Патент USA US2378388код для вставки
June 19, 1945. _ 5. J. BEGUN ' 2,378,388 ‘RECORDING AND REPRQDUCING DEVICE Filed Jan. 1, 1942 22 ‘ ' a' 6 MODULATOR 4 Sheets-Sheet l AMPLIFIER M = fquAuzzR AMPLIHER FILTER B‘P'HLTER / 7 Y - 225 <''' 227 ¥ ~ 7%.? _ June 19, 1945. 5. J. BZEGUN 2,378,388 RECORDING AND REPRODUCING- DEVICE Filed Jan. 1, 1942 4 Sheets-Sheet 2 Eg .: “L8 8% . “83205 HECA 88wRa June-11.9, 1945. _ s. _‘|. BEGUN 2,378,333v RECORDING AND REPRODUCING' DEVIYCE" ‘ Filed Jan; 1, 1942 4 Sheets-Sheet 3 f?» ' ‘ ~ 3 I ZTTORNEY June 19, 1945. 5. J. BEGUN 2,378,388 I RECORDING AND REPRODUCINGI DEVICE Filed Jan. 1, 1942 4 Sheets-Sheet 4 “mg/vQ |_.________ X9 8, , § [email protected]?3:6|.2;83: w» .HY @b . .\ , .v.McJzo3rgC9-mu‘0kzQ3jvom; \&_ \Q "I IA’ ‘ATTORNEY. 2,378,388 Patented June 19, 1945 UNITED STATES PATENT OFFICE 2,378,388 RECORDING AND REPRODUCING DEVICE Semi Joseph Begun, Cleveland Heights, Ohio, as slgnor to The Brush Development Company, Cleveland, Ohio, a corporation 01' Ohio Application January 1, 1942, Serial No. 425,304 31 Claims. (Cl. 171-95) Figure 2, showing the transient recording cir This invention relates to systems and methods cuit in detail and the trigger circuit and the for studying transient phenomena and more transient reproduction circuits in block diagra particularly to such systems and methods for re cording on a recording medium a transient cir form and connected to the transient recording‘ cuit condition and utilizing the record of the transient for studying the characteristics of the circuit. Figure 5 is an illustration of the trigger circuit and showing the recording and reproducing cir transient. , v Among the objects of the invention are novel , cuits in block diagram form. Figure 6 is an illustration of the circuit used systems and methods of the foregoing type which operate to make a continuous obliterable record 10 ‘for reproducing the transient, and showing the recording and trigger circuits in block diagram of the circuit conditions under study on an end form and connected to the reproducing circuit. lessly-operating cyclically-effective recording me Figure '7 is a plan view of a magnetic head in dium, such as a magnetic recording medium, so its open position. that the circuit conditions are continuously re corded; the continuous recording operation be 15 Figure 8 is a plan view of the magnetic head in its closed position. . ing accompanied by a continuous obliteration Figure 9 is a diagrammatic illustration of a of the recordings and the obliterating action be timing device utilizing my transient recording ing stopped upon the occurrence of a transient device. condition so as to retain on the recording medium a record of a signal corresponding to the tran 20 My invention comprises means and a method for recording a transient signal'on a storage me sient occurrence and the recording operation be ing discontinued after the transient occurrence dium and repeatedly reproducing it therefrom has been recorded on the medium in such man ner as to enable the study of the transient oc atv regular intervals to establish a wave, each cycle of which is substantially a facsimile of the currence by cyclically reproducing the record and utilizing the reproduced record for operating . original transient. The device may use any re cording medium, and suitable means for record ing the transient thereon and reproducing the a cyclically-operative indicating device, such as transient therefrom. I prefer to use a medium an oscilloscope, which presents an image corre which can be used over and over again such, for sponding to the reproduced signal upon each cycle of the recording medium; such systems 30 example, as a magnetic tape or disc, etc. Such preferred embodiment is illustrated in and methods which are effective for studying low Figure 1, in which is shown means for a method frequency and direct current transients by modu of storing a transient by electrically recording it lating with the signal which is to be recorded a on an endless magnetic tape l0, means for and source of carrier oscillations of a frequency which is reproducibly recordable on the endless 35 a method of reproducing the recorded transient from the recording medium and presenting it magnetic recording medium, so as to provide a visually by repeatedly reproducing it on an oscil modulated carrier signal which is continuously lograph I I or other indicating device; and associ recorded on the endless recording medium and ated circuits for controlling the operations of the obliterated immediately thereafter, the obliterat ing action being stopped upon the occurrence of a 40 means and method. Electrical recording may in elude electromagnetic, photoelectric, or any transient—the reproduced recorded modulated other process or device utilizing electricity in the signal being modulated so as to cyclically provide recording and/or reproducing process. . a demodulated reproduced signal corresponding The'endless tape I0 is driven about rollers 12 to the transient signal which is utilized for oper ating the cyclically operative indicating device; 45 and 13 by a motor l4. A magnetic obliterating head I5 and a magnetic recording head l6 are and various other novel and desirable features associated with the tape Ill. The obliterating forming part of such systems. head I5 is adapted to apply a steady saturating The foregoing and other objects of the inven ?ux (such as the ?ux derived from battery H) tion will be best understood from the following to the tape ID as the tape passes, and to bring description of exempli?cations thereof, reference each incremental portion of the tape to a state being had to the accompanying drawings where of substantially uniform saturation. With the switch 23 closed in its downward position the re Figure 1 is an illustration of my invention in cording head It is connected to a signal record block diagram form. Figure 2 is an illustration of another form of 55 ing circuit which may include a source I 8 of polarizing current. The transient signal to be my invention, also in block diagram form. recorded on the tape I0 is applied at the input Figure 3 is a diagrammatic illustration of a terminals I9, 20, of the recording circuit. In modulated carrier current and a magnetization cluded in the recording circuit is an ampli?er curve. Figure 4 is an illustration of the circuit of 60 2| and an equalizer 22. The equalizer 22 is to in . ' 2 2,878,388 provide substantially constant current to the re cording head IS. The instantaneous current which is in the recording head I6 is given by the superposition of the instantaneous values of the transient signal current and the polarizing cur rent. As the saturated tape passes the record ing head a magnetic pattern corresponding to the current in the recording head is recorded on the tape in the well-known manner, and as quency modulation and phase modulation. A de tailed description of one carrier method of re cording may be found in my application entitled Apparatus and method for magnetic recording, Serial No. 399,909, ?led June 26, 1941. ‘ Figure 2 illustrates a form of my invention adapted to record transients in direct current circuits or circuits normally carrying no current, and using the method detailed in the above-cle soon as‘the transient has been recorded the ob 10 scribed patent application. ;Examples of tran literatin‘g and recording process are stopped by sients which this particular form of the apparatus automatically or manually opening'switches 23 is adapted to record are the current in spot weld and 28 so that the recorded transient will not be ers and the charge or discharge of condensers, erased or have further transients superimposed etc. upon it. A playback‘ head separate from the re The input terminals I9, 20 are connected to cording head l6 may be used in association with the circuit in which a transient is expected, such the endless tape III by connecting it to an equal for example, as across a low resistance in the izer 24, an ampli?er 25, and the oscilloscope Ii circuit of an impact welder. The motor il drives the roller l2 to cause the endless magnetic tape or"_other indicating device, but I prefer to use the'recording head IS in a dual capacity; that is, 20 III to continuously rotate about rollers l2 and I! as both a recording and playback head, and pro at a uniform velocity in the direction shown by - vide the switch 23 for switching the head I6 from the arrow. The time of one cycle of the tape loop the recording circuit to the playback circuit. preferably is slightly longer than the transient After the transient, which may occur only once, which may, for example, be of about one-tenth -isl»recorded on the endless tape ill, the tape can be 25 of a second duration, thereby establishing on the tape loop a record of the normal circuit condi driven around the rollers l2, l3 and, with switch 23 thrown to cause the head IE to act as a play back head, each complete transit of the tape will tions and a record of the transient condition. An oscillator 26 is tuned to a frequency somewhat higher than the highest frequency component to cause the signal recorded on the tape to produce a trace of the transient on the oscillograph I I. In 30 be recorded. When the highest frequency com ponent of the signal is in the neighborhood of this manner repeated reproduction of the tran sient signal on an oscilloscope II, in which the 500 cycles per second a carrier frequency on the horizontal sweep of the oscilloscope is synchro order of 2000 cycles per second is satisfactory. nized with a point on the tape ill, will produce The oscillator is connected to and caused to ex a su?iciently bright and sustained trace to enable 35 cite an obliterating ampli?er 21, which in turn supplies 2000 cycle current to the obliterating a person to study the transient, and no time need head l5. As the tape l0 passes the obliterating head l5 each incremental portion of the tape is subjected to a 2000 cycle alternating magnetic a switch. If the transient is of an acoustical nature it 40 force which is suf?ciently strong to saturate the part of the tape closest to the coils. As each in ' may be converted by means of an electromechan cremental portion of the tape leaves the coils the ical transducer vinto an electrical transient and applied at the input i9, 20 of the recording'cir magnetic ?eld active on it is gradually reduced be lost between the recording and playback oper ations other than the time necessary to throw and thus the successive increments of the tape are cuit. In this manner an acoustical transient may be studied the same as an electrical transient, 45 brought to an unmagnetized state. In this con dition the tape is ready to have a new record also, transients of a physical nature such as pres sure, etc, may be changed to electrical tran sients and recorded for study. iliéipressed on it at the magnetic recording head The oscillator 26 also supples 2000 cycle car With the above described method it is di?icult » to reproduce the recorded signal from the mag 50 rier current to the magnetic head IE, but before reachingthe magnetic head I6 the carrier cur netic medium if the signal has low frequency rent passes through a modulator 29 to which components as the rate of change of flux in the is also connected the transient signal input ter magnetic head is low for the low frequency com ponents. For the above described means and minals I9. 20. In the modulator 29 the transient method of recording this makes necessary‘ the 65 signal modulates the 2000 cycle carrier current use of considerable equalization for low frequen from the oscillator, and the signal modulated carrier then passes to an ampli?er 30. The mod cies with consequent introduction of phase shift ulator 29 is of the balanced type arranged to bal and background noise. With this method the ance out the signal and pass the modulated car quick interruption of the recording and obliterat ing current by throwing switches 23 and 28 after 60 rier. A high pass ?lter 3I- may be connected in the recording circuit between the ampli?er 30 the signal transient is on the tape causes an un and the magnetic head iii. For recording tran desired transient to be recorded on the tape which sients whose highest frequency components are is apt to interfere with the desired signal tran in the neighborhood of 500 cycles per second the sient. In order to obviate these undesirable con 65 high pass ?lter may be designed to cut off some what below 1500 cycles. The exact point at which ditions I use a signal modulated carrier cur the high pass ?lter cuts on‘. depends upon the fre rent to record on the tape. i‘his method per quency range of the transient to be recorded and mits the recording without phase distortion upon the chosen carrier current frequency. The of frequencies substantially down to zero fre quency corresponding to direct current, and can 70 ?lter 3i is not essential but is useful in taking out hum and the residual transient signal which be arranged to avoid introduction of undesirable may have gotten through the modulator 29. If transients caused by switching operations. Sev no transient is being recorded the 2000 cycle al eral methods of modulating a carrier current to ternating ?ux set up in the magnetic head I6 by record on the magnetic medium may be used; among them being amplitude modulation, fre 75 the carrier current causes a 2000 cycle magnetic 2,378,888 wave to be recorded on the moving tape Ill. Upon nearly completing a. circuit of rollers I2, I 3, the recorded wave is removed by the obliterating 3 time intervals such that it can be viewed on a cathode ray oscillograph. The oscillograph H shown may be a standard commercial cathode-ray oscillograph, such as head l5. When a transient signal is applied to the signal Cl type TMV—122—-B sold by the Radio Corporation of America, as described in its instruction book input terminals I9, 20, the carrier current is mod IB-23,339, published in 1937. As is well known, ulated by the transient and a corresponding mod such standard cathode-ray oscillographs are ulated magnetic carrier wave is recorded on the equipped with a synchronizing switch which is tape. To prevent obliteration of the transient modulated magnetic carrier wave, and to avoid 10 used to control the synchronization of the hori zontal time-axis sweep with the investigated sig nal. The synchronizing switch usually has at after the tape H] has completed a cycle around the least two positions, namely, an internal syn rollers l2, l3, a transientpperated control circuit chronizing position, in which the time-axis sweep is energized to block the obliterating ampli?er 21 and to open the recording circuit after suitable 15 is automatically synchronized with the investi gated input signal, and an external synchroniz time intervals. ing position, in which the time-axis sweep is syn The gain of the ampli?er 30 which feeds the chronized with an external synchronizing signal. magnetic head I6 is preset to swing the record The number of repetitions per second at which ing ?ux set up in recording head l6 by the carrier current, over the proper part of the magnetic 20 the recorded transient is repeated on the oscillo graph II depends on the number of tape cycles curve of the tape. (This is explained in detail in per second. For example, this frequency of repe connection with Figure 3.) The strength of the tition may be ten transient facsimiles per sec transient signal input may be adjusted by a po ond on the oscillograph. The time-axis sweep tentiometer 32 connected across the signal input of the cathode-ray may be internally synchro terminals 19, 20. nized with the reproduced, demodulated and ill The transient operated control circuit consists tered signal, which is impressed upon the oscillo of a trigger device 33 connected to the transient graph II, or the tape joint 49 or a nick in the signal input terminals I9, 20, the obliterating am tape maybe used as a trigger for synchronizing pli?er 21, switching means 34, and sometimes, if desired, to a switch 41 connected to the tape 30 the time-axis sweep of the cathode-ray. In order to record on the steel tape l0 an elec-' drive motor I4. The trigger means is actuated by tric current is used to set up a proportional mag the incoming transient to cause the obliterating netizing force which is applied to the tape l0. ampli?er 21 to be blocked thereby preventing the Therefore, as the electric current varies in ac obliterating head I5 from “erasing” the record of the transient which is made on the moving tape 35 cordance with the instantaneous value of the sig nal to be recorded, the magnetizing force im I 0, and the actuation of the trigger means 33 also pressed on the tape varies in proportion to the causes the switch means 34 to be thrown to break original signal. the recording circuit to the magnetic head I6 and The relationship between the magnetizing force to make ‘a playback circuit from the magnetic head Hi to the indicating instrument II. If 40 H and the resultant magnetic induction B for in desired the trigger circuit may iloe used to break ' creasing and decreasing values of H is expressed graphically by a hysteresis loop, and for increas the circuit to the motor l4 and stop the tape l0 ing values of H starting with a demagnetized tape immediately after a transient has occurred. it is expressed by a virgin magnetization curve. Thus, shortly after a transient has been recorded on the tape I0, the entire device automatically 4.5 Every magnetic material has a particular virgin magnetization curve and hysteresis loop which becomes inoperative due to the action of the trig identi?es the magnetic characteristic of the ma ger means. terial. ~ . For applications in which it is not desired to From hysteresis loops it is obvious that mag have an automatic control of the trigger circuit, an external control 4| is provided. The external 50 netic effects are not reversible, and that the mag netic induction obtained from a given magnetiz control may be a push button or other similar de ing force depends upon the previous magnetic his vice for initiating the action of the trigger device superimposing the carrier on the recorded wave 33 to effect the same results as the actuation of the trigger device 33 by the incoming transient signal. After the transient is recorded on the tape II] in the form of a modulated carrier magnetic re cording, it is ready to be observed by repeatedly tory of the material on which the magnetizing force is impressed. Accordingly, with a tape upon 55 which previous magnetic records have been made it is necessary to produce a substantially uniform condition either of saturation or demagnetiza tion in order to "erase” the magnetic record. In a. magnetic tape it is necessary to obliterate reproducing the tape record on an oscillograph II or other indicating instrument. From the 60 the previous record before a new record is put on the tape or mixed records are apt to result. magnetic pickup head I B the reproduced signal This obliteration may be obtained by applying a goes through an ampli?er I30 then through a magnetizing force to the tape which is sui?ciently band pass ?lter 36 which is designed to pass, high in value to cause an induction which is in in addition to the carrier, the side bands corre sponding to modulation frequencies up to about 65 the saturation range on the magnetization loop of the material. That is, in the neighborhood of 500 cycles. The signal then passes to the de point S1 or S2 in Figure 3, in which the heavy line modulator 31 where a recti?er “detects” the out 38 represents a typical virgin magnetization curve put of the band pass filter and the carrier and for a material which has been demagnetized. its harmonics are ?ltered out, and then to an in > dicating instrument such as an oscillograph I I. 70 The obliteration may also be obtained by apply ing over a relatively large area" of the moving The output from the demodulator consists of a tape an alternating magnetizing force derived direct current component upon which is super imposed a wave composed of a series of tran from an alternating current, and gradually re ducing the magnetizing force to zero to reduce sients each one being substantially a facsimile of the original transient, and following at regular 75 the residual magnetism to substantially zero. 4 2,878,388 signal will have a 3-H relationship in accordance with the virgin magnetization curve 33 of the inates the need for an extra oscillator and makes a more simple device. However, if the need arises it is to be understood that the obliterating material. The decrease in strength of the mag netizing force is obtained for each portion of the current and the carrier current may be produced by separate sources (such as oscillators) and tape by removing that portion of the tape farther and farther from the center of the magnetizing that the obliterating current frequency may be of any value which will give a su?icient number force. of reversals of polarity to reduce the residual Subsequent magnetization in accordance with a This is the method of obliteration em magnetism in' the tape to substantially zero. In Figure 3 the line 38 represents a magnetiza ‘ Continuous alternating current is applied to In tion curve for a material which may be used as the coils‘ of obliterating pole pieces which are a magnetic tape. The curve comprises two sub positioned near the moving tape. This causes stantially straight portions 232 and 233 and three a rapidly reversing diffuse magnetic ?ux to be curved portions 234, 235, and 238. The curved ' impressed- through an area of the tape which is portion 236 lies between the two substantially large in comparison to the area through which straight portions 232 and 233 and represents non the recording flux is impressed, and as each por4 linearity between the magnetizing force and the tion of the tape ‘moves away from the pole pieces induced ?ux density for small values of the mag which are the center of the flux distribution, the netizing force. From zone 231, which is sub strength of the ?eld on each such portion of the stantially the junction of curved line 236 with tape decreases gradually to zero. The pole pieces line 232, to zone 238, which is substantially the of the obliterating head have their like magnetic junction of line 232 with curved line 234, the line poles toward each other. However, the use of ployed in the preferred form of my apparatus. alternating current in the coils causes the mag netic polarity of each pole to alternate; at one instant the north poles are toward each other, the next instant the south poles are- toward each other. This establishes a magnetic ?eld about each pole piece which bucks the other magnetic 232 is substantially straight. This means that for each unit increase in magnetizing force H be tween zones 231’ and 238' there is substantially a proportional increase in the flux density B in the tape I0 from 231" to 238". Above zone 238 partial saturation takes place and B does not ?eld and results in a relatively large leakage or diffuse magnetic ?eld through which the tape . moves during the obliterating process Each portion of the tape which has been re increase on a substantially constant ratio with H. Below the H axis the same effects take Place for magnetizing forces created by currents of the moved suf?ciently far from the obliterating poles tion of lines 236 and 233; and zone 240 repre sents the junction between lines 233 and 235. Zones 231, 238, and 239, 240 may be referred to is now reduced to substantially zero residual mag netism and is ready to have a magnetizing force ; corresponding to a signal impressed on it. This is done by the recording head indicated generally by the reference character It and comprising opposite polarity. Zone 239 represents the junc as critical zones or points as they de?ne substan tially the extremities of the substantially straight portions of the magnetization curve. In order that a signal recorded on the tape Hi two pole pieces, one of which is surrounded ‘by a coil. In the coil there is a current correspond 40 can be reproduced without considerable distortion it is necessary that the maximum magnetic ?ux ing to the signal to be recorded on the tape. The induced in the tape during each cycle of the mod current establishes a varying magnetizing force ulated carrier current correspond to a point in the pole piece which in turn establishes vary which lies on the substantially straight portion ing magnetic flux density in successive portions 45 232 or 233 of the magnetization curve of the ma of the tape. terial. Figure 3 diagrammatically illustrates my pre Figure 3 further illustrates how the magnetiz ferred method of recording a low frequency tran ing forces H corresponding to a modulated car sient on a magnetic materlalwhich has pre rier current induce maximum magnetic ?ux den viously been demagnetized to substantially its virgin state, and comprises modulating a carrier 50 sities in the tape l0 which correspond to points on the straight portions 232 and 233 of the mag frequency current 39 by the transient signal to establish two envelopes 40, and applying to the netization curve of the tape material, and how tape l0 magnetizing forces having successive distortion in the reproduced signal may be re peak values corresponding to both of the en duced by preventing the maximum flux densities velopes 40, and by adjusting the modulation of 55 for each cycle in the tape from corresponding to the carrier current by the signal to cause it to points on the curved portions 234, 235, and 233 be at all times below 100 per cent. of the magnetization curve of the material. This Recording a signal on a tape introduces con may be referred to as recording on the substan siderable distortion due to non-linearity of por tially straight portions of the curve. In record tions of the magnetization curve of the tape ma 60 ing a substantially symmetrical transient on a terial unless steps are taken to cause the re substantially demagnetized tape by my modulated cording to be only on the substantially linear carrier current system, the greatest dynamic portions of the magnetization curve. I effect re range can be obtained by adjusting the normal cording on the substantially linear portions of peak amplitude of the unmodulated carrier cur rent to have a value which corresponds to a mag the magnetization curve of the tape material by netizing force H having a value which lies sub applying to the coils a current comprised of a stantially midway between the value of the forces carrier current modulated by a signal to be re corresponding to zones or points 231' and 238'. corded, the highest value of the modulated car The value of this force is represented by the point rier current being insufficient to cause magnetic saturation in the tape l0, and the percentage of 70 having the reference character 245. Point 248 modulation of the carrier by the signal being at represents the value of this force for the opposite all times substantially less than 100 per cent. polarity of the carrier current. The minimum I have found that for most carrier frequencies amount of distortion‘ due to recording on the the same oscillator can be used as a source of curved portion of the magnetization curve is ob both carrier and obliterating current. This elim 75 tained by adjusting the percentage of modulation 2,378,888 5 Fig. 4' is supplied by the power supply P1 which may be of conventional design. of the carrier current to a value which is at all times su?lciently below 100%: that is, with the The modulator 29 comprises a pair of pentode tubes 15, 16 with plate and screen voltage stabi lized by a glow tube voltage regulator 11. Car rier signal supplied by oscillator 26 is applied in opposite phase to the grids of the two modulator tubes by center tapped transformer 64. The produced by each cycle of the modulated carrier transformer secondary 66 is tuned to the oscillator current will not be greater than the value of the magnetization force H represented by the 10 frequency by shunt condenser 18. The transient signal derived from potentiometer 32 connected points 238 and 240, nor less than the value of the magnetization force H represented by the across input terminals I9 and 20 is supplied in the same phase to both modulator grids through points 231 and 233. I have found that 50 to 60 per cent modulation is satisfactory for some mag the connection 80 and the center tap of the trans netic materials. By this process the maximum 15 former secondary 66. Bias for the modulator tubes is produced by the‘ plate and screen current values of the ?ux densities, in the tape for each ?owing through resistor 19. The plates of the carrier cycle correspond to points which lie only on the substantially straight portions of the mag modulator are connected in push-pull fashion to the center tapped primary I45 of transformer 85. netization curve of the material, and therefore distortion of the signal reproduced from the en 20 The secondary of this transformer supplies the modulated carrier to ampli?er 30. Since the velope of the carrier is reduced to a minimum. The magnetizing force H corresponding to the transient signal is applied to the two grids in the same phase while the plates of the tubes are con amplitude of the peak of each cycle of the mod nected in push-pull fashion, the transient signal ulated carrier current is always less than the itself cannot appear at the secondary of the out- ' value of zones or points 236', 240’, to prevent recording on the curved portions 234, 235 of the put transformer, provided that the modulator cir magnetization curve, and is always greater than cult is properly balanced. Presence of the tran sient signal itself in the recording circuit is un the value of zones or points 231', 239' to prevent recording on the curved portion 236 of the mag desirable as it may interfere with proper record netization curve. Depending upon the material 30 ing of the modulated carrier. Rather than pro vide means for accurate balancing, a high pass ?l used for the endless tape the size of the curved ter 3| is employed at the output of. the ampli?er portions 234, 235, and 236 varies and the degree of curvature of the substantially straight por to ?lter out any residual transient signal due to modulator unbalance. tions varies. For each kind of tape it is possible The oscillator 26 employs a dual triode 55. to adjust the amplitude of the unmodulated car normal peak amplitude of the carrier current ad justed substantially midway between zones or points 231' and 238’ for one polarity and be tween zones or points 239 and 240 for the other polarity, the peak value of the magnetizing force The oscillator circuit proper is of the resistance rier current to cause the normal peak value of stabilized Hartley type and employs one triode section 56 of the tube 55. The frequency deter points 231' and 238’ and between 238' and 240', mining elements are tapped inductance 59 and and to adjust the amount or percentage of modu lation of the carrier current by the signal to be 40 condenser 60. Resistor BI is the stabilizing re sistor and 63 is a blocking condenser. The plate recorded to cause the peak value of each cycle circuit is supplied through choke coil 42. The of the modulated carrier current to lie between tube is biased by means of the cathode resistor points 231' and 238’ for one polarity of the car 5| which is bypassed by condenser 52. The sec rier current, and between points 239' and 240' for 45 ond section 51 of the tube 55 is employed as a the other polarity of the carrier current. buffer ampli?er. Its grid is connected through In certain applications, the transients to be re blocking condenser 46 to the plate end of the corded will all be of the same general nature and oscillator coil 59 and has a bias path to ground may consist of unidirectional pulses. A typical through grid leak 48. In the plate cathode cir example is the transient voltage developed across each cycle to fall substantially half way between cuit are connected three impedances, plate re a resistor when a condenser is discharged there through. In such cases, the amplitude of the unmodulated carrier may be so adjusted that the resulting magnetizing forces, corresponding to the peak values of the wave, fall near points 237 and 233 and the transient circuit so connected that ' the carrier is modulated upwardly toward but not exceeding points 238 and 240; or downward modulation may be used with unmodulated car rier peaks producing magnetizing forces falling near points 238 and 240. For cases between sym metrical transients and completely unsymmetri cal transients, intermediate carrier amplitudes may be used. By following this procedure thus substantially straight portion of the virgin mag netization curve is used to the maximum advan tage. Detailed description of recording circuit Figure 4 is a detailed circuit of a transient sig nal recording means somewhat similar to the re cording means of Figure 2 but differing in that a single ampli?er is shown, and relay 34 does not sistance 44, bias resistor 45, and primary 65 of the modulator input transformer 66. The plate voltage for both sections of the tube is stabilized by the same regulator tube 11 that functions for the modulator. The ampli?ed carrier voltage developed across resistance 44 is supplied to the obliterating ampli?er 21. Carrier current flow ing through primary 65 supplies carrier signal to the modulator. Resistor 45 supplies bias for 60 the buffer tube and also introduces some degen eration. The ampli?er 30 is a two stage resistance capacity coupled type of conventional design. A ?xed voltage divider comprising resistors 16 and ‘H is provided at the input to select a suitable portion of the modulated carrier output of modu lator 29. The output of the second stage ampli ?er tube 81 is coupled to high pass ?lter 3| through a suitable matching transformer BI and the output of the ?lter is supplied via switch or relay 34 to recording head I6. The high pass ?lter 3| is of a simple con?guration, compris ing two condensers 88 and inductance 89. The carrier frequency supplied by the oscilla make the playback circuit. ,Plate power for the various tubes detailed in 75 tor, and the frequency response characteristics 1 2378.838 6 I 05 which is not energized during the recording of the associated circuits just described depend on process. the range of transient frequency components to A trigger relay circuit (to be described later) be recorded. For transient components up to 500 is provided to block the amplifier to cut off the cycles per second, the carrier frequency may be obliterating current a short time after the tran 2000 cycles. The modulator input transformer sient occurs and just before the recording of circuit would then be tuned to 2000 cycles and the transient modulated carrier reaches the oblit the low pass ?lter would have its cuto? frequency erating head. This is done by causing the trigger somewhat below 1500 cycles to allow for tran circuit to energize relay I05 which breaks the sient signal side bands. The ampli?er 30 will be required to pass frequencies only in the range 10 ground connection for grid resistor I00 and con I nects the resistor to a negative bias tap I09 of of 1500 to 2500 cycles and may be designed ac ‘power Supply P1. This bias is sumcient to stop cordingly. the flow of plate current to tube 01 and thereby The magnetic head l6 functions as a recording head and is connected to the recording circuit - ‘stop the obliterating process. Condenser I08 is only as long as the trigger relay switch 34 has 15 connected into this bias circuit to slow down the blocking process to prevent the recording or an not been actuated by trigger means 33 to cause undesired transient which might result if the it to become inoperative. Shortly after a tran obliterating process were stopped suddenly. sient signal is applied to the signal input ter The“ obliterating head I5 has two pole pieces, minals I9, 20 the trigger relay becomes opera ll6‘and II6, surrounded, respectively, by coils tive to cause the magnetic head to be discon II‘! and H8. The two coils are connected in nected from the recording circuit to prevent ' series opposing relationship so that at any instant superimposing extra signals in the desired re corded transient. The actuation of the trigger ' the adjacent ends of the pole pieces have the same polarity, thus causing a di?use magnetic circuit also blocks the obliterating ampli?er ?eld in the neighborhood of the tape. which prior to the coming of the transient has been continuously “erasing” the record of the Details of trigger circuit carrier on the tape I0. Blocking the obliterat Simultaneously with the recording of the ing ampli?er prevents the ampli?er from erasing transient signal on the moving tape I0, the tran the transient signal which has just been recorded sient actuates a trigger circuit shown in detail on the tape. 80 in Figure 5 to cause (after a certain time delay) The use of an obliterating current which grad the obliterating head to stop “erasing" the signal ually reduces the magnetism in the tape III to which is on the tape, and to cause the magnetic zero prevents a transient from being recorded head I6 to stop recording on the tape. The in on the tape due to the sudden blocking of the obliterating current, and the use of the modu 35 terval between the time when the ?rst part of the transient signal is put on the tape I0 and the lated carrier current recording process prevents time when the obliterating and magnetic heads a transient from being recorded on the tape due I5 and I6 cease to be operative should be slight to the sudden disconnection of the recording head ly less than the time interval for one cycle of the from the recording circuit. 40 tape.l0 around the rollers I2 and I3. This as Obliterating ampli?er sures that there will be no superposition of an other signal on top of the already recorded tran sient signal, and if the tape is long enough the entire transient will be recorded. In other words, the trigger circuit synchronizes the recording cycle with the time period in which the transient occurs; and in addition governs the length of which the unmodulated carrier is recorded on time of the recording cycle, this time being a the tape I 0, that is, during the time that the function of the speed and the length of the end apparatus is in operation in anticipation of the occurrence of a transient, the coils of the oblit 50 less tape. It is essential that overlapping in the recording process be avoided, meaning that the erating head I5 are energized by an alternating recording period should be stopped before the current of su?icient strength to saturate mag tape I0 has completed a cycle around the rollers netically the portions of the tape immediately I2 and I3. Y adjacent the head. For convenience, this oblit erating current is obtained from the oscillator 55 A gas tetrode tube I 33 has in its plate circuit the coils of relay I05 which when energized 26, a single stage ampli?er 21 being interposed blocks the obliterating ampli?er and relay I62 to obtain su?lcient current and to isolate the which interrupts the recording process. Normal head from the oscillator. The obliterating am 1y, this tube is non-conducting and the relays pli?er 21 comprises a power pentode tube 91 whose plate is coupled to the obliterating head 60 I 05 and I62 are not energized. Its control grid I58 is connected through variable resistance I6I by means of transformer I02. Condenser I04 to the cathode of another gas tetrode I32 which tunes the obliterating head circuit to the fre also normally is non-conducting. Grid I58 is by quency of the oscillator so that maximum cur passed to ground by condenser I60. When the rent may be obtained. Plate current for the tube 91 is supplied by power supply P1 which may 65 gas tetrode I32 becomes conducting the voltage drop across cathode resistor I 51 applies a posi be of conventional design. Normal operating bias tive bias to grid I58 thus "?ring” gas tetrode I33 is provided by cathode resistor IOI which is by and thereby energizing relays I05 and I62. Re passed by condenser III. Oscillator 26 ener sistor I 6| and condenser I60 introduce a time gizes control grid 98 through the connection 95 and blocking condenser 96. Grid 98 is main 70 delay, depending on the values of these two com ponents so that the relays are energized at a pre- ’ tained at the proper negative bias potential by determined interval of time after the “?ring” of the direct current path to ground comprising tetrode I32. This tube is "?red” by the transient resistor 99 in series with the parallel combina signal and the time delay provided by resistor tion of resistor I01 and resistor I00. Resistor I00 is grounded through the contacts of relay 75 IN and condenser I60 is so adjusted that the Figure 5 illustrates the details of the obliterat ing and trigger circuits in connection with the recording and playback circuits which are shown in block form. During the part of the recording process in 2,878,888 obliterating and recording processes are stopped just as the tape loop has completed the tran sient recording cycle. It is the nature of gas tetrode I32 to “?re” and become conducting upon application of positive potential to its control grid I56 but not to “?re” 7 supply to the two trigger tubes. In the record ing position the switch closes the plate circuit so that the tubes may be “?red” by the transient. In order that the tubes may be restored ‘to the non-conducting condition before making a new recording, the switch I26 is arranged to open the trigger tube plate circuits when it is turned to the playback position. This restores the contacts of relay I05 to their original condition, removing ti?er is interposed between the transient input 10 the blocking bias from the obliterating ampli?er 21. To prevent obliteration when this takes terminals I9, 20 and the control grid I56. The place, a switch blade I25 is located in the plate transient signal is applied through blocking con circuit of obliterating ampli?er tube 91 to open denser I46 to grid I40 of dual triode tube I34 con this circuit during playback. nected as a phase inverter of conventional de sign. The plates I36 and I43 are coupled through Reproducing circuit detail-Fig. 6 blocking condensers 20I and 202 to grids I39 and upon application of a negative potential. To in sure operation of the trigger at the proper time for transients of either polarity, a full wave rec After the transient signal modulates the car I42 of the dual triode I35 which is connected as rier current and is recorded on the tape I0, and a full wave biased detector. The plates I31 and after the trigger circuit has operated to stop fur MI are connected to power supply P1. The grids I39 and I42 are both biased to cut off through 20 ther recording and further obliteration, the tran sient signal, a facsimile of which is recorded on the connection of grid resistors I I2, II 3 to a neg the tape, is “played back” from the tape to an ative bias tap on power supp-1y P1. Due to the oscilloscope II or other indicating device by large negative bias no plate cathode current means of the playback circuit. Repeated repro ?ows in tube I35 so that there is no voltage drop duction of the transient on the indicating in across cathode resistor I66. strument will give an observer sufficient time to When a transient occurs either grid I39 or I42 see the transient even though it originally was a becomes less negative causing plate current to very rapid one. ?ow in its section of the tube. This current pro For the reproduction of the transient, the mag duces a voltage drop across resistor I66 which in turn “?res” trigger tube I32. As explained be SI) netic head I6, which is the recording head dur ing the recording process, becomes a playback fore, as soon as tube I32 “?res” a voltage is ap head due to switch I22 connecting it to the play plied to the time delay network I60, I6I and back circuit through line 205. It is obvious that after a suitable time interval the voltage of the separate recording and playback heads may be grid I58 rises su?iciently to “?re” tube I33, thus energizing relays I05 and I62 which stop the : associated with the tape I0 if it is so desired. Actuation of the switch blade I22 from terminal obliterating and recording processes. During the R to terminal P connects the magnetic head I6 time taken to build up a “?ring” potential at the grid of tube I33 the transient is being recorded on the tape loop in the form of a transient mod ulated carrier wave and the operation of relays to the playback circuit which consists of the pre-ampli?er I3I, the playback ampli?er I30. (which may be the same ampli?er as the record ing ampli?er 30) the band pass ?lter 36. and the demodulator and low pass ?lter 31, to the re cording or indicating instrument II. It is ap parent that the single ampli?er, which is here recorded transient. indicated by reference character 30 in the re In order to reproduce the transient from the cording circuit and I 30 in the reproducing cir moving tape I0, a switchA is thrown from the cuit, may be two separate ampli?ers if desired. recording position R to the playback position P. The pre-ampli?er I3I may employ a single The switch A has six blades I2I, I22, I23, I24, tube I10, and is coupled to the recording and I25, and I26 as shown in Figures 4 and 5. In the reproducing ampli?er I30 by a blocking conw recording circuit shown in detail in Figure 4, the denser HI and a resistor I12. The plate of the actuation of the switch A causes blade I2I to tube I10 is connected to power supply P1 through break the plate supply to oscillator 26 which is coupling resistor I69 and ?lter resistance I68. through the choke coil 42, and causes the blade and the screen grid I99 is connected to the power I22 to break the connection from the recording supply Pl through resistor I61 and is by-passed circuit to the magnetic head I6 and make a con- to ground by a condenser 209. A ?lter and iso nection from the magnetic head I6 to the play lating condenser 204 by-passes to ground the back circuit. The playback circuit may include junction of resistors I61, I68, I69. The signal a Dre-ampli?er indicated generally by the ref input from the magnetic head I6 to the pre erence character I3I, and positioned between the magnetic head I6 and the ampli?er 30. The am 60 ampli?er I3I is through line 205 to control grid 206 in the tube I10. ‘Bias for tube I10 is pro pli?er 30 is adapted to amplify the transient vided by cathode resistor 208 which is by-passed modulated carrier signal both before it is re by condenser 2I0. The tube 86 in the ampli?er corded on the tape I0 and while it is being played I30 (Fig. 4) has a grid resistor I13 which, to back from the tape. The blade I23 of switch A gether with the resistor I12, establishes a volt is adapted to control the input to the ampli?er age dividing network to cause the same voltage 30. In the recording position the input to am to be supplied to the ampli?er I30 during repro pli?er .30 is from the modulator 29 and in play duction as was applied to the ampli?er during back position the input is from the pre-amplifier the recording process. The output of the am~ I3I. The switch blade I24 is located between-the I05 and I62 ?nally takes place to prevent oblit eration of the recorded transient and to prevent superimposing additional carrier signal on the ampli?er 30 and the high pass. ?lter 3| and is " pli?er I 30 is applied through connection I92 to , adapted to direct the output of the ampli?er 30 to the magnetic head I6 when it is in the re cording position and to the band-pass ?lter 36 of the playback circuit when it is in the playback’ position. The blade I26 is located in the plate 75 the single T-section band pass ?lter 36 which is comprised of two series arms each having an inductance I14 and a condenser I15, and a shunt arm having inductance I16 and a condenser I11. For a carrier frequency of 2000 cycles per sec 8 8,378,888 0nd and transient signal frequency components transient signal is applied. The amplitude of up to 500 cycles per second, the pass band of the ?lter should extend from about 1500 cycles per second to about 2500 cycles per second. The band pass ?lter 36 ‘is connected to the demodulator 31 by means of a transformer I18, the secondary winding of which is connected to the plates of a double diode recti?er tube I19. The output of the double diode tube I19 is con the input transient signal can be controlled by the potentiometer 32. Figures '1 and 8 illustrate a type of head I6 ?lter comprised of two M-derived sections I8I and I82. There ‘are two series branches and three shunt branches in the ?lter. The. ?rst series branch is comprised of inductor I83 and a condenser I 84, and the second series branch 15 reproducing circuits, and inside the coil 2“! is a rigid pole piece M9. The movable block 2“ which is particularly useful for a transient re cording device. It comprises a base 2I5 upon which is mounted a stationary block M6 and a movable block 2I1. Inside the stationary block 2I6 there is a coil 2“! which is adapted to be nected through a resistance I80 to a low pass 10 electrically connected into the recording or the is comprised of inductor I85 and a condenser I86. , The ?rst shunt branch has a condenser I81, the second shunt branch has a condenser I88, and the third shunt branch has a condenser I89. The output of the second section I62 of the ?lter is applied across a resistor I93 and then to output terminals I94 and I95, to which may be attached an oscilloscope, oscillograph, or other indicating device lg. One of the sections of the low pass ?lter has ts frequency of maxi mum attenuation at the carrier frequency 2000 is attached to the base 2I5 by means of a screw 220 about which the block is adapted to pivot to establish an open position shown in Figure 7 and a closed position shown in Figure 8. The magnetic tape I0 is adapted to lie between the movable block 2" and the stationary block 2I8, and when the head I6 is in its open position may be slipped out from between the two blocks. This construction is particularly valuable for transient recording devices which may be located in a remote place such for example as a remote power supply line. The recording device may be connected to the line and left in an operating condition. If a transient should occur it will of the carrier, 4000 cycles. Adjusting the ?lter be recorded. For an installation of this type the switch 41 (Fig. 2) to stop the motor I 4 is val uable. Examination of the recording device at In some applications the use of the internal clip 223 is provided for latching the two blocks 2| 6 and 2H together when the head I6 is in its cycles and the other section has its frequency of maximum attenuation at the second harmonic sections I8I and I82 in this manner e?‘ectively 30 a later date will disclose the presence of the re corded transient and the tape can be removed suppresses the carrier frequency and its second from the head I6 and taken back to the labora harmonic and causes only the transient signal tory for study. A movable pole piece MI is posi to be applied to the output terminals I94 and tioned within the movable block 2 I 1 and is biased I95. toward the tape I0 by a spring 222. A spring External trigger controL-Fig. 5 automatic trigger circuit 33 may not be desir able. I, therefore, provide an external trigger operating condition. obliterating ampli?er and stopping the record having four resistances 221, 228, 229, and 230. Figure 9 illustrates diagrammatically a timing circuit which may be actuated by an operator device utilizing my invention and adapted to re 40 to effect the same results as the actuation of cord the speed of a bullet 225. The timing device the automatic circuit insofar as blocking the comprises an oscillator 226 in a bridge circuit ing process are concerned. Switch I65 is man ually controlled and switches the phase inverter out of the circuit and connects grid I56 of gas tetrode I32 to the external control circuit. The external trigger circuit comprises a switch I96 With all four resistances in the circuit there is no output to the recording head I6 as the bridge circuit is balanced. The bullet 225, upon being ?red, breaks or otherwise alters the resistance 221 thereby unbalancing the bridge circuit and which may be operated byhand or by some ex causing signal output to the recording head I6, ternal circuit. One terminal of the switch I96 is connected to the positive terminal I91 of a low voltage D. C. source whose negative termi nal is grounded, and the other terminal of the switch is connected through switch I65 to the control grid I56 of the ?rst gas tetrode tube I32. '“ Resistor I98 is provided to maintain grid I56 which signal is recorded on the tape I0 in ac cordance with my invention. The bullet then breaks or otherwise alters the resistance 228 re establishing a balance in the bridge circuit which stops the recording of the signal. The recorded transient consisting of a few cycles of a known frequency from oscillator 226, may then be re at ground potential until the external control produced on an oscillograph and the time of is actuated. Applying positive bias to the con ?ight from resistance 221 to resistance 228 de trol grid I56 causes the tube I32 to ?re thereby termined from the number of cycles of the signal initiating the sequence of events which blocks on the oscillograph and the distance d between . the obliterating ampli?er 21 and ‘stops the mag 60 resistances 221 and 228. netic head I6 from recording as has heretofore The present application is directed to features been described. of the invention disclosed and claimed- herein Modulation check-Fig. 6 and relating to systems and methods for studying transient phenomena, and more particularly to I have provided a switch 200 which connects 65 such systems and methods employing an electric the oscilloscope II directly to the output of the circuit for recording on a, recording medium a ampli?er 30 in order to make it possible to ob transient circuit condition occurring on the cir serve-‘in the oscilloscope the amount of modu cuit and utilizing the record of the transient for lation for applications where the transient can studying the characteristics of the transient by be caused at the will of an operator, such for 70 continuously making an obliterable record of the example as an impact welder. It is possible to circuit conditions under study on an endlessly regulate the amount of modulation in advance operating cyclically-effective recording medium, of recording a' transient to be studied on the such as a magnetic recording medium, so that recording medium. If there is too much or too the circuit conditions are continuously recorded; little modulation it can be adjusted before the 75 the continuous recording operation being accom 2,878,888 panied by a continuous obliteration‘ of the re comings and the obliterating action being stopped upon the occurrence of a transient condition so as to retain on the recording medium a record of a signal corresponding to the transient occur rence and the recording operation being discon tinued after the. transient occurrence has been 9 reproducibly recordable on said magnetic re cording medium and representative of the condi tions of said circuit; said recording medium being cyclically operated at a predetermined rate cor related to the frequency of said signal voltages; recording means for continuously magnetically _ recording on said recording medium a record of said signal voltage and obliterating means for re turning a portion of said medium to a uniform enable the study of the transient occurrence by cyclically reproducing the record and utilizing 10 state of magnetization a relatively short time in terval after a record has been made thereon; the reproduced record for operating a cyclically means responsive to an occurrence of a transient operative indicating device, such as an oscillo circuit condition on said circuit for discontinuing scope, which presents an image corresponding to the action Of said obliterating means on said the reproduced signal upon each cycle of the recording medium; such systems and methods 15 medium; means operative a time interval there after for rendering the recording means inopera whichrare e?ective for studying low frequency tive so as to retain on said recording medium and direct current transients by modulating with a record corresponding to said transient condi the signal which is to be recorded a source of tion; and reproducing means operative to cycli carrier oscillations of a frequency which is re cally reproduce the record recorded on said re producibly recordable on the endless magnetic 20 cording medium. recording medium, so as to provide a modulated 3. In an arrangement for recording a transient carrier signal which is continuously recorded on circuit condition of an electric circuit which oc the endless recording medium and obliterated recorded on the medium in such manner as to immediately thereafter, the obliterating action being stopped upon the occurrence of a tran sient-the reproduced recorded modulated signal curs thereon at an unpredictable instance: an endlessly operating magnetic recording medium; means associated with said circuit for continu ously supplying signal voltages of a frequency reproducibly-recordable on said magnetic record modulated reproduced signal corresponding to ing medium and representative of the conditions the transient signal which is utilized for oper said circuit; said recording medium being cycli ating the cyclically operative indicating device; 30 of cally operated at a predetermined rate correlated and various other novel and desirable features to the frequency of said signal voltages‘; record forming part of such systems. ' ing means for continuously magneticallyrecord The magnetic recording systems and'methods ing on said recording medium a record of said utilizing a signal modulated carrier frequency signal voltage and obliterating means for con which is reproducibly recordable on a magnetic 35 tinuously obliterating said record; and means re_ recording medium,‘ described herein in connec-‘ sponsive to an occurrence of a transient circuit tion with the exempli?cations of the present in condition on said circuit for rendering said ob vention, embody various other inventive features literating means ineffective and for subsequently which are claimed in my vcopending application rendering the recording means inoperative after Serial No. 540,667, filed June 16, 1944, as a con 40 a signal corresponding to a predetermined in tinuation-in-part of the application Serial No. terval of the transient condition has been re 399,909, ?led June 26, 1941. corded on said medium. It will be apparent to those skilled in the art 4. In an arrangement for recording a transient that the novel principles of the ,invention dis circuit condition of an electric circuit: an end closed herein in connection with speci?c exem 45 lessly operating magnetic recording medium; pli?cations thereof will suggest various other means for continuously supplying signal voltages modi?cations and applications of the same. It is 'of a frequency reproducibly recordable on said accordingly desired that in construing the magnetic recording medium and representative breadth of the appended claims they shall not of the conditions of said circuit; said recording . be limited to the speci?c exempli?cations of the 50 medium being cyclically operated at a predeter invention described herein. mined rate correlated to the frequency of said I claim: signal voltages; recording means for continuously 1. In a system for recording a transient circuit magnetically recording on said recording medium condition which may occur in an electric circuit a record of said signal voltage and obliterating at an unpredictable instant and for reproducing 55 means for returning a portion of said medium the record: an endlessly-operating cyclically-ef to a uniform state of magnetization a relatively fective recording medium; recording means con short time interval after a record has been made being modulated so as to cyclically provide a de nected to the circuit in which a transient is ex thereon; and means responsive to an occurrence pected for continuously recording the circuit con of a transient circuit condition on said circuit for ditions; means for obliterating the recorded sig 60 discontinuing the action of said obliterating nal; means responsive to an occurrence of a tran means on said medium and operative a time in sient circuit condition for rendering the obliter ating means inoperative; means operative a time interval thereafter for rendering the recording terval thereafter for discontinuing the action of said recording means on said medium. means inoperative so as to retain on said record ing medium a record corresponding to said tran sient condition; and reproducing means operative to cyclically reproduce the record recorded on said recording medium. 5. A device for recording a transient which may 65 occur at an unpredictable instant comprising, in combination, an endless recording medium, means for driving said endless medium, recording means connected to the circuit in which the transient is expected for continuously recording the circuit 2. In a system for recording a transient circuit 70 conditions, means for obliterating the recorded signal, and means responsive to a‘circuit tran condition which may occur in an electric circuit sient condition for rendering the obliterating at an unpredictable instant and for reproducing means inoperative and for rendering the record the record: an endless-operating cyclically-effec ing means inoperative after the transient condi tive magnetic recording medium; means for con tinuously supplying signal voltages of a frequency 76 tion has been recorded on the recording medium. 1O 2,878,888 6. The method of visually presenting on an oscillagraph a non-repetitive wave which com prises the steps of: electrically recording the non repetitive wave on an endless medium, repeatedly reproducing said record from said medium to es tablish a cyclic signal the frequency of which cor responds to the rate of repetition of said record of saidv non-repetitive wave, and controlling the os cillograph by said cyclic signal, the rate of occur magnetic record material, means for driving said record material, magnetic recording means as sociated with said record material and connected to a circuit in which said transient is expected, said recording means being adapted to record on said record material a signal corresponding to the normal and abnormal conditions of the circuit, magnetic obliterating means continuously oblit erating the recorded signal during normal con , rence of said record of said non-repetitive wave 10 ditions of the circuit, means operable upon the being su?iciently high that together with the per occurrence of an abnormal condition for render sistence of the observer’s eye the trace on the oscillograph corresponding to one cycle of said ing said obliterating means inoperative whereby repetitive wave appears substantially s‘teady. 7. The method of visually presenting on an os a signal corresponding to the obnormal condition recorded on said record material is retained. and means operable upon the occurrence of the ob cillograph a wave of short duration which com normal condition and after a time delay for ren prises'the steps of: electrically recording the short dering said recording means inoperative to pre wave on a short endless medium, repeatedly elec vent a. subsequent record from being superimposed trically reproducing said record from said short on said recorded transient signal. endless medium to establish a cyclic signal hav— 20 12. A device for recording a transient signal ing a frequency which equals or exceeds the rate comprising, in combination, endless record mate of repetition of said record of said short Wave, and rial, means" for cyclically driving said record ma controlling the oscillograph by said reproduced terial, recording means associated with said rec signal, the rate of repetition of said record of said ord material and connected to a circuit in which short wave being suf?ciently high that together 25 said transient is expected, said recording means with the persistence of the observer's eye the trace being adapted to record on said record material established by said oscillograph appears substan a signal corresponding to the conditions of the tially steady. circuit, means for continuously erasing said rec 8. A device for visually presenting on an os ord during normal conditions of the circuit, cillograph the wave form of a non-repetitive elec 30 switching means operable upon the occurrence trical transient comprising; endless signal storage of an abnormal condition for rendering said eras ing means inoperative whereby a signal corre sponding to the abnormal condition recorded on said record material is retained, and switching peatedly rotating said endless signal storage 35 means operable upon the occurrence of the ab means at a substantially constant rate of speed, normal condition and after a time delay of a electrical reproducing means in association with duration no greater than the length of time for said signal storage means for reproducing the one cycle of the record material for rendering record thereon upon each rotation thereof to es said recording means inoperative to prevent a tablish a cyclic signal the frequency of which 40 subsequent record from being recorded on said corresponds to the rate of repetition of said rec record means. ord of said non-repetitive wave, means connect 13. A device for recording a transient compris ing said electrical reproducing means to said os ing in combination, an endless recording medium, cillograph for controlling the oscillograph in ac means for cyclically driving said recording me cordance with said cyclic signal, the rate of oc 45 dium, recording means associated with said re currence of said record of said non-repetitive cording medium and adapted to be connected wave being su?iciently high that together with to a circuit in which a transient might occur for the persistence of the observer’s eye the trace on recording the circuit conditions on said medium, the oscillograph corresponding to one cycle of said obliterating means for destroying the recorded non-repetitive wave appears substantially steady. record after a short time interval, means oper means, electrical recording means in association with said signal storage means for recording thereon said non-repetitive wave, means for re 9. A device for visually presenting on an oscil lograph the wave form of an electrical transient able upon the occurrence of a transient in the circuit for rendering said obliterating means in of short duration comprising, endless signal stor operative, and means operable upon the occur rence of said transient for rendering said record tion with said signal storage means for recording 55 ing means inoperative after a short time delay thereon said wave form of short duration, means 14. A device as set forth in claim 13 in which for repeatedly rotating said endless signal stor said recording means includes a source of carrier age means at a substantially constant rate of current and means for modulating said carrier speed, the period of rotation of said storage means current by the transient. being comparable to the duration of said electri 60 15. A device for visually presenting on an oscil cal transient, electrical reproducing means in as loscope the wave form of a non-repetitive elec sociation with said signal storage means for re trical transient comprising: endless magnetic producing the record thereon upon each rotation tape means, magnetic means for recording the thereof to establish a repeating wave, means con entire non-repetitive transient on said magnetic necting said electrical reproducing means to said 65 tape means, means for cyclically driving said age means, electrical recording means in associa oscillograph for controlling the oscillograph in accordance with said repeating wave, the rate of occurrence of said repeating wave being suf? ciently high that the trace on the oscillograph appears substantially steady. magnetic tape means, magnetic reproducing means actuated by the record of the non-repeti tive transient during the cyclic rotation of the endless tape means, said magnetic reproducing 70 means controlling said oscilloscope means to re peatedly show the transient wave form, the rate of reproduction of the wave form being su?iciently second long. high, and the persistence of the screen and of the 11. A device for use in recording a transient human eye being such that the trace on the oscil signal comprising, in combination, an endless 75 loscope screen appears substantially steady. 10. A device as set forth in claim 9 in which said transient of short duration is less than one 2,378,388 11 duced signals passed by said ?lter means and so correlated to the other elements of the system that the demodulated reproduced signals corre 'nal which can be seen on an oscilloscope unit spond in a predetermined manner to said original comprising, an endless magnetic tape, means for magnetically recording the entire non-repetitive U! transient; and visual indicating means actuated by said demodulated reproduced signals; the rate transient on said magnetic tape, magnetic re of the cyclical operation of the recording medi producing means actuated by the record on the um being correlated to the characteristics of the magnetic tape and connected to the said oscillo indicating means so that in response to actuation scope unit for producing on the oscilloscope a visual trace of said entire non-repetitive tran 10 by said demodulated reproduced signals it pro duces a visually observable characteristic image sient, and means for repeatedly rotating said end of said transient signal. less tape to cause said visual trace to repeatedly 20. In a system for reproducing a character appear on said oscilloscope, the rate of repetition istic image of a transient signal: an endless re of said trace being sufliciently high, and the per 16. A device» for converting a non-repetitive signal transient into a substantially constant sig sistence of the screen and of the human eye 15 cording medium; means for providing a carrier current; said recording medium being cyclically .being such that the trace on the screen of the oscilloscope unit appears substantially steady. 17. A device for use in recording a transient signal comprising in combination, an endless rec ord member, means for driving said record mem ber, recording means associated with said record member and connected to a circuit in which said transient is expected, said recording means in cluding a source of carrier current and means for modulating said carrier current by the signal in operated at a predetermined rate correlated to the frequency of the carrier current; modulator means adapted to combine said carrier current and said transient signal and cause said signal to modulate said carrier current and provide a modulated signal; said modulator means being arranged to substantially balance out the said transient signal; recording means including 25 means for amplifying said modulated signal and said circuit whereby said recording means re means for recording said modulated signal on cords continuously on said record member, ob literating means associated with said record member for continuously restoring said record said recording medium; reproducing means in cluding means for reproducing said modulated signal from said recording means and means for member to the condition it was in prior to record 30 amplifying said reproduced signal; said repro ing, ?rst switching means operable upon the event ducing means including means for demodulating of a transient in said circuit for rendering said said modulated signal so as to provide an image obliterating means inoperative, and second signal corresponding to said original transient switching means operable upon the event of the signal; and visual indicating means actuated by transient in said circuit for rendering said re said image signal; the rate of the cyclical opera cording means inoperative. tion of the recording medium being correlated to 18. A device as set forth in claim 17 in which the characteristics of the indicating means so said record member is cyclically driven and the that in response to actuation by said demodu second switching means operates to render the lated reproduced signals it produces a visually recording means inoperative after a time delay 40 observable characteristic image of said transient which is equal to or slightly less than the time signal. ' for one cycle of said record member whereby the 21. In the method of recording a transient cir transient is retained on the record member, cuit condition which may occur at an unpredict 19. In a system for reproducing a character able instant on an electric circuit subjected to istic image of an electric transient signal: an 45 predetermined normal circuit conditions, the endless recording medium; means for providing procedure of : continuously supplying signal volt a carrier current of a frequency reproducibly re ages of a frequency reproducibly recordable on a cordable on said recording medium; said record magnetic recording-medium and representative ing medium being cyclically operated at a pre of the conditions of said circuit; continuously determined rate correlated to the frequency of 50 magnetically recording on a cyclically operating the carrier current; modulator means for caus endless magnetic recording medium a record of ing said signal to modulate said carrier current said signal voltages and continuously obliterating and providing a modulated signal; said modu said record; stopping further obliteration of said lator means being arranged to substantially bal record upon the occurrence of a transient circuit ance out the said transient signal; recording 55 condition; and stopping further recording a pre means for recording said modulated signal on determined time after the obliteration of the said recording medium; said recording means in record was stopped. cluding means for amplifying said modulated 22. In the method of observing a transient sig signal and ?lter means interposed in the path nal, the procedure of: providing a carrier cur of the ampli?ed modulated signal and designed 60 rent of a frequency reproducibly-recordable on to pass a range of frequencies including the fre quency of the modulated carrier current and side a magnetic recording medium; producing a mod ulated signal by modulating said carrier current bands corresponding to said transient signal and by the transient signal; recording the modulated to restrict the} passage of other frequencies so signal on a magnetic recording medium which is that the signals of the passed frequency range 65 cyclically operated at a frequency correlated to are e?ectively recorded; reproducing means in the carrier frequency; cyclically reproducing cluding amplifying means for reproducing said from the recording medium the recorded modu modulated signal from said recording medium lated sign-a1 and demodulating the reproduced signal; and controlling an indicating device in and for amplifying the reproduced signal; said reproducing means including ?lter means de-' 70 accordance with said cyclically reproduced de signed to pass a range of frequencies including modulated signal. 23. In the method of observing a transient sig the frequency of the modulated carrier current nal, the procedure of : providing a carrier cur and side bands corresponding to said transient rent of a frequency reproducibly-recordable on signal and to restrict other frequencies and de modulator means for demodulating the repro 76 a magnetic recording medium; producing a mod 12 ’ ‘2,378,888 ulated signal by modulating said carrier current by the transient signal; recording the modulated and to render, a relatively short time interval thereafter, said reproducing means inoperative signal on a magnetic recording medium which is cyclically operated at a frequency correlated to so as to retain on said medium a record of a the carrier frequency; cyclically reproducing from the recording medium the recorded modu lated signal and demodulating the reproduced signal; and controlling a trace-producing elec tron beam by the cyclically reproduced demodu lated signal so as to provide a visually observable trace. 24. In the method of observing a signal, the procedure of: providing a carrier current. of a frequency reproducibly-recordable on a magnetic recording medium; producing a modulated sig nal by modulating said carrier current by the signal; recording the modulated signal on a mag netic. recording medium which is cyclically oper -, ated alt-"a, frequency correlated to the carrier fre quency; cyclically reproducing from the record ing medium the recorded modulated signal and demodulating the reproduced signal; and con trolling a trace-producing electron beam by the cyclically reproduced demodulated signal so as to .providea visually observable trace. ‘ 25. In a system for studying a transient signal; an endless magnetic recording medium; a source of carrier current of a frequency reproducibly modulated signal corresponding to the transient signal; oscilloscope means; and reproducing means including demodulating means associated with said medium and interconected with said oscilloscope means for cyclically reproducing the signals recorded on said medium during each entire cycle and for cyclically impressing on said oscilloscope means unmodulated or modulated signals corresponding to the signals reproduced from said medium so as to indicate overmodula tion of the carrier by comparing the recorded and unrecorded portions of the medium. 27. In the method of recording a transient cin cuit condition of an electric circuit, the procedure of: continuously supplying signal voltages of a frequency reproducibly-recordable on a magnetic recording medium and representative of the con ditions of said circuit; continuously magneti cally recording on a cyclically-operating endless magnetic medium a record of said signal volt ages; obliterating each record element recorded on the medium prior to the end of the cycle during which it was recorded; stopping oblitera tion of said record upon the occurrence of a transient circuit condition which it is desired to recordable on said recording medium; said mag record; and stopping further recording a pre I netic recording medium being cyclically operated 30 determined time after stopping the obliteration. at a predetermined rate correlated to the fre 28. In a system for studying a transient signal: quency of said carrier current; modulator means an endless magnetic recording medium; a source for causing said signal to modulate said carrier of carrier current of a frequency reproducibly current by said transient signal and providing a recordable on said recording medium; said mag correspondingly modulated signal; recording means for magnetically recording on said me dium a signal corresponding to said modulated signal; reproducing means including demodulat ing means for cyclically reproducing from said medium the recorded modulated signal and for demodulating the reproduced signal so as to cyclically provide a demodulated reproduced sig nal corresponding to the transient signal; and cyclically-operative indicating means cyclically actuated by said demodulated reproduced signal for presenting said reproduced signal upon each cycle of said medium. 26. In a ‘system for studying a transient signal: an endless cyclically-operating magnetic record netic recording medium being cyclically operated at a predetermined rate correlated to the fre quency of said carrier current; modulator means for causing said signal to modulate said carrier current by said transient signal and providing a correspondingly modulated signal; recording means for magnetically recording on said me dium a signal corresponding to said modulated signal; reproducing means including demodulat ing means for cyclically reproducing from said medium the recorded modulated signal and for demodulating the reproduced signal so as to cyclically provide a demodulated reproduced signal corresponding to the transient signal; and oscilloscope means cyclically actuated by said ing medium; a source of carrier current of a 50 reproduced demodulated signal for presenting frequency reproducibly-recordable on said me dium; modulator means adapted to modulate said carrier current by said transient signal for providing a correspondingly modulated carrier current; magnetic recording means arranged to continuously record on said medium _a magnetic said signal upon'each cycle of said medium, the cyclical rate of said medium being suf?ciently high so that a substantially steady picture of said signal is produced on said oscilloscope. ' 29. A system as de?ned in claim 28 in which said transient signal is a direct current signal. signal corresponding to the said carrier current 30. A system as de?ned in claim 28 in which and operative upon the occurrence of a transient said carrier current has a frequency sufficiently to record on said medium a modulated signal low that when modulated by an alternating tran corresponding to the said modulated carrier cur 60 sient signal the resulting upper side band is with rent; magnetic obliterating means spaced from in the range which can be magnetically recorded said recording means for continuously obliterat~ and reproduced. 1 ing the recorded signal so that said endless me 31. A system as de?ned in claim 28 in which dium always includes a short medium portion said carrier current has a frequency su?iciently corresponding to the space between the record 65 high that when modulated by a very low or ing and obliterating means upon which the rec direct current transient signal the resulting lower ord has been obliterated and a medium portion side band is within the range which can be mag upon which a record has been made; means netically recorded and reproduced. actuated upon the occurence of a transient to ?rst render said obliterating means inoperative 70 SEMI JOSEPH BEGUN.