US2426208A - Cathode-ray tube control circuit - Google Patents

Description

' 'cATHoDE-RAY TUBE coN'rRoL lcrIRcUIT Filed may 28, 194sv 2 sheets-sheet 1 Y INVENToR. E FEA/E J /f/WPLY ATTORNEY R. J. HARDY 2,426,208 l Ag. ze, i947. R. J. HARDY 2,426,208

CATHODE-.RAY TUBE CONTROL CIRCUIT Filed May-28.' 1943 2 sheets-sheet y2 ./y f .J S i. Z E AK NM I 0 o I JJ TIME POTENTIAL Patented Aug. 26, 1947 Unire FHECE CATHODE-RAY TUBE CONTROL CIRCUIT Application May A28, 1943, Serial No. 488,873 In France December 28, 1940 (Cl. Z50- 27) l1 Claims. 1

The present invention refers to cathode-ray tube control circuits, and particularly to circuits for producing a circular scanning of the cathode beam on the fluorescent screen.

In numerous applications of cathode-ray tubes in measuring-instruments, it is particularly desirable to obtain a cathode-beam scanning that will follow an exactly circular path on the fluorescent or luminescent screen of the tube. This condition generally is obtained by means of two sinusoidal voltages in quadrature applied to the two pairs of plates or other deflecting-elements of the cathode-ray tube.

One method of applying these voltages in quadrature to the deilecting-elements of the tube is to use a collector device having rotating resistances and brushes, hereinafter termed resistance-collector, driven at the desired speed for the rotation of the cathode beam. The contacts of this collector are connected by sinusoidal-distribution resistances and the brushes, placed `at right angles with respect to each other, pick up voltages out of phase by 90 when the collector is rotating. The image obtained on the screen of the cathode-ray tube consists then in a succession of juxtaposed dots, roughly forming as a whole a circle that is defined to a larger or lesser extent depending upon the number of contacts, the quality of the resistances and of the contacts, and degree of wear, as also the uniformity of electrical values, hereinafter termed calibration, of each of them.

However, these collectors having resistances must generally comprise a relatively large number of contacts, this being for two main reasons. The rst is, that the greater the number of contacts, the greater the continuity of the circle on the screen of the cathode oscillograph, and the second is that the control of this circle, by radial or intensity modulation, for example, will be rendered all the more flexible, in proportion as the circle becomes more nearly continuous. It is, in fact, readily understandable that the luminous spot is displaced step by step as a function of the distribution of the contacts in the potentiometer and that the possibility of an additional modulation will be all the greater and the control more denite if the spot changes rapidly from position and covers a smaller interval of the circle. This is what has led to the designing of resistance-collectors having a large number of contacts, 300 to 400, for example.

'Howeven in proportion as the number of contacts increases, so does the number of needed resistances, and hence the diiliculty of calibration of the collector, because it becomes much more diiiicultto design small resistances calibrated with precision and to ensure a uniform Contact around the periphery of the collector the segments of which are too close together. In certain applications, moreover, it is desirable to have collectors of small size and consequently of small weight.

The present invention, therefore, has among its objects to provide resistance-collectors of the above-mentioned type having but a relatively small number of contacts and, hence, of calibrated resistances, while ensuring the appearance on the screen of the cathode-ray tube of aV practically continuous circle and allowing effective and convenient control, by radial modulation, for example, of the luminous spot describing this circle.

According to certain of its features, the invention provides a collector having sinusoidaldistribution resistances, for controlling the circular scanning of a cathode-ray oscillograph, which collector includes only a limited number of contacts and, hence, of resistance members, the brushes of the collector being connected to the deflecting-elements of the cathode-ray oscillograph via time-constant circuits that eliminate labrupt variations of the output voltages of the collector from contact to contact. It is clear, further, that the invention is not limited to sinusoidal-distribution collectors for providing a circular scanning on the screen of a cathode-ray oscillograph but can be applied to any other collector for controlling the appearance, by discontinuous displacements, of the luminous spot on the screen of an oscillograph, according to desired curves differing from the circle.

The invention will be explained in detail in the description thatfollows, given with reference to the accompanying drawings, in which:

Fig. 1 shows schematically lthe arrangement of the successive locations of the spot on the screen of a cathode-ray oscillograph as obtained with a collector having `an insuiiicient number of discrete segments, according to the prior art;

Fig. 2 shows in the same manner a portion of a desirable indication pattern on the screen of the oscillograph;

Fig. 3A shows a portion of an indication ypattern obtained by using a collector having a relatively large number of segments;

Fig. 3B shows an example of distortions of the indication of Fig. 3A resulting from difficulties of uniformity of calibration or fromthe wear of the resistances, in a collector having a large number of contacts;

Fig. 4 shows a portion of a collector having a relatively small number of contacts and incorporating features of the invention;

Figs. 5 and 6 are graphs showing voltage distributions for a collector of the prior art and a collector incorporating features of the invention, respectively;

Fig. 7 shows schematically an example of a control circuit for a collector incorporating features of the invention; and

Fig. 8 shows schematically one example of an embodiment of the circuit shown in Fig. 7.

In order to use cathode indicating-devices, for radio direction-finding, for example, it is often necessary to produce a circle through a displacement of the luminous spot on the screen in synchronism with a rotating member or element, a receiving-loop or a finder, for example. The screen of the cathode-ray tube must contain an indication such as that shown at L in Fig. 2. In fact, with a collector having resistances furnishing two voltages in quadrature to the pairs of deflecting elements of the oscillograph, an indication is obtained similar to that shown at M in Fig. l, the number of spots on the screen corresponding with the number of contacts and, hence, with the number of resistances of the rotating collector, because the spot advances from position to position practically instantaneously and stands at each position for the time the brushes of the collector remain on each segment.

The indication shown in Fig. 1 improves as the number of segments of the collector increases. In addition, it becomes more readily measurable as the number of segments increases,because the standing time of the spot at each position of the circle becomes shorter and because the spot thus controlled is displaced more uniformly in the direction normal to that of the radial modulation that must then be applied to the indicator in order to obtain the desired information. In the case of a collector having 48 segments, for example, the image on the screen of the oscillograph is such as shown in Fig. 1 and cannot therefore efficiently be deflected radially, because each contact already represents by itself an angle of '7.5". By raising the number of segments to between 300 to 400, for example, one increases the continuity of the luminous circle, which then appears as shown, for example, at N in Fig. 3A, where the successive spots are so close together and so short that they allow radial control in a manner nearly as eflicient as in the case of the continuous circle shown in Fig. 2.

In practice, instead of obtaining a suitable trace, such as that of Fig. 3A, a trace generally is obtained of the form shown at S in Fig. 3B; that is, the circle in which the successive spots should appear is distorted irregularly.

The image obtained on the screen of the cathode tube can be improved in order to obtain a more uniform appearance by means of certain arrangements of the invention thatv will now be described.

Fig. 4 shows schematically a portion of a rotating resistance-collector comprising sinusoidal-distribution resistances Rl, R2, R3, R4, etc., associated with segments VI, V2, V3, V4, etc., respectively, over which passes a brush shown schematically at D with its contact-holder and its` pressure springs.

Brush D passes successively over segments VI to V4, which gives a voltage that varies in the manner indicated in Fig. 5, where the voltages are designated by the same reference numbers as the studs. If the resistances are given a suitable sinusoidal distribution, the curve obtained will be shown at A in Fig. 6, which corresponds to a curve at successive points if two brushes at from each other are taken and are connected respectively to the pairs of deflecting-plates of the cathode oscillograph.

According to one embodiment of the invention, a retardation circuit of suitable time constant,

constituted for example by a resistance R and a capacity C, is inserted between brush D and its output. Capacity C is charged in parallel, and series-resistance R provides the charging delay of that capacity. A voltage U thus is obtained that varies more or less sinusoidally around the collector. When the compensation is insuicient, a voltage curve is obtained having substantially the form shown at B in Fig. 6; but with high values of R.-C., it will approximate curve C of Fig. 6, i. e., a substantially sinusoidal curve, which will give on the cathode-tube screen a circle without appreciable distortion, and Without gaps, similar to circle L of Fig. 2.

A practical arrangement of such a resistancecollector is shown schematically by way of eX- ample in Fig. 7. The resistances and the segments are not shown in detail, but they are indicated as a whole at Q, because any well-known mechanical collector-arrangement can be used, but each brush DI to D4 is provided with a connection leading to an output terminal SI to S4 together with a retardation circuit constituted by resistances Rl to R4 and capacities CI to C4, all preferably of the same electrical Value. Output terminals SI, S2 and S3, S4 are connected respectively to the pairs of deecting-elements of the cathode-ray indicating oscillograph (not shown). This circuit is rendered symmetrical by a common connection to the mid-point of the respective connections between the condensers of each group CI-CZ and C3-C4. Potentiometers R5, R6 allow adjusting the values to be applied to each pair of deflecting-plates in order to obtain a regular circle or a figure of any desired degree of ellipticity.

It is clear that any inductance or any complex circuit, such as articial lines, or other types of ltering-circuits that are suitable, according to the frequencies desired, can be employed, an advantage of the invention being the provision of a voltage variation equal to the mean variation. of the voltages of the successive contacts of a suitable collector supplied by a source of direct or alternating current.

In one embodiment of a 48-segment collector according to the present invention, this collector rotated at 4 revolutions per second and sinusoidal-distribution resistances and retardation circuits were inserted in each branch. The resistances were designed and calibrated within only about 3%. With a time constant T=R.C. of 10,000 milliseconds, the circle obtained was even then very regular.

Fig. 8 shows an example of application of the collector arrangement of Fig. 7 to a circuit suit-- able particularly for the production of two scanning current sinusoids to provide a circular deflection of the beam of a cathode-ray indicator, for example such as those used in radio direction-ndersl The collector Q,4 which is of the type of Figs. 4 and 6, described above, is supplied by means of a voltaic cell P or other power source by two diametrically opposite contacts. Over brushes DI to D4 are picked up composite voltages constituted by voltage peaks determined at each segment but giving a sinusoidal voltage due to timeeconstant circuits Ri, C i-RZ, C2--R3, CB-RIS, C4. The current sinusoids obtained at terminals GI, G2 and G3, Gli or potentiometers R5 and R6 are respectively displaced by 90. The common return N is supplied by the deflection voltage E to be measured on a cathode ray tube, at the terminals of a charging-resistance R1.

The voltages at terminals Gl to Gli are applied respectively to the control grids M, i5, I, H of triode or pentode tubes, which are shown in the form of two dual function tubes L! and L2. It is the output plate-voltages of these tubes that are applied directly to the deecting-plates Pm, Px and P1 Py of the cathode-ray indicator (not shown), in order to produce the circular deflection of the spot on the screen of this indicator, at the same time as the desired indication by radial deection, due to the variable voltage applied at E.

It is obvious that the invention is not limited to the embodiment examples shown and described but that on the contrary it is capable of many modifications and applications within the scope of the hereunto appended claims.

I claim:

1. Cathode ray tube sweep control device including a resistance in circular form, means for feeding potential thereto a't points substantially 180 apart, a plurality of segments connected to points spaced along said resistance to form a commutator, brushes spaced substantially 90 apart and making contact with said segments, means for rotating said commutator, and a time delay circuit connected in the output lead from each brush, whereby discontinuous current impulses derived from said segments are smoothed out.

2. Device according to claim 1, in which each of said time delay circuits includes a resistance and condenser in series between each brush and ground respectively with a delayed output connection being taken across the condenser.

3. Device according to claim 1, in which each of said time delay circuits includes a resistance and condenser in series between each brush and ground respectively with a delayed output connection being taken across the condenser and the potential supplied to said first named resistance being direct current, whereby sinusoidal output current is obtained therefrom.

4. Device according to claim 1, in which said segments are relatively few in number and said time delay circuits have such time constants in comparison to the number of segments and the speed of rotation of said commutator as to maintain a relatively continuous sweep control current.

5. Device according to claim 1, also including a plurality of electronic tubes, each having two grids and two anodes, each opposite pair of brushes being connected via said time delay circuits to the two control grids of one tube, and means for connecting the anodes of said tube to deflection elements determining deection in one direction of a cathode ray tube.

6. Device according to claim 1, in which each time delay circuit includes a series resistor, including two condensers, each connected at one terminal to the output end of a resistor and joined together at the other terminals, a potentiometer shunted across the output of two time delay circuits proceeding from brushes substantially 180 apart, and connections from the common junction of said condensers to the tap of said potentiometer and to ground.

7. Cathode ray tube sweep circuit power supply device, including a resistance in circular form, means for rotating said resistance, slip rings rotating therewith, brushes resting on said slip rings and means for feeding direct current thereto, said slip rings being connected to points on said resistance substantially 180 apart, segments connected to predetermined points along said resistance, brushes bearing on said segments at points substantially apart, a iilter circuit connected to each pair of brushes, a dual electronic tube having two grids and two anodes, connections from the output of each filter so as to shunt both said grids, a potentiometer also shun-ted across said grids, a resistor connected to the tap of said potentiometer at one terminal and grounded at the other terminal, means for supplying deflection signals to said resistor and means for withdrawing from said anodes of said tube combined sweep and deflection signals.

8. A cathode ray tube sweep control system including a closed resistance loop, a plurality of contact members connected to points spaced along said resistance loop, said members being disposed to form a commutator, means for applying potential to said loop at points spaced degrees apart, brushes spaced substantially 90 degrees apart contacting said commutator, means for rotating said commutator, and a time delay circuit connected in the output lead from each brush, whereby discontinuous current impulses derived from said commutator are smoothed out.

9. The system of claim 8 wherein a time delay circuit consists of a resistance and reactance combination having an exponential voltage change characteristic.

10. The system of claim 8 wherein a time delay circuit includes a resistance and condenser in series between a brush and ground respectively with a delayed output connection across each condenser.

11. The system of claim 8 wherein said potential is a direct current and wherein a time delay circuit includes a resistance and condenser in series between a brush and ground respectively with a delayed output connection across the condenser whereby commutator ripples are smoothed out to provide a substantially sinusoidal output.

RENE' JEAN HARDY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,151,917 Hyland Mar. 28, 1939 2,237,604 Marique Apr. 8, 1941 2,226,990 Schlesinger Dec. 31, 1940

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