US2013398A - Vacuum switch for x-ray tube circuits - Google Patents

Description

p -"3, 1935. N. c. BEESE 2,013,398

VACUUM SWITCH FOR X-RAY TUBE CIRCUITS Filed Jan. 2, 1932 lNVENTOR /V. C. 55555 ATTORNE Patented Sept. 3, 1935 UNITED STATES PATENT OFFICE Norman C. Beese, Verona, N. J., assignor to Westinghouse Lamp of Pennsylvania Company, a corporation Application January 2, 1932, Serial No. 584,327

4 Claims.

My invention relates to X-ray systems and particularly to such a system employed in the art for taking short exposure X-ray photographs.

In order to obtain the requisite energy to ener- 5 gize the X-ray tube for infinitely short periods of time transformers of sufficient capacity are impractical for accomplishing this result. Apparatus is therefore usually provided, such as a high capacity condenser, in which the desired amount of energy is stored, and at the proper time is allowed to suddenly discharge through the X-ray tube.

In the prior art systems of this general type are known but are inefiicient and inaccurate in operation. This is due primarily to the switching means employed for permitting discharge of the condenser device through the X-ray tube. For example, it has been suggested to employ a spark gap in the high tension circuit having a predetermined break-down characteristic adapted to enable the condenser to discharge through the X-ray tube when the capacity of the condenser equals the break-down characteristic of the spark gap. The resistance or breakdown characteristic of the spark gap varies with climatic conditions thus rendering this breakdown unstable for all conditions. Furthermore, as the energy being stored in the condenser approaches the break-down value the well known brush discharge of the spark gap occurs which results in a leakage of the energy through the X-ray tube and the emanation of weak X-rays.

Another system for causing discharge of the condenser is that of maintaining the thermionic cathode of the X-ray tube below saturation value or at a temperature below that required for thermionic emission. After the condenser is completely charged a resistance connected in series with the cathode is short circuited enabling the temperature to rise to the saturation value.

In this type of system there is an appreciable time lag between closure of the short circuiting switch and the attainment of maximum heating temperature by the cathode which renders the system inaccurate. In addition to the aforementioned objection an analogous phenomenon occurs to that of the brush discharge of the spark gap. When the cathode-heating temperature is gradually rising from below saturation to the saturation value energy will flow from the condenser to the X-ray tube increasing to maximum when the cathode reaches maximum temperature. There is accordingly a variation in the intensity of the X-rays emanating from the tube in the same manner as in systems utilizing spark gaps.

A further system has been suggested for causing sudden discharge of the condenser through the X-ray tube by employing a thermionic dis- 5 charge device in series with the X-ray tube and condenser. Electron flow between the thermionic cathode and the anode is alleged to be prevented by means of a magnetic field acting on the electron stream. Due to the high potential heavy current energy, however, impressed upon the anode and cathode the magnetic field cannot be made of sufiicient strength to positively prevent all of the electrons from striking the anode with a resulting flow of energy through the X-ray tube.

This again results in weak X-rays striking the film with deleterious efiects before the passage of the full energy through the X-ray tube. Another objection to this latter system which renders the same inoperative is the necessity for insulating the magnetic field from the high potential circuit. In order to attain the requisite spacing to prevent spark over between the high and low tension circuits the effects of the magnetic field upon the electron flow is further weakened.

It is accordingly an object of my invention to provide a novel switching means in the high tension circuit operable with minimum lapse of 30 time to cause instantaneous discharge of the condenser through the X-ray tube.

Another object of my invention is the provision of a vacuum switch in the high tension circuit operably responsive to actuation from a low voltage source and in which possibility of spark over between the high and low tension source is prohibited.

A further object of my invention is the provision of a short exposure X-ray system in which instantaneous energization of the X-ray tube follows operation of the switching device with a maximum flow of energy therethrough and uni form emanation in X-ray intensity.

Still further objects of my invention will become apparent to those skilled in the art by reference to the accompanying drawing in which:

Figure l is a cross-sectional view of the vacuum switch utilized with my system;

Figure 2 is a diagrammatical representation of 50 the preferred embodiment of my system for taking short exposure X-ray photographs, and.

Figure 3 is a diagrammatical representation of a modified form which my system may take.

Referring now to the drawing in detail I have 55 shown in Figure 1 a novel vacuum switch of the type disclosed and claimed in the copending application of Clayton T. Ulrey, filed March 29, 1932, Serial No. 601,865. Although this switch per se is therein fully shown and described it briefly comprises an evacuated envelope 5 of a dielectric such as glass, provided with a reentrant stem 6. A metallic cap 1 is rigidly secured to one end of the evacuated envelope and a metallic conductor 8 extends through this cap into the evacuated envelope 5.

A small coil spring 9 is disposed interiorly of the evacuated envelope and connects the conductor 8 to a movable electrode [9 also within the envelope. This spring 9 serves the dual purpose of a conductor and a shock absorber for the movable electrode, as more fully hereinafter explained.

A movable electrode l0 comprises substantially a metallic cylinder arranged to telescopically engage the inverted reentrant stem portion 6. This electrode is provided with a rounded end I2 which upon movement of the electrode establishes contact with a concave surface l3 of a second stationary electrode [4. The opposite end of the movable electrode 10 is provided with a soft iron portion l5 to which the coil spring 9 is rigidly secured. A magnetic winding 16 is disposed exteriorly of the evacuated envelope 5 adjacent soft iron portion l5 of the movable electrode W. The magnetic winding 16 and soft iron core portion l5 together form substantially a solenoid which upon energization of the winding causes movement of the movable electrode as hereinafter more fully set forth.

Referring now more particularly to Figure 2 I have shown a suitable source of commercial alternating potential, such as the conductors LI and L2. An auto-transformer 22 has its adjustable arm 23 connected to the source of supply Li and a conductor 24 extends from the winding of this auto-transformer to the primary winding 25 of a high tension transformer 26. A conductor 21 then extends from the opposite end of the primary winding 25 to a contact terminal 28 of a suitable switching device 29. This switching device 29 is provided with a movable contact arm 30 to which the remaining supply conductor L2 is secured.

The magnetic winding l6 of the vacuum device 5 has one of its ends connected by means of a conductor 32 to the supply conductor Ll while the remaining end of this winding is connected by means of a conductor 33 to a second elongated contact terminal 34 of the switching device 29. A coil spring 35 is rigidly secured to the movable arm 30 of the switch and to a suitable bracket portion 36 for the purpose of main taining the switching device normally in the open position.

The secondary winding 42 of the high tension transformer 26 has one of its ends connected to the cathode 43 of a suitable rectifying valve 44. The anode 45 of this rectifying valve is connected by means of a conductor 46 to the cathode end of an X-ray tube 41. The opposite end of the secondary winding 42 is connected to the movable electrode [0 of the vacuum switch 5 by means of a conductor 48 which is suitably grounded at 49, and a conductor 50 connects the stationary electrode of the vacuum switch 5 to the anode of the X-ray tube M. The movable electrode which is connected toone side of the high tension secondary winding 42 and grounded at 49 is thus at zero or ground potential relative to the opposite side of the secondary winding and the stationary electrode.

A high capacity condenser 52 has one of its plates connected to the conductor 45 and the opposite plate connected to the conductor 48 thus shunting the high capacity condenser across the secondary winding 42 when the vacuum switch is in the open position as shown in the figure.

A pair of low tension heating transformers or batteries 53 are provided for heating the thermionic cathodes of the rectifying tube 44 and X-ray tube 41. If it is desired to employ transformers instead of batteries the primary windings of these transformers may be connected to the source of supply LI and L2, but are not thus shown in the figure for the sake of simplicity.

The operation of my system as just described may be best understood from a given problem. Assuming, therefore, that it is desired to take a short exposure X-ray photograph the movable arm 38 of the switching device 29 is moved to the left as shown in the figure, against the tension of the spring 35. This movement causes the arm 30 to first establish contact with the elongated terminal 34. This completes a circuit to the ma netic winding [6 of the vacuum switch 5 through a circuit which may be traced as follows:

From the source of supply Ll by means of conductor 32 to the winding l5, thence by means of conductor 33 to the elongated terminal 34, through the movable arm 30 back to the source of supply L2. Energization of the winding It will, therefore, cause upward movement of the movable electrode in, with the movement thereof being cushioned by means of spring 9, as shown in the figure. Movement of the electrode in in response to energization of the winding I6 is very rapid as no potential is, at this time, impressed upon the electrodes l0 and M of the vacuum switch. There is, therefore, an entire absence of all electrical stresses which might tend to retard the rapidity of movement of the electrode.

Further movement of the switch arm 30 then establishes contact with the terminal 28. This accordingly establishes a circuit to the primary winding 25 of the high tension transformer 26 which may be traced as follows: From the source of supply LE, to the movable arm 23 of the autotransformer 22, which is set to give the desired amount of energy required for the X-ray exposure. Thence from the winding of the autotransformer 22, by means of conductor 24, to the primary winding 25, through conductor 21, to the switch terminal 28, thence through switch arm 35 back to the source of supply L2. The primary winding 25 will, therefore, be energized by closure of the switch 29 which is maintained in the closed position for a predetermined period of time in order to permit energy to be stored in the condenser device 52.

The condenser 52 receives energy from the secondary winding 42 during each half wave of the alternating current cycle by a circuit which may be traced as follows: From one end of the winding 42 to the cathode 43 of the rectifying device 44 to the anode 45 thereof, and thence by means of conductor 46, to one plate of the condenser 52, and thence by means of conductor 48 back to the secondary winding 42. Although it must be appreciated that energy, strictly speaking, does not flow through the condenser device the same will be stored with energy from the secondary Winding by means of the circuit as just traced.

After the switch device 29 has been maintained in its closed position for the desire period of time the same is released which causes movement of the switch arm 30 to the right as shown in the figure by means of the potential energy stored in the spring 35. During movement of this switch arm contact will first be broken with the contact terminal 28, thus de-energizing the primary winding 25 of the high tension transformer 26 before breaking contact with the elongated terminal 34 to cause de-energization of the magnetic winding I6.

Upon the complete opening of the switch device 29, with the de-energization of both the primary winding 26 and the magnetic winding I6, the movable electrode I rapidly drops due to its weight, which is increased by the iron core portion I5, to establish contact with the concave portion of the stationary electrode I4. The rapidity with which closure of the switch follows deenergization of the magnetic winding I6 is further augmented because a high potential has now been stored in the condenser and is being impressed upon the electrodes of the switch. This creates an electrical field which also tends to cause closure of the electrodes and thus increases the rapidity of operation.

Contact therefore of these two electrodes completes a circuit from the condenser device to the X-ray tube through a circuit as follows: From the condenser 52, by means of conductor 46, through the X-ray tube 41, then by means of conductor 50, electrode I4, movable electrode III, and thence back to the condenser device 52, by means of conductor 48.

The energy previously stored in the condenser device 52 will thus instantaneously discharge through the X-ray tube upon the establishment of a contact between the electrodes of the vacuum switch 5. This results in a complete discharge of the condenser with an infinitely small time lapse after the opening of the switch device 29 and a substantially uniform intensity of the X- rays emanating from the X-ray tube.

In Figure 3 I have shown a system similar in most respects to that just described relative to Figure 2, but which differs slightly in operation. The switching device 29 in this modification is adapted to assume two positions, namely one to the right which establishes contact with the contact terminal 28, thus energizing the primary winding 25 of the high tension transformer 26. The switch is then maintained in this closed position for a predetermined period of time in order to permit the condenser device 52 to be charged with the desired amount of energy in the same manner as previously described relative to Figure 2.

After the condenser is completely charge the switching device 29 is then moved to the left establishing contact with the contact terminal 34, thus completing a circuit to the winding I6 of the vacuum switch .5 and causing upward movement of the movable electrode III to establish contact with the stationary electrode I4 thereof. It can thus be readily seen that in the latter modiflcation the vacuum switch 5 is substantially in an inverted position relative to that in Figure 2.

In Figure 2, therefore, the normal position of the electrodes of the vacuum device 5 is a closed one, i. e. the electrodes are in contact, and initial movement of the switch arm 30 first causes energization of the winding I6 with corresponding movement of the movable electrode Ill out of contact with the stationary electrode I4, while the condenser is being charged by further movement of the switch arm 30 into contact with the terminal 26, and upon opening of the switch the movable electrode I0 due to its gravity, which is augmented by the electrical field, reestablishes contact with the stationary electrode I4 with great rapidity to cause discharge of the condenser 52.

In Figure 3, on the other hand, the normal position of the electrode I0 is one in which the electrode is out of contact with the stationary electrode l4 and the switch arm 30 is adapted to as sume two positions, the first of which enables the condenser to be charged with the desired amount of energy after which the switch arm 30 is moved to its other position energizing the magnetic winding I6 and causing movement ofthe movable elec trode into contact with the stationary electrode.

In one instance, therefore, de-energization of the magnetic winding, as shown in Figure 2, causes closure of the vacuum switch while in Figure 3 energization thereof causes closure of the vacuum switch.

In the preferred form of my invention, namely Figure 2, I find that the operation of the switch in response to de-energization of the winding I6 is exceptionally rapid due to the gravitation of the movable electrode III which is aided by the weight of the iron core portion I5 and the aforementioned electrical field.

0n the other hand in Figure 3 where energization of the winding I6 causes movement of the electrode to close the vacuum switch the operation thereof is not as rapid because of inherent losses occurring in the usual operation. of solenoids, which, however, is infinitely small.

Although the movement of the electrode Ii! in response to energization of the magnetic winding I6 is not quite as rapid perhaps as in the preferred embodiment previously described, due to the necessity for the magnetic field to lift the weight of the movable electrode, the electrical field assists the movement in the same manner as in Figure 2 as a potential is now impressed upon the electrodes of the switch.

The conductor 48 extending from the source of supply, namely the secondary winding 42 and condenser 52, which connects to the movable electrode I0 is grounded at 49. Furthermore, the magnetic winding I6 which in both modifications operates to cause movement of this electrode is disposed adjacent the latter in close proximity to the metallic conductor extending through the metallic can I and the evacuated envelope.

The spacing between this high tension conductor which is carrying the operating potentials of the X-ray tube and the magnetic winding I6 is considerably less than Would be ordinarily required to prevent spark over therebetween, with deleterious results, were it not for the fact that this electrode is at ground potential as the conductor 48 supplying the potential thereto is suitably grounded as aforementioned at 49. This feature, therefore, prohibits any high potential from being transmitted to the low tension source and switching device 29 thus rendering the entire apparatus entirely safe to both operator and patient.

It can thus be appreciated by those skilled in the art that I have provided an X-ray system for taking short exposure X-ray photographs in which the switching device for causing discharge of the high capacity condenser is connected in series with the high tension circuit and that the same is operable with a minimum lapse of time and instantaneous discharge of the high tension energy through the X-ray tube occurs immediately upon closure of the switch. Furthermore as the switching device operates in a vacuum there is an entire absence of leakage between the electrodes, such for example, as brush discharge in the spark gaps and leakage caused by slight electron flow in thermionic discharge devices, and no energy therefor flows in the high tension circuit until the complete closure of the electrodes of the vacuum switch. The prohibition of the entire flow of energy, until the establishment of the contact between the electrodes, enables the energy stored in the condenser device to suddenly discharge through the X-ray tube. This results in substanstantially a uniform intensity of the X-rays emanating from the X-ray tube which heretofore has been impossible with short exposure X-ray systems of the prior art.

Although I have shown and described several specific embodiments of my invention I do not desire to be limited thereto as various other modifications oi the same may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. In an X-ray system for taking short exposure X-ray photographs, an X-ray tube, a source of high potential electrical energy including an energy storage device for energizing said X-ray tube, a vacuum device provided with a stationary electrode and a movable electrode, and connected to said high potential source and said X-ray tube to control energization of the same by said source, said movable electrode constituting substantially an iron core, a magnetic winding surrounding said vacuum device adjacent said movable electrode and operable upon energization thereof to cause movement of said movable electrode, a source of electrical energy for energizing said magnetic winding, and means operable to cause a portion of said high potential source to accumulate a charge in said energy storage device and said last mentioned source to energize said magnetic winding in order to cause movement of said movable electrode.

2. In an X-ray system for taking short exposure X-ray photographs, a circuit including therein an X-ray tube, a high capacity condenser for energizing said X-ray tube, and a vacuum device, said vacuum device having a stationary electrode, a movable electrode, and a magnetic winding adjacent said movable electrode for controlling the movement of the same, a source of electrical energy for causing energy to be stored in said condenser, a low tension circuit including said magnetic winding and a low tension source for energizing said magnetic winding, and a switch in one position completing said last mentioned circuit and causing movement of said movable electrode out of contact with said stationary electrode, and said switch in another position causing said first mentioned source to store energy in said condenser, said movable electrode being adapted to contact said stationary electrode and cause said condenser to energize said X-ray tube upon opening of said switch.

3. The combination with an X-ray tube and a source of high potential electrical energy for energizing said X-ray tube including a condenser adapted to accumulate a charge, of a vacuum device for controlling the energization of said X-ray tube by said high potential source upon the discharge of said condenser, said vacuum device comprising a stationary electrode and a movable electrode connected to said source and to said X-ray tube, electrically responsive means adjacent said movable electrode and energizable from a source of electrical energy for causing said movable electrode to move out of contact with said stationary electrode, and means connected to said electrically responsive means together with the source of energy therefor and electrically associated with said high potential source, and operable to cause operation of said electrically responsive means with attendant movement of said movable electrode together with the accumulation of a charge in said condenser, said movable electrode being freely movable under the influence of gravity upon said last mentioned means being rendered inoperative to cause the engagement of said electrodes and discharge of said condenser with attendant energization of said X-ray tube, and said high potential energy in initially discharging assisting the rapidity of movement of said movable electrode.

4. The combination with an X-ray tube and a source of high potential electrical energy for energizing said X-ray tube including a condenser adapted to accumulate a charge, of a vacuum device for controlling the energization of said X-ray tube by said high potential source upon the discharge of said condenser, said vacuum device comprising a stationary electrode and a movable electrode connected to said source and to said X-ray tube, electrically responsive means adjacent said movable electrode and energizable from a source of electrical energy for causing said movable electrode to move out of contact with said stationary electrode, and means connected to said electrically responsive means together with the source of energy therefor and electrically associated with said high potential source, and operable to cause operation of said electrically responsive means with attendant movement of said movable electrode together with the accumulation of a charge in said condenser, said movable electrode being freely movable under the influence of gravity upon said last men tioned means being rendered inoperative to cause the engagement of said electrodes and discharge of said condenser with attendant energization of said X-ray tube, and said high potential source of energy being connected to the electrodes of said vacuum device and upon initial discharge of said condenser creating an electrical field adapted to increase the rapidity of movement of said movable electrode.

NORMAN C. BEESE.

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