete interrupting function and means for reducing the potential of the anode below the ionization potential of the anode circuit in the 3. In combination, a source of direct current, a vapor electron discharge device having an anode and a cathode connected respectively with the positive and negative sides of said source, a circuit interrupter in said anode connection and a resistance connection between the anode and the negative side of said source.

WILLIAM D. COCKREIL.

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