US2691735A - X-ray tube - Google Patents

Description

Oct. 12, 1954 w. H. BOLDINGH 2,691,735

X-RAY TUBE Filed June 6, 1952 in 1 3 2' x9 5 L a I i i 1 BY E Patented Oct. 12, 1954 X-RAY TUBE Willem Hondius Boldingh, Eindhoven. Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application June 6, 1952, Serial No. 292,032

Claims priority, application Netherlands June 15, 1951 3 Claims. (01. 250-65) In medical examinations with X-rays, more particularly of the stomach and intestine canals, it is known to determine with the use of an X-ray screen the favourable area and the useful moment for taking an X-ray photograph. It is then possible to proceed in different ways. Use is preferably made of an X-ray tube comprising two filaments, one of which is switched-in during screening and other when photographic images are taken. The filaments are so proportioned that one of them produces a small focal spot on the anode which is used for screening and which provides an image of high definition on the X-ray screen, whereas the other cathode produces a larger focal spot, so that the tube is loaded more heavily in taking photographs.

After the investigation with the use of the X-ray screen has been terminated, the high tension is switched off and the heating current switched-over from the cathode for screening to the cathode for photographing. Subsequently, the screen is replaced by the X-ray film cassette. Upon again switching on the high tension for taking photographs, the filament intended therefor requires to be heated up to the required temperature. The time required for heating up said filament, that is the time in which the temperature increases to that at which the required electron emission takes place, causes the moment of photographing to be delayed,

The object of the present invention is to limit this delay as much as possible. The invention relates to circuits for incandescent-cathode X-ray tubes comprising two filaments connected to a source of supply, for example the secondary winding of a heating-current transformer, and furthermore to X-ray devices comprising such circuits.

According to a feature of the circuit according to the invention, the two filaments are connected to the source of supply by means of a common current conductor, the second supply wire for one filament including a switching arm for closing and interrupting the circuit which, in the open position, short-circuits a resistance in-. cluded in the second supply wire for the other filament. By suitable proportioning of the said resistance it is ensured that, during the screening process, when the filaments are both connected to the source of supply, the incandescence temperature of the cathode for photographing acquires a value at which any appreciable electron emission just does not take place. The current flowing through the said cathode is then too small for producing active X-rays, but the time required to heat the filament to the emission temperature for obtaining sufiicient radiation is considerably reduced.

The invention will now be described in greater detail with reference to the circuit-arrangements shown by way of example in Fig. l and Fig. 2 of the accompanying drawings.

Fig. 1 shows an X-ray tube 1, of which the cathode 2 and the anode 3 are arranged with suitable spacing within a glass vessel 4. The cathode is constituted by a focussing device 5 having a cup-shaped cavity 6. This shape is advantageous for focussing the electrons emitted by the filaments 'l and 8, when travelling to the anode under the action of a voltage provided between the cathode and the anode, the electrons thus being concentrated on the anode to form a focus. The filaments arranged in the focussing device are of different lengths. The long filament 1 produces on the anode surface a band-shaped focal spot of a size larger than that of the focal spot produced by means of the short filament 8. The two impact areas for the electrons preferably coincide.

The filaments are heated by a heating-current transformer B, of which secondary winding It] is connected, at one end, by way of a supply wire I l to the two filaments l and '8. The other end of the secondary winding is connected to a movable arm 'l2 of a switch having two stationary contacts l3 and M, which are connected by way of supply wires l5 and I6 respectively to the free extremity of the short filament 8 and the free extremity of the long filament 9 respectively. The switch is shunted by a resistance it between the stationary contact i4 and the movable arm l2. During the screening operation, the arm I? of the switch engages the stationary contact 13, so that the short filament 8 is connected to the transformer winding l0. As soon as the primary winding I8 of the transformer 9 is con nected to the mains, said filament is heated up to the tempera-ture at which electron emission takes place. It takes some time before this temperature is attained, but this is not objectionable. However, this would be disadvantageous if, after screening, it would be necessary to wait for an equal time before a photograph can be taken. Upon switching-in the heating-current transformer 9, a current already flows from the secondary winding H] through the long filament '1', said current being limited to a determined value due to the presence of resistance I! in this circuit, the filament thus being heated but just not reaching the temperature at which electron emission takes place. By switching-over the movable arm 12 of the switch from the stationary contact l3 to the other stationary contact 14, resistance l! is short-circuited, the current flowing through the filament I increasing to a value at which the full amount of X-rays is produced. Upon switching-over, the current flowing through filament 8 is interrupted.

The time in which the cathode for photographing attains the emission temperature after the screening operation is terminated may be very short, for example 0.8 sec. A particular circumstance in this circuit is that the heating time of the cathode for photographing corresponds to the time which normally elapses between screening and photographing and in which the preparations for taking the photograph are made.

The anode current is supplied to the X-ray tube from a high-tension device i9 by way of supply wires 20.

In an X-ray device comprising the above-described circuit, use may be made of the particular circumstance mentioned above for rendering the device automatic.

According to a further feature of the invention, for this purpose use is made of an electromagnetic switch comprising a break-contact and a make-contact, which is operated by a hand switch and which is adapted to occupy two positions, in one of which the X-ray tube is switched-in for screening and in the other the photographing process is automatically initiated and carried out. In Fig. 2, the electro-magnetic switch and the hand switch are designated 21 and 22 respectively. The hand switch 22 is operated when from screening has to be changed-over to photographing. Of the two contacts 23 and 24 provided on the switch 2!, contact 23 is interrupted and contact 24 is closed when the hand switch 22 is closed as a result of the magnet coil 25 being energised due to current starting to fiow from a source of supply 26 through a conductor 21, through the coil 25 and by way of the hand switch 22 through a conductor 28 back to the source of supply. When the contact 23 between the points of contact 29 and 30 is opened, the energising current flowing through a relay coil 3| is interrupted thus causing a switch 32 to interrupt the supply of current to the primary winding 33 of a high-tension transformer 34. Then there is no longer any voltage set up between the anode 3 and the cathode of the X-r-ay tube I.

In this position of the electro-magnetic switch 2|, the circuits of two relay coils 35 and 36 are connected to the source of supply 26. The coil 35 operates an X-ray film cassette 37, shifting it to the position required for photographing. The coil 36 causes a movable arm 52 of a switch included in the common heating-current conductor, corresponding to the arm l2 of Fig. 1, to be switched-over from a stationary contact 53 to a stationary contact 54, a resistance 51 thus being short-circuited. This results in the filament 8 being switched off and the filament I having supplied to it the full current through the secondary winding of a heating-current transformer 9'. The use of a heating- current transformer 9 and 9 respectively for each of the two filaments 1 and 8 affords the advantage that the switching arm 52 is included in a circuit having a low potential with respect to earth. In this case it is not necessary to take special steps for insulating the relay coil 36 with respect to the switching arm.

When the cassette 3! has been moved into position, which is, for example, 0.8 sec. later than the moment at which the hand switch was operated, the contacts 38 and 39 engage one another, thus closing the circuit including the coil 3| and shunting the break-contact 23 of switch 2!. The circuit includes a time switch 40 which, after a preset duration, causes the energizing current for the coil 3i, which closed the switch 32 in the supply mains to the primary winding of the high-tension transformer due to closure of the contacts 38 and 39 to be interrupted and thus the photographing process to be terminated.

The primary windings of the heating- current transformer 9, 9" and of the high-tension transformer 32 are connected by way of a main switch 4i to the mains.

What I claim is:

1. The combination of an X-ray tube having an anode and a pair oi filaments and a circuit arrangement for energizing the same, comprising a source of heating current, means coupling one terminal of said current source to both of said filaments, a resistor connected between the other terminal of said source and one of said filaments, switching means connected between said other terminal of said source and the other filament and adapted to close the circuit to said other filament in one position and to open that circuit and short out the resistor in another position, a first relay having a normally-closed contact and a normally open contact, means for applying a high potential. between said anode and said filaments of said X-ray tube, a movable cassette adapted to receive a photographic film, a source of potential, a second relay having a winding in series with said normally-closed switch and said potential source and contacts adapted to energize and deenergize the high potential means, a third relay having a winding in series with said normally open contact and said potential source and adapted to actuate said switching means from said one position to said other position, a fourth relay having a winding in series with said normally-open contact and said potential source and coupled to said cassette such that upon energization the cassette is moved to a position to receive X-rays emanating from the anode, and manual means for energizing the first relay to thereby initiate an automatic process for taking a radiograph.

2. The combination of an X-ray tube having an anode and a pair of filaments and a circuit arrangement for energizing the same, comprising a source of heating current, means coupling one terminal of said current source to both of said filaments, a resistor connected between the other terminal of said source and one of said filaments, switching means connected between said other terminal of said source and the other filament and adapted to close the circuit to said other filament in one position and to open that circuit and short out the resistor in another position, a first relay having a normally-closed contact and a normally-open contact, means for applying a high potential between said anode and said filaments of said X-ray tube, a movable cassette adapted to receive a photographic film, a source of potential, a second relay having a winding in series with said normally-closed switch and said potential source and contacts adapted to energize and deenergize the high potential means, a third relay having a winding in series with said normally-open contact and said potential source and adapted to actuate said switching means from said one position to said other position,'a fourth relay having a winding in series with said normally-open contact and said potential source and coupled to said cassette such that upon energization the cassette is moved to a position to receive X-rays emanating from the anode, a contact device responsive to movement of said cassette and adapted to short out said normally-closed contact when said cassette is moved into the position toreceive X-rays and thereby connect the high potential means to said tube, timing means connected in series with said contact device for determining the duration of the application of said high potential to said tube, and manual means for energizing the first relay to thereby initiate an automatic process for taking a radiograph.

3. The combination of an X-ray tube having an anode and a pair of filaments and a circuit arrangement for energizing the same, comprising a source of heating current, means coupling one terminal of said current source to both of said filaments, a resistor connected between the other terminal of said source and one of said filaments, switching means connected between said other terminal of said source and the other filament and, adapted to close the circuit to said other filament in one position and to open that circuit and short out the resistor in another position, a first relay having a normally-closed contact and a normally-open contact, means for applying a high potential between said anode and said filaments of said X-ray tube, a movable cassette adapted to receive a photographic film, means responsive to energization of said relay to successively move said cassette to a position to receive X-rays emanating from the anode, actuate said switching means from said one position to said other position and apply the high potential between said anode and said filaments, and means for energizing said first relay to thereby initiate an automatic process for taking a radiograph.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,907,508 Coolidge May 9, 1933 2,132,537 McCurdy Oct. 11, 1938 2,146,900 Klinckmann Feb. 14, 1939 2,160,605 Suits May 30, 1939

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