US2747135A

US2747135A - Apparatus for producing a rotating time base display

Info

Publication number: US2747135A
Application number: US377096A
Authority: US
Inventors: John F Mccoy
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-08-28
Filing date: 1953-08-28
Publication date: 1956-05-22
Anticipated expiration: 1973-05-22

Description

.1. F. MCCOY 2,747,135

APPARATUS FOR PRODUCING A ROTATING TIME BASE DISPLAY 2 Sheets-Sheet l IN1/E NTOR. F.. M 'E E U Y .JUHN

ATTORNEY mw @L l MN may 22, 1956 Filed Aug. 28, 1953 J. F. MCCOY May 2z, 1956 APPARATUS FOR PRODUCING A ROTATING TIME BASE DISPLAY Filed Aug. 28,` 1953 2 Sheets-Shea?. 2

ATTORNEY United States Patent() APPARATUS FOR PRODUCING A ROTATING TllVIE BASE DISPLAY John F. McCoy, Haddonfeld, N. J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 2s, 1953, serial No. 377,096 7 Claims. (Cl. 315-24) This invention relates generally to apparatus for producing a rotating time base display on a cathode ray tube. More particularly, the invention relates to apparatus for producing a rotating time base display on a cathode ray tube, using a sine-cosine potentiometer as a resolver. While neither specifically nor exclusively limited thereto, the apparatus of the present invention is particularly useful in radar apparatus of the type employing relatively slow moving, mechanical systems for indicating instantaneously and continuously the azimuth and the elevation of objects.

It has been proposed previously to use the sine-cosine potentiometer as a resolver in apparatus for producing a rotating time base display on a cathode ray tube. Circuity for such apparatus is described in the book Cathode Ray Tube Displays, MIT Radiation Laboratory Series, volume 22, page 451, published by McGraw-Hill Book Company, Incorporated, New York, N. Y., 1948. This prior art apparatus uses two power supplies offset with respect to ground in order to produce a zero voltage across the sine-cosine potentiometer during the wait time. Each of the power supplies provides operating potentials for a separate, associated saw-tooth generator. The output voltages of each saw-tooth generator are applied to the ends of the sine-cosine potentiometer, respectively. The resistor of the sine-cosine potentiometer is rotated and four brushes spaced 90 apart on a circle of rotation on the rotating resistor, take ofi four voltages, respectively, whose instantaneous peak amplitudes depend on the instantaneous positions of the brushes on the rotating resistor. Voltages from two pairs of alternate brushes are fed to the horizontal and vertical deflection electrodes of a cathode ray tube. The particular construction of the sine-cosine potentiometer is also described on page 202 of the aforementioned book. v

It is a principal object of the present invention to provide improved apparatus for producing a rotating time base display on a cathode ray tube.

It is a further object of the present invention to provide improved apparatus for producing a rotating time base display on a cathode ray tube, that will require fewer components than the prior art apparatus for accomplishing the same purpose.

It is still a further object of the present invention to provide improved apparatus for producing a rotating time base display, for a cathode ray tube, that may be used in radar apparatus employing low frequenecy saw-tooth waves and detlectioncircuits that have good low frequency responses.

Another object of the present invention is to provide improved apparatus for producing a rotating time base display, on a cathode ray tube, which is simple in construction, uses fewer components than prior art apparatus, and is highly efficient in use.

These and further objects of the present invention are attained in improved apparatus using a sine-cosine potentiometer as a resolver, for producing a rotating time base display on a cathode ray tube. Briey, the output ICC of a saw-tooth generator is applied to the input of a phase-splitter which may be a push-pull paraphase amplitier. The output of the phase-splitter is fed push-pull to a pair of push-pull vcathode followers. The ends of a sine-cosine potentiometer are connected to the cathodes of the push-pull cathode followers, respectively. Each of a pair of sliding contacts or brushes, spaced apart on the circle of rotation of the sine-cosine potentiometer resistor, picks ofi voltages which vary from a maximum peak voltage of one polarity, through zero, to a maximum peak yvoltage of an opposite polarity. The voltages picked off by the brushes are fed to horizontal and vertical deilection amplifiers, respectfully. The output voltages of the deflection amplifiers are then fed to the deection plates of the `cathode ray tube. The rotating time base display on the cathode ray tube is thatof a trace in the form of a diameter of a circle on the face of the tube, revolving about its mid-point. Should enough drive be available at the brushes of the sine-cosine potentiometer, the output voltages from four brushes could then be applied directly to the deflection plates of the cathode ray tube, and the horizontal and vertical amplifiers could be eliminated. In the latter case, four brushes placed 90 apart with respect to the circle of rotation of the potentiometer resistance would be employed.

The novel features of the present invention, as well as the invention itself, both as to its organization and method ot' operation, will be understood in detail from the following description when considered in connection with the accompanying drawings in which Fig. l is a schematic diagram partly in block diagram form, of apparatus for producing a rotating time base display on a cathode ray tube, in accordance with the invention; and Fig. 2 is a schematic diagram, partly in block diagram form, of av modified form of the invention illustrated in Fig. l.

Referring now to Fig. 1 of the drawings, there is shown apparatus for producing a rotating time base display on the face of a cathode ray tube 10. The apparatus comprises an alternating voltage generator, such as a saw-tooth generator 12, of conventional design, adapted to produce at its output a saw-tooth voltage, as shown by the waveform 14. The saw-tooth output voltage of the saw-tooth generator 12 may be of a relatively low frequency, say in the order of about 30 cycles per second, as encountered in certain radar applications. The saw-tooth output voltage of the saw-tooth generator 12 is applied to the input of a phase-splitter 16 which may be of the push-pull paraphase amplifier type. The out-v put saw-tooth voltage from the phase-splitter 16 is applied in push-pull to the grids of two electron discharge devices, vacuum tubes 13 and 20, respectively, through output capacitors 22 and 24, respectively. The anodes of the tubes 1S and 20 are connected to each other, and to a source of operatingvoltage (not shown). The cathode of the tube 18 is connected to ground through resistors 26 and 23; and the cathode of the tube 20 is connected to ground through resistors 30 and 32.

While the tubes 18 and 20 are shown as two separate tubes, it is understood that they may be a duotriode within a single envelope, such as a type 5687 duotriode tube. The tubes 18 and 20 and their operating points should be chosen to produce a high degree of linearity in their output.

The resistor 26 should be equal to the resistance 30,

and the resistance 28 should be equal to the resistance 32.

lf conduction through the tubes 18 and 20, under these circumstances is not equal, means well known in the art may be used to vary these resistors so that conduction through the tubes 18 and 20 will be equalized. The grid of the tube 18 is connected to the junction of the resistors 26 and 28, through a grid leak resistor 34; and the grid 3 of the tube 20 is connected to the junction of the resistors 3U 'd 32, through grid leak resistor 36.

A sine-cosine potentiometer 38, of the type described in the aforementioned book, comprises a resistor 4t) in the form 'ofa wire wound Ion a 'square sheet of insulating material 42, such' as akelite. One end of the resistor 40 is connected to the cathode of the tube 1S through a Contact brush 44 which rides on a ring 46, illustrated in part by a curved, dashed line, attached to one end of the resistor 40. The other end of the resistor 4i) is connected to the cathode of the tube 20 through a Contact brush 48y in sliding contact `with a ring 50, illustrated in part by a curved, *dashed line. The resistor 40 of the sinecosine potentiometer 3g is adapted to be rotated about an axis perpendicular to the'4 insulating material 42, at its center JS2. Brushes 54, 56,58 and 60 of the potentiomet`er138 are positioned 90 from each other on a circle of rotation 62. The circle of rotation 62 represents bare portions of'L the wire of the resistor 46, and the brushes 54, 56, 58 and 60 are in slideable contact therewith.

An important feature of the present invention is the D. C. voltage across the resistor 4l) of the sine-cosine potentiometer 38 is zero at all times. It is this condition which permits the use of the circuit of the present invention with low frequency saw-tooth voltages and low frequency response deflection amplifiers. It is noted that if a difference of D. C. potential were to appear across the ends of resistor 40,` the rotating time base display on the cathode ray tube would wobble.

In a preferred embodiment of the present invention, the output voltages from the two brushes S4 and 56, spaced 90 apart on the circle of rotation 62 of the sinecosine potentiometer 3S,- are fed to horizontal and vertical deflection amplifiers 64 and 66, respectively. The horizontal and vertical amplifiers 64 and 66 are of the push-pull paraphase amplifier type, well known in the art; each amplifier producing at its output voltages in push-pull relationship for application to the deflection controls or plates of a cathode ray tube. The horizontal deflection amplifier 64 has its output connected across the horizontal deflection plates 68 and 70 of the cathode ray tube 10; and the vertical deflection amplifier 66 has its output connected in push-pull to the vertical deflection plates 72 and 74 of the cathode ray tube 10. Since the apparatus of the present invention is particularly applicable for producing rotating time base displays whose time bases are a' relatively long time duration, say onethirtieth of a second, the horizontal and vertical deflection amplifiers V64 and 66 are designed to have a relatively good low frequency response.

The operation of the' apparatus for producing the rotating'` time base display will now be described. The output saw-tooth wave 14 of the saw-tooth generator 12 is fed to the input of the phase-splitter 16. The amplified sawtooth voltages at the outputs of the phase splitter 16 are applied in push-pull to the grids of the cathode followers 18 and 20', connected in push-pull circuit. The inputs to the grids of the cathode followers 155 and 20 are shown as

waveforms

76 and 78, which are' equal in magnitude but of opposite polarity.

In order Ato produce a rotating time base display on the cathode ray tube 10 inthe form of a trace of a diameter line'ro'tat'in'g about its center, it is necessary to provide one set of deflection plates with saw-tooth voltages whose peak-to-peakamplitudes vary as a sine function, and the other set of deflection plates with a set of saw-tooth v'oltages whose peak-to-peak amplitudes vary as a cosine function. To this end,.the resistor 4t) isrotated substantially in the plane of the insulating material 42 about its center 52, by any's'uitable means (not shown). The voltage picked offby any on'e brush, such as the brush 54', in slideable contact with the circle of rotation' 62 on the resist-ance 40,-v will be a voltage whose amplitude varies sinusoidally from a mixinium o'f one polarity, through 4 zero, to a maximum of the opposite polarity. The voltage deivd at the ct't' briisl 56 will va'y iii a siila' manner but will be related to the voltage at the brush 54 in a quadrature relationship. In other words, when the brush 54 is adjacent one end of the resistor 40 a positive-going saw-toothvoltage of maximum amplitude will be derived. After the resistance has rotated this voltage will be reduced in amplitude to zero. Rotating the resistance 90 more in the same direction will result in a negative-going Asaw-tooth voltageat the brush 54,` and rotating the resistance another 90" will result in the voltage at the brush 54- ietu'rning to zero.

It is important that no D. C. voltage appear across the resistor 40. For example, a D. C. voltmeter connected across the brushes 44 and 48 should read zero at all times. if this were not so, a low frequency sinusoidal voltage would be picked off by the brushes 54 to 60, as the resistor 40 rotates, and provide the deflection electrodes 68 to 74 with voltages that willJ cause `the trace 80 on the face of the cathode ray tube 10 to wobble instead of rotating` about its center.

i ln the preferred embodiment of the present invention, the voltages picked off by` the brushes 54 and 56 of the sine-cosine potentiometer 38 are applied to thedeflection plates of the cathode ray tube 10' through the horizontal and vertical deflection amplifiers 64 and 66. However, the horizontal and vertical amplifiers 64 and 66 could be eliminated if enough drive is available at the brushes 54 to 60 of the potentiometer 38. in the latter embodiment, shown in Fig. 2, the brushes 54, 56, 5 8 and 60 of the sine-cosine potentiometer are connected directly to the deflection electrodes 68, 74, 72 and 70, respectively, ofthe cathode ray tube 10.

Thus, there has been s hownv and described in accordance with the objects of the present invention, highly improved apparatus for producing a rotating time base display on a cathode ray tube. The apparatus of the present invention uses fewer components for accomplishing the same purpose as prior art apparatus, and provides a unique arrangement for maintaining a zero D. C. potential across the resistor of the sine-cosine potentiometer at all times. Because of this latter feature, the apparatus of the present invention is particularly adaptable for use with relatively low frequency saw-tooth voltages and the lo,I frequency-response deflection amplifiers used therewith.

What is claimed is:

l'. Apparatus for producing a rotating time base display on a cathode ray tube having deflection means, said apparatus comprising means to produce an alternating voltage, phase-splitting means connected to said alternating voltage producing means to produce push-pull alternating output voltages, a push-pull cathode follower circuit comprising a pair of vacuum tubes each having an anode, a grid and a cathode, a sine-cosine potentiometer having a rotatable resistor, means connecting said rotatable' resistor between the cathodes of said pair of vacuum tubes, a plurality of bmshes in slideable contact with said resistor, means coupled to said grids to apply saidV pushpull alternating output voltages thereto, and means connecting said brushes to said deflection means of said cathode ray tube.

2. Apparatus forv producing a rotating time base display on aV cathode ray tube having deflection means, said apparatus comprising `means to produce an alternating voltage, phase-splitting means connected to said alternating' voltage producing means to produce push-pull alternating output voltages, a push-pull cathode follower circuit comprising a p'air of vacuum tubes each having an anode, a grid and a cathode, a sine-cosine potentiometer having a resistor rotatable in a circle of rotation, means connecting said rotatable resistor between the cathodes of said pair of vacuum tubes, a plurality of brushes in slideable Contact withsaidl resistor, means coupled to said grids: to apply said push-pull alternatingoutput voltages thereto, and means connecting said brushes to said deflection means of said cathode ray tube, said means to produce an alternating voltage comprising a saw-tooth generator.

3. Apparatus for producing a rotating time base display on a cathode ray tube having deiiection means, said apparatus comprising means to produce an alternating voltage, phase-splitting means connected to said alternating voltage producing means to produce push-pull alternating output voltages, a push-pull cathode follower circuit comprising a pair of vacuum tubes each having an anode, a grid and a cathode, a sine-cosine potentiometer having a resistor rotatable in a circle of rotation, means connecting said rotatable resistor between the cathodes of said pair of vacuum tubes, a plurality of brushes in slideable contact with said resistor, means coupled to said grids to apply said push-pull alternating output voltages thereto, and means connecting said brushes to said detlection means of said cathode ray tube, said plurality of brushes comprising four brushes spaced 90 from each other on said circle of rotation of said resistor.

4. Apparatus for producing a rotating time base display on a cathode ray tube having deflection means, said apparatus comprising means to produce an alternating voltage, phase-splitting means connected to said alternating voltage producing means to produce push-pull alternating output voltages, a push-pull cathode follower circuit comprising a pair of vacuum tubes each having an anode, a grid and a cathode, a sine-cosine potentiometer having a resistor rotatable in a circle of rotation, means n connecting said rotatable resistor between the cathodes of said pair of vacuum tubes, a plurality of brushes in slideable Contact with said resistor, means coupled to said grids to apply said push-pull alternating output voltages thereto, means connecting said brushes to said dellection means of said cathode ray tube, said plurality of brushes comprising two brushes spaced 90 from each other on said circle of rotation of said resistor, and said means connecting said brushes to said deflection means including push-pull horizontal and vertical deflection ampliliers connected between said brushes respectively and said cathode ray tube.

5. Apparatus for producing a rotating time base display on a cathode ray tube having horizontal and vertical delection electrodes, said apparatus comprising a saw-tooth generator, a phase-splitter connected to said generator whereby to provide a push-pull output voltage, a cathode follower circuit comprising two electron discharge devices each having a grid, and a cathode, means to couple said push-pull output voltage in push-pull to said grids of said devices, a sine-cosine potentiometer having a resistor rotatable in a circle of rotation, means connecting said rotatable resistor between the cathodes of said devices, a plurality of brushes in slideable contact with said rotatable resistor on said circle of rotation, selected ones of said brushes being connected to selected ones of said horizontal and vertical electrodes.

6, Apparatus for producing a rotating time base display on a cathode ray tube having horizontal and vertical dellection electrodes, said apparatus comprising a sawtooth generator, a phase-splitter connected to said generator whcreby to provide a push-pull output voltage, a cathode follower circuit comprising two electron discharge devices each having a grid, and a cathode, means to couple said push-pull output voltage in push-pull to said grids of said devices, a sine-cosine potentiometer having a resistor rotatable in a circle of rotation, means connecting said rotatable resistor between the cathodes or said devices, four brushes in slideable contact with said rotatable resistor spaced apart on said circle of rotation, and means connecting pairs of alternately spaced brushes to said horizontal and vertical deflection electrodes, respectively.

7. Apparatus for producing a rotating time base display on a cathode ray tube having horizontal and vertical delection electrodes, said apparatus comprising a saw-tooth generator, a phase-splitter connected to said generator whereby to provide a push-pull output voltage, a cathode follower circuit comprising two electron discharge devices each having a grid, and a cathode, means to couple said push-pull output voltage in push-pull to said grids to said devices, a sine-cosine potentiometer having a resistor rotatable in a circle or" rotation, means connecting said rotatable resistor between the cathodes of said devices, a horizontal and a vertical del'lection amplifier, a pair of brushes in slideable contact with said rotatable resistor each spaced 90 with respect to the other on said circle of rotation, means connecting said horizontal amplier between one of said brushes and said horizontal deflection electrodes, and means connecting said vertical amplier between the other of said brushes and said vertical dellection electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,030 De Ryder Nov. 12, 1946 2,474,177 Wild June 21, 1949 2,575,477 Weimer Nov. 20, 1951 2,637,026 Koehler a- Apr. 28, 1953 2,660,691 Bertram Nov. 24, 1953