US1919985A - Cathode ray oscillograph sweep circuit - Google Patents

Description

y 1933- F. G. PATTERSON 1,919,985

CATHODE RAY OSCILLOG'RAPH SWEEP CIRCUIT Filed July 23, 1931 Inventor: Franklin G. Patterson,

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Patented July 25,

II'UNITED STATES PATENT OFFICE FRANKLIN G. PATTERSON, OF. SCHENECTA DY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK CATHODE RAY OSCILLOGRAPH SWEEP OIRCUIT Application filed July 23, 1931.

My invention relates to cathode ray oscillographs and more particularly to a method and means for causing the image on the screen of such an oscillograph to appear stationary.

The cathode ray oscillograph as is well known by those skilled in the art, comprises a pair of plates at right angles toanother pair of plates with means for applying potentials to the plates for deflecting a beam of electrons in accordance with the electrical characteristics which are to be observed. In

order to get a stationary image of arecurring wave the electron beam must retrace the wave at definite intervals, thus causing the impression of a continuous stationary wave due to the persistence of vision. The retracing of the wave is accomplished by applying to one pair of plates a sweep voltage of such a character that the electron beam is moved in a plane at a uniform rate of speed in one direction and then moved in the same plane in the opposite direction very rapidly. The sweeping motion of the beam must obviously be properly synchronized with the incoming signal which is to be observed.

To guard against drifting of the image across the observation screen due to variations in sweep or signal frequency I lock the sweep voltage with the signal Wave so that the image will always start at the'same point thus insuring a clear stationary image of the phenomenon to'be observed.

The method of locking which I have adopted has no frequency limitations and can be used for the highest as well as for the lowest frequencies. As herein used the term high frequency will mean those frequencies substantially above 5000 cycles.

The invention will be more fully understood and further objects of the invention will appear from the following detailed description and claims taken in connection with the accompanying drawing in which Fig. 1 is a schematic representation of what I consider to be the best embodiment thereof and Fig. 2- is a representation of the rethe vo tage of the line.-

with the adjustable resistance 12. The

Serial No. 552,704.

The electrons which are to be deflected are produced by the cathode 13, this cathode being heated to various degrees of incandesccnce by means of the battery 11 in series anode 14 has a positive potential impressed on it by means of the battery 15. The electrons pass from the cathode to the anode at a very high rate of speed, and a portion of them continue through the'hole 10 in the anode between the deflecting plates 16 and 17-and the sweep plates 18 and 19. It will be understood that these elements are enclosed in a vacuum chamber 'not shown. The deflecting plates 16 and 17'are so. arranged as to cause the electrons to be deflected from their normal path toward these plates themselves and being connected across the lines 20 and 21, the voltage characteristics of which are to be observed, cause the electrons to move responsive to such characteristics.

The sweep plates 18 and 19 also cause the electrons to be deflected from their normal path toward these plates and the method of 75 doing this will be explained in detail. The sweep plates are connected across a saturated vacuum tube 22, the plate of which is positively biased by means of battery ,34. The degree of saturation of this tube can be regulated by means of a resistance 23 connected in its filament circuit. This vacuum tube in turn is connected across a variable condenser 25 which is periodically charged by means of oscillator 26 and periodically discharged by tube 22. The type of oscillator 26 is well known to those skilled in the art and consists essentially of vacuum tube 29, inductively coupled coils 31 and 32 and'the by-pass condenser 33. The operation of this oscillator will be described in so far as it is necessary to show its rela- .tion to my invention.

The oscillator charges condenser 25 until it becomes so negatively charged due to the electrons leaking to the grid 27 that the pacity of condenser 25 is about .007 microwhich causes the sweep lates 18 and 19 to sweep the beam at a uni orm rate. When a sufficient number of electrons have leaked off of grid 27, the grid 27 becomes sufficiently positive with respect to the cathode of tube 29 to allow the oscillator to start generating, thus charging the condenser 25 almost instantaneously. It will be obvious to those skilled in the'art that the charge and discharge voltage of condenser 25 will be essentially in the form of a saw tooth ware such as described in U. S. Patent No. 1,695,- 719 issued to Reinhold Rudenberg. Deeem ber 18, 1928, the frequency of which wave will hereinafter be called the sweep 'frequency. The means for generating such waves will accordingly hereafter be called the sweep frequency generator. In Fig. 2 I have shown such a sawtooth wave 40.

IVithout any means of locking the circuit the characteristics of which are to be ob served, with the saw tooth wave generator, the image will drift across the screen (not shown), due to variation of either sweep or incoming signal frequency. In order to insure that the image will start in the same phase relation for each cycle of operation I insertsvariable locking condenser 28 between line 21 and oscillation circuit 26 which by causing the waveof the incoming signal to be superimposed on the grid voltage will cause the oscillator to start or stop oscillating at a particular time which will be prior to the time the oscillator would have started or stopped respectively had condenser 28 not been inserted. The result is that for each cycle the sweep voltage is returned to its starting position at the instant required to trace the signal voltage in the same phase for each successive cycle. The locking effect of condenser 28 depends directly upon the ratlo of its capacity to the capacity of condenser 25; the greater thecapacity of condenser 28 in proportion to that of condenser 25 the greater will be the locking effect. Th s locking effect must be limited since. if it is too great, the image will be distorted. The sweep frequency is adjusted by means of changing the voltage of the filament of tube 22 and is further adjustable by means of variable condenser 25. In describing the operation of my device in greater detail I will refer to Fig. 2 in which 40 is the voltage curve of the charge and discharge of condenser 25 and 41 is the voltage of the incoming signal superimposed on the first mentioned voltage by means of condenser 28. The condenser 25 must have a large capacity as compared with condenser 28, and although various combinations can be used, I have found that my invention operates satisfactorily if the cafarads and that of condenser 28 is about .Q00125 microfarads.

Referring to Fig. 2 it can be seen that the charging of condenser 25 takes place very rapidly as exemplified by the curve between points 35 and 37. The discharge takes place relatively slowly at a constant rate as can be seen by noting the curve between points 37 and 38. The incoming wave 41 is of the recurrent type and as shown in the drawing the positive half of this wave is added to the wave 40 and at point 38 the resultant voltage on grid 27 becomes suiliciently positive at this point to enable the oscillator to start charging. This takes place again at point 42 and keeps the sawtooth wave and the recurrent wave locked or synchronized. The relationship of these waves can also be adjusted so that the negative half of the recurrent wave is added to the sawtooth Wave as the latter approaches its maximum negative value to stop the oscillator. By properly relating curves 40 and 41, both the starting and stopping of the oscillator can be caused by the recurrent wave.

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

1. In a cathode ray oscillograph the method of producing stationary images of recurrent alternating waves which consists in electrostatically locking the sweep frequency with the phenomena to be observed.

2. In combination with a circuit to be tested a cathode ray oscillograph comprising deflecting plates connected across said circuit, sweep plates, a sweep frequency generator connected across said sweep plates and condenser means in said circuit coupling said circuit to said frequency generator so arranged as to cause an image produced by the joint action of said sweep plates and said deflecting plates to appear stationary.

3. In combination with a circuit to be tested, a cathode ray oscillograph comprising an oscillation generator, a condenser arranged to be charged by said generator, a saturated vacuum tube through which said condenser discharges and condenser means responsive to the condition of said circuit to be tested to control said oscillation generator.

4. In combination with a circuit to be tested, a cathode ray oscillograph comprising an oscillation generator,, a. condenser periodically charged thereby, sweep plates which are influenced in accordance with the discharge of said condenser and condenser means influenced by the phenomena of said circuit to cause the charging of said condenser to start in the same phase relation to the frequency of said circuit for each cycle of operation.

5. In combination with a circuit to be tested a cathode ray oscillograph comprising deflecting plates connected across said circuit, a sweep frequency generator, condenser means coupling said circuit to said sweep frequency generator for controlling the latter and sweep plates so influence by said generator that an image of recurring phenomena of said circuit produced by the joint action of said sweep plates and said deflecting plates will appear stationary.

' 6. A cathode ray oscillograph comprising deflecting plates adapted to be energized by a voltage the characteristics of which are to be observed, a sweep frequency generator including a vacuum tube with a grid, and condenser means connected to be influenced by said voltage and to influence said grid to synchronize the frequency of said generator with the frequency of said voltage.

7. In combination with a circuit to be tested, a cathode ray oscillograph comprising an oscillation generator, a condenser periodically charged thereby, sweep plates which are influenced in accordance with the discharge of said condenser and condenser means influenced by the phenomena of said circuit to cause the operation of said generator to start in the same phase relation to the frequency of said circuit for each cycle of operation.

8. In combination with a circuit to be tested, a cathode ray oscillograph comprising an oscillation generator, a condenser pcriodically charged thereby, sweep plates which are influenced in accordance with the discharge of said condenser and condenser means influenced by the phenomena of said circuit to cause both the starting and stopping of said generator to take place in the same relation to the frequency of said circuit to be tested.

9. A cathode ray oscillograph comprising deflecting plates adapted to be energized by a voltage to be tested, sweep plates, a sweep frequency generator and condenser means adapted to couple said sweep frequency generator with said voltage to be tested to cause an image produced by the joint action of said sweep plates and said deflecting plates to'appear stationary.

10. A cathode ray oscillograph having deflection plates and sweep plates, means for producing a sweep voltage for ,the sweep plates comprising a vacuum tube oscillation generator, a condenser connected across the sweep plates and charged by said generator, means for discharging said condenser at a slower rate than the charging rate, means rcsponsive to a predetermined high voltage charge on said condenser for stopping the operation of said generator and to a predetermined lower voltage charge on said condenser for starting said generator and means responsive to an alternating voltage to be investigated for modifying said condenser voltage.

11. In combination with a source of signal voltage and a source of high frequency oscillations, a cathode ray oscillograph comprising deflecting plates influenced by said source of signal voltage, sweep plates influenced by said high frequency oscillations and means controlled by said signal voltage for synchronizing said high frequency oscillations with said signal Volta e.

FRANKLIN G. PATTERSON.

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