US2347008A

US2347008A - Electrical circuits

Info

Publication number: US2347008A
Application number: US367937A
Authority: US
Inventors: Arthur W Vance
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-11-30
Filing date: 1940-11-30
Publication date: 1944-04-18
Anticipated expiration: 1961-04-18

Description

A? r i1 18, 1.944. A, w VANCE 2,347,008

ELECTRICAL CIRCUIT Filed Nov. 30, 1940 2 Sheets-Sheet 1 PUWER 0 S URCEUF SUPPLY POTENTIAL UNDER STUDY 3 23 AMPLIFIER M4 vs- GENERATOR UUT PUT 8/ INVENTOR ARTHUR W- A/VCE M-u-W ATTORNEY April 18, 1944. A w. VANCE" ELECTRICAL CIRCUIT Filed Nov. 50, 1940 2 Sheets-Sheet 2 W RC Y N 7 m4 v W m l A U I I H 4m 3 m I I B m n F. E W M n T T m J 0 M Q,

l .4 C. da. n Q

mu NQL EQRQW whms Patented Apr. 18, 1 944 ELECTRICAL CIRCUITS Arthur W..Vance, Moorestown, N. 5., assignor to Radio Corporation of America, a corporation of Delaware Application November 30, 1940, Serial No. 367,937

6 Claims.

duration of that portion of the wave change which it is desired to observe, is, therefore, extremely small. To observe such phenomena on a linear time axis whose frequency is the same as that of the fundamental frequency would require an enormously large deflection distance, if the small details are to be stretched out sulficientlyto be seen. n the other hand, if the time axisfrequency is raised to a very large value, the small portion which it is desired to study, would be stretched out enough for observation, but would thenbe obscured by overlapping of the other portions of the waves which have difierent wave shape.

Therefore, it will be readily apparent that the use of an ordinary linear time axis is unserviceable in such cases. For example, supposing it is desired to observe the wave form of the output of a television camera operating at a frame frequency of 30 cycles and it is desired to observe the details of the wave form at the junction of an abrupt change of white to black, which may last only for a time period of the order of one millionth of a second, the desired observations can be seen by noting the steepness of the wave front which determines the linearityrof the system with respectto frequency and phase. It will be readily apparent that if 40 91011 150418 the time axis frequency is 30 cycles, the scale to resolve the details as a one inch deflection, would require that the total deflection be on the order of 30,000 times this, which is unreasonably large when it is considered that the usual 45 sensitivity is on the order of one inch per 25 volts. 0n the other hand, if the frequency were raised to a million cycles, it will be apparent that there will be such a tremendous overlapping of the other portions of the waves as to obscure the phenomena which is to be studied.

' My invention provides a means of generating a time axis which is linear over'a relatively short period of time, which short periods of time oc cur periodically at relatively widely spaced time 55 intervals.

generating a large (Cl. I'll-95) Moreover, my invention provides a method and means for adjusting the relative time at which the short linear deflection interval takes place. Under these conditions, it will be seen that a 5 small part of the observed wave is seenon the screen of a cathode ray tube having a linear time deflection without the necessity of providing an excessively large deflection voltage, and without overlapping of undesired portions of the 10 fundamental wave. Different portions of the observed wave can be studied by adjusting the time of occurrence of this short period linear deflection.

Briefly, my invention utilizes the method of sawtooth wave voltage and impressing the generated wave on the input of an amplifier, which amplifier has a small range of input voltage over which linear output of the amplifier is obtained, and has the further charm acteristics of saturating sharply above the maximum value of linear output and zero output below a predetermined value. By varying th bias of the amplifier, the input range may be selected from any desired portion of the generated sawtooth wave voltage, and thus it is possible to obtain a very rapid linear swing for a short time at any desired portion of the sawtooth wave without the necessity of generating excessively high voltages and without overlapping images.

Accordingly, it will be recognized that it is the object of myinvention to provid a novel and useful timing axis for a cathode ray tube.

Another object of my invention is to provide a method and means for obtaining recurrent linear sweep voltages of short duration.

A further objector my invention is to provide a method and means for studying a small portion on an extended scale of electrical wave shapes, and to be able to select the small pordied and to render it visible on a cathode ray screen in a simple manner.

parent upon reading a detailed description taken together with the drawings, in which Fig. 1 shows schematically an embodiment of my invention used with a cathode ray oscilloscope;

Fig. 2 shows a family of deflection voltage curves in graphical forms to illustrate the principle of 0 my invention, where Fig. 2a shows the generated sawtooth voltage from the oscillator and Figs. 2b, 2c, and 2d show the output or deflection voltage for increasing bias voltage conditions all plotted against time, while Fig. '3 shows a. de form of sawtooth oscillator, together with means ed circuit diagram of one.

for providing short time recurrent linear voltage waves from the sawtooth waveprovided by the generator. I

In Fig. l, I have shown a source of potential 8 under observation, which is connected to supply energy to a pair of deflection plates 1 of a cathode ray tube I. A sawtooth wave generator I I is supplied with energy from the source 8 to synchronize the wave generator so that the frequency will be an integer sub-multiple of the fundamental frequency oi the potential under study to provide a stationary image on the oscilloscope. An attenuator I3 supplies sawtooth wave energy from the generator ll to the selector I5, which comprises an amplifier II having a bias source I9 and a potentiometer 2| for varying the value of bias supplied to the amplifier II. The output of the selector I5 may then be supplied directly to another pair of deflecting plates 5 mounted perpendicularly with respect to the pair of plates 7 or, optionally, the output of the selector I5 may be connected through an amplifier 28 to the Plates 5.

An electron gun 3 positioned within the neck of the cathode ray tube I serves to project a beam of high velocity electrons toward a luminescent target or screen 2 and the beam of electrons, un-.

der the joint influence of the deflecting fleld set up by the pairs of plates 5 and I, serves to produce upon the target 2 a visible trace of the wave form of the source 9 which is under study. The power supply 4 serves to supply the operating voltages in substantially conventional manner.

The selector, incorporating the tube I1, is so arranged as to saturate when the supplied input voltage exceeds a predetermined value so that, above the predetermined input voltage, no further increase in output voltage is available from the selector. If this output voltage is made sufllciently large so as to deflect thebeam of electrons from the gun 3 just off the screen 2, it will be readily apparent that the beam of electrons will make excursions from one side of the screen to the other. The point at which output voltage is available for deflection is controlled by varying the bias of the tube I'l. For example, if the bias is made quite large, it is readily apparent that the attenuator I 3 must be set so as to provide a very large deflectionvoltage. By shifting the bias on the tube 5? the point at which output current will commence to flow will, therefore, become a function of the amplitude of the output of the wave generator. Sincethe wave generator produces a linearly varying output with respect to time, the bias, in reality, determines the time at which the sweep of the cathode ray beam across the target 2 takes place.

.The above described effect may be clearly understood by referring to Fig. 2 and first to part a thereof, in which the curve IUI represents the substantially linear output of the sawtooth wave generator with its abrupt return along the path I03. If now, the bias on the tube I1 is made zero, it is apparent that the output voltage of the selector I5 which is supplied to the amplifier 23, or, optionally, directly to the deflecting plates, will immediately commence along the path III, as shown by part b of the curve, until saturation sets in, whereupon the tube output voltage follows the path H3 and abruptly drops along the path I I5 in accordance with the abrupt return to substantially a zero value of the sawtooth voltage wave along the'path I05. Thereafter, the voltage immediately commences to grow again along'the path III. If now the bias is set to a 75 value equal to I in curve a, then the tube II provides no output until it reaches a point I in curve 0, where the voltage then commences to increase linearly along the path I2I. If the bias is still further increased to I43, as shown at a, then the linear sweep available does not begin until a point I is reached, as shown by curve d of Fig. 2. It will thus be seen by changing the bias, the deflection, with respect to the phenomena to be studied, can be made to commence at any desired point of the fundamental wave.

One detailed embodiment of my invention is shown by Fig. 3 in which the tube serves, together with the charging resistance 43 and the condenser 45, as a relaxation type of sawtooth wave generator of the kind well known in the art. Synchronizing impulses are fed to the input terminals 3| and are capacitively coupled to a control electrode of the tube 35 to determine precisely the frequency of the generated oscillations. A voltage source 39 of any desired type provides suitable bias voltage for the tube 35 and this volt age is fed through a resistor 31 to an input electrode of this tube. This bias serves as a further means of regulating the wave shape of the sawtooth wave generated. The frequency at which the sawtooth shaped waves are generated, as is well known, may be varied by adjustment of the size of the resistor 43 or by varying the size of the condenser 45, or by varying both; while the tube 35 is usually of the so-called hard type, it also may be of the gaseous discharge type within the scope of this invention. The generated sawtooth wave energy which is developed across the terminal points 44 and 48 may be impressed across an electrostatic potential divider comprising the

condensers

41 and 49 and used to energize a linear amplifier 55, which is suitably biased by a source 53 through a resistor 5|. The output voltage set up across the output resistor 51 of the tube 55 is then fed capacitively to the input of the selector tube 65, the tube 55 acting more or less as a bufl'er to prevent changes in the bias or grid current of thetube 86 from reacting on the frequency of the sawtooth wave oscillator. The control electrode of the tube has a resistor 63 connected in series therewith, which, in turn, is connected to thecapacity coupling 59. A resistor GI has one terminal connected to the junction of the coupling condenser 59 and resistor 63 and its other terminal is connected to a suitably chosen point in a potentiometer I3. The potentiometer I3 is connected in shunt with a power supply 4| and it serves to provide a variable bias for the tube 65. A second potentiometer I1 is also connected in shunt with the power supply 4| and potentiometer I3. The variable terminal I8 of the potentiometer TI is connected through the output resistor 61 to the output electrode of the tube 65. A condenser I9 serves to provide capacitive coupled output across the terminals 8|. A large condenser I5 is connected in parallel to both the potentiometers I3 and I1 to provide suilicient high frequency bypassing to avoid any interaction between various ampliiier stages of the system.

In the cathode circuit of the tube 85, there is provided a gaseous discharge voltage regulator tube II shunted by a condenser I0, and energized from the voltage supply 4| through a resistor I59. By means. of the gaseous discharge tub II the cathode of the tube 65 is maintained at a positive voltage with respect to ground and for the usual type of gaseous discharge tube, such as the RCA-874, this voltage would be volts. When the variable contact or the potentiometer I3 is at the negative side of the power supply, the tube t has 90 volts negative bias between its control electrode and cathode, and when the potentiometer arm is on the high side, then the :bias will be 90 volts plus ormore bias. The resistor 63 is of large value and serves to provide a sharp saturation characteristic above the value of input voltage at which grid current commences to flow. The grid current flowing through resistor 53, which may be on the order of 1 megohm', produces a potential drop of opposite polarity to that of the input voltage and since resistor 63 is of large magnitude, the value of the produced potential drop is substantially the same value as the increase of input voltage above that which produces grid current. The produced potential drop, therefore, substantially prevents any further increase in output voltage.

The tube 65 is one that requires only a relatively small input voltage to give full undistorted output voltage and is chosen so that only a very small bias voltage, of the order of, say, 2 volts. is necessary to provide cut-oil? of the plate current. Under these conditions, therefore, an effective input voltage over two volts will produce saturation, while an efiective input voltage between zero and two volts will give linear output voltage. The valueof input voltage supplied to the control electrode of the tube 65, which overcomes the cut-ofi bias supplied thereto, can be selected by suitable variation of the arm of the potentiometer 13.

Referring now again to Fig. 2, it will be observed, therefore, that with very high bias obtained when the arm of the potentiometer I3 is at the negative end of the regulator tube 1 I, only the tip of the generated sawtooth Wave is suiiicient to overcome the bias on the tube 65 and consequently, only the end Portion of the wave under study, would actually be reproduced upon the luminescent screen, as represented by the linearly increasing portion l3l of the curve in Fig. 2d. If the bias is made zero, only the beginning of the wave will be Observed on the screen, as represented by the linearly increasing port-ion Ill in Fig. 2b, and for an immediate value of bias, intermediate portions of the wave will be rendered visible for study, coinciding with the y increasing portion of the curve l2l in Fig. 2c.

The amount of stretching out of the desired por i n of h W ve to be studied, 1. e., the effective deflection sensitivity, may be adjusted by means of the potentiometer 11. If the voltage is increased on the output electrode of the tube 55, greater output voltage will be obtained which will provide a wider sweep upon the screen. Alternatively, of course, the output voltage at the terminals 8| may be fed through an amplifier to the deflection system of the cathode ra tube to provide even greater deflection of the light trace across the screen of the cathode ray tube.

It will be understood, of course, that other means for providing saturation of the tube may be used, and other forms of sawtooth wave oscillators may be used, other than those shown for e ur so of illustration. Tfie i ention is not limited to the specific embodiments shown in the drawings and described in the specification, but may make use of any and all modifications which fall fairly within the spirit and scope of the foregoing disclosure as it is defined by the hereinafter appended claims. Having described my invention, what I claim 1. The method of producing an expanded visual trace of a predetermined portion of a recurrent electrical wave of predetermined periodicity which comprises the steps of generating a sawtooth wave voltage synchronously with the recurrent electrical wave, each successive cycle of said voltage wave including a linearly generated voltage occupying substantially a complete cycle of said recurrent electric wave, selecting a predetermined small portion of said linearly changing voltage of the generated wave and modifying its slope, translating the selected portion of the generated wave into a visual trace in one direction effectively expanded to substantially the dimension of a full cycle trace of said generated sawtooth wave and simultaneously translating the predetermined portion of the recurrent wave into alterations of the direction of the visual trace, said alterations being made in a direction perpendicular with respect to the direction of the visual trace.

2. The method of producing an expanded luminous trace of a predetermined portion of a recurrent electrical wave of predetermined periodicity I which comprises the steps of generating a sawsaw-tooth wave and simultaneously translating the predetermined portion of the recurrent wave into alterations of the direction of the luminous trace, said alterations being made in a, direction perpendicular with respect to the direction of the luminous trace.

3. A measuring system comprising a source of electrical eiTects having a periodically varying characteristic to be observed, an oscillograph comprising a deflectable radiant energy beam, means to deflect said beam in one direction, a connection from said source to said beam deflecting means to cause said beam to trace a path determined by said deflecting means, means to generate a periodic voltage varying linearly with respect to time in timed relationship with said varying characteristic to be observed, means'to select a portion of each successive period of said periodic voltage and modify its slope, means to vary the path traced by said beam, and means to apply the selected portion of said periodic voltage to said path varying means whereby said beam traces a path representative of a selected portion of said varying characteristic to be observed effectively expanded to the extent of the normal full cycle path traced by said periodically varying characteristic combined with a full cycle Of said generated periodic voltage.

4. A measuring system comprising a source of electrical efiects having a periodicall varying characteristic to be observed, a cathode ray tube having means to produce a visible trace displayed for inspection upon a given portion of said tube, a connection from said source to said trace producing means to produce a visible trace along a path determined by said trace producing means, means to generate a periodic voltage varying linearly with respect to time in timed relationship with said varying characteristic to be observed,

means to select a portion of each successive period of said periodic voltage and modify .its slope, means in said tube to vary the path of said visible trace, and means to apply the selected portion 01. said periodic voltage to said path varying means whereby a selected portion of said varying characteristic to be observed appears as a visible trace effectively expanded to the extent of the normal full cycle trace of said periodically varying characteristic combined with a full cycle of said generated periodic voltage.

5. A measuring system comprising a source oi periodically varying potential to be measured, a cathode ray tube having deflectable means to produce a luminous trace, deflection means to produce a luminous trace alon a predetermined path, a connection from said source to said deflection means, a saw tooth wave generator, means to synchronize said generator from said potential source, a saturable discharge tube comprising a cathode, an input electrode,- and an output electrode, means for maintaining a positive bias on said cathode comprising a gas discharge tube, an input circuit for said discharge tube including an adjustable source oi biasing potential for said input electrode, a connection from said input circuit to said generator, means in said input circuitto cause saturation of said discharge tube, deflection means to alter the path of said luminous trace in a direction perpendicular to said first named trace path, and means connecting said output electrode or said discharge device and said cathode to said second named deflection means.

6. A measuring system comprising a source of periodically varying potential to be measured. a cathode ray tube having deflectable means to produce a luminous trace, deflection means to produce a luminous trace along a predetermined path, a connection from said source to said deflection means of said cathode ray tube, a saw tooth wave generator, means to synchronize said generator from said potential source, a saturable "discharge tube comprising a cathode, an input electrode, and an output electrode, means for maintaining a positive bias on said cathode comprising a gas discharge tube, an input circuit for, said discharge tube including an adjustable source of biasing potential for said input electrode, a connection from said input circuit to said generator including an attenuator, means comprising a resistor in said input circuit adjacent said input electrode to cause saturation of said discharge tube, deflection means to alter the path of said luminous trace in a direction perpendicular to said first named trace path, and means connecting said output electrode 01' said discharge device and said cathode to said'second named deflection means.

- ARTHUR W. VANCE.