US2088198A - Electrical system - Google Patents

Description

y 3 H. GEFFCKEN ET AL 2,088,198

ELECTRICAL SYSTEM Filed June 21, 1933 INVENTOR HENRIEH GEFFEKEN (KANE RIHTER BY %4/ %M ATTORN EY Patented July 27, 1937 UN'l'ED STATS Parr.

'i FFIC ELECTRICAL SYSTEM Application June 21, 1933, Serial No. 676,887 lln Germany July 16, 1932 5 Claims.

This invention relates to electric control systerns and more particularly to control and amplifying circuits using electronic or ionic discharge tubes controlled by photoelectric or similar devices.

One object of our invention is to increase the sensitivity of response of control systems comprising photoelectric devices controlling an ionic or electronic discharge amplifier.

Another object of the invention is to provide means in a photoelectric control circuit comprising a discharge amplifier operated from a photoelectric device whereby the operation of the circuit may be adjusted to the most favorable condition to secure a maximum of sensitivity and effici ncy during operation.

A further object of the invention consists in the provision of a control circuit comprising a discharge amplifier operated by a photoelectric cell and the like, which may be similarly used with both alternating or direct current supply.

Further objects and aspects of our invention will become more apparent from the following detailed description taken in reference to the accompanying drawing in which We have illustrated by Way of example a few embodiments of the invention.

Figure 1 illustrates a circuit embodying the novel feature of the invention.

Figure 2 shows an electronic discharge device used as an adjustable high ohmic resistor in a circuit according to Figure l in accordance with the novel features of the invention.

Figure 3 shows a similar circuit embodying the invention, and;

Figure l illustrates a circuit especially adapted for operating a relay and for use with a source of alternating current.

It is customary in controlling the grid or other control electrode of an ionic or electronic discharge tube by means of photoelectric cells to connect the grid electrode on the one hand with one terminal of the controlling photoelectric cell, and on the other hand to a suitable biasing voltage through a high ohmic resistance. In view of the low conductivity of photoelectric cells, it is mostly necessary to provide a very high resistance, especially in cases when it is desired to secure a reliable relay operation by very small variations of illumination efiecting the photoelectric cell.

In accordance with the present invention, a thermionic discharge tube of small size is provided to act as a grid resistance in a circuit of the type as described. Such tubes have the advantage that their conductivity may be varied within extraordinary wide limits (about 1:10 by adjusting the heating current of the incan descent cathode. Thus, by using a device of this type the sensitivity of response and the degree of inertia of the circuit may practically be regulated in any manner desired.

Furthermore, by using a thermionic discharge tube as a high ohmic resistance, constant values of conductivity may be secured of such low value as would be impossible to obtain by using high ohmic resistors without resorting to means prohibitive for practical purposes. Finally, such a tube acts as a rectifier, and if properly designed has a saturation characteristic thereby resulting in a considerable increase of the voltage variations produced by the variations of the photoelectric current at the control grid of an amplitying tube operated from the photoelectric cell.

When using a circuit according to the invention embodying a thermionic discharge device as a variable resistor, it is necessary to separate the heating of the cathode of the thermionic resistance device from the heating of the cathode of the tube being controlled. This may be accomplished, for instance, by using a transformer with separate secondary heating windings. We have found it especially advisable, however, to design the filament of the thermionic discharge resistance for equal current consumption as the cathode of the tube being controlled, and to connect both filaments in series in conjunction with a suitable series resistance.

Referring to Figure 1, We have shown a circuit embodying the aforementioned features in accordance with the invention. At I, we have shown a thermionic discharge tube acting as a high ohmic resistor and comprising a heatable cathode 2 and anode 3. The tube to be controlled is shown at i being of the ordinary type of thermionic vacuum tubes having a heatable cathode 5, a grid or control electrode 6, and an anode electrode 1. The operating current is supplied from a direct currentsource indicated by the plus and minus signs in the drawing.

Filaments. 3 and 5 of the tubes l and 4, respectively, are designed for equal current consumption and are connected in series together with voltage drop or bleeder resistors 8 and It! as shown, to secure the proper terminal voltages for the filaments. The anode of the thermionic tube is connected with the grid 6 of the tube 4 being controlled, to secure a negative grid bias relative to the cathode 5, provided the sizes of the resistors 8 and iii are properly chosen to obtain the proper potential at the cathode 5. The photoelectric device shown at II comprising a photoelectric cathode I2 and anode electrode is arranged in a vacuum or attenuated atmosphere of known design, is connected in the well known manner between the grid 6 of the tube 4 and the positive pole of the source of operating potential. It is understood that in place of the particular type of photoelectric cell Ii, any other type of light sensitive or other controlling device may be provided without materially Changing the circuit and function according to the invention.

In order to adjust the value of the resistance presented by the thermionic discharge device I, we have furthermore shown a regulating resistance 9 placed in parallel to the cathode 3 for adjusting the cathode heating current, thus producing resultant variations of the conductivity of the tube I, in turn. causing the sensitivity to incoming light variations of the circuit to be varied within wide limits.

A further means for additionally varying the sensitivity consists in providing a variable condenser I5 connected between the grid and cathode of the tube 4. This condenser acts in. the known manner by accumulating an electric charge dependent on the variations of the current through the photoelectric cell, resulting in varying controlling potentials at the grid IS of the tube 4. The output or translating device, such as a transformer, relay, and the like, is connected in the anode circuit of the tube 4 for which purpose terminals I4 are provided as shown in the drawing.

We have furthermore found it advisable to insert an induction coil 2I in the grid circuit arranged close to the tube 4. A wire wound resistance of about 10,000 to 20,000 ohms provided for this purpose was found to give favorable results. The function of this induction coil is to improve the working of the circuit by stabilizing the operation and preventing disturbing influences of high frequency oscillations induced from the outside, such as from the current source in the form of switching surges (if the system is operated from a power network) or also high frequency oscillations of short wave length produced by self-oscillation in the circuits of the tube 4.

A circuit arrangement as described may be used for various purposes, such as for sound picture recording, picture telegraphy, and primarily for the control of a relay by extremely small variations of photoelectric or other electric input currents. In the latter case, either direct or alternating current may be used for operation due to the rectifying characteristics of the discharge tube I without decreasing or otherwise impairing the sensitivity and effectiveness of the circuit.

The discharge tube I, used in accordance with the invention in a control circuit as described, may be of extremely small size and manufactured at small cost. A suitable form of such a discharge tube is shown in Figure 2. This comprises a small cylindrical shaped bulb I6 of the size of a flashlight bulb including a filament I1 and a wire I8 sealed into the tube and serving as an anode electrode. to a hook at its end, forming a portion substantially parallel to the filament heating wire, as shown. The tube may be provided in a known manner with a screw base I9 for easy mounting in a socket.

Figure 3 illustrates a circuit according to the invention similar to the circuit shown according to Figure 1 but somewhat different in function.

The anode wire I8 is preferably bent Whereas with the circuit of Figure 1 the anode current of the tube 4 being controlled increases with increasing illumination of the photoelectric cell, the opposite effect takes place in a circuit according to Figure 3 and the anode current of tube 4 being controlled decreases with increasing illumination of the photoelectric cell II. This is explained as follows: Referring to the circuit according to Figure 1, the potential of the grid electrode ii is determined by the difference in potential drop through the filament 3 of the tube I plus the resistance 8 produced by the heating current, on the one hand, and of the drop through the tube I resulting from the current flowing through the photoelectric circuit comprised of the photoelectric cell II and the tube I in series, on the'other hand. If the drop through the resistor 8 plus filament 3 is greater than the drop through the tube I, the grid 6 is at a negative potential and it is seen that with an increase of illumination of the cell H, the photoelectric current will increase, resulting in a corresponding increase of the drop across the tube I. This has in turn the effect of a decreased difference be tween the potentials existing at the filament 5 and at the grid 5 of the tube 4, resulting in an increase of the anode current of the tube 4. Referring, on the other hand, to the circuit as shown by Figure 3 which differs from the circuit according to Figure 1 in that the cathode of the tube I 7 is connected to the positive terminal of the current supply source in place of to the negative terminal as shown by Figure l, the grid biasing potential of the tube 4 is determined by the algebraical difference of the potential drops through filament 3 plus resistance I0 caused by the heating current on one hand and the drop through tube I caused by the photoelectric current, on the other hand. In this case, in order to secure a negative grid potential relative to the cathode for the tube 4, it is necessary that the drop through the tube I be larger than the potential drop through filament 3 plus the resistance I 0. If now the current through the photoelectric cell II increases due to increasing illumination, the potential drop across tube I will increase, thus making the grid Ii more negative and accordingly effecting a decrease of the anode current of tube 4. Circuits of this kind in general have a specially high sensitivity which may be explained by the known shape of the grid current charac teristic of tubes containing a certain amount of gaseous ions.

In order to secure an adjustable impedance of the tube I in this case, the invention in accordance with a further feature makes use of the well known effect that certain gases or vapors, especially caesium vapor, become ionized by an incandescent anode electrode, in the present case, the filament 3 of the tube I. For this purpose, the tube I is filled with a small amount of caesium vapor.

Thus, the tube has a certain low conductivity due to the mentioned ionization effect, the value of which may be controlled within very wide limits by adjusting the heating current of the oathode by means of the variable resistance 5.

Figure 4 illustrates a circuit primarily adapted for control of a relay placed in the output circuit of the vacuum tube amplifier 4. This circuit is especially suited for operation with alternating current, such as from a source 20 as shown, specially when the available voltage is of low value. The discharge tube in this circuit is only weakly heated in a manner to act as a Pit thermionic rectifier. Accordingly, the tube I Will allow current to pass only during the half cycle during which the tube 4 being controlled passes no current, and it will pass no current or act as a high ohmic resistance during the other half cycles, when the tube i is passing current; that is, when the anode 'l is at a positive potential. On the other hand, the photoelectric cell i! will pass current during the same half cycle as the tube 3 being controlled since both are connected in the same manner to the source 25. Thus, if the photoelectric cell 5 is illuminated, the grid potential of the tube 3 being controlled is shifted during one half cycle towards negative values and is returned during the other half cycle through the photoelectric cell towards more or less positive values in such a manner as to establish a mean value by the action of the condenser l5 substantially proportional to the illumination of the photoelectric cell ll.

Although the invention has been described in connection with the specific showings of the drawing, it is understood that many variations and modifications may be made to the drawing coming within the broader scope of the invention, as expressed in the ensuing claims.

We claim:

1. An electrical system comprising a discharge amplifier having a heatable cathode, an anode and a grid; a source of current supply; a thermionic discharge tube having a heatable cathode and an anode, said heatable cathodes of said amplifier and of. said discharge tube being designed for equal current consumption being connected across said source in series with electric resistance devices means in parallel with the cathode of said discharge tube for varying a discharge characteristic of said device; a photoelectric control device, said discharge device and said photoelectric control device being also connected in series across said source; a connection from the junction point of said photoelectric device and of said discharge device to the grid of said amplifier; and an output circuit connected across the anode of said amplifier and said source.

2. An electrical system comprising in combination a discharge amplifier having a heatable cathode, grid and anode; a thermionic discharge resistor having a heatable cathode designed for the same current consumption as the cathode of the amplifier and an anode; a source of current; a branch circuit connected across said source including the cathodes of said amplifier and of said thermionic device in series with resistance means; a photoelectric control device; a further branch circuit connected across said source including said photoelectric control device and said thermionic discharge device; resistance means in parallel with the cathode of said thermionic discharge device for varying a discharge characteristic of said device, a connection from the common connecting point of said photoelectric control device and said thermionic discharge device to the grid of said amplifier; and an output circuit including a relay device connected between said source and the anode of said amplifier.

3. An electrical system comprising a discharge amplifier having a heatable cathode, an anode and a grid; a source of current supply; a thermionic discharge tube having a heatable cathode and an anode, said heatable cathodes of said amplifier and of said discharge tubes being connected across said source in series with electric resistance devices; means in parallel with the cathode of said discharge tube for varying a discharge characteristic of said device; a photoelectric control device, said discharge device and said photoelectric control device being also connected in series across said source; a connection from the common connecting point of said photoelectric device and of said discharge device to the grid of said amplifier; and an output circuit connected across the anode of said amplifier and said source.

4. An electrical system comprising in combination a discharge amplifier having a heatable cathode, grid and anode; a thermionic discharge resistor having a heatable cathode and an anode; a source of current; a branch circuit connected across said source including the cathodes of said amplifier and of said thermionic device in series with resistance means; a photoelectric control device; a further branch circuit connected across said source including said photoelectric control device and said thermionic discharge device; resistance means in parallel with the cathode of said thermionic discharge device for varying a discharge characteristic of said device; a connection from the common connecting point of said photoelectric control device and said thermionic discharge device to the grid of said amplifier; and an output circuit including a relay device connected between said source and the anode of said amplifier.

5. An electrical system comprising a discharge amplifier having a heatable cathode, an anode and a grid; a source of current supply; a thermionic discharge tube having a heatable cathode and an anode, said heatable cathodes of said amplifier and of said discharge tube being connected across said source in a series with electric resistance devices one or which is connected between the cathodes of the tubes; means in parallel with the cathode of said discharge tube for varying a discharge characteristic of said device; a photoelectric control device, said discharge device and said photoelectric control device being also connected in series across said source; a connection from the common connecting point of said photoelectric device and of said discharge device to the grid of. said amplifier; and an out put circuit connected across the anode of said amplifier and said source.

HEINRICH GEFFCKEN. HANS RICHTER.

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