US3233141A - Rotation monitor protection system for p.p.i. display tube - Google Patents

Description

Feb- 1, 1966 N. T. SIMOPOULOS ROTATION MONITOR PROTECTION SYSTEM FOR P.P.I. DISPLAY TUBE Filed May 29, 1965 INTENSITY CUT-OFF CONTROL -28V.D.C

FIG-1 FIG-2 INVENTOR NICHOLAS T. SIMOPOULOS wwww ATTORNEYS United; States Patent 3,233,141 ROTATION MONITOR PROTECTION SYSTEM FOR P.P.I. DISPLAY TUBE Nicholas T. Simopoulos, Dayton, Ohio, assignor to Dayton Electronic Products Company, Inc., Dayton, Ohio, a corporation of Ohio Filed May 29, 1963, Ser. No. 284,174

7 Claims. (Cl. 315-) This invention relates to a cathode ray tube protection device and more particularly to an apparatus and a circuit for protecting the tube phosphor from damage due to the cessation of movement of a trace or beam which movement is dependent upon the continued movement of a '"rnemb'er' external to the 'tube.'

*This invention is particularly adapted and useful for the protection of the phosphor of cathode ray tubes which are employed to reproduce or simulate a position of a {moving or a rotary member. Such a cathode ray' tube ir 'stallation may have a P.P.I. presentation witha rotat- "in'g sweepwhich is generated by a-rotating yoke tructure. fIfi-for' any reason, the yoke should fail to rotate, the phosphor of the tube'would be damaged or burned in a short ams-by the electron beam, in the absence of a protective arrangement. It is therefore a primary object of this "invention to provide a cathode ray tube protecting device for tubes which have beams or traces which depend. for their movement on the movement of another member and whic'hfdevice is responsive to the cessation of movement of-such inember external to the tube to remove or otherwise blockth e trace'from the cathode ray tube. '"f "A notiiler-l object 'of this invention is'to provide a cathtbde 'raiitubfe protecting device which is positive in opratioir'to prevent damage to the tube phosphor upon the surrea jor conditions which" would otherwise permit *thejelctroris todamage the phosphor.

further object'of this' invention is the-provision of a'eathoder ay tube-protecting device for a CRT tube employing a'rotating yoke. 3 A still further object of this invention is the provision f ofa'cathod'e ray tube protecting device wherein a photoconductive transducer, such as a photosensitive diode, is arran ed with respect to a light modulating or chopping device and a light source to sense cessations-of movement or a rotating yoke to remove or block the trace from the screen-of the tube, and to reapply the trace upon the recurrence of yoke rotation;

These and other objects and advantages of the invention 'will bejapparent from the following description, the acc'om'pa'nying' drawings and the appended claims.

In the drawingsi FIG. 1 isa diagram of a preferred embodiment of the invention; and

FIG. 2 is awiring diagram of' the electrical portion of the device of FIG. 1. I

, Referring to the figures of the drawing, a cathode ray tube which is protected by this device is somewhat diagrammatically illustrated at 10 in FIG. 1 as including the usual face or screen 12 and neck 13. A deflection yoke 14 is surmounted over the neck 13 and includes means (not shown) .mounting the yoke 14 for rotation. The cathode ray tube 10 may, for instance, form part of apparatus for simulating or following the movement of a radar antenna, and displaying P.P.I. traces, such as the trace shown at 15, which effectively rotate angularly v to rotate the yoke 14 through suitable reduction gearing 3,233,141 Patented Feb. 1, 1966 ice about the center axis of the tube in synchronism with the rotation of a radar search antenna. A specific example is the tube incorporated within a video mapping set which forms a luminous rotating trace for the purpose of projection through a transparency or a map which is then displayed by superimposition on an operators radar scope. The simulation and reproduction of the search antenna position is provided on the cathode ray tube in part by a deflection yoke which is rotated. through a suitable reduction drive in synchronism with the antenna drive.

In such CRT installations where spot or trace movement is dependent upon the continued movement of another member, such as a search antenna, the antenna may stop or cease to rotate. Even though this stoppage may be temporary, if it persists more than a minute or so, it may be sufiicient to cause the tube 10 to be damaged. This invention provides means which is responsive to the continued rotation of the yoke 14 and which operates upon the cessation of yoke rotation to remove the trace, such as by removing the Z axis input at the grid of the 'tube, 'by biasing the tube gun below cutoff, removing anode voltage, or any other means convenient to protect the phosphor.

Thus, a motor 20, which may .be synchronously controlled by any means well known in the art, is connected reflecting surfaces 32 are formed. The light source 25 and transducer 26 are positioned with respect to the wheel 31 so that the rotation of the wheel 31 causes the light from the source 25 to sweep across the transducer 26 thereby chopping or modulating the light falling on the transducer. It isobvious that other arrangements may be used for the interrupter 30, such as a slotted or segmented disk, or'a scanner With multi-sided planar reflector surfaces.

The output of the transducer 26 is applied to an intensity cutolf circuit indicated generally at 35 which, upon cessation of rotation of the wheel 31, operates to block or remove the trace 15 from the screen, such as by blocking the'Z axis input.

Referring to FIG. 2, the power supply for the lamp 25 is shown as including a -28 volt D.C. supply, a dropping resistor 38 and a small filter capacitor 39. The transducer 26 may be of any suitable type which undergoes a change of resistance with a change in intensity oflight falling thereon, and a photoconductive diode of the type 1N2175 may be used. A volt DC. power supply for the diode 26 is applied through voltage dividing resistor 40 and potentiometer 41, load resistor 42 and a lead 43. The voltage adjusting potentiometer 41 determines the operating bias on the diode 26.

The change in voltage developed across the load resistor 42, due to the change in resistance of the diode 26, is reflected at the coupling capacitor 50 essentially as a a) square wave which is amplified. in the tube section 52A and capacitively coupled through a capacitor 53 to the junction of a pair of series-connected diodes 55 and 56. The diodes 55 and 56 lead from the grid of the tube section 523 to ground and thus form a DC). rectifying circuit for the varying or changing diode 26 output and. which holds the grid of the tube section 52B below cutolf as long as the member 30 and yoke 14 are rotating. The tube section 528 may be considered as a current control device which is held inoperative during the detection of modulated signals from the transducer.

Controllable switch or circuit means effective to block the trace includes a control relay 60 which is connected in series with the plate of the tube portion 523 and which is normally unenergized due to the catch condition of this tube section. The relay 60 including normally closed contacts 62 which form a closed circuit path for the z axis input to the cathode ray tube. However, upon the cessation ofpulses to the tube 52 signalling the stoppage of the antenna, the relay 65 is energized to open or block the Z axis input thus removing the trace 15 from the face of the cathode ray tube.

The operation of the invention described is mainly selfcvident from the foregoing description. The motor 20 will normally operate in synchronism with the radar antenna and rotate the yoke 14 through suitable gearing, such as the reduction gearing 22. The light falling on the photo-diode 26 will be modulated by means of the individual reflectors 32 intercepting the light from the lamp 25 with the rotation of the Wheel 30. The changing output of the diode 26 is amplified in the tube section 52A and detected by the diodes and 56 to hold the tube section 52B below cutoff. If, for any reason, the motor 20 should cease to drive the yoke 14, a steady state condition is caused at the diode 26, thus operating the relay 60 through the tube 523 and removing the Z axis input to the tube. in this manner, the phosphor on the screen of the tube is protected against electron burn. However, just as soon as the motor again operates, the relay 60 is automatically released by the grid of the tube section 52B being driven to cutoff, and the Z axis input is reapplied to the tube 10.

It will therefore be seen that this invention provides a cathode ray tube protecting device Which is both positive and automatic in its operation. It may be incorporated into compact equipment with a minimum of space requirements.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A cathode ray tube protecting device wherein movement of the electron beam on the phosphor screen is controlled by a rotary member, the improvement comprising light-interrupting means connected to rotate With said member, a light source directing a beam of light for interruption by said interrupting means, a photoelectric transducer positioned to receive interrupted light when said member is turning and to receive a steady state light condition when said member is stationary, and control circuit means connected to said transducer and responsive to the absence of a changing output signalling the cessation of movement of said member to remove said beam from said cathode ray tube.

2. A cathode ray tube protecting device wherein movement of the electron beam on the phosphor screen is controlled by a rotary member, the improvement comprising light-interrupting means connected to rotate with said member, a light source directing a beam of light for interruption by said interrupting means, a photoelectric transducer positioned to receiver interrupted light when said member is turning and to receive a steady state light con 4 dition when said member is stationary, control circuit means connected to said transducer and responsive to the absence of a changing output signalling the cessation of movement of said member to remove said beam from said cathode ray tube, and further responsive to a re-establishment of said changing output signalling the resumption of rotation of said member to reestablish said beam.

3. A cathode ray tube phosphor protecting device for preventing a phosphor burn in a cathode ray tube where a trace on the tube is moved in synchronism with an externally rotated member, comprising a light source, a photoconductive transducer, a light modulating wheel rotated in response to the rotation of said member and effectively interposed between said light source and transducer to modulate the light falling thereon from said source upon the rotation of said member and providing an essentially steady state condition upon the cessation of member rotation, means connected to receive the output of said transducer, and control means responsive to the absence of a change in said output for removing said trace from said cathode ray tube.

4. A cathode ray tube phosphor protecting device for preventing a phosphor burn in a cathode ray tube where a PPI trace on the tube is swept radially and rotated by a rotating yoke on said tube, comprising means normally rotating said yoke, a light source, a photoconductive transducer, a light modulating device connected for rotation by said yoke rotating means and efiectively interposed between said light source and transducer to modulate the light falling thereon from said source upon the rotation of said yoke and providing an essentially steady state condition upon the cessation of yoke rotation, means connected to receive the output of said transducer, and control means responsive to the absence of a change in said output having controllable switch means connected to remove said trace from said cathode ray tube upon said cessation of yoke rotation.

5. A phosphor protecting device for a cathode ray tube having a rotating yoke and arranged to simulate the position of a radar search antenna for preventing phosphor burn in the event that the search antenna is stopped, comprising drive means for rotating said yoke in synchronism with the rotation of said antenna, means defining a light source, a photoconductive transducer, a light modulating wheel connected for rotation with said yoke drive means and elfectively interposed between said light source and transducer to modulate the light falling thereon from said source upon the rotation of said drive means and providing an essentially steady state condition upon said transducer with the cessation of drive means rotation signalling the cessation of antenna movement, detector means connected to receive the output of said transducer, and relay control means responsive to the failure of a change in transducer output connected to remove the trace from said cathode ray tube upon said failure and further responsive to the resumption of changing transducer output signalling resumption of antenna movement to reestablish said trace.

6. A cathode ray tube phosphor protecting device for protecting the phosphor of a cathode ray tube including a rotating deflection yoke, comprising a rotating reflector member connected in driven relation to said yoke, a light source, a photoconductive transducer positioned to intercept from said source a light swept by said member upon the rotation thereof, an amplifier connected to said transducer to amplify the signal therefrom, a detector connected to said amplifier, a current control device connected to said detector and normally held inoperative during the detection of modulated signals from said transducer, and controllable switch means connected for operation by said current control device and operable upon the cessation of detection of said modulated signal to remove the trace from said cathode ray tube.

"1'. A cathode ray tube phosphor protecting device for protecting the phosphor of a cathode ray tube including a rotating deflection yoke, comprising a rotating light modulating member connected to rotate With said yoke, 21 light source, a photoconductive diode positioned to receive from said source a light modulated by said member upon the rotation thereof, an amplifier connected to said transducer to amplify the signal therefrom, a rectifier connected to said amplifier, a control tube having a grid connected to said rectifier and normally held at cutoff during the detection of modulated signals from said transducer during rotation of said yoke, and a relay connected for operation by said control tube and operable with the conduction of said control tube upon the cessation of 6 detection of said modulated signal to open a circuit effective to remove the trace from said cathode ray tube, and to close said circuit upon the reestablishment of yoke rotation.

References Cited by the Examiner UNITED STATES PATENTS 2,401,432 6/1946 Luck 315-27 X 2,404,147 7/1946 Strickland 250215 X 2,882,445 4/1959 Sprengeler et a1 315-20 DAVID G. REDINBAUGH, Primary Examiner.

Claims (1)

1. A CATHODE RAY TUBE PROTECTING DEVICE WHEREIN MOVEMENT OF THE ELECTRON BEAM ON THE PHOSPHOR SCREEN IS CONTROLLED BY A ROTARY MEMBER, THE IMPROVEMENT COMPRISING LIGHT-INTERRUPTING MEANS CONNECTED TO ROTATE WITH SAID MEMBER, A LIGHT SOURCE DIRECTING A BEAM OF LIGHT FOR INTERRUPTION BY SAID INTERRUPTING MEANS, A PHOTOELECTRIC TRANSDUCER POSITIONED TO RECEIVE INTERRUPTED LIGHT WHEN

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