US2489155A

US2489155A - Electric control circuit

Info

Publication number: US2489155A
Application number: US570523A
Authority: US
Inventors: Richter Walther
Original assignee: ALLIS CHALMCRS Manufacturing Co
Current assignee: ALLIS CHALMCRS Manufacturing Co; ALLIS-CHALMCRS MANUFACTURING Co
Priority date: 1944-12-30
Filing date: 1944-12-30
Publication date: 1949-11-22
Anticipated expiration: 1966-11-22

Description

Nov. 22, 1949 w. RICHTER 8 ELECTRI C CONTROL CIRCUIT Filed Dec. 30, 1944 Patented Nov. 22, 1949 ELECTRIC CONTRGL CIRCUIT Walther Richter, Milwaukee, Wis., assignor 'to Allis-(lhalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application December 30, 1944, Serial No. 1527-0523 22 Claims.

This invention relates in general to improvements in electric control circuits and more particularly to static means for abruptly and permanently varying the potential of an element of an electron discharge device which is connected to a source of relatively high potential.

.In the operation of electron discharge devices .such as cathode ray tubes and oscillator tubes, it is often desired to control the flow of electrons through the tube in an abrupt manner by varying the potential of a control electrode or grid. This result may easily be obtained when the cathode is grounded or when the potential difference between cathode and ground does not exceed a few hundred volts. In cathode ray oscilloscopes, however, the current supply may have a voltage of several thousand volts, and it is desirable to ground the anode to permit grounding of the sweep circuit without establishing excessive potential difierences between the anode and the deflection plates.

When such :an oscilloscope is to-be used to obtain a photographic record of a controlled transient phenomenon it is advantageous to leave the sweep potential continuously impressed on the deflection plates and to suppress the cathode ray beam by constant impression of a suitable negative potential on the grid until shortly before initiation :of a transient. The beam is abruptly released by raising the grid potential when an exposure of the trace on the screen is to be made to obtain a photograph of the trace over the desired number of sweeps, and the beam is thereafter abruptly suppressed .by permanently returning the grid to the lower potential.

As this operation cannot be performed with the desired rapidity by mechanical switching means, it is necessary to resort to static means including electric valves. The cathode of the cathode ray tube being at a high negative potential with respect to ground, it is advantageous a vacuum tube utilized in a high voltage oscillator may be keyed by means of a trigger circuit coupled with a grounded source of control potential through a coupling transformer or of a coupling capacitor.

It is therefore an object of the present invention to provide a static system for shifting at will the potential of an element of a high voltage circuit from one value to another responsive to control potentials obtained from a grounded source of potential.

Another object of the present invention is to provide a static system for imparting different constant potentials to an element of an electric circuit in response to impulses transmitted inductively or capacitively from a source of control potential.

Another object .of the present invention is to provide a static system for abruptly releasing and suppressing at will the beam .of a cathode ray tube having .a grounded anode.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, inwhich;

Fig. 1 diagrammatically illustrates one embodi- .ment of the present invention comprising a trigger circuit controlled by impression of positive or negative potential impulses thereon through capacitive means for impressing at .will, on the grid of a cathode ray tube, potentials suppressing and releasing the cathode ray beam; and

Fig. 2 diagrammatically illustrates a portion of a modified embodiment of the present invention in which the control of the beam is effected by shifting the potential of the cathode instead of thepotential of the ,grid.

Referring more particularly to Fig. l of the drawing by characters of reference, reference numeral 6 designates a cathode ray tube of any suitable known type represented conventionally .on the drawing. Tube 6 is provided with the usual electrodes comprising a cathode I, a plurality of electron accelerating and focusing electrodes 8, 9 and two pairs .of deflection plates ll, l2. The deflection plates are connected with grounded sources of potentials l3, M of which at least one is a source of potential to be observed by inspection of the trace produced by the beam .on the screen of the tube or by photographic recording of such trace.

Electrode 8 is the ,anode and is connected with cathode I through a suitable source of potential conventionally represented as a dynamoelectric generator l5 to accelerate electrons emitted at a cathode toward the screen. Anode 8 is grounded at It to prevent disturbances in the operation of the tube which might result from excessive difierences of potential between the anode and the deflection electrodes 1 I, I2.

Electrode 9 is a grid to .be impressed with an adjustable control potential which is negative with respect to the potential of cathode T to focus the electron beam on the screen. The grid may also be impressed with a more negative potential for controlling the beam intensity to the extent of suppressing the beam in the manner set forth hereinafter.

The different voltages to be abruptly impressed between grid 9 and cathode I may be obtained from any suitable source of low potential such as a direct current circuit l1, l8 energized from an alternating current circuit 19 through a transformer 20 and a thermionic rectifier 2|. The current supplied from rectifier 2| to circuit I1, I8 is preferably filtered by a reactor 22 and a capacitor 23. As circuit 51, I8 is to be connected with the negative or high potential terminal of generator 15, the primary winding of transformer 20 is insulated against the core and the associated secondary winding for the full voltage of generator l5. Transformer 20, the conductors of circuit ll, I8 and all the elements conductively connected therewith are preferably mounted on a common support insulated from ground for the full voltage of generator l5.

Circuit 55,13 supplies current to a so-called bleeder resistor or voltage divider comprising serially connected resistors 24, 25 and 28. Resistor 25 is bridged by a stabilizing capacitor 25 and has a terminal 21 directly connected to cathode 1. Resistor 23 comprises a variable portion defined by a movable tap 29 and serially connected with another resistor 30 between cathode 1 and grid 9 to impress on the grid a predetermined adjustable control potential lower than the potential of terminal 21 and cathode l.

The potential of grid 9 may be abruptly varied from the potential of tap 29 by means of a polarized trigger circuit 3! comprising a vacuum triode 32 having an anode 33, a grid 34 and a cathode 35. Anode 33 is connected with conductor I! through a resistor 36 and cathode is connected with conductor [8 through a resistor 31 bridged by a stabilizing capacitor 38, whereby triode 32 and resistors 35, 31 are serially connected across circuit I1, is serving as source of control potentials different from the potential of tap 29.

The trigger circuit comprises a second triode 39 having an anode 4| connected with conductor.

I! through a resistor 42, a grid 43 and a cathode 44 connected with cathode 35 through a low resistance connection. The point of juncture of resistor 35 with anode 33 of triode 32 is connected with grid 9 through any suitable rectifying device such as a vacuum diode 45 having an anode 45 connected with grid 9 and a cathode 41 connected with anode 33.

Grids 34, 43 are connected with circuit ll, 18 and with resistors 36, 42 in such manner as to render triodes 32, 39 selectively conductive. More particularly, grid 34 is connected with anode 4! through a resistor 48 and is connected with conductor l8 through a resistor 49 bridged by a stabilizing capacitor 5i. Grid 43 is similarly connected with anode 33 through a resistor 52 and with conductor is through a resistor 53- bridged by a stabilizing capacitor 54.

Potential impulses of steep wave front may be impressed on grid 34 from a source of positive potential, such as a battery 55, through a switch 56 and a coupling device such as capacitor 5! preventing transmission of the potential of generator l5 to switch and to battery 55. Battery 55 may therefore be grounded at 58. Negative potential impulses may also be impressed on grid 34 through switch 55 from a second battery 59 having its positive terminal grounded. The charge supplied to capacitor 5'l by battery 55 or battery 59 is discharged between actuations of switch 55 through a resistor 5|.

Potential impulses of either polarity may similarly be impressed on grid 43 from batteries 55 and 53 through a switch 52 and a capacitor 63 associated with a discharge resistor 64.

While the cathode ray beam is released by the trigger circuit it is advantageous to periodically suppress the beam by means of timing potential impulses. These impulses may be obtained from any source of alternating current of suitable frequency such as circuit l9 through a transformer 55 having its secondary winding 55 grounded at 55. Winding 66 may be connected with grid 9 through a switch 37, an insulating capacitor 68 and a rectifying device such as a vacuum diode 69 having its anode it connected with grid 9 and its cathode El connected with capacitor 58. A resistor 32 serves to discharge capacitor 68 between successive cycles of the voltage of circuit I9.

The characteristics of the different elements of the system may be varied over a wide range of values in dependence upon the operating requirements imposed on the system. It has been found that the system operates satisfactorily when built up of elements identified by the following engineering data.

Cathode ray tube 6, type 5LP5 Triodes 32, 39, type 6SN7 Diodes 45, 59, type 6H6 Resistor 25, 5,000 ohms Resistor 28, 25,000 ohms Resistor 24, 50,000 ohms Resistor 31, 10,000 ohms Resistors I2, 30, 49, 53, 100,000 ohms Resistors 42, 35, 20,000 ohms Resistors 48, 52, 200,000 ohms Resistors 5!, 54, 1 m'egohm Capacitor 23, 20 microfarads Capacitor 26, 0.5 microfarad Capacitor 38, 0.25 microfarad Capacitors 5|, 54, 0.0005 microfarad Capacitors 5?, 53, 0.001 microfarad Capacitor 68, 0.006 microfarad Batteries 55, 59,20 volts Generator I 5, 2000 volts Circuit H, I 8, 200 volts The operation of the system will first be considered assuming switch 31 to be open. When circuit i9 is energized, circuit H, l9 impresses a unidirectional potential on anodes 33, M. As a result of the connections of grids 34, 43 a stable parallel operation of triodes, 32,39 is not possible. Assuming that triode 39 is carrying current, the voltage drop in resistor 3? raises cathodes 35, M to a common potential intermediate those of conductors I I and I8, and raises anode d! to a potential which is higher by the voltage drop in triode 39. As a result of the current flow from conductor I! through resistor 42 and triode 39 and of the voltage dividing action of resistors 48, 49, grid 34 assumes a potential lower than the potential of cathode 35 to the extent of rendering triode 32 nonconductive. Anode 33 is thereby maintained at substantially the potential of conductor H, and current flowing from conductor i'l through resistors 35, 52 and 53 causes grid 43 to assume a potential so related to the potential of cathode 44 as to maintain triode 39 conductive.

accepts The potential of anode 33 is then higher than the potential of tap 29 but current cannot flow between these elements as a result of the valve action of diode 4'5 which operatively interrupts the connection therebetween. maintained at the potential of tap '29 and the tap may be so adjusted that the cathode ray beam is properly focused on the screen.

When it is desired to lower abruptly the potential of grid 9 to suppress the cathode ray beam, a potential im-pulseof proper'polarity is impressed on the grid of one of the triodes whereby the flow of current is transferred abruptly from triode 39 to triode 32. For example, switch 62 may be actuated momentarily to impress a negative potential impulse from battery 59 on grid 43 through capacitor 153. 'Triode 39 is thereby rendered abruptly nonconductive and the flow-of current through resistor 12 is interrupted. The potential of grid 34 is thereby raised while the potential of cathode 35 is maintained substantially unchanged by energy stored in capacitor 38 so that triode '32 becomes conductive and takes over the current previously carried by triode 39. The flow of current through triode 32 also maintains grid 43 at a potential lower than the common potential of cathodes 35, 44 to maintain triode 39 nonconducti-ve upon termination of the potential impulse impressed on grid 43 from battery 59.

Upon initiation of the flow of current through triode 32 the potential of anode 38 drops to a value below the potential of tap 29. Current then flows from tap 29 through resistor 80 and diode to abruptly bring grid '9 to substantially the potential of anode 33. If the characteristics of the elements of the system are suitably proportioned, the cathode ray beam of tube 15 is thereby abruptly suppressed. The same result would be obtained by momentarily impressing a positive potential impulse *from battery 55 on grid '34 to render triode 32 conductive and thereby cause impression on grid 43- of a potential rendering '56 or of switch 52 or by alternate actuation of the two switches.

During the above described operation, cathode 'H is maintained at the potential of cathode I and of terminal 2"! by a connection including resistor l2. Cathode 'H is therefore 'at :a potential higher than the potential of the associatedanode regardless of which of the two triod'es is conduc 'tive and diode 69 therefore functions as an open connection. .If switch 61 is closed, winding '56-" impresses an alternating potential on cathode "H through capacitor 68. The positive potential so impressed during alternate half cycles only raises the-potential of cathode H to a higher valuewithout affecting the operation of the system. 5

While grid 9 is at the potential of tap 29 the negative potential impressed on cathode 7| during the remaining half cycles causes the flow of current from tap 29 through resistor and diode 69 to supply charging current to capacitor 68/ Grid '9 is then The potential of grid 9 is thereby momentarily lowered whereby the :beam is momentarily suppressed. The grid is :thus impressed with a succession of timing potential impulses at the frequency .of the voltage of circuit I9 to suppress the beam once during each cycle of the voltage, whereby :the trace on the screen is caused to conrsist of dots producedat known time intervals.

The variation .of the potentialof grid 9 resulting from each .timi-ng impulse is gradual rather than abrupt :so that the suppression of the beam takes place gradually and is accompanied by some de- :focusing, but the trace on the screen remains satisfactory as the beam remains sharply focused while it has its flullintensity.

While the beam is fsuppress ed by the action of the trigger circuits the negative impulses im pressed on cathode 1:] from winding '66 have the :only result of further lowering the potential of :grid 9..

As the trigger circuit "is equally effective to raise and lower the potentials of circuit elements connected therewith, "it may be used for raising the cathode potential instead of lowering the :grid potential to suppress the cathode ray beam. The system may then be modified as shown .in Fig. 2, in which cathode l is connected with tap l5 through resistor 30 and grid 9 is connected with terminal 21, whichis then at a lower potential than tap 29. The connections of diodes 45, 592,115 reversed from those shown in Fig. 1.

The operation :of the trigger circuit remains identical to that :of the embodiment illustrated in Fig. 1. When t-r'iode 32 is conductive the potential of anode 3.3 is lower than the potentialof tap 29. The valve action of diode 45 main- .tains cathode 1 at the potential of tap 29, which may bead justedby displacing the tap to focus the beam. When 'triode 32 is nonconductive the potential of anode 33 :is above the potential of tap :29 and current flows ifrom conductor I! through resistor 3 5, diode 45 and resistor 30 to tap 29. The potential of cathode l is thereby raised to a potential higher than the potential of tap '29 by the voltage drop in resistor 30, whereby the cathode ray beam is suppressed.

When the beam is released the positive potentials impressed in halfcycles on anode "H3 from winding 6 1811.16 transmitted to cathode 1 through 'diode B9 'and alikew-iseiraise the potential of cathode '1 to suppress the .beam intermittently and thereby give a timing indication on the trace produced by the :beam on the screen.

Although but two embodiments of the present invention have been illustrated and described it will "be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

-triode comprising an anode connected with the positive terminal-oi said source through a third resistor and a cathode connected with the negative terminal of said source, a diode having an anode connected with the said grid of said cathode ray tube and a cathode connected with the said anode of said triode, and means for abruptly rendering said triode conductive to lower abruptly the potential of said grid of said cathode ray tube below said predetermined potential.

2. In combination, a cathode ray tube having an anode, a cathode and a grid for controlling the intensity of the cathode ray beam, a source of unidirectional potential, a first resistor connected across said source, a connection comprising a second resistor between said grid and a point of said first resistor at a predetermined potential, a connection between said cathode and a point of said first resistor at a potential higher than said predetermined potential, a triode comprising an anode connected with the positive terminal of said source through a third resistor and a cathode connected with the negative terminal of said source, a diode having an anode connected with the said grid of said cathode ray tube and a cathode connected with the said anode of said triode, means for rendering said triode conductive to lower the potential of said grid of saidicathode ray tube below said predetermined potential, and

.means for abruptly rendering said triode nonconductive to raise abruptly the potential of said grid of said cathode ray tube to said predetermined potential.

3. In combination, a source of relatively high potential having a high potential terminal and a grounded terminal, an electric valve having an element conductively connected with said high potential terminal, a polarized trigger circuit comprising a source of relatively low potential conductively connected with said element and with said high potential terminal for varying the potential of said element, a grounded source of control potential, and a coupling device providing an insulating connection between said source of control potential and said trigger circuit for impressing abrupt control potential impulses from said source of control potential on said trigger circuit.

4. In combination, a cathode ray tube comprising first and second electrodes for producing and controlling the intensity of a cathode ray beam, a source of unidirectional potential, a first resistor connected across said source, a connection comprising a second resistor between said first electrode and a point of said first resistor at a predetermined potential, a connection between said second electrode and a point of said first resistor at a potential different from said predetermined potential, a third resistor, a triode comprising an anode connected with the positive terminal of said source through said third resistor and a cathode connected with the negative terminal of said source, a diode having an electrode connected with the said anode of said triode and another electrode connected with said first electrode, and means for abruptly rendering said triode conductive to lower abruptly the potential of said first electrode with respect to the potential of said second electrode.

5. In combination, a cathode ray tube comprising first and. second electrodes for producing and controlling the intensity of a cathode ray beam, a source of unidirectional potential, a first resistor connected across said source, a connection comprising a second resistor between said first electrode and a point of said first resistor at a predetermined potential, a connection between said second electrode and a point of said first resistor at a potential difierent from said predetermined potential, a third resistor, a triode comprising an anode connected with the positive terminal of said source through said third resistor and a cathode connected with the negative terminal of said source, a diode having an electrode connected with the said anode of said triode and another electrode connected with said first electrode, means for abruptly rendering said triode conductive to lower abruptly the potential of said first electrode with respect to the potential of said second electrode, and means for abruptly rendering said triode nonconductive to raise abruptly the potential of said first electrode with respect to the potential of said second electrode.

6. In combination, a cathode ray tube comprising first and second electrodes for producing and controlling the intensity of a cathode ray beam, a source of potential and a resistor serially connected between said electrodes, a second source of potential, a pair of triodes comprising each an anode, a grid and a cathode, a low resistance connection between the said cathodes of said triodes, a resistor connecting the said cathodes of said triodes with said second source of potential, a pair of resistors severally connecting the said anodes of said triodes with said second source of potential, a rectifying device connecting one of said electrodes with the anode of one of said triodes, means connecting said grids of said triodes with said second source of potential and with said pair of resistors for causing said triodes to be selectively conductive, and means for impressing a potential impulse on the grid of one of said triodes for causing abrupt transfer of the flow of current from one of said triodes to the other of said triodes.

7. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said grid, a second source of potential connected with said cathode, a second resistor and an electric valve serially connected across said second source, a rectifying device conductively connecting'said grid with the point of juncture of said second resistor with said valve to cause said first potential to be overcome by the potential of said 7 point of juncture only when said first potential is higher than the potential of said point of juncture, and means for controlling the conductivity of said valve to cause alternate impression of said potentials on said grid.

8. In combination, a cathode ra tube having an anode, a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said grid, an electri valve comprising a second anode and a second cathode, a second source of potential connected with said second cathode, a second resistor connecting said second anode with said second source, a rectifying device comprising a third anode connected with said grid and a third cathode connected with said second anode to cause said first potential to be overcome by the potential of said second anode only when said first potential is higher than the potential of said second anode, and means for controlling the conductivity of said, valve to cause alternate impression of said potentials on said grid.

9. In combination, a cathode ray tube havin a cathode and a grid for controlling the intensity 9,. of the cathode ray beam, a source of potential connected with said cathode, a resistor connecting said source with said grid for impressing a first :potential on said grid, and means for impressing timing impulses on said grid comprising a source of alternating lpotential connected with said cathode and a rectifying device having an anode conductively connected with said grid and a cathode connected with said source of alternating potential to cause said first potential to be overcome by the potential of the cathode of said rectifying device only when said first potential is higher than the potential of the oathode of said rectifying device.

10. In combination, a cathode ray tube having, a cathode and a grid for controlling the intensity of the cathode ray beam, 2. source of potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said grid, a polarized trigger circuit connected with said cathode, a rectifying device having a cathode conductively connected between said. grid and said trigger circuit to cause said first potential to be overcome by the potential of the cathode of said rectifying device only when said first potential is higher than the potential of the cathode of said rectifying device, and means for impressing abrupt potential impulses on said trigger circuit to cause alternate impression of said {potentials on said grid.

11. In combination, acathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said grid, a second source .of potential, a pair of triodes comprising each an anode, -a grid and a cathode, a low resistance connection between said cathodes of said triodes, a resistor connecting the cathodes of said triodes with said second source of potential, a pair of resistors severally connecting the anodes of said triodes with said second source of potential, a rectif ing device connecting the grid of said cathode ray tube with the anode of one of said triodes to cause said first potential to be overcome by the potential of the anode of said one of said triodes only when said first potentia1 is higher than the potential of the anode of said one of said triodes, means connecting the grids of said triodes with said second source of potential and with said pair of resistors for causing said triodes to be selectively conductive, and means for impressing a potential impulse on the grid of one of said triodes for causing abrupt transfer of the flow of current from one of said triodes to the other of said triodes to cause alternate impression of said potentials on the grid of said cathode ray tube.

12. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said grid, a second source of potential, a; [pair of triodes comprising each an anode, a grid and a cathode, a low resistance connection between said cathodes of said triodes with said second source of potential, a pair of resistors severally connecting the anodes of said triodes with said second source of potential, a rectifying device connecting the grid of said cathode ray tube with the anode of one of said triodes to cause said first potential to be overcome by the potential of the anode of said one of said triodes only when said first potential ishigher than the potential of the anode of said one of said triodes, means connecting the grids of said triodes with said second source of potential and with said pair of resistors for causing said triodes to be selectively conductive, and means for impressing a negative potential impulse on the grid of the said triode carrying current for causing abrupt transfer of the flow of current there- "from to the other of said triodes to cause alternate impression of said potentials on the grid of said cathode ray tube.

13. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, 9, source of potential and a resistor seriall connected between said cathode and said grid for impressing a first potential on said grid, a second source of potential, a pair of triodes comprising each an anode, :a grid and a cathode, a low resistance connection between the cathodes of said triodes, a resistor connecting the cathodes of said triodes with said second source of potential, a pair of resistors severally connecting the anodes of said triodes with said second source of potential, a rectifying device connecting the grid of said cathode ray tube with the anode of one of said triodes to cause said first potential to be overcome by the potential of the anode of said one Of said triodes only when said first potential is higher than the potential of the anode of said one of said triodes, means connecting the grids of said triodes with said second source of potential and with said pair of resistors for causing said triodes to be selectively conductive, and means for impressing a positive potential impulse on the grid of the said triode not carrying current for causing abrupt transfer thereto of the flow of current of the other of said triodes to cause alternate impression of said potentials on the grid of said cathode ray tube.

14. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said grid, a second source of potential, a pair of triodes comprising each an anode, a grid and a cathode, a low resistance connection between the cathodes of said triodes, a resistor connecting the cathodes of said triodes with said second source of potential, a pair of resistors severally connecting the anodes of said triodes with said second source of potential, a diode having an anode connected with the grid of said cathode ray tube and a cathode connected with one of the anodes of said triodes to cause said first potential to be overcome by the potential of the anode of said one of said triodes only when said first potential is higher than the potential of the anode of said one of said triodes, means connecting the grids of said triodes with said second source of potential and with said pair of resistors for causing said triodes to be selectively conductive, means for impressing a potential impulse on the grid of one of said triodes for causing transfer of the flow of current from the said triode connected with said diode to the other of said triodes to release the cathode ray beam, and means for suppressing said cathode ray beam during predetermined time intervals comprising a source of alternating potential connected with the cathode of said cathode ray tube and a diode having an anode connected with the grid of said cathode ray tube and a cathode connected with said source of alternating potential.

15. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential and a resistor serially connected between said cathode and said grid for impressing a first pot'ential on said cathode, a second source of potential connected with said cathode, a second resistor and an electric valve serially connected across said second source, a rectifying device connecting said cathode with the point of juncture of said second resistor with said valve to cause said first potential to be overcome by the potential of said point of junction only when said first potential is lower than the potential of said point of juncture, and means for controlling the conductivity of said valve to cause alternate impression of said potentials on said cathode.

- 16. Means for varying the potential of a circuit element comprising a source of potential, a resistor connecting said source with said element for impressing a first potential on said element, an electric valve comprising an anode and a cathode, a second source of potential connected with said cathode, a second resistor connecting said second source with said anode, a rectifying device having a cathode connected with said element and an anode connected with the first said anode to cause said first potential to be overcome by the potential of said anodes only when said first potential is lower than the potential of said anodes, and means for controlling the conductivity of said valve to cause alternate impression of said potentials on said circuit element.

1'7. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, a source of potential connected with said grid, a resistor connecting said source with said cathode for impressing a first potential on said cathode, and means for impressing timing impulses between said cathode and said grid comprising a source of alternating potential connected with said grid and a rectifying device having an anode connected with said source of alternating potential and a cathode con nected with the first said cathode to cause said first potential to be overcome by the potential of the anode of said rectifying device only when said first potential is lower than the potential of said anode of said rectifying device to cause alternate impression of said potentials on the cathode of said cathode ray tube.

18. In combination, a cathode ray tube comprising electrodes for producing cathode rays and for controlling the intensity of the cathode ray beam, a source of potential connected with one of said electrodes, a resistor connecting said source with another of said electrodes for impressing a first potential on said other of said electrodes, an electric valve comprising an anode and a cathode, a second source of potential connected with said cathode, a second resistor connecting said anode with said second source, a

rectifying device connecting said anode with said other of said electrodes to cause said first potential to be overcome by the potential of said anode only when the diiference between said first potential and the potential of said anode has a predetermined sign, and means for controlling the conductivity of said valve to cause alternate impression of said potentials on said other electrode.

19. In combination, a cathode ray tube havof potential and a resistor serially connected between said cathode and said grid for impressing a first potential on said cathode, an electric valve comprising an anode and a cathode, a source'of potential connected with the said cathode of said valve, a second resistor connecting the said anode of said valve with said source, a rectifying device comprising an anode connected with the said anode of said valve and a cathode connected with the said cathode of said cathode ray tube to cause said first potential to be overcome by the potential of the anode of said valve only when the first potential is lower than the potential of the anode of said valve, and means for controlling the conductivity of said valve to cause alternate impression of said potentials on the cathode of said cathode ray tube.

20. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, means for impressing a control potential on said grid, a polarized trigger circuit connected with said cathode and comprising a triode having an anode, rectifying means comprising cathode means and anode means, a conductive connection between said cathode means and said anode for maintaining said cathode means and said anode at the same potential,

potential of said anode to be impressed on said grid to overcome said control potential only when the potential of said anode is more negative than said control potential.

21. In combination, a cathode ray tube having a cathode and a grid for controlling the intensity of the cathode ray beam, means for impressing a control potential on said cathode, a polarized trigger circuit connected with said grid and comprising a triode having an anode, rectifying means comprising cathode means and anode means, a conductive connection between said cathode means and said cathode for maintaining said cathode means and said cathode at the same potential, and a conductive connection between said anode means and said anode to cause the potential of said anode to be impressed on said cathode to overcome said control potential only when the potential of said anode is more positive than said control potential.

22. Means for varying the potential of a circuit element comprising means including a first potential source for impressing a control potential on said element, a second source of potential, an electric valve comprising an anode and a cathode connected across said second source, a rectifying device having an anode and a cathode, a conductive connection between the cathode of said rectifying device and said element, and a conductive connection between said anodes for maintaining said anodes at the, same potential and to cause the potential of said anodes to be impressed on said element to overcome said control potential only when said control potential is more negative than the potential of said anodes.

WALTHER RICHTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,906,246 Browne May 2, 1933 7 2,036,532 Knoll et al. Apr. 7, 1936 (Other references on following page) and a conductive connection between said anode means and said grid to cause the Number 13 UNITED STATES PATENTS Name Date Leeds Oct. 27, 1936 Wendt May 31, 1938 Kuehni Oct. 22, 1940 George Nov. 26, 1940 Gould. May 6, 1941 Dome Sept. 9, 1941 Dome Sept. 9, 1941 Schlesinger Dec. 9, 1941 Reeves Feb. 3, 1942 Number 14 Name Date White Apr. 28, 1942 Smyth Sept, 8, 1942 Faudell Dec. 1, 1942 Mahoney, Jr. Mar. 14, 1944 Schrader et a1 May 30, 1944 Schrader et a1 Nov. 28, 1944 Shepherd et a1 Sept. 3, 1946 Moe Jan. 14, 1947 Depp Feb. 25, 1947 Bischofi May 13, 1947 Certificate of Correction Patent No. 2,489,155 November 22, 1949 WALTHER RICHTER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 11, line 13, for the word junction read juncture;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the casein the Patent Ofiice. Signed and sealed this 14th day of March, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,489,155 November 22, 1949 WALTHER RICHTER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 11, line 13, for the word junction read juncture;

and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 14th day of March, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.