US2383758A

US2383758A - Electronic translating device

Info

Publication number: US2383758A
Application number: US503553A
Authority: US
Inventors: Ziebolz Herbert
Original assignee: ELECTRONBEAM Ltd
Current assignee: ELECTRONBEAM Ltd
Priority date: 1943-09-23
Filing date: 1943-09-23
Publication date: 1945-08-28
Anticipated expiration: 1962-08-28

Description

Aug. 28, 1945. zlEBOLZ 2,383,758

ELECTRONIC TRANSLATING DEVICE Filed Sept. 23, 194s 3 Sheets-Sheet 1 ,2 ig Z b 6% I 45 A60 :54 (FA i2 P -C G'-T I: :iljj

, 25 2O .t v 6&6 1 gm HERBERT ZIEBOLZ w, W M

Aug. 28, 1945. H. ZIEBOLZ 2,383,758

ELECTRONIC TRANSLATING DEVICE 7 Filed Sept. 25, 1943' 3 Sheets-Sheet 2 YYI Ci 6.

HERBERT 21, 32 012 Aug. 28, 1945. H ZEB'OLZ 2,383,758

ELECTRONIC TRANSLATING. DEVICE Filed Sept. 23, 1943 3 Sheets-Sheet 3 iv c gf. *9. 71 70.

. l L11 I 16- i 46"- i HERBERT ZIEBOLZ Patented Ag i' 28, 1945 UNITED STATES PATENT orrlcr.

2,383,758 ELECTRONIC TRANSLATING DEVICE Herbert Ziebolz, Chicago, IlL, assignor, by mesne assignments, to Electronbeam, Ltd., Chicago, 111., a partnership of Illinois Application September 23, 1943, Serial No. 593,553

Claims.

The invention relates to electronic translating devices of the cathode-ray tube type for relaying, amplifying, converting, transforming or otherwise translating mechanical movements into proporfor performing these translating functions with a minimum of distortion due to any change in the characteristics of the means or of the electronic device.

converted into electrica1 signals with a minimum of distortion due to changes in the characteristics of the converting means. I

This invention relates to a cathode-ray or vacuum type tube in which an electron stream or beam is deflected by mechanically moving a beam deflecting means or controlling element to vary the number of electrons intercepted by electron receiving means or an anode, the deflecting means being moved in accordance with the magnitude of a variable condition to be translated into proportional electrical signals. A second deflecting means is provided to act upon the electron stream in opposition to the first deflecting means, and the second deflecting means is energized .in accordance with variations in the number of electrons acting upon the electron receiving means or anode. the arrangement being such that the stream is deflected to establish a state of equilibrium between the two deflecting means.

This application is a continuation-in-part of my copending application Serial No. 435,092, filed March 17, 1942, which is a continuation-in-part of Serial No. 417,871, filed November 4, 1941, now Patent 2,314,302, granted March 16, 1943.

Other aims and advantages of the invention will appear in the specification, when considered in connection with the accompanying drawings, wherein:

Figure 1 is a circuit diagram showing one form I of device in which the primary deflection is accomplished by a, movable magnetic field; while the balancing deflection is accomplished by a magnetic coil.

Figure 2 shows a modified form of the device, wherein the primary deflection is accomplished by a movable magnetic field and the balancing deflection involves a pair of deflecting plates.

Figure 3 shows another modification, wherein both deflecting means comprise movable magnetic fields.

Figures 4, 5, 6, 7 and 8 show various arrangements in which the primary deflection of the beam is controlled by a magnet movable longitudinally of the electron beam.

Figures 4a and 4b are for explaining the operation of Figure 4.

Figure 9 illustrates an arrangement generally like Figure 4 for-measuring and indicating the rate of flow of fluid in a conduit.

Figure 10 illustrates an arrangement generally like Figure 4 for indicating the level of fluid in a container.

Figures 11 and 12 illustrate different magnetic circuit arrangements useful for indicating liquid level or fluid flow.

Figure 13 illustrates another arrangement for indicating fluid flow in a conduit.

In the arrangement shown in Figure 1, there is diagrammatically represented a cathode-ray tube consisting of an insulating-envelope 20. The internal construction of the cathode-ray tube may be of any suitable and well known type, but

for the purpose of illustration, the tube has a source of electrons represented by a heater or filament 2| for heating an electron emitting cathode 22. The electrons emitted by cathode 22 are accelerated and focused into an electron beam of suitable shapedirected alongtthe axis of the tube by means of an accelerating and concentrating electrode 23 mounted in the tube and maintained at apositive potential with respect to the cathode 22 by means of a suitable source of potential, represented by the battery 24. The elecmay be employed if desired. The anodes 26 and I direction or toward plate 21.

21 are connected through

suitable coupling resistances

28 and 29 to a source or positive potential, represented by the battery 30, the negative terminal of which is connected to the positive terminal of battery 24. In some instances, the battery 36 may be omitted. Moreover, it is not

essential'that resistances

26 and 29 be connected to the battery 24, but they may be connected to ground. A load circuit or any other device 3| utilizing load current is connected directly across the leads to

plates

26 and 21.

The electron beam 25 may be initially concentrated or focused on either

plate

26 or 21 or it may be focused to impinge upon both plates to an equal extent. In Figure l, the primary deflection of the beam 25 is secured by mechanical displacement of a deflecting magnetic field established from a suitable source represented by a permanent magnet 46 which is mounted for relative movement with respect to the tube 20.

equilibrium and, under this condition, the potential difference existing between plates 26 and In this arrangement the fleld is moved transversely of the electron beam. Suitable means may be provided for counteracting the effect of magnet 46 on the electron beam when the magnet is in its normal or zero position. For example, a deflectin coil 46a energized from a suitable source 46b through an adjustable resistance 460 may be provided to establish a magnetic field tending to deflect the beam in the opposite direction from the magnet 46 and to normally center the beam between the

plates

26 and 21 or cause the beam to assume any other desired position.

Deflection of the beam 25 in accordance with the movements of magnet 46 causes corresponding variations in the number of electrons impinging upon

plates

26 and 21, thereby causing

plates

26 and 21 to vary in potential in response to the movements of magnet 46. Where two plates are employed and the beam is initially positioned midway between the plates, the potential variations on plate 26 are opposite to the variations on plate 21, and the difference in potential between the plates supplies the load 3i with current which varies in accordance with the movements of magnet 46. It will be understood that the load may be connected from either plate 26 or plate 21 to ground or to source 30,or one of the plates may be omitted and the load connected between the remaining plate and ground or source 30.

A bending or counterbalancin magnetic field is established transversely of the beam 25 by means of a magnetic coil 34 which is shown as being energized by current derived from the potential variations existing between

plates

26 and 21. The amount of current supplied to coil 34 may be regulated or proportioned by means of a potentiometer 35 having its input circuit connected between

plates

26 and 21 and in parallel with the load 3|. The coil 34 is so connected that its field tends to deflect the beam 25 in an opposite direction from the deflecting magnet 46.

The operation of the arrangement shown in Figure 1 is believed to be clear from the foregoing description. It is assumed that magnet 46 has been moved from its normal position so that it tends to deflect the beam from mid-position toward the plate 26 and a potential diiierence is established between

plates

26 and 21. This potential difference energizes coil 34 and establishes a deflecting or counterbalancing magnetic field which tends to deflect the beam in the opposite The beam 25 will assume a position in which the deflecting actions of the magnet and of coil 34 are in a state of 21 will be substantially proportional to the amount oi movement of magnet 46. The amount of mechanical displacement of an element movable with magnet 53 may be indicated by including an indicating meter 45 in the circuit to the coil 34. The electric signals produced by movement oi the primary control element 46 are translated into corresponding mechanical. movements of a secondary element. the movable indicator of meter 45. The proportion or ratio between the input signal and the signal supplied to the load may be adjusted or controlled by adjustment of the potentiometer 35.

The arrangement shown in Figure 2 is a variation of the arrangement shown in Figure 1, in that the counterbalancing deflection is secured by means of electrostatic deflecting plates 36 and 31. This figure also illustrates an alternative arrangement for normally counterbalancing the action of the magnet 46 in its zero or normal position. In this instance, a second magnet 46d is provided and is adjustably mounted for movement toward and away from the electron tube so that the beam may be centered or adjusted to any desired position.

In Figure 3, both the primary deflection and the counterbalancing deflection of the beam is accomplished by means of two movable magnetic fields, such as those of a. permanent magnet 39 and an electromagnet 41 mounted to move transversely of the beam. Electromagnet 41 may be energized from a suitable source 410: through an adjustable resistance 41b. The deflecting actions of the electromagnet 41 and permanent magnet 39 when in their zero position may be arranged to counterbalance each other on the electron beam 25, and the counterbalanced condition may be obtained by adjusting the normal position of electromagnet 41 or by adjusting the value of the current in magnet 41. If desired, an additional counterbalancing deflecting means such as shown in Figure 1 or Figure 2- may be provided in Figure 3.

In the arrangements involving

permanent magnets

39 and 46, it will be obvious that electromagnets may be employed instead of permanent magnets. Magnet 39 may be mounted upon a pivoted lever 40 which is restrained in its movement by a biasing spring 4! and is moved by a solenoid 42 which, in turn, is energized by ourrent-derived from the potential difference developed across plates 26 and 21.-

It will be obvious to those skilled in the art that the input signal or movements of magnets 46 or 41 may be derived from any condition or conditions which can be translated into movements of such magnets or deflecting field. If desired, the potential variations developed across

plates

26 and 21, or in the output circuit of the relay, may be amplified before :being impressed upon the load device or supplied to the secondary deflecting means, as disclosed in my Patent 2,314,302.

Figure 4 shows a modification somewhat like Figure 1 in which only one anode is employed and the controlling magnet 46 is arranged to move parallel with the cathode beam instead of transversely thereto. Similar parts are represented by like reference numerals. In this arrangement, the counter-balancing coil 34 is connected in series with the circuit to anode 26 which also includes the current meter 45. A variable resistance 340. may be connected in shunt with stead of transversely thereof.

parallel with the electron beam '25 and is arranged to move longitudinally of the beam in- A graduated scale I is positioned adjacent magnet 46 and the position of the magnet is indicated on the scale by a pointer Illa carried by the magnet.

The operation of Figure 4 may be explained by reference to Figure 4a which is a view of the anode end of the tube as'seen from the center of the tube. 25 has a round cross-section as shownby the solid circle 25 in Figure 4a. The beam is normally positioned by adjustment of the current 'in coil 460. (or by other focusing means) so that it normally occupies the position shown by the solid circle 25 and substantially no electrons are intercepted by the anode 26 when the magnet 46 is withdrawn to the fullest extent away from the tube. The'magnetic lines of force of I magnet 46 pass out of the north pole and enter the south pole in a known manner as shown by the dotted line II in Figure 4. The lines of force which effect movement of the beam are Itwill be assumed that the beam the magnetic lines ll (Figure 4a), the beam will travel along a curved path represented by the line 25a in Figure 4a. Thus, continued movement of the magnet to the left will cause the beam to shift towards the anode 26 until finally the entire beam falls upon the ano e as sho n by the dotted circle 25 in Figure ea As the beam moves from its normal position 25 to the position 25, the current in the anode-circuit increases in value and the current in counterbalancing coil 34 also increases in value. It will be understood that coil 34 tends to shift the beam back towards its normal position at 25 in Figure 4a.

In Figure 4b I have shown two curves representing the operation of Figure 4. The horizontal axis is graduated to represent the extent of movement of the magnet 46 and the verti al axis is graduated for current values proportional to current in the anode circuit. Curve A represents the manner in which the current varies in the anode circuit with movement of magnet 46 from right to left'where counterbalancing c il 34 carries only fifteen per cent of the total anode current, while curve B shows how the ano'ie current varies with movement of ma net 46 where coil 34 carries fifty per cent of the anode current. From these two curves it will be seen that variation in the .anode current is substantially linear with respect to movement of magnet 46 over a substantial range of movement of the magnet. Furthermore, it will be seen that a greater range of linear relation is secured by increasing the percentage of current flowing through the counterbalancing coil 34.

By reversing magnet 46 so that the north p le is nearest the cathode, the beam will be deflected in the opposite direction. In'this case, the normal position for the beam would be in the position shown by the dotted circle 25', and the deflected position would be that shown by the solid circle 25 of Figure 4a. In this case, the

current in meter 45 would decrease in value as the magnet 46 is'moved from right to left in' Figure 4.

The controlling magnet need not be arranged parallel with the electron beam as shown in Figure 4, but it may be arranged transversely of the :beam as shown in Figure 5, it being understood, however, that the magnet is mounted for movement longitudinally of the tube and parallel with the beam. In this case, the magnetic lines I I which act on the beam are shown in Figure 5. Due to the curvature of the magnetic lines, the tube 20 is rotated about its axis so that the anode 26 is substantially bisected by the line of travel of the beam represented by the line 25a.

In the modification shown in' Figure 6 the controlling magnet 46 is formed as a horseshoe mag- In the modification shown in Figure 7 the controlling magnet 46 is also in the form of a horseshoe magnet arranged transversely of the tube 26 and positioned above the tube so that the south pole is lowermost. Due to the curvature of the magnetic lines II, it is preferable to rotate the tube so that the anode 26 is substantially bisected by the path of movement of the beam represented by the line 25a. .Here also, the magnet 46 is moved longitudinally of the tube 26.

The modification shown in Figure 8 is substantially like that shown in Figure 6 except that the horseshoe magnet, does not embrace the tube." The action of this modification is the same as in Figure 6. In each of Figures 4', 5, 6, 7 and 8, reversal of the poles of the magnet will result in reversal of the direction of deflection of the electron beam, and the amount of deflection increases as the magnet approaches the cathode.

Instead of having the zero or normal position of the magnet 46 located at a point farthest removedfrom the cathode, the normal position of the magnet may be at a point nearest the oathode. In this case, the graduations on the scale H1 in Figure 4 would be reversed, and the normal position of the magnet would be at the left end of the scale. In this position, it is possible to obtain two modes of operation as described above. Th'at is, the beam adjusting means (coil 46a) may be adjusted so that the beam normally falls upon the anode, or it may be adjusted so that the beam passes to one side of the anode.

If the adjustment is such that the beam normally falls upon the anode, th'en movement of the magnet from its normal position away from the cathode will allow the beam to be deflected away from the anode, and the anode current will decrease as the magnet is moved. In this case the It will be obvious that any of the arrangements illustrated in Figures 4, 5, 6, 7 and 8 whereby the controlling magnet is moved longitudinally of the tube may be employed in the double anode tube and circuit arrangements shown in any ofFlgures 1 to 3. I

The cross-section of the electron beam need not be circular as illustrated in the drawings, but it may have other shapes, such as rectangular or triangular.

In Figures 9 to 12 I have shown various applications of the arrangements described above.

In -Figure 9 an arrangement somewhat like Figure 4 is employedior indicating the flow of fluid through a conduit. In this arrangement, the fluid to be measured flows through a conduit having a vertical section I! provided with a tapered inner wall, and a tapered plug I3 is positioned within the tapered tube II, This general arrangement is the same as disclosed in the patent to Fischer et a1. 2,130,981 and is commonly known as a rotameter. The plug or float I3 i normally cording many of the arrangements described herein.

Figure 11 is a fragmentary view showing another construction useful for indicating liquid level or fluid flow. In this arrangement the magnet 46 is embodied in a float positioned within a fluid tube 16. The magnet is provided at its two ends with

circular heads

46' and 46 formed of magnetic material. A bar of magnetic material I1 is positioned adjacent tube 16 and 0pposite the range of travel of the head 46', and this bar has an extension I'Ia which extends parallel with the tube l6 and spaced therefrom. The cathode ray tube 20 is mounted between fluid tube l6 and the extension Ila of magnetic bar 11, the arrangement being such that the path of travel of head 46' parallels the path of the elecurged by gravity downwardly, but it is forced upwardly by the flow of fluid through the tube l2, and as it rises it also rotates, although rotation is not essential in the present case: The float I3 is not buoyant, but it must rise under the pressure of the fluid to a point where the annular space between the inner wall of the tube [2 and the outer periphery of the float is sufllcient to allow the fluid to pass around the float. Usually the tube l2 will he graduated along its length so that the level of the float l3 in the tube at any instant serves as an indication of the rate of flow in the tube.

In adapting my invention for use in indicating the rate of flow of fluid in the tube I2, I use an arrangement generally like that shown in Figure 4 where the cathode-ray tube 20 is mounted adjacent the fluid tube l2 and parallel thereto, and the controlling magnet 46 is embodied in and carried by the float L3. The circuit arrangement for the cathode ray tube may be according to Figures 1, 2 or 4, but I have shown in Figure 9 a slight variation over Figure 4. In this arrangement, the counterbalanclng coil 34 is energized by an amplifier 29a, the-input of which is connected across resistance 28 included in the anode circuit, and the indicating meter 45 is connected in the circuit of coil 34 or in the anode circuit as at 45'. The connections to the-beam positioning plates 36 and 31 have been omitted for the sake of simplicity in showing and any other suitable beam positioning means may be employed. The manner of operation of Figure 9 is believed to be clear from the foregoing description of operation of Figure 4. As the float l3 rises in the tube I2 and carries magnet 46 with it, the reading on meter 45 will vary and will serve to indicate the rate of flow of fluid within tube l2. Obviously, meter 45 may be located at a distance from the tube l2.

In Figure 10 I have shown how the arrangement of Figure 4 may be used for indicating the level of liquid within a closed container H which may be liquid and fluid-tight. In this arrangement-a sightgauge I4a is provided, and a buoyant float l5 is arranged within the sight gauge to follow the level of the liquid indicated by the dotted line I411. The controlling magnet 36 is carried by the float l5 and serves to control the cathode ray tube 201m the manner described above in connection with Figure 4. The electrical connections have not been shown in Figure 10 but it will be understood that they may be actron beam in tube 20. The main path of the magnetic flux produced by magnet 46 is indi cated by the dotted line H in Figure 11. It will be seen that there is a relatively small gap between the head 46' and the magnetic bar l1, and the head 46 serves to localize the point at which the magnetic flux passes through the tube 20 to the extension Ila of the bar 11. The electrical connections for Figure 11 may be according to any of the arrangements heretofore described.

A further modification of the arrangement shown in Figure 11 is shown in Figure 12. In this arrangement, the fluid tube [6 is provided with an enlarged section l6a in which is located the head 46 of magnet 46 which is of larger diameter than the lower head 46". Also, in this arrangement the bar I1 i not provided with the extension Ila but it is located parallel with the enlarged section Ilia and extends downwardly and is located on one side of the cathode-ray tube 20 which is positioned between the fluid tube l6 and the bar I1. Here also, the main path of the magnetic flux through the tube 20 is indicated by the dotted line II.

In Figure 13 I have shown another arrangement for indicating the rate of flow of fluid in a conduit l6. vIn this arrangement a restricting oriflce i617 is provided in the tube and a U-tube I1 is connected to the conduit IS on opposite sides of the orifice in a known manner. Tube l'l contains the usual quantity of mercury Fla, and the. diflerence in the level or the mercury in the two arms of the tube I'I serves as an indication of the rate of flow Within the tube II in a known manher. For the purpose of producing an electrical indication of the rate of flow, I mount the cathode-ray tube 20 parallel. 'with one leg of the U- tube l1 and arrange the controlling magnet 46 within the adjacent arm Of U-tube I! so that it follows the level of the mercury therein and controls the anode current in the manner already dmcribed.

While I have shown and described the use of an electric meter for indicating the extent of movement of the controllingmagnet acting upon the cathode ray tube, it will be understood that other known arrangements may be employed for indicating or repeating this movement either 10- cally or at a remote point. For example, the anode current may be employed to control known forms of repeater devices for controlling the movement of a secondary element.

Obviously, the present invention is capable of various modifications and is not restricted to the particular embodiments herein shown and described.

In the appended claims the term magnet is to be interpreted as applying to either a permanent magnet or to an electromagnet.

I claim:

1. An electronic translating device comprising, in combination; means for producing an electronic beam; means for receiving electrons from said beam; a first deflecting mean comprising a movable element having a field acting directly on said beamand being operative by movement of said field with respect to said beam to vary the number of electrons intercepted by the re ceiving means; a second deflecting means acting on said beam; and means responsive to the variations in the number of electrons intercepted by said receiving means for variably energizing the second deflecting means in a direction tending to deflect said beam in opposition to said first deflecting means, whereby said beam is deflected until equilibrium is established between said first and said second deflecting means.

8. Electronic translating apparatus comprising, in combination, a primary movable element movable along a predetermined. path, a magnetic field producing means movable along said path with said primary element, a cathode ray tube positioned adjacent said path and having the beam thereof arranged parallel with said path, whereby movement of 'said magnetic element along said path variably deflects said beam with respect to the anode of said tube, a second deflecting means acting on said beam, means responsive to the current in the anode circuit of said tube for variably energizing said second deflecting means in a direction tending to deflect said beam in opposition to said first deflecting means.

9. Apparatus according to claim 8 wherein said primary movable element comprises a float contained within a conduit for fluids, and said magnetic field producing means comprises a 2. An electronic translating device according to" claim 1, wherein said first deflecting means comprises means forestablishing a constant magnetic field transversely of said electronic beam, and means for moving said constant magnetic flel-d transversely of said electronic beam.

3. An electronic translating device according to claim 1, wherein said first deflecting means comprises means for establishing a constant magnetic field transversely of said electronic beam, and means for moving said constant magnetic field longitudinally of said electronic beam.

4. An electronic translating device according to claim 1; wherein the second deflecting means comprises means for establishing a constant magnetic field transversely of said beam, and means responsive to the variation in the number of electrons intercepted by said receiving means for variably shifting said constant magnetic field with respect to said beam.

5. An electronic translating device comprising, in combination, means for producing an electronic beam, a pair of electrodes for receiving electrons from said beam, a first deflecting means comprising a movable element having a field acting directly on said beam and being operative by movement of said field with respect to said beam to bend the beam and thereby vary the number of electrons intercepted by said electrodes, a second deflecting means for acting on said beam, and means responsive to the potential difference developed between said electrodes for variably energizing the second deflecting means in a direction tending to deflect said beam in opposition to said first deflecting means whereby said beam is deflected until equilibrium is established between said first and said second deflecting means.

6. An electronic translating device according to claim 5, wherein the second deflecting means comprises means for establishing a constant magnetic field transversely of said beam, and means responsive to the potential variations developed between said electrodes for variably shifting said constant magnetic field transversely of said beam.

7. An electronic translating device according to claim 1 wherein said first deflecting means comprises a movable magnet mounted in a tube containing a fluid, and including means for moving said magnet according toa' condition of said fluid, and means for indicating the magnitude of the opposing force required to establish equilibrium between said first and second deflecting means.

magnet mounted for movement with said float, whereby said magnet deflects the beam of said cathode ray tube in accordance with a condition of the fluid in said conduit.

10. Electronic translating apparatus comprising, in combination, an electronic tube embodying means for producing an electron beam directed along a predetermined linear path, a

movable control element mounted for movement along a path substantially parallel with the path of said electron beam, and a magnet carried by said movable control element and having a magnetic field which traverses the path of said electron beam and moves along the path of said beam with movement of said control element.

11. An electronic translating device comprising, in combination, means for producing an electronic beam, means for receiving electrons from said beam, electron deflecting means comprising a movable element having a deflecting field acting directly on said beam and being operative by movement of said field with respect to said beam to deflect at least some of the electrons of said beam andto thereby vary the numberof electrons intercepted by the receiving means, a second electron control means acting on said beam,

and means responsive to variations in the number of electrons intercepted by said receiving means for variably energizing thesecond control means to control said beam in opposition to said electron deflecting means and thereby establish equilibrium between said electron deflecting means and said second control means.

12. In combination, an electronic tube provided with means for producing an electron beam directed along a predetermined vertical path, a conduit for: fluids arranged adjacent and parallel with said electron beam, a float contained within said conduit and being movable along a path parallel with said electron beam in accordance with a condition of fluid in said conduit, and magnetic field producing means can said field with respect to said beam to vary the number of electrons intercepted by the receiving means, a second deflecting means acting on said beam, means responsive to the variations in the lating mechanical movements into substantially proportional electric signals comprising, in combination, means for producing an electronic beam, a pair of electrodes for receiving electrons from said beam, a first deflecting means comprising a movable element having a field acting directly on said beam and being operative by movement of said field with respect to said beam to bend the beam and thereby vary the number of electrons intercepted by said electrodes, a second deflecting means for acting on said beam, means responsive to the potential difference developed between said electrodes for variably energizing the second deflecting means synchronously with variations in electron interception and serving to deflect said beam in opposition to said first deflecting means and thereby establish equilibrium between saidflrst and said second deflecting. means, and an output circuit connected between said electrodes for deriving a signal current having a value substantially proportional to the movement oi said movable element.

15. An electronic translating device for translating mechanical movements into substantially proportional electric signals comprising, in combination, means for producing an electronic beam, means for receiving electrons from said beam, electron deflecting means comprising a movable element having a deflecting field acting directly on saidbeam and being operative by movement or said field with respect to said beam to deflect at least some of the electrons of said beam and to thereby vary the number of electrons intercepted by the receiving means, a second electron control means acting on said beam, means responsive to variations in the number of electrons intercepted by said receiving means for variably energizing the second control means synchronously with variations in electron interception and serving to control said beam in opposition to said electron deflecting means and thereby establish equilibrium between said electron deflecting means and said second control means, and means for deriving from said electron receiving means a signal current having a value substantially proportional to the extent of movement of said movable element.

HERBERT ZIEBOLZ.