US2165307A

US2165307A - Means for translating magnetic variations into electric variations

Info

Publication number: US2165307A
Application number: US134067A
Authority: US
Inventors: Albert M Skellett
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-03-31
Filing date: 1937-03-31
Publication date: 1939-07-11
Anticipated expiration: 1956-07-11
Also published as: GB498721A; DE706780C; FR835934A

Description

July 11, 1939. A. M. SKELLETT MEANS FOR TRANSLATING MAGNETIC VARIATIONS INTO ELECTRIC VARIATIONS Filed March 31, 1957 IN I/E N TOR AM SKELLETT Br ATT RNE'V UNITED STATES PATENT err-ice 2,165,307 MEANS FOR. TRANSLATING MAGNETIC VA- RIATIONS IN TO ELECTRIC VARIATIONS Albert M. Skellett, Madison,

N. 3., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., 'a corporation of New York Application March 31, 1937, Serial No. 134,067

22 Claims.

This invention relates to means for transforming magnetic variations into electric variations and more specifically to means for reading a magnetic record upon which signals representative of the light-tone values of a picture or view are recorded.

When an ordinary magnetic pick-up device is used for reading a magnetic record, the currents delivered by the pick-up coil have all been shifted in phase by degrees from that of the original current. This is caused by the fact that in the magnetic pick-up the output current is proportional to the rate of change of flux rather than to the flux itself. This shift in phase of 90 degrees is not important in the case of sound recording as the human ear is insensitive to this shift. In the case of television image currents, however, the shift is enough to make the image unrecognizable because a shift of 90 degrees is a variable shift with respect to time even though it is a constant angular shift. For example, a shift of 90 degrees for a 30-cycle signal is a displacement in time of 1/ of a second, while a shift of the same phase angle for a 5000-cyele signal is a time displacement of only 1/20,000 of a second. i

It is an object of this invention to provide a reading or translating device for a magnetic record which does not produce the above mentioned phase shifts and which is suitable for use with records of signals representative of a picture or view which is to be reproduced in the form of a facsimile or image by television methods.

It is a further object of the invention to provide inductionless means for translating magnetic variations into variations of an electronic beam. v

Another object is to provide means for translating magnetic variations into electric current variations the amplitudes of which are proportional to those of the magnetic variations and not dependent upon the frequency of the latter. In the ordinary magnetic pick-up device used to translate a magnetic record and similar devices used. elsewhere for translating magnetic variations into electric variations, the amplitudes of the electric var ations are in part dependent upon the frequency of the variations, thus producing distortion of the current variations.

In an embodiment of the invention which is given by way of example to illustrate the invention, a yoke of soft iron is set up around a cathode ray tube adjacent some pole-pieces of similar material therein in such a manner that there are two gaps in the magnetic circuit (in addition to the gaps filled by the walls of the tube), one just large enough for the magnetic tape or other movable means carrying magnetic variations to pass therethrough and the other through which the electron beam passes. No magnetic coils are used on this yoke which serves to guide the magnetic flux from the tape directly to and into the cathode ray tube so as to deflect the cathode ray beam in such a manner that it divides its energy between a pair of anode plates connected in pushpull manner. A relatively small accelerating voltage, that is, of the order of hundreds of volts or less, is preferably used for accelerating the beam generated in the cathode ray device so that the beam is appreciably bent for the small fluxes available. The two anode plates are preferably connected, in opposition, to the primary winding of a transformer, the mid-point of which is connected through a battery to the accelerating anode of the cathode ray tube. The output current in the secondary winding of the transformer is thus always substantially in phase with the flux in the magnetic tape and the amplitude is independent of the frequency of the signal. Another advantage of this arrangement is the high output due to the amplification of the original energy because the entire energy of the electron beam is controlled by the small fiux in the tape.

It is found that this device operates satisfactorily when the yoke is of soft iron but a preferred material is permalloy or other similar material having high permeability at low magnetizing forces.

The invention will be more readily understood from the following description taken in connection with the accompanying drawing forming a part thereof, in which:

Fig. 1 is a perspective view of an electronic pick-up device for magnetic recording;

Fig. 2 is a transverse cross-sectional view of the device shown in Fig. 1; and

Fig. 3 is a longitudinal cross-sectional view of the device shown in Fig. 1 taken from the top.

Referring more particularly to the drawing, Fig. 1 shows in perspective an electronic pick-up device for reproducing signals previously recorded on a magnetic tape. The electronic pick-up arrangement comprises a tape l0 adapted to be passed through a narrow gap I I in a magnetic circuit l2 through a second gap 53 of which the beam generated in a cathode ray device I3 is adapted to pass, the deflection of the beam being controlled by the signals on the magnetic tape. The record member I0 is preferably a tape or any suitable magnetic material about .001 inch thick and .125 inch wide, the ends of which are secured to and wound on reels l4 and I5, respectively. The tape has been previously magnetized with signal currents in a manner well known in the art. For an example of a suitable arrangement for recording varying signals on magnetic tape, reference may be made to Patent 1,944,238 to Clarence N. Hickman, issued January 23, 1934. The tape is preferably moved in the gap II at the speed at which the signals were recorded, any suitable means, such as the driving means shown in the Hickman patent, being suitable for this purpose.

For the sake of clarity in describing the oathode ray device |3, reference will now be made to Fig. 3 which shows a longitudinal cross-sec tion of the cathode ray device l3 taken from the top. The position of the yoke surrounding the tube is indicated by dotted lines in this figure. The device l3 preferably comprises a gas-tight container l6 enclosing a cathode an accelerating anode l8, a second anode IS, a pair of magnetic pole-pieces 20 and 2|, and a target or screen T.

The cathode l1 comprises a metal cylinder which is heated by a filament 22 supplied with current by a suitable source of potential 21. The cathode may have a coating of material which produces a large electron emission when heated.

The accelerating anode l8 comprises a long cylinder surrounding the cathode l1 and having an aperture plate 23 therein. The plate 23 is located near the end of the cylinder remote from the cathode. Accelerating anode |9 comprises a cylinder around one end of the cylinder l8 and extending toward the target T. The cylinder |9 has a diaphragm 24 at the end near the target T. This diaphragm 24 has an aperture 25 therein which is of substantially square or rectangular cross-section. The anodes l8 and I9 together comprise an electron lens system which focuses a beam of electrons of a cross-section determined by the shape of the aperture 25 upon the target T, The inside of the container I6 contains a coating 26 of aquadag, this coating extending substantially from the region of the target T to the polepieces 20 and 2|. Accelerating anode |8 is placed at a positive potential with respect to the cathode IT by means of a source of potential such as the battery 28, and the anode |9 is placed at a positive potential with respect to the anode l8 by means of a source of potential such as the battery 29. The screen 26 is preferably placed at the same potential as the anode I9.

The cathode I1 and the accelerating anodes l8 and H! are supported from a bifurcated press 30. Supporting wires 3| support the anode from the outstanding portionsof the bifurcated press. A flange 32 of insulating material surrounds the end of the cylinder 3 near the target T and the cylinder H! is partially supported from this flange by supporting wires 33, the cylinder I9 being further supported by a disc 34 which is fastened to the pole-pieces 20 and 2| by screws 35.

The target T comprises plates 40 and 4|, a screen or partition member 42 located between the plates, and a mesh or grid member 43 parallel to the plates and located a small distance in front thereof. The plates 40 and 4| are electrically connected to the primary winding 44 of an output transformer 45, the secondary winding 46 of which may be connected to any suitable circuit. The partition member 42 is electrically connected to the mesh screen or grid member 43 and to the mid-point of the primary winding 44 of the transformer 45 through a source of potential 41 which is so poled that the partitionmember 42 and the screen 43 are placed at a negative potential with respect to the plates 40 and 4|. The negative terminal of battery 41 is also connected to the coating 26 and to the second accelerating anode l9.

Surrounding the cathode ray device l3 and completing the magnetic circuit |2 between the magnetic tape I0 and the cathode ray beam (which is adapted to pass between the pole-pieces 20 and 2|) is a yoke 50 of soft iron which is shown diagrammatically in Fig. 1 and in further detail in Fig. 2. Supported in grooves in the two parts of the yoke 50 are metallic pole-pieces and 52 which are so placed as to leave a very narrow air-gap through which the magnetic tape I0 is adapted to pass. The yokes 50 terminate around the cathode ray tube l3 adjacent the polepieces 2|! and 2| located within the tube.

The magnetic circuit l2 thus has two aps therein, the gap H which is large enough for the magnetic tape to pass therethrough and the gap 53 through which the beam generated by the cathode and accelerated and focussed by the anodes l8 and H! is adapted to pass on its path to the divided target T. a

The operation of the electronic pick-up arrangement shown in Fig. 1 will now be described. Electrons are emitted by the cathode l'I, accelerated by the anodes I8 and I9, and focused by these anodes in cooperation with the coating into a beam of electrons which is directed toward the target or screen T; A relatively low voltage is used to accelerate this beam as, for example, of the order of 100 volts. Because of this low voltage the beam may be appreciably bent when it passes between the pole-pieces 20 and 2| due to the magnetic flux present in the gap between the pole-pieces. Let it be assumed that a portion of the tape l0 having no signals impressed thereon is in the gap l of the magnetic circuit l2. When this condition exists, the electron beam is not bent as it passes between the pole-pieces 20 and 2| and the energy of the beam is evenly divided between the two target plates 40 and 4|. Due to the fact that the plates 40 and 4| are hooked up in push-pull fashion, no current will flow in the secondary winding 46 of the transformer 45. Now assume that the portion of the tape l0 having a signal current impressed thereon is passing through the gap The flux from this magnetic tape thus passes through the magnetic circuit l2 and causes the beam to be bent in such a manner that its energy is divided unequally between the two plates 40 and 4|. The balance between the currents flowing in the primary winding 44 of the transformer 45 is thus disturbed and an output current flows in the secondary winding 46 of the transformer 45 which is proportional to the signal magnetically recorded on the tape.

The accompanying drawing shows one preferred dimensioning of the various parts of a structure in accordance with the invention. The main diameter of the actual cathode ray tube shown is one and three-fourths inches, all dimensions in the drawing being scaled down in the same ratio.

In order to more fully study the operation of this device let it be assumed that the recording electromagnet used with the ordinary magnetic tape recorder induces magnetization proportional to the amplitude of the current flowing in the coils. Suppose that an alternating current of the form a=A sin or. is put into the recorder. The intensity of the resultant flux through the tape will be rp=KA sin wt. The voltage delivered amass? Various modifications may obviously be made y he-Pickp coils that an ordinary electromagnetic pick-up device isused) will begiven by the equation ;=Agoi cos cot 'lhus with this form of quenciesareshiftedinphasebyflodegrees and the output is proportional As the tape moves through the gap H, its flux is guided by the yoke 50 to the cathode ray tube l3 where it deflects the electron beam by shifting it away from anode plate towards the other plate 4| and vice versa, depending upon the secondary 48 and 4| to pick-up device all frean air-gap of small area,

without departing from the spirit of the'invention, the scope of which is defined by the appended claims.

What is claimed is:

1. The combination with an electron beam discharge tube of beam deflecting means comprising a magnetic flux path terminating at one end within the tube in the vicinity of the beam, a magnetic signal record member adiacent the other end of ing relative and said record member.

2. The combination with an electron beam discharge tube of beam deflecting means comprising a magnetic flux path of high permeability terminating at one end within the tube in a pole-piece in the vicinity of said beam and at the other end in a surface of area small enough to read a magnetic tape record of the kind used to record speech-and other signals.

3. The combination with a magnetic circuit,

of an electric beam discharge tube in a gap in said circuit, a magnetic signal record member in a second gap in said circuit, and means for producing relative movement between said circuit and said member.

yoke arranged so as to define of an electron beam discharge tube located between the legs of said yoke, said discharge tube having therein a pair of pole-pieces of magnetic pieces have a narrow gap therebetween through which said beam passes.

5. In combination, a magnetic tape record of a varying current,

of said flow of electrons.

6. A cathode ray device comprising means for generating a beam of electrons, a pair of anode members in the path of said beam, each anode with the successive vanations of said record material which pole- 8. A cathode ray device comprising means for generating a. beam of electrons, a pair of anode members in the path of said beam, each anode being in the neutral position of the beam contacted by substantially half the electrons of said beam, a magnetic record member, a, path of high permeability between said magnetic record and said beam for causing said beam to be deflected in accordance with the successive variations of said record member to thereby change the dis tribution of electrons between the anode members, and an external circuit connected to said anode. v

9. The combination with a yoke of magnetic material of a pair 01' tapered pole-pieces within an electric discharge tube, and adjacent the respective legs of said y'oke, said yoke having a gap therein external'to said tube, and means within said tube for directing the electric discharge between said pole-pieces.

10. The combination with a yoke of magnetic material of a pair of tapered pole-pieces within an electric discharge tube and adjacent the respective legs of said yoke, said yoke having a gap therein external to said tube, means within said tube for directing the electric discharge between said pole-pieces, and means for applying a varying magneto-motive force to said yoke from within said external gap.

11. The combination with a yoke of magnetic material of a pair of tapered pole-pieces within an electric discharge tube, said yoke having a gap therein external to said tube, means within said tube for directing the electric discharge between said pole-pieces, means for applying a varying magneto-motive force to said yoke from within said external gap, and means for utilizing the resultant change of direction of the electric discharge toset up corresponding current variations in a circuit external to said tube.

12. The combination with a yoke member of magnetic material, a vacuum tube extending between the extremities of the legs of said member, and tapered members of magnetic material mounted inside said vacuum tube in such position that their outer extremities register respectively with the extremities of said yoke member and their inner extremities are spaced apart to form a small gap therebetween.

13. A cathode ray tube comprising a cathode for emitting electrons, a target, means for forming said electrons into a beam and directing said beam toward said target and members of magnetic material mounted between said cathode and said target, each member consisting of a tapered element having its outer and larger port'on shaped to conform to the contour of the tube wall and its inner and smaller portion ad-' jacent the path of the cathode beam.

14. The combination with an electron beam discharge tube, of means for deflecting said beam comprising a magnetizable element having different portions differently magnetized, a magnetic flux path extending from pole pieces within the tube in the vicinity of said beam to the vicinity of said element, and means for moving said element so that said portions in succession vary the flux of said flux path.

15. The combination with an electron beam discharge tube, of a magnetic flux path including a yoke of material of high magnetic perme-' ability and having a gap through which said beam passes and a second gap at a distance from said beam, a magnetic record element located in said second gap, and means for moving said element through said second gap.

16. A device for reading magnetic record elements-comprising the combination with an electron beam discharge tube, of a magnetic flux I portions of said legs path including a yoke of materialoi high permeability, said yoke being divided into two legs and each leg being divided into two parts with one part of each being external to said tube and the other in alinement therewith within said tube, both said parts being shaped to closely fit the contour of the tube wall and being substantially in contact therewith, said parts within said tube being spaced to form a narrow gap between which the electron beam passes, and said external parts being spaced to form another narrow gap suitable for having a magnetic record element passed therethrough.

17. The combination with an electron beam discharge tube, of a magnetic flux path including a yokeof material of high magnetic permeability outside said-tube, each of the two legs of said yoke terminating at opposite sides of the wall of said tube and conforming to the shape of said wall, tapered pole-pieces within said tube and respectively in alinement with said shaped outside portions of said legs and shaped to fit the wall of said tube, said pole-pieces being positioned to form a gap therebetween, means for forming and projecting a beam of electrons through said gap, the dimension of said gap perpendicular to the axis of said beam being only slightly greater than the dimension of the beam in that direction, and a target for said beam at a distance from said gap many times the dimension of said gap in the direction of the axis of the beam, each of said legs being tapered at its extremity opposite the one at said wall and forming with the corresponding extremity of the other leg a small gap of the order of the size of said first-mentioned gap.

18. The combination with an electron beam discharge tube of a magnetic flux path including a yoke of material of high magnetic permeability outside said tube, each of the two legs of said yoke terminating at opposite sides of the wall of said tube and conforming to the shape of said wall, tapered pole-pieces within said tube and respectively in alinement with said shaped outside and shaped to fit the wall of said tube, said pole-pieces being positioned to form a gap therebetween, means for forming and projecting a beam of electrons through said gap, the dimension of said gap perpendicular to the axis of said beam being only slightly greater than the dimension of the beam in that direction, and a target for said beam at a distance from said gap many times the dimension oi said gap in the direction of the axis of the beam, each of said legs being tapered at its extremity opposite the one at said wall and forming with the corresponding extremity of the other leg a small gap of the order of size of said first-mentioned gap, the dimensions of said gap within said tube in the direction of the axis ofthe beam being much greater than its dimensions at right angles thereto. a

19. The combination with an electron beam discharge tube of a magnetic flux path including a yoke of material of high magnetic permeability outside said tube, each of the two legs of said yoke terminating at opposite sides of the wall of said tube and conforming to the shape of said wall, tapered pole-pieces within said tube and respectively in alinement with said shaped outside portions of said legs and shaped to fit the wall of said tube, said pole-pieces being positioned to form a gap therebetween, means ifor forming and projecting a beam of electrons through said gap, the dimension of said gap perpendicular to ammo-r the axis of said beam being only slightly greater than the dimension of the beam in that direction, and a target for said beam at a distance from said gap many times the dimension of said gap in the direction of the axis of the beam, each of said legs being tapered at its extremity opposite the one at said wall and forming with the corresponding extremity of the other leg a small gap of the order of size of said first-mentioned gap, said means for producing and projecting said beam comprising-a gun structure and means for supporting said on said gun structure.

20. The combination with an electron beam discharge tube comprising an evacuated container substantially free of gas content enclosing means for generating a beam of electrons, a target comprising two elements spaced from each other, and a pair of pole-pieces on opposite sides of the beam, and means outside said enclosure for deflecting said beam from one of said target elements to the other so that the energy of the beam is divided between said elements comprising a magnetizable element having different portions difierently magnetized, and magnetic flux paths extending from the vicinity of said pole-pieces within the tube to the vicinity of said magnetizable element, and means for moving said magnetizable element so that said difierently magnetized portions in succession vary the flux in said paths to vary the distribution of said beam between said target portions.

21. A cathode ray device comprising means for generating a beam of electrons, a target for said beam having two portions displaced from each other, a transformer, means for connecting the primary of said transformer between said two portions of said target, means for connecting substantially the midpoint of said primary to said beam generating means, means for connecting the secondary of said transformer to an output circuit, a pair of pole-pieces within said tube bepole-pieces within said tube tween said beam generating means and said taret member, a magnetic signal record member, a magnetic flux path comprising two leg members of magnetic material extending from a re gion closely adjacent said pole-pieces to a region on opposite sides of and closely adjacent the magnetic record member, and means for moving said magnetic record member in the gap created by the space between said legs so that said beam is caused to divide its energy between the two portions of the target member in such a manner that an amplified output current is produced in the secondary of said transformer.

22. A cathode my device comprising means for generating a beam of electrons, a target for said beam having two portions displaced from each other, a transformer, means for connecting the primary of said transformer between said two portions of said target, means for connecting substantially the mid-point of said primary to said beam generating means, means for connecting the secondary of said transformer to an output circuit, a pair of pole-pieces within said tube between said beam generating means and said target member, a magnetic signal record member, a magnetic flux path comprising two leg members of magnetic material extending from a region closely adjacent said pole-pieces to a region on opposite sides of and closely ad- Jacent the magnetic record member, means for moving said magnetic record member in the gap created by the space between said legs so that said beam is caused to divide its energy between the two portions of the target member in such a manner that ,an amplified output current is produced in the secondary of said transformer, and means between said two portions of said target for preventing secondary electrons caused to be emitted by the primary beam impinging upon each of said target portions from passing to the other of said target portions.