US2102146A - X-ray apparatus - Google Patents

Description

X-RAY APPARATUS Filed July 13, 1954 INVENTOR ATTO R N EY Patented Dec. 14, 1937 N ta STATES PATENT 6 Claims.

This invention relates to X-ray systems, and is concerned more particularly with a novel X-ray system including a condenser, the system of the invention being so constructed that the discharge of the condenser may be controlled. The new system affords special advantages when used for the operation of X-ray tubes in the making of radiographs with a bucky grid, and an adaptation of the invention for that use will accordingly be described for purposes of explanation, although it is to be understoodthat the utility of the invention is not restricted to that specific application.

In the making of bucky radiographs, it is highly important that the exposure be terminated before the bucky grid movement ceases, but the systems now in common use for making such radiographs cannot include condensers, because the current flow through the X-ray tube cannot be terminated in this manner but dies down gradually with the current curve displaying a slope to zero instead of an abrupt substantially vertical fall.

The present invention is accordingly directed to the provision of a novel system which includes apparatus by which the result specified can be obtained, and in the new system, the flow of current through the tube can be terminated substantially instantaneously. In one form of the new system which includes a pair of condensers, the current flow through the tube is cut ofi by the opening of a switch in the line supplying current to the high potential transiormer, and practically simultaneously with the opening of that switch the tube circuit is opened at both ends of the tube and the condensers are discharged. In this circuit, a substantially constant potential is employed in another form of the system, the discharge is at a rapidly falling potential, but in each case the potential curve is free of pulsations or large ripples and this makes it possible toobtain bucky radiographs free of grid marks.

For a better understanding of the invention, reference may be had to the accompanying drawing in which one form of the novel system suitable for the operation of an X-ray tube to be used in the making of radiographs is illustrated diagrammatically.

In the circuit shown, current is supplied through a line iii including a switch H, which may be manually operated, to the low potential side of a step-up transformer l2, the high tension coil of which is grounded at its mid-point. In the transformer leads l3 are the Usual valve tubes l4, the filaments of which are supplied'by filament transformers E5.

The leads l6 from the valve tubes are connected to switches generally designated I1 and these switches are preferably of the construction disclosed in my Patent No. 1,941,081, December 26, 1933, each switch including a pair of spheres I8, I51, respectively, with each transformer lead connected to one of the spheres !8. The sphere IQ of each switch contains a rod 20 of metal which is movable into and out of the sphere and is connected to a rod 2| of insulating material which extends out through an opening in the sphere and lies within guides in a tube 22, one end of which lies within a solenoid 23. An iron core 24 is carriedon the rod 2| within the tube 22, and the solenoids 23. of the two switches are connected in parallel to supply wires 25 which are connected tov supply wires It. So long as the solenoids are de-energized, the rods 20 extend out of their spheres and contact with the spheres it, thus connecting the spheres conductively, but upon energization of the-solenoids by the closing of the switch II, the rods. 2! are raised to draw the metal rods 2i! into the spheres I9, thus establishing an air gap betweenthe spheres l8 and 19 of each switch ll.

The sphere I9 of each switch is connected through a resistance 2% to ground, and the sphere i8 is connected by a line H through a resistance 28 to one plate of condenser 29, the other plate of which is connected by a line 36 to ground. Each line 21 is also connected to one sphere 3| of a switch 32 similar to switch II, the sphere 3| containing a metal rod 33 movable into and out of the sphere and mounted on a rod 34 of insulating material on which is mounted the iron core 35 acted on by solenoid 36. A line 38 leads from the sphere 31 of one switch 32 to the anode 39 of the X-ray tube 49, while the sphere 31 of the other switch 32 is connected by a line 38 to the filament 4! of the tube, the filament being supplied by a filament transformer 42.

With the arrangement described, it will be apparent that so long as switch I! is open, the rod 2i] of each switch I? will bridge the gap between the spheres l8 and IQ of the switch, and the switches will thus be closed. With the switches in this conditioruboth plates of both condensers 2d are grounded, one plate of each condenser being permanently grounded and the other plate being grounded through a switch ll. Similarly, with switch H open, the leads to the tube will both be disconnected since the rod 33 of each switch 32 lies in its down position and the spheres 3| and 31 of each switch are separated by an air gap.

When the switch II is closed, the solenoid 23 of switches l1 and the solenoids 36 of switches 32 are simultaneously energized. The conducting rods 20 of each switch I! are immediately moved upward out of contact with the sphere l 8, so that both switches I! are open. The conducting rods 33 of each switch 32 are also moved upward and contact with sphere 31, bridging the air gap, so that both switches 32 are closed. With the circuit in this condition and assuming that the left-hand end of transformer I2 is of positive polarity, current flows through valve tube l4 and sphere H! at the left, part of the current then flowing to condenser 29 at the .left to charge the condenser, and the remainder flowing through switch 32 to the X-ray tube "40. The ungrounded plate of condenser 29 at the right is then negatively charged, current flowing through the valve tube M at the right back to the transformer. When the polarity of the transformer is reversed, the charge on condenser 29 at the left flows through the X-ray tube and the connections illustrated to the ungrounded plate of condenser 29 at the right. This circuit consequently supplies current to the X-ray tube at substantially constant potential.

When the flow to the tube is to be cut off, the switch H is opened, whereupon the solenoids 23 and 36 of switches l1 and 32, respectively, become tie-energized, and the rods 20 and 33 move down by gravity. The downward movement of the rods 20 causes the gap between spheres l 8 and IQ of switches I! to be closed and the downward movement of rods 34 of switches 32 causes gaps to be established between spheres 3| and 31 of switches 32. The closing of switches l1 grounds the charged plate of each condenser 29and the closing of switches I! may be effected without disruptive discharges and with the formation of only minor arcs, which quickly disappear as the rods 2!] drop down .and contact with spheres l8.

With the circuit as described, it will be apparent that upon the closing of the supply switch II, the connection between one plate of each condenser and ground is broken almost instantaneously and at the same time and quite as rapidly a circuit through the tube is established. Upon the opening of the switch H, the current flow through the tube is cut oif abruptly by a reversal of the events mentioned and the highly charged parts of the apparatus are all discharged. A curve illustrating the flow of current through the apparatus discloses that the current builds up rapidly'to'the maximum value and upon the opening of the switch H falls almost vertically to zero. The apparatus, therefore, makes it possible to obtain bucky pictures of a quality superior to that of pictures produced by former apparatus in that the exposure may be made with a condenser discharge.

Another effective use of the system described involves the disconnection of transformer l2 before switches I! and 32 are operated. In that form of system, an additional switch similar to the switch H is placed in the supply line of the transformer beyond the points where the lines 25 are connected to the supply lines III. In this modified form of the system, the additional switch can be opened to disconnect transformer l2 so that the discharge isat a rapidly falling potential, switch ll being opened following the disconnection of transformer l2. With the system thus modified, the potential curve is free of pulsations or large ripples and this insures a bucky radiograph free of grid marks.

While I have disclosed a system embodying the principles of the invention and including a pair of condensers, a pair of switches controlling the connections between one plate of each condenser and ground. and a pair of switches controlling the connections between the tube and the source of energy, it is to be understood that the system may include only one condenser, and only one switch of each kind if desired.

What I claim:

1. In an X-ray circuit for making bucky radiographs, a transformer, an X-ray tube, a control switch for interrupting a source of current leading to the transformer, a pair of normally closed switches between the transformer and tube, a pair of normally open switches in said circuit, a pair of condensers, rectifying means between the transformer and condensers one plate of each condenser being connected to a contact of one of the closed switches and also to a contact of one of the open switches, the other plate or each of the condensers being grounded, the second contact of each of the closed switches being grounded and the second contact of each of the open switches being connected to the anode and cathode respectively of the X-ray tube.

2. In an X-ray circuit, a transformer, an X- ray tube adapted to be electrically connected thereto, a condenser having one of its plates grounded and its second plate connected to a point in the circuit between the tube and the transformer, a normally closed switch having one of its contacts grounded and its other contact connected to the second plate of the condenser, rectifying means between the transformer and condenser a normally open switch having one of its contacts connected to the second plate of the condenser and its other contact connected to the tube, and means for substantially simultaneously opening the normallyclosed switch and closing the normally-open switch whereby the condenser is charged and the tube is energized.

3. In an X-ray circuit, a source of high tension current, an X-ray tube, a condenser having a first plate in circuit to the tube and a second plate grounded, rectifying means between the source of current and condenser, a switching device for initiating a charge to and abruptly terminating a charge from the condenser, said device including a pair of switches, one of which is normally closed and has a contact connected to the first plate of the condenser and its other plate grounded and the second switch being normally open and having a contact connected to the first plate of the condenser and its second contact connected to .the tube, and means for substantially simultaneously opening one switch and closing the other.

4. In an X-ray system, a transformer, an X- ray tube adapted to be connected thereto, an open and a closed switch between the transformer and the tube, means for substantially simultaneously opening the closed switch and closing the open switch, a condenser having a grounded plate and having a second plate connected to the switches, rectifying means between the condenser and transformer, a connection between the normally open switch and the X-ray tube and a connection between the normally closed switch and ground whereby the second plate of thecondenser will be grounded while said normally closed switch remains closed and will be charged and the circuit to the tube will be closed when said closed switch is opened and the normally open switch is closed.

5. An X-ray system including a transformer, an X-ray tube having anode and cathode connections to the transformer, cathode energizing means an open and a closed switch in circuit between the anode and the transformer, a second open and closed switch in circuit between the cathode of the tube and the transformer, means for opening both closed switches and closing both open switches substantially simultaneously, a condenser having a grounded plate and having a second plate connected to one of the open and one of the closed switches, a second condenser similarly connected to ground and to the other open and closed switches, rectifying means between said condensers and the transformer and a connection between both of the normally closed switches and ground whereby the second plate of each condenser will be grounded while the normally closed switches remain closed and will be charged and circuit to the tube anode and cathode will be closed when the closed switches are opened and the normally open switches are closed.

6. An X-ray circuit comprising, a transformer, an X-ray tube, the transformer adapted to be electrically connected to the electrodes of the tube, a condenser having one plate grounded and a second plate in circuit to the tube, a switch for controlling the connections between the transformer and tube, said switch being located between the X-ray tube and the condenser and transformer, rectifying means located between the condenser and transformer, a second switch connected to the ground and to the second plate of the condenser, said controlling switch being open whenever the ground switch is closed and vice versa, and means for operating said switches.

HARRY D. GARRETSON.

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