US2667587A

US2667587A - Protecting device for x-ray apparatus

Info

Publication number: US2667587A
Application number: US259408A
Authority: US
Inventors: Kuntke Alfred; Mester Heinz
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1950-12-15
Filing date: 1951-12-01
Publication date: 1954-01-26
Anticipated expiration: 1971-01-26

Description

Lulu- Jan. 26, 1954 A. KUNTKE ET AL 2,667,587

PROTECTING DEVICE FOR X-RAY APPARATUS Filed Dec. 1, 1951 INVENTORS ALFRED K N K HEINZ MES FER AGENT Patented Jan. 26, 1954 PROTECTING; DEVICE FOR X-RAY APPARATUS Alfred Kuntke, Hamburg-Wellingsbuttel, and

Heinz Mester, Hamburg, to Hartford National Bank Germany, assignors and Trust Company,

Hartford, Conn., as trustee Application December 1, 1951, Serial No. 259,408

Claims priority, ap

December 4 Claims.

Improvements in or relating to X-ray apparatus for diagnosis In X-ray apparatus the operating voltage i. e. the potential difference between anode and cathode of the X-ray-tube during normal operation is much lower than the no-load voltage, since voltage losses occur in the apparatus and supply mains upon loading it. On putting an X-rayapparatus into operation first the current for heating the incandescent cathode is switched on, the high-voltage being applied after the cathode has been heated. The loading current directly rising to its full value prevents the voltage of the tube from becoming too high.

Application of the high voltage when the cathode is cold or insufiiciently heated may cause break-down of a supply conductor, sparking in the envelope of the tube or damage to the X-ray tube. Consequently, care must be exercised, particularly according as the voltage used is higher and if, since the size is preferably minimized, the apparatus is incapable of withstanding the noload Voltage corresponding to the maximum permissible operating voltage.

Overvoltages may also be produced by mains voltage variations and transient phenomena, but particular switching means generally permit of avoiding them, without avoiding however the production of overvoltages in taking X-ray exposures due to the absence of the expected and previously adjusted tube current. This may be caused by interruption of the heating circuit or by shortcircuits. It might be attempted to infer from the primary heating current the data required for detecting a fault in the heating circuit, but this is not very reliable owing to the slight difference between the no-load current strength and the strength of the loading current of the heating transformer.

The present invention has for its object to prevent the X-ray apparatus from being connected into circuit in the absence of emission of the incandescent cathode in X-ray tubes. It concerns X-ray diagnosis apparatus comprising a circuit supplying a voltage which is lower than the normal supply voltage and, with the heating circuit cut in, is supplied to the primary of the highvoltage transformer, the discharge current resulting from emission of the incandescent cathode operating a device and the apparatus being adapted to be connected into circuit for taking an exposure after said device has been made operative.

The low voltage preferably has a value at which the X-ray tube works in the space charge range plication Germany at the high voltage end of the transformer. Frequently, different current intensities and sometimes diiierent X-ray tubes must be used. it being advantageous duced on applying the voltage is substantially independent of the adjusted heating current.

The resistance of an X-ray tube, which is practically infinite in the absence of cathode-emission, is of the order of 1 to 2 megohm in the space charge range. The impedance diiference is sulficient to change over a relay of a relay tube at the earthed centre of the secondary winding of the high-voltage transformer.

Ii the transformer ratio of the high-voltage transformer is chosen to be approximately to 290, the resistance variationof the X-ray tube reduces the impedance at the primary side from about 10 ohms to about 200 ohms. This impedance variation is suflicient to provide for the desired protection at the primary side by means of an alternating current relay. The low voltage circuit may include the exciter winding of such a relay and this winding may, by the action of the supply current, close a relay contact closing an interruption in a circuit including the exciter winding of an electromagnetic switch for connecting the high voltage-transformer to the nor mal supply voltage.

In order that the invention may be readily carried into efiect it will now be described in detail with reference to the accompanying drawing i1lustrating two examples of circuit-arrangements for apparatus according to the invention, and in which a Fig. 1 shows the use of protective means at the primary side of the transformer.

Fig. 2 shows them at the secondary side.

An autotransformer 3 is connected by wayof main switch 2 to terminals I of the A. C. mains.

This transformer supplies the normal voltage through a regulating contact for the high-voltage transformer 4 and is connected through supply conductors t, l to the primary winding 5. Supply conductor 6 includes a switch arm 8 and supply conductor I may also comprise such an arm 9.

These switch arms form part of an electromag-.

netic switch it and are open if the apparatus is inoperative. A. secondary winding II is connected to an X-ray tube I5 comprising an anode l4 and an incandescent cathode i3, according to Fig. l with the interposition of rectifiers l2.

The cathode it of X-ray tube I5 is supplied from a heating transformer I6, whose primary comprises the regulating resistor I 1 for adjusting the heating current.

that the current strength pro- In Fig. 1 an electric circuit connected to the mains-voltage includes a switch I8 adapted to occupy three positions 0, I, 11. In position 0 there is no flow of current. In position I, current is supplied to an exciter winding IQ of the relay so that the movable contact 20 completes the circuit connecting the auxiliary winding 2| of autotransformer 3 to the primary 5 or the high-volt age transformer 4. The voltage supplied by this. winding has a value lower than that supplied by autotransformer 3. After switch 2 has been closed and no deviation occurs in the heating current, the X-ray tube passes current by which the low voltage winding 2| is loaded. The loading current passes through an exciter winding 22 of an electromagnetic relay and closes contact 23 of a circuit including a time switch 24 and the- In position II of switch winding of switch H). 18 this circuit is closed. Besides switch arms 8 and 9 the winding l0 operates a switch arm 2'! interrupting the low-voltage circuit and a switch arm 26 shunting the contact 23. The trans former 4 is connected to the normal supply voltage by connecting the arms 8 and 9 into circuit. The duration of the load is adjusted by means of the time switch 24, the latter subsequently interrupting the current so that switch I0 is released.

If, however, the incandescent cathode I3 of X-ray tube l5 does not emit, for example, due to a short-circuit or a defective cathode, the impedance transformed on to the primary circuit is such that no sufiiciently strong current passes in the low-voltage circuit to excite relay wind ing 22. Contact 23 remains open and switch H3 remains inoperative.

This also holds in Fig. 2, wherein the exciter Winding 22 for contact 23 is included in the anode circuit of a relay tube 33 comprising a source of anodevoltage 35 Relay tube33 comprises an earthed cathode 34 at the grid 32; which is connected to a point of resistor 30. This point may be displaceable to permit adjustment of the instant at which the anode current is suificiently strong to energise winding 22 in accordance with the emission of the cathode l3 of the X-ray tube.

The resistance 30 is connected throughrectifier 29 to the ends of resistor 28 at the centre of the secondary l I of the high-voltage transformer.

In parallel with this resistor is connected another rectifier 3| so that a rectified current passes through resistor 30. The center of resistor 2 8v is connected to earth.

The operation of the device corresponds to that shown in Fig. 1.

What we claim is; r

1. An X-ray diagnostic apparatus comprising an X-ray tube includin an anode and meandescent cathode, a high-voltage transformer coupled to said tube and including a primary winding, first means for applying, a heating current to said cathode, second means for applyingv a given operating potential to the primary winding of said transformer, third means for applying a potential which is lower than said given poten-- tial' to the primary winding of said transformer, first current-responsive means coupled to saidv tube and responsive to the current flow therethrough when said lower potential is applied to said primary winding, second current-responsive means responsive to actuation of said first ourrent-responsive means when emission from said cathode reaches a given value for connecting said second means, to said primary winding, and timing means operatively associated with said second current-responsive means for determining the duration of the application of said given operating potential to said primary winding.

2;. 'An X ray diagnostic apparatus comprising an X-ray tube including an anode and incandescent cathode, a. high-voltage transformer coupled to said tube and including a primary winding, first means for applying a heating current to said cathode, second means for applying a given operating potential to the primary winding of said transformer, third means for applying a potential which is lower than said given potential and at which the X-ray tube will operate in the space charge region to the primary winding of said transformer, first current-responsive means coupled to said tube and responsive to the current flowtherethrough when. said lower potential is applied to said primary winding, second current-responsive means responsive to actuation of said first current-responsive. means when emission from said cathode reaches a given value for connecting said second means to said primary winding, and timing means operatively associated with said second currentresponsive means for determining the duration of the application of said given operating potential to said primary winding;

3. An X-ray diagnostic apparatus comprising an X-ray tube including an anode and incane descent cathode, a high-voltage transformer" coupled to said tube and including a primary winding and a center-tapped secondary winding, first means for applying a heating current to said cathode, second means for applying a given operating potential to the primary winding of said transformer, third means for applying a potential which is lower than said given'potenti'al and at which the X-ray tubewill operate in the space charge region to the primary windin iof said transformer, first current responsive means coupled to said tube and the center tap of said secondary windingand responsive to the current flow through said tube when said'lower'potential" is applied to said primarywinding, second current-responsive means" responsive to actuation" of said first current-responsive means when emission from said cathode reaches a given valuefor connecting said second'means to said primary winding, and timing means'operatively; as-'-- sociated with said second current-responsive means for determining the duration of the ap;-- plication of said given operating potential to said primary winding.

4. An- X ray diagnostic apparatus as claimed in claim 3' in which said first current-responsivemeans is an electric discharge tube.

ALFRED KUNTKEZ HEINZ' MESTER.

References Cited in the file of thispatent? UNITED STATESPATENTS Number Name- Date;-

2,100,735 Dawson.v ;.Nov-. 30, 1937- 2,2-15,'744 Silbermanns .Sept..24,-.l940, 2,244,137 Bischofi, et a1. June,-3, 194-1,

' 2,512,193 Zavales June 20, 195.0-