US2838681A - X-ray method and apparatus - Google Patents

Description

ite tates Patent() X-RAY METHOD AND APPARATUS Edward B. Graves, South Euclid, and Jack Ball, Chesterland, Ohio, assignors to Picker X-Ray Corporation, Waitlell Mfg. Div. Inc., Cleveland, hio, :i corporation of 'o Application June 1, 1953, Serial No. 358,366

7 l Claims. (Cl. Z50-94) This invention relates to a method and apparatus for controlling X-ray tubes and more particularly to the independent stabilization of a plurality of X-ray tubes operating from a common source.

X-ray tubes are preferably operated at a predetermined constant load current selected by the operator. Stable operation of a single X-ray tube at such constant load current has heretofore been accomplished by controlling the filament current of the tube to compensate for changes in tube operation. One type of tube filament control is described in Patent No. 2,627,035, granted January 27, 1953 to I ack Ball in the form of an electronic stabilizer or other mechanism wherein the load current passing through the mid-secondary point of the high voltage transformer modulates the stabilizer to vary the filament current of the tube and thereby control the operation of the tube. Certain applications of X-ray equip ment contemplate operating more than one X-ray tube from a common source. Since the characteristics of X- ray tubes vary considerably and since the tubes are extremely sensitive to variation of filament current, it is not feasible to control the tube filaments :through a common stabilizer or from a common connection in the tube energizing circuit.

Accordingly, it is an object of this invention to provide for independent stabilization of the operation of a plurality of X-ray tubes operating from a common source.

Itl is a further object of this invention to independently control the filament current in each of a plurality of X- ray tubes operating from a common source in accordance with the operating condition of the corresponding tube.

Briefly, in accordance with this invention, independent stabilizers are connected in the filament circuits of each of a plurality of X-ray tubes which are operated from a common high potential source of electrical energy. Independent modulation of each of the stabilizers in accordance with the operating condition of the corresponding tube is accomplished by modulating each of the stan bilizers with a signal corresponding to a change in the operating condition of the corresponding tube. The signal is obtained by inserting a primary coil in series with the anode of each tube and reiiecting the corresponding signal through a coupled secondary coil to the modulating input of the corresponding stabilizer. The signal may be reflected through a step-up ratio of the coils which is determined by the characteristics of the particular stabilizing method employed. Each of the signals is respectively proportional to the load current of the corresponding tube and each independently modulates the corresponding stabilizer to control the respective filaments for stabilization of tube operation.

In the drawings, Fig. l is a diagram schematically showing the energizing and modulating connections between each of the tubes and their corresponding stabilizers.

Referring now to Fig. l of the drawings, there is shown two stabilizers A and B connected respectively in the filament circuits to X-ray tubes 10 and 11. The stabilizersV are diagrammatically shown in block form and preferably are of the'type described in Patent 2,627,035 issued to I ack Ball wherein an electronic comparison circuit compares the load current of an X-ray tube with a predetermined Xed and constant value of desired load current and passes the difference, if any, through an ampliiier to the control grid of a space charge device to provide an output control voltage of proper sign to be added or substracted from the excitation of the X-ray tube lament, and thereby vary the filament current to compensate for any change in the operating condition of the tube to maintain the desired load current. Each of the X-ray tubes 10 and i1 are operated from a common high potential source which originates at the supply lines L1 and L2 from approximately 220 volts A. C. and is fed through a selector switch S1 to an auto-transformer i2 where further operating voltage selection may be applied to the primary winding 13 of a high tension transformer through a major and minor selector switch S3 and S4 and the X-ray exposure Contact button Siti. The secondary 15 of the high tension transformer is centrally grounded and is connected across a rectifying bridge i6, to applya high operating potential across each of the X-ray tubes.

The filament circuits of the X-ray tubes 1t) and 11 are also supplied from the common source by lines L3 and L4 through suitable lament transformers 17 and l respectively. The iilament circuit includes a limiting resistor 20 which is pre-set by the operator to select the proper charge on the tube iilarnents in accordance with the desired operating conditions.

The modulating signal ifor each or" the stabilizers A and B is independently obtained from each of the corresponding tubes by connecting primary coiis 21 and 22.2 in series with the anodes of the respective tubes, whereby each primary carries a current proportional to the load current infthe corresponding tube. Separate ondary pick-up coils 23 and24 are coupled to the respective primaries to reiiect any change in the load current of a corresponding tube in the form of an induced signal through the connecting leads to the inputs 25 and 26 of the corresponding stabilizer, where the signal is in turn rectified and compared with the predetermined desired constant value of load current. This provides a control potential for varying the filament current in a direction to compensate for the change in load current, and thereby stabilizes the operation of the corresponding tube independent of the other tube.

The primary 21 and 22 and secondary 23 and 24 coils, which reect any change in the operating condition of the tube to modulate the corresponding stabilizer, should preferably have a step-up ratio in order to compensate for the loss of partV of the signal in the lead circuits. We have found that a step-up ratio of one to four has been adequate to modulate the stabilizer of the type shown and described in Patent 2,627,035 heretofore noted. However, the step-up ratio will largely be determined by the characteristics of the particular stabilizing method employed and canbe selected to provide optimum operation in any arrangement utilized. It is apparent that the signal reflected from the primary coil in series with the tube anode provides a step function input and we have found that an electronic stabilizer of the type contemplated herein has a stable response to this type of input which is satisfactory in normal usage.

Thus, we have provided a method and apparatus for independently controlling the iilament current in a plurality of X-ray tubes operating from a common source, in accordance with changes in the operating condition of each tube.

We have shown and described what we consider to be the preferred embodiments of our invention and it will be obvious to those skilled in the art that changes and modifications may be made without departing from the scope of our invention as defined by the appended claims.

We claim:

1. In combination with an X-ray generator having a plurality of X-ray tubes, each having an anode and a lament adapted to be energized from a common source of electrical energy, a plurality of independent means isolated from each other and respectively coacting in the corresponding anode circuit of each tube to 'each provide a signal proportional to the corresponding tube current7 and a plurality of other independent means each coacting in a separate tube tilament circuit in response to the signal corresponding to that tube respectively to stabilize the operation of each tube at a predetermined value,

2. In combination with an X-ray generator having a plurality of Xray tubes, each with an anode and a filament operating from a common source of electrical energy, independent means for controlling the filament excitation ot each tube respectively, and independent means respectively isolated from each other in the anode circuit of each tube for supplying independent signals proportional to the operating condition in each tube respectively to the corresponding filament excitation control means to independently stabilize the operation of each of the tubes at predetermined levels respectively.

3. ln an X-ray vgenerator having a plurality of X-ray tubes each having an anode and filament, the combination of means for connecting a common source of high potential electrical energy across each of the tubes, an independent stabilizing circuit for controlling the lament excitation to each tube respectively, means for independently coupling separate reference voltages each respectively corresponding to a predetermined constant condition of operation for each tube to the corresponding tube stabilizing circuits, and independent means isolated from each other in the anode circuit of each tube for in dependently couplingchanges in the individual tube currents respectively for comparison with the reference volty age in the corresponding stabilizing circuit to independently stabilize the operation of each tube.

4. In combination with a plurality of X-ray tubes each having an anode and a lament circuit adapted to operate from a common source of electrical energy, independent means in the anode circuit of each tube for respectively obtaining electrical signals proportional to the load current through the corresponding tubes, an independent stabilizing circuit for comparing the corresponding signal with a predetermined constant value of tube current for each tube respectively, and means for independently ap plying the result of each such comparison to the filament circuit of the correspondingtube to vary the lament current in a direction to maintain the load current in cach tube at the corresponding predetermined constant value.

5. ln combination with a plurality of X-ray tubes each having an anode and a filament circuit adapted to be energized from a common source of electrical energy, a separate primary coil in series with the anode of each tube respectively, a separate secondary coil respectively coupled to each primary coil to reect an electrical signal proportional to a change in the load current through the corresponding tube, an independent stabilizing circuit respectively coupled to each secondary coil to compare the corresponding signal with a predetermined constant valve of tube current for each tube, and means for applying the result of each comparison to the corresponding filament circuit of each tube, whereby the respective lament currents are varied in directions to maintain the load current in each tube at the corresponding predetermined constant valve.

6. The combination of claim 5 wherein cach of the respectively coupled primary and secondary coils are arranged to provide a step-up current ratio.

7. The combination of claim 5 including a source of electrical energy and a parallel connection between the p source and each of the tubes.

References Cited in the le of this patent UNITED STATES PATENTS

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