US2627036A - Photorelay circuit - Google Patents

Description

Jan. 27, 1953 N. D. GLYPTIS PHOTORELAY CIRCUIT Filed March 25, 1948 \\g l S Patented Jan. 27, 1953 UNITED STATES PATENT OFFICE PHOTORELAY CIRCUIT Nicholas D. Glyptis, Chicago, Ill.

Application March 25, 1948, Serial N o. 17,016

2 Claims. l

This invention relates to a photo-relay circuit that comprises a photoelectric cell and a cooperating rectier tube. The photoelectric cell is a gas iilled tube wherein conduction is produced by ionization of the gas. It has a cathode adapted to emit electrons in proportion to the intensity of light directed thereto, and it has an anode for collecting electrons that are attached thereto by reason of the anode potential.

Whenever` a negatively charged conducting surface is placed in an atmosphere of an ionizable gas such as mercury vapor or one of the rare gases, electrons are emitted by the surface having a Fermi-Dirac velocity distribution, which electrons are accelerated depending on the applied electric eld.

These electrons travel a relatively short distance until an ionizing collision with a gas atom occurs. When an electron having suilicient kinetic energy passes through matter, it disrupts the atoms that it strikes by reason of the initial trajectory forces present which are converted to short range electrical forces when the electron trajectory is within the vcollision cross section of the encountering gas atom. If the material is gaseous, the resulting fragments or ions may move apart and, if there is an electric eld present., the electrons knocked out of the atoms move in one direction and the residual positive ions move in another direction. Since each ionization process gives Iboth a positive ion and one or more electrons, the whole process is similar to an avalanche, the only limitation being that the kinetic energy or velocity of the electrons produced as an atom is ionized is less than or equal to that of the incident electron.

The output of an ionization type or photocell is dependent on the number of electrons striking the anode, and, if this number can be increased the output of the tube or cell is proportionally increased. In a gas-filled tube the number of electrons striking the anode depends not only on the original number of electrons emitted by the cathode but on the number of ionizing, electron producing collisions which occur. One method of increasing the number of collisions is to increase the length of the path of electrons from the cathode to the anode. This may be done by building a larger tube with greater spacing between the electrodes which is prohibitive.

One object of this invention is, therefore, to increase the length of the electron path from cathode to anode in a. gas-lled tube or cell y (Cl. Z50-214) without changing the spacing of the electrodes.

Another object is to subject a gas-nlled tube to a magnetic eld to cause a deflection of the electron path from a straight line.

A further object is to increase the sensitivity of current output of a given tube by providing an alternating magnetic eld having a sinusoidal wave form so as to impose on the owing electrons forces which cause them to follow helical rather than straight line paths.

Other and additional objects and advantages of this invention will of course present themselves to those familiar with the art on reading the following specification in conjunction with the drawings and the appended claims.

In the drawings:

Fig. 1 is a schematic view showing a photoelectric tube and relay circuit in which the photocell is used in an optical balance comparator system;

Fig. 2 is a perspective view showing one form of coil which may be used in conjunction with a photocell.

As has been stated, the basic principle of this invention is to increase the sensitivity or current output of a gas-lled photocell or other tube by subjecting the space Ibetween the anode and cathode to a magnetic eld to bring about a deflection of electrons moving from one to the other and thereby increase the length of the ionization path. This increase in the path length brings a corresponding increase in the number of ionizing collisions between electrons and gas atoms to raise the output current of the tube or cell and increase the eiciency.

A preferred embodiment of this invention is shown in Fig. 1. A photo-emissive cell I0 is mounted so as to receive light from two mirrors II and I2, the mirror II being concave and having an opening in its center through which passes light from the mirror I2. Both mirrors are focused on the cathode surface I3 of the cell I0. Thus two separate beams of light I5 and I6 represented by arrows are simultaneously focused on the electron emitting surface of the cell I 0.

The cathode I3 is connected by a conductor I'I through resistors I8 and I9 to the grid 20 of a trigger tube 2 I, and through resistor I9 only to the variable tap on a potentiometer 22 connected between a pair of fixed resistors 23 and 24 across a 110 volt. A. C. line.

The anode Ill of the photocell I!) is connected by a conductor 25 to one side 2S of the line. The cathode 28 of the trigger or relay tube 2| is connected to the same side of the line as the anode I4 through the resistors 23 and 29 by a conductor 38. The opposite side 2'I of the line is connected through the relay or load coil 3| to the plate 32 of the tube 2|.

As thus far described the circuit is substantially the same as conventional A. C. photocell relay circuits. However, the filament supply arrangement is novel in that a special filament transformer 33 is mounted proximate to the photocell III so that a magnetic field is impressed across the photocell in the space between the anode I4 and cathode I3. The laminated core 34 of the transformer 33 is U-shaped and terminates in two opposed poles 35 and 36 disposed on either side of the cell III. connected directly across the line, and the secondary winding 38 is connected to the filament 40 of the tube 2|. For purposes of simplicity the two windings 3'I and 38 are shown as being separated from one another. that they be coaxial, one superimposed on top of the other on the top portion of the core as viewed in Fig. 1.

In one embodiment which proved quite satisfactory a #2050 grid 4controlled rectier tube was connected to the photocell I through a 10 megohm resistor. The resistor 24 had a value of 4 megohms and the variable resistor 22, and the other resistor 23 had values of 2 megohms each. The operation of the cell and relay circuit when the cell is used as a comparator is as follows: A beam of light of unknown intensity indicated at IIS is reflected on the sensitive cathode |3. A variable beam of known intensity indicated at I5 is also reflected on the surface I3. Alternating current is then applied to the line conductors 23 and 2l. Since the resistors 22, 23 and 24 are connected in series across the line, an alternating voltage less than that of the line voltage is applied between the anode I4 and the cathode I3 of the cell I0. Similarly an alternating voltage is applied between the anode 32 and cathode 28 of thegrid controlled rectifier tube 2|.

Both the photocell I3 and the tube 2| behave as rectiers and therefore only function during the half of the alternating current cycle when their anodes are positively charged. Since the grid is connected to the potentiometer 22 and to the cathode I3 of the cell I8 its potential is at all times less than that of the plate 32 and varies according to the amount .of current passing through the tube I0.

The tube 2| being a gas-lled rectifier behaves more or less as a trigger as the grid potential rises. As this potential rises, proportionately more plate current flows until the electron current has sufficient velocity and intensity to ionize the gas within the tube. When this value is reached the plate current suddenly increases to full value.

Thus when the potentiometer 22 has been adjusted to the proper position the tube 2| responds to very slight changes in the amount of light falling on the photocell lil to pass a relatively large current at one light intensity and to pass only a very small current at a slightly different intensity.

Since the plate current must ow through the relay coil 3|, the relay (not shown). which is adjusted to be actuated at full plate current, is responsive to changes in the intensity of light striking the photocell Ill.

When the apparatus is used as a comparator, the unknown light beam I6 is focused on the cell I0 and the intensity of the known variable beam I5 is gradually increased until a critical value is Actually it is preferred z The primary winding 31 is 1,;

reached and the maximum plate current flows through the relay coil 3| to operate a signal. Since the light intensity at which the circuit is preset to respond is known, as is the intensity of the variable beam at the moment the signal gave an indication, it is but a simple calculation to determine the intensity of the unknown beam.

The sensitivity of the photocell I0 itself is increased greatly by the mounting of the filament transformer 33 adjacent the cell I0 so that a transverse magnetic eld is applied between the anode I4 and the cathode I3. As has been described heretofore, this eld causes electrons emitted from the cathode to follow a spiral path as inuenced by the alternating magnetic field and the electrostatic eld within the cell. Since this path is substantially longer than the straight line path between anode and cathode the number of ionizing collisions is greatly increased due to the magnetic eld. The increase in ionization collisions causes a corresponding increase in the current passed by the cell I, which current controls the potential of the grid 2U in the trigger tube 2|. This makes possible greater variation due to light changes in the grid potential possible with a given photocell in a magnetic field over that of the same tube not subjected to that field.

Another novel feature of this circuit is the use of the resistor I8 in the grid circuit. |This resistor which may have a value of from one to five megohms serves to prevent damage to the photocell I0 when the trigger tube 2| fires. When the potential on the grid 20 becomes sufficiently high to cause ionization of the gas in the tube 2|. electrons travel from the cathode 28 to the grid 20. Without the relatively high resistor I8 a high voltage above the ionization potential of the cell IE] would be applied across the cell I causing a glow discharge and damage to the electrodes. However the resistor I8, because the grid current is relatively heavy when the tube 2U has fired, introduces an IR drop in the circuit which prevents a high potential reaching the cell I0.

In Fig. 2 an embodiment at one coil form for use with a photocell I0 is shown. This sort of coil may be directly connected to a source of a1- ternating current, pulsating direct current or to nonpulsating current. The coil may be mounted outside the glass envelope of the cell Ill or may be mounted within so as to be closer to the cathode I3. To substitute such a coil arrangement in the circuit of Fig. 1, a conventional filament transformer is preferably substituted for the one shown, and the coil 4I] is mounted in its place, being connected across the line through a suitable transformer to supply the proper voltage.

The fundamental principle yof this invention may be employed to improve the performance of many other types of aparatus among them Thyratron tubes, glow tubes, ignitrons, Geiger- Mueller counters, and rectiers, where electrons are emitted by a surface to ionize gas atoms and produce additional electrons which successively ionize other atoms as .they travely toward an anode surface.'

Where electromagnets or coils are employed, the choice of What type of current is to be supplied to the coil is often governed by the use to which the tube or cell is put. For example, when an amplier tube in the audio stage of an amplifier is to be subjected to a magnetic eld, if an oscillating current is employed the frequency of oscillation should be above the audible range.

In some instances where it was desired to use a simple tube as a mixer, one of the signals to be mixed was applied to the control grid of the tube while the other, suitably amplied, was applied to the external magnetic coil. Thus the output current of the tube was controlled by two variables.

Other changes and modifications in the apparatus and method of this invention will of course present themselves to those familiar with the art and may be made without departing from the spirit of this invention whose scope is dened by the following claims.

What is claimed is:

1. In a photo-relay circuit the combination including an ionizable gas-filled photocell, a grid controlled rectier tube, means for impressing voltages across said cell and said tube, a conductor connecting the grid of said tube to the cathode of said cell, and a ilament transformer for said tube, said transformer being mounted adjacent said photocell to produce an oscillating magnetic iield between the anode and cathode of said cell.

2. In a photo-relay circuit the combination including an ionizable gas-lled photocell, a grid controlled rectifier tube, and a filament transformer for said tube, said transformer being mounted adjacent said photocell to produce an oscillating magnetic field between the electrodes of said cell.

NICHOLAS D. GLYPI'IS.

REFERENCES CITED The following references are of record in the

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