US2439050A

US2439050A - Vibratory switching device for oscillographs

Info

Publication number: US2439050A
Application number: US552425A
Authority: US
Inventors: Mallory Henry Rogers
Original assignee: PR Mallory and Co Inc
Current assignee: Duracell Inc USA
Priority date: 1944-09-02
Filing date: 1944-09-02
Publication date: 1948-04-06
Anticipated expiration: 1965-04-06

Description

VApril 6, .1948.

H. R. MALLORY VIBRATORY SWITCHING DEVICE FOR OSCILLOGRAPHS Filed Sepc. 2, 1944 2 Sheets-Sheet 1 Kaz` OUTPUT Q/enf? Eggers fla/lary INVENTOR.

April 6, w194s.

H. RMALLORY VIBRATORY SWITCHING DEVICE FOR OSCILLOGRAPHS Filed Sept. '2, 1944 2 Sheets-Sheet 2 INVENTOR.

Paten'tecl Apr. 1948 VIBRATORY swT'rcmNG DEVICE Fon l oscmLoGaArns Henry Rogers Mallory, Indianapolis, Ind., assignor to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application September 2, 1944, Serial No. 552,425

A Y 1 Y The present invention relates to switching devices, and, .more particularly, to a novel and im- .proved `vibratory switching device for cathode ray tube oscillographs, string oscillographs, and the like, whereby two traces corresponding to a a claims. (c1. sis- 26) pair Vof variable voltages may be simultaneously exhibited. u

Y .As those skilled in the art know, conventional cathode ray tubesare, essentially, single element indicators, andperlnit the Visual observation of agsingle variable only at a time. There are many cases, however, where itis desirable to exhibit twoor more unrelated phenomena at the same time, for example in electrical studies for the comparison of amplitude, wave-form, phase, and frequency relationships. The same applies to sound, light, mechanical vibrations and displacements and to other quantities which may be translatedfinto electrical functions, and which may be visually represented and may be studied by means of corresponding traces on the screen of the oscillograph.

Heretofore, the device most commonly employed for thispurpose was an electronic switch comprisingI two vacuum-tube amplifiers, to the grid circuits of which were connected the two signals to beinvestigated. A multivibrator generating a square-wave signal was employed to alternately biasv the grids` of the two amplifiers v:to cutoif. Ihe plate circuits of these twotampli- .ers were combinedu to produce an output alternately constitutedof first the one, then the other,

signal. Provided that the rate of switching was fast enough,}the output of the amplifiers when ventional electronic switches were quite bulky and heavy and in most cases `were hardly smaller than thecathode ray oscillograph itself. These circumstances v have iconsiderably reduced their practical applications.

Y gIthas been already suggested to employ rotary commutators, self-interrupters, and relays operated bymeans of la low-frequency vacuum-tube oscillator for alternately switching two input signals to acommonoutput.connected to one set Ofdell'ecting elements of the oscillograph. These prior switching devices were in general unreliable in operation and their cost and space requirements were not far below those of an electronic switch. Although various suggestions and proposals of this type have been made, as far as is known, none of these suggestions and proposals was completely satisfactory and successful when carried into practice on a practical and commercial scale.

It is an object of the present invention to prol vide a simple and completely satisfactory solution of the outstanding problem.

It is another-object of the present invention to provide a vibratory switching device for cathode ray tube oscillographs in which a vibratory electromagnetic interrupter energized from a source of low-frequency alternating current is employed for alternatelyl supplying signals from two independent -sources to the same set of deflecting elements of the 'oscillograpn It is a further object of the invention to provide a novel vibratory switching device comprising a vibratory interrupter operated from the alternating current power line, from which also the oscillograph is energized, said interrupter alternately closing a pair of input circuits at the rate of the power line frequency and thereby alternately applying voltages from two sources to the common output circuit for simultaneous visual observation of such voltages upon the screen of the cathode ray tube.

It is also within the contemplation of the invention to provide a vibratory switch energized from the alternating current mains and maintained in continuous vibratory motion of constant frequency foi` periodically and alternately impressing two diiferent signals upon the deflecting system of the tube, means being provided for varying and adjusting the phase relation of vibrator operation withrespect to the frequency of the mains. f Y

The invention also contemplates a vibratory switching device for cathode kray tube oscillographs in the form of an independent unit directly energized from the alternating current mains which is extremely simple irl-character, small in size, may bereadily placed in operative relation with any conventional `cathode ray oscillograph, and which may be built on a practical and commercial scale at a low cost.

Other and further objects and advantages of the invention will become apparent 'from the following description, taken inV conjunction with the accompanying drawings; 'in which:A

Fig. lillustrate's the vcircuit diagram of afvlvi eheri'zed'frin the same source of alternating energized from the alternating current mains;

and

Figs. 4, 5, 6, and 7 show variousvvave patterns".

on the screen of the cathode .ray-tube 'oscillograph, obtained by the device of the invention, 516

the traces corresponding tothe twoinput signals being shown juxtaposed, ratlerlthan sperposed upon one another, for greater clarity.

While a few preferredQembodiments of vention.are1-desorbed-herein ,it is contemplated that considerable-,warmem maybe made; in the method; oi fprooeolurooaod ,the "onsirllotionk of partstvithou -departinairom the spirit of the invention. inthe tono-,wine desoriptiomand .in

the claims, .partsni1.1.be idontifwd by specific naines,orgconveniene, butA they are intended tobe as genericin tirait-application to similar parts as the art will permit.

Reierring non .mrerarbou1ar1lli0 Fg- .1. 0f the drawing, reforopoefnharaoter lilv generally denotes a conventiQnaLpathode ray tube having a heater il a ca t liod e l 2, and a set of control electrodes I3 cooperating withfeach other for producinga cathode ray beam. 'Deflecting forces are applied tosad beamby means of a pair of horizontal deflectng plates M and a pair of vertical deflecting plates l5, the -horizontal deiiecting voltage being. lobtained from a horizontal sweep frequencygenerator [6. AThe vertical delecting .voltage is `amplified by, means of a vertical voltage amplierl'l priortobeing appliedto the corresponding.deflecting plates I5. The various operatingvoltages forthe oscillograph tube minals of input -circuit A and 30 constitute the terminals of input circuit B. One side of

terminals

29 and 30 are connected together and to one terminal of vertical voltage amplifier I1 while the other, hot, side of said

terminals

29 and 30 are respectivelyhconneoted. 'tjd contacts 21. Reed 24, bearing vibratry contacts 26, is connected to the other, hot, terminal of the said vertical voltage amplier I1.

The driver circuit of the vibratory interruptor c rt 2l, preferably the alternating current .mainsjja'smtlie cathode ray tube. For this purjpefse-tranfsforren'l is provided with an additional secondary l'winding 3l, producing a rela- Vtiyelylew alternating voltage, such as, for examthe v are obtainedfrom a power supply I3 energized generally .'denot'e'df. by, reference character 23.

.This interrupter. essentially comprises a vibratory reed 2,4.,clarnped .at one end-:thereof and bearing a ferromagnetic armature, or weight v25 at the other end thereof. The reed also carriesa pair of. reed. arms. or contactarme. att-he end offwhioh there. are mounted vibratory contacts 26. llhese ,vibratolycontacts mayicooperate with relatively ,fixed,c nias=.t.sA 21 mountedatheende of. Sido. arms or. eidespringeofthe, usualy type,- ,Amawfo or Weight 25 is. under the. Control of a drivel. @9H 28, so thatuponsaidc l being energized from a'source of alternating current or of. intermittent direct'curreiitthe'rd:will@be maintained in' a continuous vvibration 'and will.' alternately Aclose contactSfZBl and 2l on the two sides thereof.

. To.' permit'thol alterntejappliooti-on of two sienals to the'sameset of'deilecting elem-ents of the cathode ray 'tubalther are provided twojpairs ple,12`.6 volts, which through a phase shifter 32 4antifa'half-wave rectier 33 may be impressed upon the driver coil. Although in the illustrated embodimentof the -invention a .separate Isecondary winding has be'enfshown .for 'operating the` vibratory .interrupte'n obviously any 'of the vusual .low-.voltage windings of a conventional power-transformer may be utilized for' the` same purpose. ,of

From the foregoing description, the operation of the vibratory switching deviceof the'invention willV be readily understood'by those'skilled in th'eart. Upon closingfinain'orpowefswtch 22, power transformer I9,`will"be"energized"and the operation of the 'cathode ray tube will loen'itiated in the conventional manner. 'At'th'e's'am'e time, however, an alternating volta'ge will be 'also developed across secondary winding '3| and through' phase shifter 32 andhalf-wave'r'ectiiier 33,. driver coil 28 will beperiodically energized every 'other 'half-cycle. Reed "'24 'willlb'e maintained in continuousvibration'at'the frequency of thepower line and'will alternately close contacts 126 and 21'011 the -Ieft'ad'tlie Yri'gl'it `side thereof. In this manner, inputcircuits A and `B, connected kto the two signals to4 be'studidfwill be alternately connected 'to 'the'cor'nm'on output circuit represented by'tlie input "side`of vertical `voltage amplifier 11, Aand "after"ainpliiicatinare impressed upon vvertical defiec'ting plates ""I-5. Thus, two traces, corresponding tothe two'signals to 'be studied, will simultaneously 'appear on the screen of the cathode ray 'tube 'and in'ay be Vsub-jectt'ed Ato comparative study,

It' hasjbeen found tiiatajvibratry:i'tromgnetic interruptor Aliavirg'a vibratory v"system ii'or- 'mally'tuned toan operating frequencyof 'about 'llilto -120l(3yt`31`e's"per seblfd will Ybe -515("J'Si't'iiely locked into the'60` cycle' power line frequencyfeven Athough is"`vbr"atirg at'fduble' 'freqr''y. JAn interrupter' tuned to' ai frequency' 'f 55 t0"l 60 V"cycles per second, however, will'give .sornwhat'inore 'satisfactory results, particularly 'for theoiise/ation 'of tillcy'cle phenomena, inasmuch" fas ''the Aswit'iiirg 'trate' isjeiit "in 'half' making it' 'Ip sible to `'observe-approximatelyone-half of a.`60v cycle alternation. A 'I he` object"v 'of'- the' provisin of'the half-Wave rec'tierin'f the driverv "circuit is' to" cut o everyotherhalficycle. TliefsafineY result'iiay those sk'illedfi'n the "art Vwill 'readily un'der- Y being particularly desirable when power line frequencyphen'omena are to`be investigated..

The modification of the invention depicted in Fig.`2 is in most respects similar to the one described in the foregoing andlsimilar reference characters have been used to denotecorresponding parts. Also, illustration of the cathode ray tube and of its power supplyhave been to a large extent omittedfor the sake of simplicity. The difference resides in the provision of ,a reversing ,switch 40 between the two input circuits andthe vibratory switch 23. Reversing switch 40 is in the form of a double-pole, double-throw switch having vtwo movable contact arms 4l, respectively connected to the two fixed contacts 21 of the vibratory switch. The upper contact arm may selectively close

contacts

42 or 43, while the lower contact arm may selectively close

contacts

44 or 45.

Contacts

42 and 45 are connected together yand to onelof terminals 29, and

contacts

43 and 4,4 are likewise connected together and to one of the terminals 30. The other one of

terminals

29 and 30 are connected together and to one of the, vertical deflecting plates of the cathode ray tube (not shown), the other vertical deflecting plate Vbeing connected to reed 24. The driver circuit comprises secondary winding 3l of power transformer I9, half-wave rectifier 33, driver coil 28, and the phase shifter network generally denoted by reference character 46. The phase shifter network may take various convenient and well-known forms.` Its illustrated form comprises a c9ndenser41of about 50 microfarads connected in series with an inductance 48 of about 100 millihenries, a potentiometer 49 of about200 ohms being connected across both, the sliding contact of which isconnected to the common terminal of condenser and inductance. By means of a phase shifter of theV described character the phase may be varied approximately between plus 45Hdegrees and minus 45 degrees in amanner well understood. l

vIriview of the similarity of circuit arrangement the operation of this modied embodiment of the Vinvention will be obvious. The purpose of the .provision of polarity switch 40 is to invert the respective connections of inputs A and B to the fixed contacts 21 of the vibratory switch. This is 4particularly desirable when observing power line frequency phenomena as it permits, with the phase shifter 46, the investigation of any part of theLcycle. s Y

'I'he further modified embodiment of the invention shown in Fig. .3 is in the form of an individual and independent unit which may be manufactured and sold as an accessory to conventional cathode ray oscillographs to permit the simultaneous observation of two oscillatory phenomena. It comprises input terminals 5U and input terminals 5l which are for connection of the twol signals thereto. A potentiometer 52 is connected across terminals 5l] and a similar. potentiometer 531s connected across terminalsv I. The sliding contacts of potentiometers 52Vand 53 are respectively connected to

stationary contacts

54 and 55 of vibrator 56. One of input terminals 50 andinput terminals 5l are connected together Yand to ground. In this manner the input voltage of b'oth signals may be independently adjusted. Vibratory reed 56a is'clamped at one end thereof and carries a soft iron armature 51 at the other end thereof'under the control of adrivercoil 58. Thereedv also supports vibratorycontacts 59 and 60,.respectively cooperating with stationary con- ,.tactsand 5.5 duringvibrationsofthe reed. One

of .output terminals 6| is connected to reed Sa and the other to ground.V

The driver circuit is energized from the alternating current power line 62 through a switch 63 and the primary winding 64 of a step-down transformer 65. The driver circuit proper cornprises secondary winding 66, phase vshifter network 61, driver coil 58, reversing switch S8 and half-wave rectifier E59.v The reversing switch includes a pair of jointly operable contact arms 10 and 1l. Of these, arm 1l) may selectively close

contacts

12 and 13, and arm 1I may selectively close contacts 14 and 15. Contacts 12 and 15 are connected together and also to one terminal of half-wave rectifier 69, while

contacts

13 and 14 are likewise connected together and to the other terminal of said half-wave rectifier, From this circuit arrangement it obviously follows that by placing reversing switch 68 from one into the other of its positions, the direction of connecting the half-wave rectifier in the driver circuit will be reversed. Phase shifter 61 is identical with the corresponding element 4S of Fig. 2 so that it will not be necessary to repeat its description.

When it is desired to operate the vibratory switch of Fig. 3, the two signal sources to be investigated are respectively connected to terminals 59 and 5|, the voltage of the sources being adjusted to the proper value by means of

potentiometers

52 and 53. Output terminals 5l of the device are connected to the vertical deflection terminals of the cathode ray oscillograph. Reversing switch 68 is placed into one of its positions and main switch 63 is closed to energize driver coil 58. Upon said driver coil being energized every other half-cycle, reed 56a will be maintained in continuous vibration and

contacts

54, 59, and 55, 6i) will be alternately closed. Consequently, input circuits A and VB will be alternately connected to the common output circuit. Inthis manner, traces corresponding to both signal inputs A and B will simultaneously appear upon the screen of the cathode ray oscillograph and may be readily compared with each other.

The phase of vibratory interrupter operation may be continuously adjusted by means of phase shifter 61. On the other hand, reversing the position of switch 68 will reverse the polarity of half-wave rectifier 69 whereby the said phase may be changedby degrees. As it has been stated in the foregoing, this is of particular value when investigating power line frequency phenomena, as it permits with the phase shifter the investigation of any part of the cycle.

Reference character 1G denotes the contact arm of a single-'pole double-throw switch adapted to selectively

close contacts

11 and 18, respectively connected to the lhotvsides of inputs A and B. One of terminals 19 is connected to ground, and theother to contact arm 16, so that a synchronizing voltage connected between terminals 19 may be selectively impressed uponthe one or the s other of the two signal inputs.

Figures 4 to l'7 lare various cathode ray oscillograph traces, or patterns, obtained by the vibratorswitch of the invention. In Figures 4, 6 and 7 thetraces corresponding to the two inputs areushownjuxtaposed for the sake of clarity, rather than superposed and each extending along -thefull width of the screen, as they actually appear. In Fig. 4, the horizontal sweep frequency generator has been adjusted to the fundamental power line frequency, the frequency applied to input B is at fundamental power line frequency, and .thefrequencypf inputA. is four ,timesthe fun.-

accanto damental power line frequency. The pattern of Fig. has been obtainedunder identical conditions, with the exception that the horizontal sweep frequencyv generator i'srset for a frequency twice the power line frequency. Fig. 6A shows a pattern obtained-under the same conditions-'as that of Fig. 4 but the polarity reversingv switch in its other position -sothat both signals are inverted. Fig.. 7 illustrates a pattern corresponding to thesame conditionsasitha't of- F-ig. 2lewith the exception that lthe -phase shifter control has been operated so asfto'observe different -partsof the signal.

It will be noted that the vibrator switchfo the invention provides 'numerous important advantages. Thus, rst of all, ith-lay bevemployed for the complete observation ofi any.` twolsi'gnal'shaving a frequency -of 60 cycles, -or more, andv Afor the partial observation ofy` suc'li .signals 'having frequencies less than 60- cycles. The switch -embodying the invention is `particularly advantageous for the observation of power line frequency phenomena, such as, for instance, the output wave-formv of a rectier circuit, phase-displacement of' power line frequency equipment, etc. The rectifier reversing switch together with the phase shift control permits the -completefobservat-ionA of a power lline frequency signal.

It is also to :be observed that the operation of the switching device rofthe invention is notrestricted to the Vobservation of 60- cycle phenomena but extends at least throughout fthe-audiofrequency range. Thus, it has been -`found that the device will faithfully vcom-paresignals :of `va frequency as high as 20,000` cycles vper 'secondi In addition, while 'the signal will be somewhat interrupted, it is perfectly feasible to investigate and to compare the phaserela'tion between frequencies as low as cycles per secondi'. In other words, the device has a useful frequency range of approximately 20 to v20,000 `cycles per second. and provides particularadvantages -in observing power line lfrequency phenomena.

Moreover, the vibrator switch: of the invention is extremely simplein: construction, vis very reliable in operation and'lm-a-ybeifmandacturedin the form` of a small and inexpensive unit, ingeneral costing only a mere fraction-ofl conventional electronic switches -now used yfor substantially the same purpose. Due tothe'fact that no vacuum tubes or networks of yany kind fare employed in the switching circuit `of thel device, complete freedom from `phase shift, asiregards one signal to the other, is obtained. For -this reason, the present device maybe -use'dfito-compare very accurately fthe vexact phase relation between, for example, the current Vand lvoltage existing in a loudspeaker voicecoil', while'being driven by a 'test oscillator. These-'new' results, particularly the freedom -from-phase shift, fcannot be obtained by means Vof'conventionalelec-- tronic switches.

Although the present invention has' been disclosed in connection with a few prefer-redembodimentsl thereof, variations and modifications may be resorted `to by those skilledfin -theart without departing from 'the' principles fof the invention. For example, the principles 'oil' the-invention are not restricted' to-ca-thoderray tube oscillographs `but may be Vapplied A'tofpractical-ly any type of visual, photographic, or record-ing oscillograph, such Vas string oscillographs, crystal or electromagnetic recorders, andf'lthelike. All of these variations and 4`modilcatiorrsfare .considered-'to` be withinthe' truespirit and-scope of'the' present invention, as disclosed; in the forca'- goingdescription andL d enedv by' theA appended claims.

While .the present invention, as vto its objects and:y advantages, has been described herein:v as car-ried out inl specific embodiments thereof, it is not desired tobe limited thereby but it is intended t'o cover the invention broadly Withinthe spirit andi scope off the appended claims.

What is claimed is:

1. In a deviceV for simultanetmsly exhibiting traces corresponding to a pair of: variablevoltages by means of an oscill'ograph, the combination which comprises a vibratory electromagnetic iin-- terrupter having a vibratory reed adaptedl toalternately actuate a pairof contacts anda-driver coil therefor, an input circuit for `each off said voltages respectively connected 'to said contacts, and a common output circuit connected' -to said reed and electrically associated withsaidl esci-llograph, saiddri-ver coil-beinghenergizedat a constan-t low frequency rate-from an--externali current sourcel thereby to cause vibrationof said reed-and alternate connection of saidl input circuits -to -thecommon output circuit', 'the' resonant frequency of said reed being substantially an integral multiplev of the frequency ofdriver coil energiaation whereby the frequency of= the vibratory interrupter is locked in withthe frequency of saidv externa-l current source.

'2; In a switching device for cathode ray/tube osci-liographs energized from the alternating Acurrent mains whereby two independent variable lvoltages Ymay be simultaneously exhibited-0n the screen of said tube;l ythe combination Awhich comprises `a 'vibratory electromagnetic interrupter 'including a vibratory reed, a pairtof' contacts valternately operable during vibration of said reed, and a driver coil for said' reed; 'an input circuit vfor leach of said 'voltages respectively connected to said contacts; a common 011tput circuit connected between said, reedf'and one set of deflecting elements of Vthe cathode Aray tube; and connections between Asaid driver coil land the alternating current mains to maintain said reed in vibration `and to alternately lapply said'two variable voltages Yto said deectinggelements by said contacts, the resonant lfrequency of-said reed being substantiallyan integral-multiple ofthe frequency of the alternatingv current mains wherebyv the frequency of the vibratory interrupter is locked in with that of the alter nating current mains.

3. lIn -avibratory switch for cathode rayfitube oscillographs-energized fromthealternating current Vma-ins whereby two variable voltages `may Ibe exhibited on the screen of said-tube at lthe same time; -the ycombination* which comprisesa magnetically polarized vibratory interrupterhav- Ving a' vibratory freed, a driverf'coiltherefor, `and `a pair of contacts alternately operable duri-ngvi- `vloration-of'sa-id reed; an input circuit for eachof said voltages respectively connected Ltoesaidfconltacts; -a common output 'circuit -connectedfbevtween said reed and one -setof vdeiiecti-ng-ele- =ments of'V they cathode ray tube; and `'connections between said driver coiland `the alternating-curfrentinains whereby saidreed will ber'caused to vibrate at the frequency of the mains and fwi-ll alternately Aapply sai'd two variable voltagesto said deiiecting elements fby said contacts, ithe resonant 'frequency 'of' said reed being ysubstan- Jtially .an integral multipleof the ifrequencylof vthe alternating current mains iwhereby-Ithe firequencypof the :vibratory interrupter is.' locked .in

with that of the alternating current mains.

4. In a switching device for cathode ray tube oscillographs operated from the alternating current power line to simultaneously exhibit vtwo variable voltages on the screen of the tube; the combination which comprises an electromagnetic vibratory interrupter having a vibratory reed with a driver coil therefor and a pair of contacts alternately operable during vibrations thereof, an input circuit for each of said voltages respectively connected to said contacts, a common output circuit connected between said reed and one set of deflecting elements of the cathode ray tube, connections between said driver coil and the alternating current power line, and a halfwave rectifier interposed in said connections whereby said reed will be caused to vibrate at the power line frequency and will alternately apply said two variable voltages to said deflecting elements by said contacts.

5. In a switching device for cathode ray tube.

oscillographs operated from the alternating current power line to simultaneously exhibit two variable voltages on the screen of the tube, the combination which comprises an electromagnetic vibratory interrupter having a vibratory reed with a driver coil therefor and a pair of contacts alternately operable during vibrations thereof, an input circuit for each of said voltages respectively connected to said contacts, a common output circuit connected between said reed and one set of deflecting elements of the cathode ray tube, means including a half-wave rectifier for energizing said driver coil from the power line thereby to cause vibration oi said reed at the power line frequency and alternate application of said two variable voltages to said defiecting elements by said contacts, and switching means for reversing the polarity of said rectier to change the phase of operation of the vibratory interrupter substantially by 180 degrees. d

6. In a switching device for cathode ray tube oscillographs operated from the alternating current power line to simultaneously exhibit two variable voltages on the screen of the tube; the combination which comprises a vibratory interrupter including a reed bearing vibratory contacts, relatively fixed contacts cooperating with said vibratory contacts, and a driver coil for said reed; an input circuit for each of said voltages respectively connected to said xed contacts; a common output circuit forming a connection between said reed and one set of deflecting elements of the cathode ray tube; means for energizing said driver coil from the power line thereby to cause vibration of said reed at the power line frequency and alternate connection of said input circuits to said common output circuit by said contacts; and phase-shifting means interposed between the power line and the driver coil to continuously adjust the phase relation of vibrator operation with respect to the power line frequency.

7. In a switching device for alternating current 'power line-operated cathode ray tube oscillographs to simultaneouslyl exhibit two variable voltages on the screen of the tube; the combination which comprises a vibratory interrupter including a reed bearing a vibratory contact on each side thereof, a relatively fixed contact for cooperation with each of said vibratory contacts, and a driver coil for said reed; a pair of input circuits anda common output circuit having one of their sides connected together; the other side of said input circuits being respectively connected to said fixed contacts and the other side of said output circuit being connected to said reed; means including a half-wave rectier for energizing said driver coil from the power line thereby to cause vibration of said reed at power line frequency and alternate connectionof said input circuits to the output circuit by said contacts; and switching y means for reversing the connection of said input circuits with respect to the fixed contacts of the vibratory interrupter.

8. In a switching device for alternating current power line-operated cathode ray tube oscillographs to simultaneously exhibit two variable voltages on the screen of the tube; the combination which comprises a vibratory interrupter including a reed bearing vibratory contacts, relatively fixed contacts cooperating with said vibratory contacts, and a driver coil, an input circuit for each of said variable voltages respectively connected to said fixed contacts; means for individually adjusting the voltages applied to said input circuits; a common output circuit between said reed and one set of deflecting elements of the cathode ray tube; means including a halfwave rectiiier for energizing said driver coil from the power line thereby to cause vibration of said reed at power line frequency and alternate connection of said input circuits to said common output circuit; and means for selectively impressing a synchronizing voltage upon one of the input circuits.

9. In a switching device for alternating current power line-operated cathode ray tube oscillographs to simultaneously exhibit two variable voltages on the screen of the tube; the combination which comprises a vibratory interrupter in-` cluding a reed bearing vibratory contacts, xed contacts cooperating with said vibratory contacts, and a driver coil; an input circuit for each of said variable voltages respectively connected 'to said xed contacts; a common output circuit between said reed and one set of deiiecting plates of the cathode ray tube; a driver circuit for energizing the driver coil from the power line thereby to cause vibration of the reed at power line frequency and alternate connection of the input circuits to the common output circuit; a half-wave rectifier in said driver circuit; phase shifter means in said driver circuit to continuously change the phase of operation of the vibratory interrupter; and switching means for reversing the connections of said rectifier to change the phase of operation oi the vibratory interrupter by degrees.

HENRY ROGERS MALLORY.

' permissions CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS