US2146889A - X-ray apparatus - Google Patents

Description

Feb. 14, 1939. H. FRANKEET AL 2,146,889

' X-RAY APPARATUS Filed Feb. 9, 1954 2 Sheets-Sheetl Feb. 14, 1939. H. FRANKE ET AL 2,146,889

X-RAY APPARATUS Filed Feb. 9, 1934 2 Sheets-Sheet 2 Patented Feb. 14, 1939 UNITED STATES alias Artur OFFICE X-RAY APPARATUS Application February 9, 1934, Serial No. 710,516

' In Germany February 22, 1933 8 Claims.

For interrupting the operating current of an X-ray tube when making photographs with short exposure time, a switch in the anode current circuit is not suitable, because an arc is formed when the contacts of such a switch are separated, due to which the current does not immediately drop to zero. Another drawback of such a switch is that it has a very large size due to the fact that the contacts must be insulated from each other for high tension, and the switch gap must be sufficiently long that the breakingarc extinguishes. Furthermore. such a switch must be operated by the intermediary of highly insulated means and the contact members must have a large radius of curvature.

Therefore in most X-ray apparatus the tube is placed into operation by the closure of a switch in the primary low-tension circuit of the high' tension transformer and the exposure is interrupted by opening this switch. For short exposures the influence of the transients caused by the switching on of the transformer is quite pronounced. The secondary-voltage does not immediately follow its regular curve, but only after a time interval of a few cycles and the amplitudes of the transients due to switching-on are not always of the same order. A stabilizing resistance, temporarily inserted in the circuit, is sometimes used to eliminate this difficulty, but for instantaneous radiographs the use of such a resistance brings about an undue lengthening of the exposure time.

Moreover the current in the primary circuit is in general comparatively large, especially when the loading time is short, and the switch must therefore be designed for such large currents and must be of robust construction. This impairs the speed of operation. It is evident that a small and light switching mechanism may operate faster than a big one. Particularly when a great number of exposures are to be made in rapid succession. for example when making radiographs of the stomach or cinematographic radiographs, a small, easily movable, and rapidly acting switch is needed.

The invention has for its object to provide for a switching arrangement permitting a quick and z pertialess switching-on and interruption of the operating current of an X-ray tube.

Another object of the present invention is the provision of a switching arrangement which permits a rapid succession of the exposures.

A further object of the present invention is the provision of a switching arrangement in which a low tension switch is included in the anode circuit of the tube.

Other objects will appear from the following description.

It is known that the current of an X-ray tube may be controlled by the potential of an auxiliary electrode. This auxiliary electrode may be arranged in the X-ray tube itself or in a valve connected in series with the X-ray emitting tube.

In order to suppress on one hand the current 10 through the tube and on the other hand to permit free passage for the electrons it is desirable that both a negative and a positive potential can be given to the auxiliary electrode with respect to the cathode. Commutators have been 15 used for this purpose. For example a method of controlling the anode current of an X-ray tube is known in which a rotary reversing switch serves to apply a periodically varying potential to the auxiliary electrode.

According to our present invention a considerably simpler installation is obtained by employing a resistance inserted between the cathode and the auxiliary electrode of a discharge gap through which the anode current of the X-ray tube has to pass, this resistance being connected in the circuit of the anode current.

Thereby a negative biasing voltage is applied to the auxiliary electrode. The use of a resistance connected in the same way is known for the purpose of keeping the current constant, or for preventing the current from exceeding a predetermined value or for regulating the dimensions of the focus. In the latter case it is necessary that the auxiliary electrode be disposed in the X-ray emitting tube itself.

When the resistance is sufliciently great, a small anode current produces a voltage drop in the resistance which is suflicient to limit the current to so small a value that no appreciable X- ray emission takes place. Accordingly to our invention the switch for timing the exposure is connected across this resistance.

The novel features of our invention will be best understood by reference to the accompanying drawings and the following explanation thereof.

Figures 1-5 are schematic diagrams showing some examples of switching arrangements according to our invention.

Figure 6 is a perspective view of a rotary 50 switch which may be used for establishing the necessary contact in an apparatus for making a great number of radiographs in rapid succession.

Figure 7 is a schematic diagram of a modification of the arrangements represented in Fig- 5::

ures 1-5 and differs mainly from the latter by the presence of a valve tube connected in series with the X-ray tube.

Fig. 8 is a circuit diagram of another embodiment of the invention, and

Fig. 9 is a schematic diagram of an apparatus especially adapted for making single exposures of exact duration.

Like numerals in the drawings indicate corresponding parts.

Referring to Fig. 1 an X-ray tube I, having an anode 2 and an incandescible cathode 3, is connected to a source of high. tension 4 by means of the conductors 5 and 6. The conductor 6. leading to the cathode 3 contains a resistance I. The cathode is connected to a source of energizing current 8 through conductors 9 and" Ill; The X-ray tube has, in addition to the anode 2' and the cathode 3, a control electrode II forexamplein the form of a grid situated in the path of the discharge and so designed that when asmall negative potential with respect to the cathode for instance 100 volts, is applied to it; the anode current intensity is insufficient for producing X- raysto any appreciable extent. A suitable resistance is for example 50,000 ohms; The current will then be of the order of a few milliamperes.

A switch I2 is connected in multiple with resistance 1. Closing this switch will cause the potential' difference between thecontrol electrode and the cathode to be reducedto-zero. The electrons emitted by cathode 3 will then be permitted to-pass over'tothe anode 2- ina greater quantity, so that the current may sufiice for making an X ray exposure. At the end of the exposure time,,switch l2is again opened'and the tube current is practically interrupted; When switch I2 is in its open position, the voltage difference between its contacts is very small in comparison with the working voltageof'the tube. Furthermore, this switch has to interrupt only a light current, as, it is included in the high' tension circuit of the tube and not in a low tension supply circuit. The switch IZ-may, therefore, be of a simple and easily movable type, permitting a very quick switching; The cathode 3 of the tube is grounded at l3 in Fig. 1, whereby the switch 12 is also grounded and may be operated by hand or by a grounded switching mechanismas usually employed in X-ray apparatus having their operating, switch in the low tension primary circuit of a supply transformer.

In order to ensure a sufficient currentintensity, in Fig. 2, a source of electromotive force. in the form of a biasing battery l4 has been. connected between the control electrode H and resistance 1, with its negative terminal connected to, the latter. It is unnecessary that. the battery llsupply cur.- rent hence its capacity may be small; dry batteries such as are used for anode currentsupply in radio receiving. sets" aresuitable for this" purpose. The positivebiasv may amount to a few hundred volts.

The current flowing through resistance 1 when switch I2'is open produces therein a potential drop that eliminates the positive bias of battery l 42 Consequently the current limits itself because higher current would produce a higher voltage drop andwouldcausethe potential of the control electrodeto-becomemore negative and the repulsive eifect on the electrons emitted by the cathode to be greater. When resistance 1 is short circuited by switch l2, the voltageof battery l4 alone acts on the control electrode, so that the latter no longer acts as an obstruction, but as a boosting element.

In Fig. 3, instead of a battery, a condenser l5 serves for applying a positive charge to the control electrode II. This condenser is charged up to a suitable voltage by a transformer winding I6 through a rectifying element IT. The latter may be an electric discharge tube, but other types of rectifying apparatus, such as contact rectifiers may be used as well. The E. M. F. in transformer winding I6 is induced by the winding l8 which isthe primary winding of a heating current transformer of which I9 is the secondary coil. The current to winding 18 is obtained from an -A. C..network not shown in the figure.

The condenser and rectifying element may be dispensed with and an alternating voltage may be applied to the control electrode, because during the half cycles in which the anode of the X-ray tube is negative, the tube becomes currentless automatically. In Fig. 4 an arrangement is shown wherein a transformer winding 20 is connected between the control electrode I l and resistance 1. The transformer'of which winding 20' forms part has four coils, namely, a primary 2 I, a secondary 22, and two'additional coils 20 and 23. The primary winding 2| is supplied with current from a network not shown in the figure. The secondary 22 is a high tension winding, and is connected by Wire 5 to the anode 2" of the X-ray tube I and by wire 6 throughresistance l to the cathode 3. Transformer winding 23 serves for energizing the cathode and is connected thereto through wires 9 and I: Winding 20 is so arranged that its end'connected' to the control electrode is positive simultaneouslywith the anode 2 of" the X-ray tube. If winding 2|] does not bias the control electrode in the proper direction, the connections should be interchanged. In this arrangement'the effect of the positive bias is smaller in the first and last part'of the active half" waves than when a constant positive potential is applied to the control electrode.

The arrangement shown in Fig. acts in almost the sameway as that of Fig. 4'. The control electrode H is connectedto one of a pluralityof taps 24 of 'the transformer winding 20' by wire 21. Thepositive bias is thus'derived from the high tension' transformer winding. The presence of more than one tap has the advantage that the positive-bias is regulable.

A signalling device 26 is included'in wire 21 for indicating thefiow of grid current over the control' electrode. This device is shown as a small glow discharge tube but a small incandescent lamp maybe 'used'instead thereof or a fuse may serve to prevent too great a grid current.

TheXray tube is fully loaded as long as switch I2 is closed. The arrangement described is very suitable for making cinematographic radiographs. Apparatus serving for this purpose comprises a mechanism for conveying the film, and the number of exposures during one minute depends on the-velocity with which the film travels. The film travel device may be made subservient to the movement of switch l2. Therefore this switch is preferably constructed as a switch drum as shown inllig. 6. This switch comprises a contact segment 28 mounted on the periphery of a drum 29 rotatable on a shaft 30 and driven by the travel device of a film apparatus not shown in the drawings. Two contact brushes 3| and 32, connected by wires 33 and 34 respectively to the ends of the resistance 1 (see other figures), are provided with contact points which slide over the switch valve.

drum 21 and which are electrically interconnected by the segment 28 during its passage past the contact points. With the drum 29 rotating with constant velocity, the time during which the contact brushes 3| and 32 are interconnected, which is the exposure time of the radiograph, would be invariable. In order to permit variations of this time, the drum 29 is provided with a plurality of additional contact segments such as 35 and 36, mutually differing in length. The contact fingers 3i and 32 are mounted upon an internally threaded member 31 which can be displaced in axial direction of the rotating drum by means of a screw spindle 38 and a small handwheel 39. By turning the handwheel 39 one may make the contact fingers 3| and 32 cooperate with any of the contact segments 28, 35 or 36 and thereby vary the exposure time.

In the arrangements shown in Figs. 1-5 the control electrode is in the X-ray tube itself.

Fig. '7 shows an arrangement in which a valve tube 46 is connected in series with the X-ray tube 5. The valve tube has an anode 4|, an incandescible cathode 42 and a control electrode 43. Anode 4| is connected through wire 44 with one of the terminals of the source of high tension 4, the other terminal being connected through wire 45 with cathode 3. Anode 2 of the X-ray tube is connected through wire 45 with one end of resistance l, the other end of this resistance being connected to cathode 42. Between that end of resistance 1 which is connected to wire 46 and control electrode 43 is connected a suitable source of positive grid bias 41, which may be either a battery as shown in Fig. 2 or some other voltage means. Cathode 42 is heated to incandescence by current supplied from a source 25.

The installation illustrated by Fig. '7 functions in a similar way as those of Figs. 1-5, except that the anode current of the X-ray tube passes two discharge gaps. When switch |2 is open a high voltage difference occurs between the anode 4| and cathode 42 of the valve tube 46. This high voltage may cause X-rays to be emitted from the The amount thereof is small since the current as above explained is limited by the grid potential, but nevertheless it may be advisable to employ screening means to make these rays harmless. Such screening means which are located so as to interrupt the X-rays leaving the valve, may be constituted by a sleeve of lead glass or other material impermeable to X-rays as is cutomary practice in X-ray plants.

When the circuit arrangement according to the invention is to be used for making one single radiograph or radiographs with any given intervals, it is desirable that the high tension and energizing current are switched off during these intervals, in order to spare the tubes and other electrostatically loaded parts. In Fig. 8 the source of high tension is shown as in Fig. 4 as a high tension step up transformer having a, primary low tension winding 2| and a secondary high tension winding 22. The source of energizing current for the cathode is shown as a transformer having a primary winding 48 and a secondary winding i5. One end of winding 2| and one end of winding 48 are connected through wires 49 and 56 respectively to a common main of an A. C. network, not shown in the figure. The other end of winding 2| and the other end of winding 48 are connected to the other main of the network through wires 5| and 52 comprising switches 53 and 54.

For placing the tube into operation, switch 54 is first closed to make the cathode attain its glow temperature. Then switch 53 is closed, high tension being thereby applied to the tube and finally when the moment has come at which the exposure should be made switch I2 is temporarily closed. After the exposure is made switches 53 and 54 are opened. This course of operation thus requires the operation of three switches, which is more or less complicated. In the arrangement according to Fig. 9 therefore these various switching manipulations are made subject to the movement of one single switching device. This device comprises a contact arm 55 connecting wire 56 leading from the network 51 to contact segments 58 and 59 and to one of the two contact segments 60 and 6|.

In its initial position the arm 55 is out of engagement with the contact segments and no current can flow to the X-ray system. When the contact arm 55 is moved in clockwise direction it first engages the segment 60, then turning further it engages also the segment 59 and finally the segment 53. Subsequently the arm 55 leaves segment 60 and still contacting with 58 and 59 it engages segment 6|. Before leaving this segment the contact with segment 58 and then that with segment 59 is broken after which the contact arm returns to its initial position.

The switch denoted in the previous figures by I2 is represented in the diagram of Fig. 9 by two 1 contact segments 62 and 63 connected through wires 64 and 65 tothe ends of resistance 1 and a contact arm 66. Thiscontact arm carries a ferromagnetic core 61 which is drawn into a magnetic coil 68 when this is energized. When coil 68 is deenergized, the contact arm and ferromagnetic core acting as a pendulum move in counterclockwise direction and contact is made by arm 66 between the segments 62 and 63 during the short time interval required for its passage along these segments. If now a second coil 69 is energized instead of coil 68,-core 6'! is drawn into coil 69 and the pendulum takes a second stationary positionv denoted by a dotted line.

The coils 68 and 69 are connected through wires "ill and H with that main of the network 5! to which are connected wires 49 and 50. The other ends of coils 68 and 69 are connected through wires 72 and E3 to segments 60 and 6| respectively. Just as in Fig. 7 the arrangement of Fig. 9 comprises a valve tube 40 in series with X-ray tube The cathode 42 of valve tube 40 is supplied with heating current by a transformer having a secondary winding 14 and a primary winding 15, the latter being connected in parallel with transformer winding 48,

It will be clear that the contact arm 55 when making one revolution, first switches on the current through coil 68, this current flowing from one side of network 51 through wire 10, coil 68, wire 12, to segment 62 over contact arm 55 and back through wire 56 to the other side of the network. Coil 68 serves to pull the contact arm 66 into the left hand end position, whilst contact arm 55 first switches on the heating current of both X-ray tube and valve tube 40 by closing the supply circuit of transformer coils 48 and 15 and thereafter switches on the anode voltage of both tubes and 43 by closing the circuit of transformer winding 2|. When the contact arm leaves segment 68 and engages segment 6|, the current through coil 68 is interrupted and instead thereof a current flows from one side of network 5'! through wires 10 and 1|, coils 69, wire 13 to segment 6| and over contact arm 55 through wire 56jback to the other side of the network. Contact arm 66 moves from its left hand terminal position to its right hand terminal position and momentarily short-circuits resistance 1, so that the X-ray tube is fully loaded during a short period'. Contact arm 55 being moved further the high voltage and heating current are switched off. At last the current through coil 69 is interrupted when contact arm 55 leaves segment 6| and returns to its initial position. The pendulum 66 no longer being retained by coil 69 moves by gravity into the position whereby it interconnects contacts 82 and 63, but this has no effect since the circuits are deenergized.

- Within the scope of the present invention the switching devices 55 and 66 may be designed in any suitable form; Fig. 9 merely being an example to illustrate the operation of such devices. If it is also desired to change the exposure time in the apparatus shown in Fig. 9, the segments 62 and 63 may be made shiftable, i. e., movable to points nearer the coils 68 and 69 at which the velocity of the pendulum is less. On the other hand, the length of the pendulum arm may be changed so as to vary the velocity with which the contact arm 66 passes over the segments 62 and 63.

If the control electrode is in the X-ray tube itself, it may be constituted by the focussing device. The method of using the focussing device of an X-ray tube, which then must be insulated from the filament, as a control electrode is well known to those skilled in the art and further explanation as to the design of such tubes is believed to be unnecessary.

The switching device 55 is shown to act directly in the primary circuit of the high tension transformer. If need be a relay switch may be included, the exciting current of which is acted upon by switching device 55.

What we claim is:

1. A high tension electric discharge tube having an envelope, an anode, an incandescible cathode and a control electrode, a high tension transformer having a primary low tension winding and a secondary high tension winding, an anode circuit for said tube including said high tension winding, a current supply circuit for said primary winding and a heating current supply for said cathode, a resistance included in said anode circuit with one end connected to said cathode, an electric connection connecting said control electrode to a point on the anode circuit between the other end of said resistance and said anode, means for short circuiting said resistance dur-- ing a predetermined time interval, said means comprising a rotatable switch drum having a plurality of contact segments of different lengths, contact brushes cooperating with said segments andstationary with respect to the rotation of said switch drum, and means for selectively bringing either one of said segments into its cooperative position with said brushes.

2. In an X-ray installation for making a series of exposures at equal intervals, in combination, an electric discharge tube having an envelope, an anode, a cathode, and a control electrode, a hightension supply circuit for said tube, a heatingcurrent supply for said cathode, a resistance included in said circuit with one end connected to said cathode, a mechanically-operated switch to periodically short-circuit said resistance, and an electric connection between said control electrode and a point on said-high-tension circuit between said switch and said anode.

3. An X-ray installation comprising, a hightension discharge tube having an envelope, an anode, an incandescible cathode and a control electrode, a high-tension supply transformer having a primary low-tension winding and a secondary high-tension winding, a current supply for said primary winding, a heating current supply for said cathode, an anode circuit for said tube including said secondary winding, a resistance included in said anode circuit with one end connected to the cathode and being independent of the heating circuit of the cathode, an electric connection between the free end of said resistance and said control electrode and including a source of biasing voltage forming part of said transformer, the terminal of said source connected to said control electrode having the same polarity as the anode, and means for short-circuiting said resistance during a predetermined time interval.

4. An X-ray installation comprising a hightension discharge tube having an envelope, an anode, an incandescible cathode, and a control electrode, a high-tension supply transformer having a primary low-tension winding and a secondary high-tension winding, a current supply for said primary winding, a heating-current supply for said cathode, an anode circuit for said tube including said secondary winding, a resistance included in said anode circuit with one end connected to the cathode and being independent of the heating circuit of the cathode, an electric connection between said control electrode and a point on said secondary Winding having a potential intermediate the potentials of the ends thereof, and means for short-circuiting said resistance during a predetermined time interval.

5. In combination, an X-ray tube having an envelope, an anode, a cathode,and a control electrode, an impedance having one end connected to said cathode, means for producing a high-tension voltage between said anode and the free end of said impedance, means for positively biasing said control electrode with respect to said impedance when said anode is positive with respect to the cathode, means for supplying heating current to said cathode, and switching means for short circuiting said impedance.

6. An X-ray installation comprising an X-ray tube having an envelope, an anode, a cathode, and a control electrode, a resistance having one end connected to said cathode, switching means for short circuiting said resistance, means for supplying heating current to said cathode, means connected between the other end of said resistance and said anode for supplying high-tension anode current to said tube, means for establishing a potential difference between said control electrode and said other end of said resistance, said control electrode being positively biased with respect to said resistance when said anode is positive with respect to said cathode.

'7. In combination, a high-tension electric discharge tube having an envelope, an anode, an incandescible cathode, and a control electrode, a step-up transformer having a primary low-tension winding, and a secondary high-tension winding having a tap connected to said control electrode, means for energizing said cathode, an operating circuit for said tube including said secondary winding, an impedance in said operating circuit with one end connected to said cathode and its other end connected to said secondary winding, and a switch to bridge said impedance.

8. An X-ray apparatus for taking a series of exposures of predetermined duration, comprising an X-ray tube having an envelope, an anode, an incandescible cathode, and a control electrode, a high-tension transformer having a low-tension primary winding and a high-tension secondary winding, an anode circuit for said tube including said secondary winding, means for energizing said primary winding, means for heating said cathode, a resistance included in said anode circuit with one end connected to said cathode, an electric connection connecting said control electrode to a point on the anode circuit between said anode and the other end of said resistance, and switching means for short-circuiting said resistance during periodically-occurring time periods of predetermined length.

HEINRICH FRANKIE.

HEINZ VOIGT.

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