US2221115A

US2221115A - Multiple trace oscillograph system

Info

Publication number: US2221115A
Application number: US151160A
Authority: US
Inventors: Jr Francis H Shepard
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1937-06-30
Filing date: 1937-06-30
Publication date: 1940-11-12
Anticipated expiration: 1957-11-12

Description

Nov. 12, 19.40. F. H. sHEPARD, JR 2,221,115

MULTIPLE TRACEA OSCILLOGRAPH SYSTEM Filed June 50, 1937 5 Sheets-Sheet l ATTORNEY AAAAAAA INVENTOR A FRANC/S l. SHED/1,90, JR. BY [f/ /W'VCA/ n ,STM Q AAAAAAAA vvvvvvvvv RAAAAA Nov. 1-2, 17940.

F. H. SHVEPARD, JR

MULTIPLE TRACE OSCILLOGRAPH SYSTEM AAAA AAAL VVyVVVV R27 INVENTOR 7 WVM/ l ATTORNEY SWEEP INI e Ol/Pl/T I l IGA/AL I OUTPUT EXT.'

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5 Sheets-Sheet 5 ATTORNEY -INvENToR FRANC/5 H. SHEPARD, Je. BY V ALLA AAAA VVV VVV F.A H. SHEPARD, JR

Filed June so, 1937 VVVVVVVV MULTIPLE TRACEI OSCILLOGRAPH SYSTEM Url@ EXT.

Nov. l2, 1940.

Nov. 12, 1940. F. H. sHE'PARD, .1R 2221,115

' MULTIPLE TRACE OSCILLOGRAPH SYSTEM Filed June 50, 1937 V5 She-ets-Sheet 4 u El:g. 6 Y I C53 ATTORN EY Nov. l2, 1940. F. H. SHEPARD, JR 2,221,15

MULTIPLE TRACE OSCILLOGRAPH SYSTEM Filed June 50, 1957 5 Sheets-Sheet 5 INVENTOR F/VC/S H. .$HEPARD, JR.

x vfw/ ATTORN EY 25 A further object .Patented Nov. 12, 1940 MULTIPLE TRACE OSCILLOGRAPH SYSTEM v Francis H. Shepard, Jr., Rutherford, N."J., assignor to Radio Corporation of America., a, corporation of Delaware Application June-3o, 1937, serial N. `151,169 1s claims. (ci. ivi-95).

The present invention relates to a circuit for` use primarily with cathode ray oscillographs in which a plurality of variables or transients may y be observed simultaneously. This observation is 5 obtainable by the provision of means for supplying signals from the pluralityl of sources in anyl U n use-i selected order to an observation oscillograph. When these signals are so 'applied in the'chosen sequence, they become visible upon the screen or y 10 target of the cathode ray tube in rapid succession. y The effect of simultaneous signal application is obtainable by virtue of the rapidity of switching v and the time lag of light decay from the lumi- `i5 nescent target, as well as the period of persistence of vision, it being understood, of course, that the switching rate is so selected as to be repeatedv tube oscillograph will permit observation of a plurality of varying signals or transients simultaneously. v'

nately switching from one signal source to an.- other at a rate of from 10 or less to 10,000 or more times per second.

30,000 or more cycles per second.

-ate with the frequency ofl either of the `input signals.

duce a system wherein the switching circuit may be operated in synchronization with an external and entirely independent 'source of impulses and/or where desired, in accordance with'the` frequency of a power supply source when A.'C. operation is selected.

A still further purpose of my invention is to produce a system wherein the saw-tooth sweep or deecting voltage for the cathode ray tubev is relation with the switch and-:also in which the amplitude of the sweep will remain constant' over the entire frequency range of the system.

, Other purposes and uses of the device will beof the invention is to produce a switching circuit which is capable of alter- A further object of the present invention is to produce a circuit which is capable of amplifyingAv uniformly and without distortion signal voltagesr which may vary in frequency from 10,000/t0" lA still further purpose of my invention y y produce a system in whichthe switching^ may bev synchronized and so interlocked as to `oper- A further purpose of my invention is to prosupplied and wherein this Voltage will always be in exact synchronization and in proper' phase choke with afcon'd y the cathodevcon f come more apparent and immediately suggest themselves to those' skilled in the art to which `vthisinvention relates from the following description ofthe circuits used, particularly when ,con-

sideredwith the "drawings, which:v

"g. YLrepresents'one formof my invention'v for y l connectionwith` a cathode ray tube oscillograph, and, if l Figufres 2'through'6 show. various modied or alternative forms ofmy invention which-may be used'to4 accomplish broadly the same'results.

Inv Figurefl, ve discharge ,tubesv serving as switching and/or control devices, are used to accomplish the purpose of this invention.v The switching voltage is generated b'y a pair of gas triodes I and II. 'I'hese triodesgbecause of the manner in which they are inter-connected, function inr a manner similar to that of a relaxation oscillation generator. The grid of tube I0 is connected to the anode of tube II by way of-condenser CIU and similarly the control electrode of tube II is connected to the anode of tube I0 by wayof condenser CII. To the anodes of each source of positive potential'is connected to these f resistances and `lcondensers byvway of the reg.sistance RI j and th Hltl.` The frequen" Adio-frequency choke coil o theg switching voltages upplied `byj'these tubes he condensers CIII czondensers rmay be order I to y-varyv the frei n Anadju'stmentof resistt l's the frequency as will'later The [control grids in each of and sweep imp s `become appa theftubes are Acl necte through resistances RII) and RII tn th ar" bl 'resistance RIZ, which latter resistan'c cff ,'Safpotentiometer connected acros'"the an vde urrent vsupply `whereby the grid bias of' each ofrthe tubes ,I0 rand II may be varied.

The frequency oscillationI` of the tubes 'I0 and lII may also be controlled-.or"synchronized by an external source through the transformerjTl.

'I'he actual sweep voltage is obtained with the aid of an additional tube I2 Ywhich `may be in v'the form of a twin diode. With each switching operation ofy thetubes I0 and II a voltagevfariation is causedto ex tgacross the choke HIO. The twin diode i'vslconnecte'd in parallel with this 'er'Cllfwhich is inserted in s Atio'nl 1 The impulses as applied to the choke reftherefore impressed upon the condenser CI4 to successively charge the same, this condenser being intermittently discharged at a relatively constant rate through the resistance RI 6 and the voltages derived therefrom are impressed upon the horizontal beam delecting means of the cathode ray tube by way of the coupling condenser CI5 and the terminal X.

A conventional cathode ray tube is shown ai I, the tube having ,a ray developing means or electron gun 2. Plates 3, 4, 5 and 6 are shown for electrostatically deiiecting the beam after it has been developed, the plates 3 and 4 operating to produce horizontal deflection of the beam when proper voltages are applied thereto and the plates 5 and 6 operating to produce vertical deflection of the beam. A fluorescent screen 1 is provided whereby movements of the electron beam may be observed. It is to be understood that the particular tube shown is only by way of example since. obviously, other forms of cathode ray tubes may be used and the electrostatic deflecting means may be replaced by electromagnetic means or a combination of electrostatic and electromagnetic deiiecting means.

A pair of tubes I3 and lI4 are also used and these tubes may be in the form of pentagrids in which the suppressor or #5 grid is connected 'internally tothe cathode of the tube. It will be noticed that the grids of the tubes I0 and II are connected to the oscillator or #3 grids of the tubes I4 and I3, respectively, in order that the latter tubes may be alternately biased beyond cut-off in synchronism with the operation of the tubes I0 and II. The two sources of signal input are impressed across the resistances IRII and IRI2, to which, by an adjustable contact, the #1 grids of the tubes I3 and I4, respectively, are connected. 'I'he anodes in each of the two tubes are tied together and are connected to the positive source of potential by way of resistance RI8. Likewise the two screen grids of the tubes are connected to the positive source of potential by way of resistance RI1. 'I'he values of these resistances RI1 and RIB are so chosen that appropriate voltages will be applied to the screen grids and the anodes of each of the tubes I3 and I4. The signal output of these tubesis applied to'the vertical beam deflecting means of the cathode ray tube by way of the condenser CI1 and the terminal X.

It will therefore be apparent that as tubes I Il and II alternately become conductive to supply the sweep voltage, the two tubes I3 and I4 are likewise alternately made conductive or non-conductive in synchronism therewith, so that the signal input voltage variations are alternately made visible on the screen of the cathode ray tube oscillograph at a frequency determined by the frequency of operation of the tubes I IJ and I I. 'Ihe amplitude of the sweep, that is, the horizontal component ci' the image on the cathode ray tube, may be controlled by varying the condenser CI4 and the resistance RIS while the amplitude of the signal, that is, the vertical component of the image on the cathode ray tube oscillograph screen, may be varied by adjusting the resistances IRI I and IRI2.

Figure 2 shows a modified form of my invention wherein only four tubes are used. The

tubes

20 and 2| are triodes and operate to supply the switch voltage and the sweep voltage. Their alternate operation is similar to the operation of tubes I0 and II of Figure 1, and the frequency of their operation may be controlled by varying the size of condensers C20 and C2I, together with a variation in the size of the resistances R22 and R23. Ihe grids of the tubes 2li and 2| are interconnected by the resistance R25 over which an adjustable contact is movable. Connected to this contact is a condenser C24 through which the sweep voltage is applied to the cathode ray tube.

The

tubes

22 and 23 operate as ampllers for the input -signals and are biased to cut oil.' alternately in synchronism with the operation of tubes 20 and 2I since the #3 grid of the

tubes

22 and 23 are connected respectively to the grids of tubes 20 and 2l. 'Ihe signal input voltage from the two sources is applied to the #1 grid of the

tubes

22 and 23 in a manner similar to that shown and described in connection with the circuit shown in Figure 1.

'I'he screen grids of the tubes 22- and 23 are connected together by resistance R21 and the positive source of potential is connected to an adjustable point along this resistance by way of the resistance R29.

The system shown may be caused to oscillate in synchronism with an external synchronizing voltage and in which case the switches SI and S2 are placed in the position marked Ext, on the drawings, in which case the external synchronizing impulses are supplied to the cathodes of the tubes 20 and 2I.

For internal synchronizing, the switches SI and S2 are placed in the alternate position marked Int. on the drawings. When such a connection is made, the screen grids of the

tubes

22 and 23 are connected to the cathodes of the tubes 20 and 2I by way of condensers C22 and C23, respectively.

This system has the advantage over the system shown in Figure 1 that the duration or percent of time that each function is amplified may be controlled by adjusting the potentiometer R24. By such adjustment, the length of time that one of the tubes 20 or 2I isconductive as compared to the length of time that the other tube is conductive, may be changed with the ell'ect that 4the horizontal component of the two signal sources as they appear on the screen of the oscillograph may be diii'erentially controlled.

Furthermore, in this system, the amplitude of the sweeps for the two functions can be diiTerentially adjusted by varying the contact along the resistance R25. By such adjustment, the length o1' the horizontal component of the images as they appear on the oscillograph may be varied diierentially.

A further advantage of this system is that the level of the zero lines of the two functions can be differentially adjusted by moving the contact along the resistance R21. This has the eiect of diii'erentially varying the voltage of the screen grid of the

tubes

22 and 23 whereby the two signals, as they appear on the oscillograph, can be made to appear about the same axis or about two axes one above the other. This is a desirable characteristic, particularlyv when two or more switch units are combined to observe several functions simultaneously since the various functions maybe isolated by vertical displacement.

Figure 3 shows another form of my invention. This system is in many ways the same as the system shown in Figure 2 with the difference that the tubes 30 and 3| are triple grid tubes. the suppressor grid being connected externally to the cathode of each tube. The use of the three grid tubes improves the operation of this circuit in that the sweep voltage is lof a truer saw-tooth form and as a result the rate of sweep of the beam 'across the screen in thefoscillograph. is mor -uniforml/ 'It will be noticed that tnesynchmnizing 1mpulses for the tubes 30.and ,f3|, regardless of whether they are derivedfrom an internal or an screen is not strictly uniform'. Wherethis effect is particularly objectionable,the circuit shown in Figure 3 should then be used. The sameadjustments that arepossible in Figure 2 with respect l vto the duration and amplitude of the sweep as `well as the zero base lines of the functions, are

alsopossible in the circuit shown in Figure 3.

Figure 4 shows a relatively vsimple two-tube electronic switch, sweep and amplifier in which the tubes are identical and. maygbe. ofthe penta.

grid type. In this circuit 'th` fubesnotonly act as a source of switch voltage ,y d sweep voltage, but also' operate as' amplifie v fo'rthe two input voltages. The frequency of opcrationof the system may of course be vcontrolled by varying the size of the condensersUC4`0z`and C4I, together with the size of the resistacesR43 and R44. In this system, thev input voltages'are applied to the oscillator or #3y grid of reach of the tubes and at the time one of the tubes isoperating to supply the sweep voltage the same tube is also operating to amplify the input voltage and to apply the same to the vertical A,defiecting means of the cathode ray tube. The sweep voltage is supplied to the horizontal deflecting means of the cathode ray tube through the condenser C244 which is connected by an adjustable contact to the potentiometer resistance R42 which inter-connects the controlgrids of the two tubes. f In this circuit there is a slight tendency for th switch to lock in step with either or both of the signals and there is a tendency for a part of the signal to appear on the sweep. Both of these effects are due to the negative trans-conductance between the #3 grid and the screen grids 2and 4 of the tubes. The latter effect is particularly noticeable when viewing a ylarge number of signal cycles on one sweep cycle. Both of these effects are more noticeable with large input signals and both can be reduced by reducing vthehfinput signals (adjusting the resistances 1R41 and 1R42), or by increasing the value of the common plate load toas high as is consistent with the desired amplier frequencyrespons'e. The common plate Y load vis represented by the resistance R48.

affected as little as possibleby the varying charg-v ing current to the grid of the other stage. To

yaccomplish this v the screen load resistor R41 should be made as low as possible. It is also essential that the potential of the #1 grid be constant during the amplifying part of the cycle for each tube and vthis is accomplishedby means of the grid current limiting resistors R40 and R4L l It is possible` with this circuit to ydifferentially adjust the amplitudes of the sweeps .for the two 4functions by varying the resistance R42, to differentially adjust the duration of the sweeps for the two functions by varying the resistance R45, and also to. raise or lower the zero lines of the two functions by adjusting the resistance R41. These adjustments operate in the same manner as do the corresponding adjustments given above with respect to the disclosure shown in Fig. 2.

Figure 5 shows a circuit similar to the circuit shown in Figure 4 with the exception that a duo-r v diode is used to improve the wave form and lncrease the amplitude of the sweep circuit and to increase the operating frequency of the system. With the type system shown it is possible to operate up to '750,000 cycles per second. If lt is desired, and by proper compensation, it is possiblev that this frequency may be considerably extended. Y

The system disclosed in Figure 5 diers from that shown in Figure 4 in that the resistances R43, R44, R45 as well as theresistance R42, are omitted and the first grids of the pentagrids are connected each respectively to the cathodes of the duo-diode. The anodes of this tube are connected together and supply the sweep output by Way of condenser C54. The source of anode potential for the duo-diode is connected through the variable resistance R52. The remainder of the system isthe same as that shown in Figure 4 and further explanationis believed to be uns IleCeSSaly.

slight tendency for the switch to synchronize with either or both of the input signals and is sufficient in most cases to maintain the operation of the device in synchronization with the signalv variations if such is desired. The condensers C60 and CBI are preferably made adjustable in order that the frequency of the devicemay be controlled in order to cause the circuit -to operate at a predetermined frequency or to maintain the circuit operating yin synchronization with uctuations of the input of the one or the other of the input signals. The resistances R63 and R64 are generally adjusted when the capacitances of the condensers C60 and C62 are changed in order to improve this control.

By varying the resistance R65 i-t is possibletol differentially control the duration or percentage of time that each function is amplified in order that the magnification of the horizontal comf ponent of the image formed on the oscillograph ,may be increased or decreased as desired. *.Also,

by adjusting the resistance R62 it is possible to differentially vary the amplitudes of the successive horizontal sweeps.

The resistances R68 and R69 are for thepurl pose of maintaining proper potentials uponithe electrodes of the tubes and the load resistances R66 are so chosen as to keep the gain constant during the amplifying part of the cycle for each stage.

From the above description of the circuits shown, it may be seen that a cathode ray -tube oscillograph may be used to observe two or more functions simultaneously, the functions appearing on the screen alternately and in rapid succession. The circuits used are relatively simple and do not entail the vuse of -a large' number of CFI . a short time lag being used when high frequenirl tubes nor a complicated circuit for producing the results.

When a cathode ray tube of the type shownin connection with Figure 1 is used, as it maybe with any of the circuits shown in the drawings. the time lag of light decay of the luminescent target may be varied in accordance with the frequency of the sweep impulses, a target having cies are employed and a target having a longer time lag being used when lower frequencies are employed. l

It is to be understoodthat various modincations may be made in any or all of the systems disclosed without departing from the spirit and scope of the invention, and it is desired that only such limitations be placed on the device as are necessary in view of the prior art and the appended claims.

I claim as my invention: l

1. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair of discharge tubes for supplying rapidly'recurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said ilrst named means whereby the amplified signals are supplied to the signal output in succession and in synchronism with the sweep impulses, and means for differentially controlling the duration or percent of time that each signal is amplied.

2. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair 0f discharge tubes for supplying rapidlyyrecurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said rst named means whereby the amplified signals are supplied to the signal output in succession and in synchronism with the sweep impulses, and means for differentially controlling the duration of alternate sweep impulses independently of the amplitudes of the impulses.

3. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair of discharge tubes for supplying rapidly recurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said ilrst named means whereby the amplified signals are supplied to the signal output in succession and in synchronism with the sweep impulses, and means for differentially controlling the amplitudes of alternate sweep impulses.

4. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair of discharge tubes for supplying rapidly recurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said rst named means whereby the amplified signals are supplied to the signal output in succession and in synchronism with the sweep impulses, and means for dierentially adjusting the zero base lines` of the amplified signals.

5. A system'for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of `signal input circuits, a pair of electron discharge tubes each having a plurality of control electrodes, means for individually impressing the input signals upon one control electrode of each of the tubes, respectively, and circuit means including another control electrode of each tube for rendering the tubes alternately conducting and non-conducting in rapid succession whereby sweep impulses are supplied to the sweep output and whereby the amplified signal impulses are alternately supplied to the signal output.

6. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, a pair of electron discharge tubes, means for impressing the input signals upon a control electrode of each of the tubes respectively, means for rendering the tubes alternately conducting and nonconducting in rapid succession whereby sweep impulses are supplied to the sweep output and the amplied signal impulses are alternately supplied tothe signal output, and means for diierentially controlling the duration or percent of time that each signal is amplified.

7. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, a pair of electron discharge tubes, means for impressing the input signals upon a control electrode of each of the tubes, respectively, means for rendering the tubes alternately conducting and non-conducting in rapid succession whereby sweep impulses are supplied to the sweep output and the amplied signal impulses are alternately supplied vto the signal output, and means for differentially controlling the duration of alternate sweep impulses independently of the amplitudes ofthe impulses.

8. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, a pair of electron discharge tubes, means for impressing the input signals upon a control electrode of each of the tubes, respectively, means for rendering the tubes alternately conducting and non-conducting in rapid succession whereby sweep impulses are supplied to the sweep output and the Aamplied signal impulses are alternately supplied to the signal output, means for dinerentially controlling the duration of alternately conducting and non-conducting periods and means -for differentially controlling the amplitudes Yof alternate sweep impulses, said two last named meansbeing independently operable.

9. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, a pair of electron discharge tubes, means for impressing the input signals upon a control electrode of each of the tubes, respectively, means for rendering the tubes alternately conducting and non-conducting in rapid succession whereby sweep impulses are supplied to the sweep output and the amplified signal impulses are alternately supplied to the signal output, and means for differentially controlling the amplitudes of alternate sweep impulses. y

10. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, a pair of electron discharge tubes, means for impressing the input signals upon a control electrode of each of the tubes, respectively, means for rendering the tubes alternately conducting and non-conducting in rapid succession whereby sweep impulses are supplied to the sweep output and the amplified signal impulses are alternately supplied to the signal output, and means for differentially adjusting the zero base lines of the amplified signals.

11. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and at least a pair of signal input circuits, means including a 4pair of discharge tubes for supplying rapidly recurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits individually, means whereby the operation of the last named means is controlled by said first named means to supply the signals lto the signal output in succession and in synchronism with the sweep impulses, and means whereby said rst pair of tubes may be operated in synchronism with an external source of impulses.

l2. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair of discharge tubes for supplying rapidly recurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said first named means whereby the amplified signals are supplied to the signal output in succession and in synchronism with the sweep impulses, and means whereby said rst pair of tubes may be operated in synchronism with the frequency of the one or the other of said input signals.

13. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair of discharge tubes for supplying rapidly recurring sweep impulses to the sweep output, means including a second pair of discharge tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said rst named means whtreby the amplified signals are supplied to the signal output in succession and in synchronism with the sweep impulses, and means whereby said rst pair of tubes may be operated in synchronism with an external source of impulses or in synchronism with the frequency of the one orthe other of said input signals.

14. A system for controlling a cathode ray tube oscillograph comprising a sweep output, a signal output and a pair of signal input circuits, means including a pair of discharge tubes for supplying rapidly recurring sweep impulses to the sweep output, means'including a second pair of discharge ,tubes for amplifying the signals from the input circuits, means to control the operation of said last named means by said first named means whereby the amplified signals are supplied to the signal output in succession and in synchronization with the sweep impulses, means for differentially controlling the duration of alternate sweep impulses, and means for differentially controllingy the amplitudes of alternate sweep impulses, lsaid two last named means being independently operable.

15. A system for controlling a. cathode ray tube oscillograph comprising electronic means for producing rapidly recurring sweep impulses, a plurality of separate input circuits, means for successively switching from one input signal to another in synchronism with the sweep impulses, said last named means being under the control of said first named means, and means for differentially controlling the duration of alternate sweep impulses.

`16. A system for controlling a cathode ray tube oscillograph comprising electronic means for producing rapidly recurring sweep impulses, a plurality of separate input signals, means for successively switching from one input signal to another in synchronism with the sweep impulses, vand means for differentially controlling the amplitudes of alternate sweep impulses.

17. A system for controlling a. cathode ray tube oscillograph wherein a plurality of signals may be caused to appear simultaneously comprising means for electronically producing a series of rapidly recurring sweep impulses, means whereby the signals may be independently and successively applied to the tube in synchronism with the sweep impulses, and means for differentially adjusting the zero base lines of the signals.

18. A system for controlling a cathode ray tube oscillograph wherein a plurality of signals may be ycaused to appear simultaneously comprising means for electronically producing a series of rapidly recurring sweep impulses, means whereby the signals may be independently and successively applied to the tube in synchronism with the sweep impulses, means for diirentially controlling the duration of alternate sweep impulses, and means for differentially controlling the amplitudes of alternate sweep impulses, said two last named means being independently operable.