US3206633A - Intensity control for oscilloscope display - Google Patents

Description

B. R. JONES INTENSITY CONTROL FOR OSCILLOSGOPE DISPLAY Sept. 14, 1965 3 Sheets-Sheet 1 Original Filed Dec. 17, 1962 444...- fmdqz als. f

Sept. 14, 1965 B. R. JONES INTENSITY CONTROL FOR OSCILLOSCOPE DISPLAY Original Filed Dec. 17, 1962 3 Sheets-Sheet 2 NMFTII.

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United States Patent O 3,206,633 INTENSITY CONTROL FOR OSCILLOSCOPE DISPLAY Billie R. Jones, Boston, Mass., assignor to the United States of America as represented by the Secretary of the Air Force Original application Dec. 17, 1962, Ser. No. 245,327. Divided and this application Dec. 3, 1963, Ser. N o.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to display apparatus, and more particluarly to graphic displays on the screen of a cathoderay oscilloscope for photographic and recording purposes suitable to both still and continuously moving film cameras.

This patent application is a division of my pending patent application entitled Method and Apparatus for Oscilloscope Photography, bearing Serial Number 245,- 327, and tiled December 17, 1962.

l Thei oscilloscope is an instrument comprised of a cathode-ray tube and associated circuits for use in viewing, photographing and recording wave shapes of voltages or currents. The cathode ray tube is comprised of three parts: an electron gun for supplying a stream of electrons in the form of a beam; deflection plates for changing the direction of the electron beam; and a screen covered with a material which gives off light when struck by the stream of electrons directed at it by the gun. There is also included an intensity modulation control which determines the amount of beam current. The intensity control feature of an oscilloscope is usually referred to as the Z axis.

The associated circuits in the oscilloscope include a time-base generator which generates an output signal utilized to move the electronbeam from left to right side of the screen at a uniform rate. The beam is then returned hurriedly to the left side where it begins another sweep across the screen. This action is accomplished by generating a voltage that rises at a uniform rate to a certain value and then quickly drops back to its starting value. A wave shape such as this is called a saw-tooth wave.

The saw-tooth Voltage wave is applied to the horizontal deflection plates, where it causes the electron stream to change direction. Since positive voltages repel and negative voltages attract electrons, the gradual rise in voltage causes the left plate to become increasingly negative and the right plate increasingly positive and thereby causes the spot to move across the screen. The quick drop of the voltage back to its starting value returns the spot from right to left in a very short time, called the iiy-back time.

The saw-tooth voltage is generated by the time base generator, and this voltage or some other desired external voltage for horizontal deflection applied at the terminals marked horizontal signal input, may then be fed into a horizontal deflection ampliiier which increases the amplitude to that needed for a trace of the desired length. The horizontal deection portion of the oscilloscope is referred to as the H axis. The voltage or current to be observed is applied to the vertical signal terminals and may be ICC amplified to the desired value before being applied to the vertical deiiection plates. With voltages thus applied simultaneously to the vertical plates and the horizontal plates, the deiiection of the beam is the resultant of the two forces. The vertical deflection portion of the oscilloscope is known as the Y axis.

One of the limitations in photographing and recording the wave shapes on the screen of an oscilloscope resides in dark background caused by the exposure of the iilm by the horizontal sweep trace. A further limitationis the fading out of the leading and trailing edges of input signals which have a very fast rise time, such as square waves.

The object of my invention is to utilize the Z axis, or intensity modulation, feature of an oscilloscope, in addition to the horizontal and vertical axes, to provide a display in which the trace of the signal to be photographed will be of a greater intensity than the horizontal sweep, thus improving measurement and analysis of transient signals.

The advantages of this type of display over the conventional type are, first, that when using a continuously moving film camera to record transients, such as contained in transmitted radio pulses, the horizontal sweep may be eliminated and the signal will still be visible, thus eliminating the dark background caused by the exposure of the film by the horizontal sweep allowing an easier and more accurate measurement and analysis of the signals; and second, the intensity modulation of the input signal will eliminate the fading out of the leading and trailing edges of input signals which have a very fast rise time, such as square waves.

The features of this invention, which are believed to be new, are set forth with particularity in the appended claim. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. l is a diagram, partly in block and partly in schematic of one embodiment of the present invention;

FIG. 2 is a diagram, partly in block and partly in schematic of a second embodiment of the present invention; and

FlG. 3 is a diagram, partly in block and partly in schematic of a third embodiment of the present invention.

Now referring in detail to FIG. l, there is shown cathode-ray oscillograph recording camera 24 which is positioned so as to record the wave form display representative of the input signals on screen 23 of cathode-ray tube 22. The camera 24 may be such as shown and described in U.S. Patent No. 2,751,275, issued June 19, 1956. Camera 24 may take either singly photographs of a particular wave form or continuons photographs of a series of wave forms. The lilm in the camera moves atiright angles to the horizontal sweep of the cathode-ray tube, so that the result may be a continuous photographing of the display of successive sweeps and wave forms of input signals visible upon screen 23 of cathode-ray tube 22.

In the embodiment of the invention shown in FIG. l, filament 15 is heated to the required temperature for electron emission. A high negative voltage is applied to terminal 25, and a positive voltage to terminal 36. Terminal 25 is connected to potentiometer 26. Cathode 16 is connected to point 27 and the voltage thereat is fixed at a slightly less negative-voltage than available at terminal 25.

Control grid 17 is connected to the variable contact of potentiometer 26. This provides variation of control grid voltages and serves as an intensity control of the beam current. Resistor 28 interconnects potentiometers 26 and 29. The variable contact of potentiometer 29 is connected to grid 18 and the position of the variable contact controls the focusing anode voltage. The focus control varies the anode voltage. Resistor 30 connects potentiometer 29 to ground by way of junction point 31. Accelerating anode 19 is kept at a fixed positive value by connecting it between resistors 34 and 35. Resistor 35 is connected to terminal 36. Vertical deflection plate 20a and horizontal deflection plate 2lb are connected to accelerating anode 19. The variable contact of potentiometer 38 is connected to vertical deflection plate 20 by way of resistor 40 and provides vertical centering. The variable contact of potentiometer 37 is connected to horizontal deflection plate 21 by way of resistor 39 and provides horizontal centering. Potentiometers 37 and 38 bridge resistors 34 and 35. Resistors 32 and 33 connect resistor 34 to ground by way of junction point 31.

Horizontal deflection plate 21 is also connected to the output of time base generator 41. Time base generator 41 is conventional and produces at its output a saw-tooth voltage which provides the necessary horizontal sweep for cathode-ray tube 22. Time Vbase generator 41 is designed so as to be synchronized by a pulse provided by way of the output of pulse generator 11. Pulse generator 11 is capable of selectively providing varying repetition frequencies. Terminal receives the input signal whose waveform Vis to be displayed on screen 23 of cathode-ray tube 22.

f An important feature of the present invention resides in the hereinafter described circuitry, wherein terminals 10 and 12 are interconnected. Terminal 12 is connected to ground by resistor 13 and to cathode 16 by capacitor 14. It is desired to have the input signal on the semilinear portion of the RC curve so the RC time constant of resistor 13 and capacitor 14 is selected to be ten times the duration of the input signal.

In the operation of the embodiment of the present invention as illustrated in FIG. 1, the intensity of the beam on cathode-ray tube 22 is controlled by varying the movable contact on potentiometer 26 so that the horizontal trace on screen 23 is just visible. Pulse generator 11 is adjusted to provide a synchronizing pulse having the same pulse repetition frequency as that of the input signal received by way of input terminal 10. The sweep sawtooth voltage provided by time base generator 41 to horizontal deflection plate 21 is now synchronized with the pulse from generator 11.

Negative input signals whose waveforms are to be displayed on screen 23 and photographed by camera 24 are received at input terminal 10. From terminal 10 the input signal passes to vertical deflection plate and also to terminal 12. It is to be noted that previously the intensity of the horizontal trace on screen 23 has been adjusted as to be just visible. The negative input signals being received by vertical deflection plate 20 are as a consequence o-f conventional cathode-ray tube operation displayed as representative waveforms on screen 23 and would normally have the same intensity as the horizontal trace. However, the negative input signals are also received at terminal 12. As previously indicated, the RC time constant of resistance 13 and capacitor 14 is ten times the duration of the negative input signal thus allowing the input signal to be on the semi-linear -portion of the RC curve. As a result of the negative input signals passing through a preselected RC network, a negative voltage appears on cathode 16 thereby decreasing the bias thereupon during the time the negative input signals are present. This decrease of bias increases the intensity of the trace only during negative input periods. It is clear that photographing the waveforms representative of the negative input signals displayed on screen 23 by means of camera 24 is greatly improved. The horizontal trace is just visible and during periods of the negative input signals, the trace is brightened automatically to display on screen 23 the waveforms representative of said negative input signals. It is also to be emphasized that the intensity of the horizontal sweep may be adjusted just below visibility and only the waveforms representative of the negative input signals will be visible on screen 23 thus eliminating completely the dark background caused by the exposure of the film in camera 24 by the conventionally visible horizontal sweep. The intensity modulation of the input signal provided by the present invention also eliminates the fading out of the leading and trailing edges of signals which have a very fast rise time, such as square waves.

Now referring to FIG. 2 which shows a second embodiment of the present invention and in structure is identical to that of FIG. l except that an RC network identical to resistor 13 and capacitor 14 of FIG. 1 is connected to control grid 17 instead of cathode 16. Terminal 42 supplies the signal input to the RC network of resistor 43 and capacitor 44. The time constant of the RC network of resistor 43 and capacitor 44 is ten times the duration of the input signal. Thus, it is possible to receive positive input signals of terminals 10 and 12 and by placing the positive signal voltage on control grid 17 by way of resistor 43 and capacitor 44 the bias thereof is decreased, causing greater intensity of the trace while a positive input signal is present.

FIG. 3 illustrates a third embodiment of the present invention in which the structure thereof is identical to that illustrated in FIG. 1 except that both cathode 16 and control grid 17 have RC networks and the input t0 each network is comprised of a unidirectional network. The RC network for cathode 16 is comprised of resistor 13 and capacitor 14. The RC network for control grid 17 is comprised of resistor 43 and capacitor 44. Input terminal 12 is interconnected to the combination of resistor 13 and capacitor 14 by diode 45. Input terminal 42 is interconnected to the combination of resistor 43 and capacitor 44 by diode 46.

In the operation of the embodiment illustrated in FIG. 3, when input signals are received by way of terminal 10, it is also received by terminals 12 and 42. The input signals which are negative cause a negative voltage to be received by cathode 17 by way of diode 45 and the RC network consisting of resistor 13 and capacitor 14, thus intensifying the trace on screen 23 during the period of said negative input signal. It is to be noted that the negative input signal, however, is not passed by diode 46. In the event that the input signals are positive then a positive voltage is received by control grid 17 by way of diode 46 and the RC network consisting of resistor 43 and capacitor 44. The positive input signals are blocked by diode 45. Thus, it is seen that during the reception of positive input signals the trace on screen 23 is intensified during periods of said positive input signals.

Therefore, the present invention permits the input signal to be used to bias the cathode-ray tube at the identical time it is being used in the vertical deflection of the trace. This allows the photographer to dim out the unimportant sections of the horizontal sweep as he desires `and thus produce better photographs of the input signal.

What is claimed is: j l

An apparatus for displaying waveforms on the screen of a cathode-ray tube, said waveforms being representative of negative and positive pulse input signals comprising means for horizontally sweeping the beam of said cathode-ray tube across said screen, means for synchronizing said horizontal sweep to the repetition frequency of said negative and positive pulse input signals, meansk to adjust the intensity of said beam to just below the level of visibility during said horizontal sweep, means to impress said negative and positive pulse input signals upon the vertical deflection plates of said cathode-ray tube, a first resistor-capacitor network having a preselected time constant connected to the cathode-ray tube, a second resistor-capacitor network having a preselected time constant connected to the control grid of said cathode-ray tube, rst unidirectional means to pass only said negative pulse input signals to said rst network simultaneously with the application thereof said vertical deection plates, and second unidirectional means to pass only said positive pulse input signals to said `second network References Cited by the Examiner UNITED STATES PATENTS 9/51 Silliman 315-22 12/ 5 2 Fockler 315-22 DAVID G. REDINBAUGH, Primary Examiner.

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