US1453314A - Current regulator for x-ray systems - Google Patents

Description

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Patented May l, 1923.

UNITED STATES CHARLES FLYER, F NEW YORK, N. Y., ASSIG'NOR TG WAPPLER ELECTRIC CO., INC.,

.A CORPORATION OF NEW YORK.

CURRENT REGULATOR FR -RAY SYSTEMS.

,Appueation sied .April e,

To all 'whom it 'ma/y concern.:

Be it known that l, CHARLES Farra, a citizen of the United States, residing in the city of New York, borou h o-ii Bronx, in the county of Bronx and tats or? New York, have invented certain new and useful Improvements .in Current Regulators for X-Ray Systems, of which the following is a full, clear, and exact description.

M invention relates to current regulators for g-ray systems, and more particularly such systems in which the X-ray tube is or the so-called Coolidge type-that is, a tube in which ionization is promoted by means of a cathode heated to incandescence.

ln such a system it is customary to energine the X-ray tube by currents from a high tension transformer ot large capacity and known as the main transformer and to heat the cathode of the tube by currents from a low-tension transformer of smaller capacity-both transformers, however, being energized by currents drawn from a single source of supply, say a pair or alternating current mains.

When, therefore, the X-ray tube is thrown I into action there is likely to be a substantial drop in the voltage of these currents and consequently a drop in the temperature. of the heating filament, so that the current passing through the tube is in ractice much 1 tice be subjected.

In addition I grender the system adgust less than would be warrantei by the vcarrylng capacity of the tube. I seek to prevent this evil, by preventing the drop in the temperature of the filament. g

I find that under ordinary conditions of operation, the number of milliamperes passing throu h theX-ray tube is nearly constent if t e heat of the cathodev is maintained constant, and that as a consequence the number of milliamperes passing through the tube may be maintained approximately constant by controlling the current used for heating the cathode. I `also find that with my device the control of the Current for heating the cathode may be rendered automatic.y

By my invention, therefore, I seek to render practi ll constant the current discharge thro g the X-ray tube, independentl of any variations in voltage to which the high-tension transformer. may in prac- 3918. Serial No. 226,l69.

able, so that the operator may, at will, vary, within reasonable limits, the degree of control exerted by the line voltage upon the flow of current through the X-ray tube.

Reference is made to the accompanying drawing forming a part oc this specication, and in which like reference characters indicate like parts in all of the figures.

Figure l is a diagram of my system complete. f

Figure 2 is a diagrammatic perspective, showing one form of the` low-tension transformer and parts immediately associated therewith.

Figure 3 is a vdiagram of another or@ the low-tension transformer.

An X-ray tube is shown at el, and is ot the hind commonly lmown in this art as a Coolidge tube, being provided with a beatinefilament 5. The clarity of the tube is in( icated conventiona ly by plus and minus signs.

A transformer heating' filament.

rlhe ft-ray tube is ener 'ized by currents from a high-tension transrormer Y, that is, the main transformer, these currents being acted upon by a rectifying device 8, which is here indicated by the legend Rectiying device.

' The mains are shown atl), 10, and are energized by alternating current from a power-plant, not shown.

The transformer 6 has practically nc magnetic leakage, and is provided with a primary Winding 11. A wire 12 leads trom the main 10 to this winding. A wire 13 leads from the main 9 to a choke coil 14,

6 is used `for energizing the and from the latter a wire 15 leads to the primary winding 11.

The transformer 6 has a secondary winding 16, and from this' Winding a wire 17 leads t0 the heating filament 5, which is the cathode ol the X-ray tube. A wire 18 is connected to this lament and also to a wire 19, which leads to the secondary winding 16.

A wire 20 is connected to the wires 18 and 19, and to the rectifyin device 8. `A wire 21 leads from the recti ying device to the X-ray tube.

Two wires 22, 23 are connected to therectifying device and also to a vsecondary winding 24 with which the high-tension transformer 7 is provided.

The main transformer 7 has a primary aiov windin 25, and to it is connected a wire 26, lea ing to a switch 27. Two wires 28, 29 extend from the mains 10, 9 to the switch 27. A wire '30 extends from the switch 27 to a winding 31, carried by a core 32. This core is made of soft iron, preferably laminated, and is used in connection with the transformer 6, relatively to which it is adjustable. From the winding 31 a wire 33 leads to the primary'winding 25 of the high-tension transformer 7, and is thus in series with this last-mentioned primary winding.

The core 32 rests loosely upon the transformer 6, and is provide with an adjusting screw 34. The operator by merely turning this screw and thereby raising or lowering the adjacent end of the core 32 relativel to the transformer if) Within Ie sona le limits control the electromagnetic relations of the transformer 6 and the core 32.

I designate the iron core 32, with its winding 31, as a compensator. When the compensator is in action, some of the magnetic flux generated in the core 32 tends to find a path through the closed core of the transformer 6.

The number of turns in the windings 11 and 31 are so apportioned, and the polarity of the core 32 relatively to that of the transformer 6 is so arranged, that the magnetic flux set up in the transformer by action of the primary winding 11 has little or no effect upon the core 32, yet the magnetic flux set up in the core 32 by action of the winding 31 may have a considerable effect upon the iron frame of the transformer. That is to say, the number of turns in the primary winding 11 (which is in series with the choke coil 14) is such that the magnetic flux set up by this lwinding is.propor tionate to the current energizing this winding, and hence proportionate to the current in the mains 9, 10; but the number of turns inthe winding 31 is such that the magnetic flux set up by this last mentioned winding is always at a maximum, and thus practically constant, independently of variations in the current energizing the winding 11 or in the current in the mains 9, 10. In

vother words, the core 32 is maintained comparatively near its saturation point even when there is a considerable drop in the voltage of the line.-

The polarity of the core 32 is so relatively to that of the transformer the magnetic flux induced by the arranged 6, that rimary winding 11 and that induced by t e compensator winding 31` both tend to pass in a common direction through the secondary winding 16. Thus, while owing to the alternating character of all currents employed, the polarity of both the transformer and the compensator is alternating, and as a consequence the magnetic flux passing through the secondary winding 16 is likewise alternating, yet at any particular moment the magnetic flux passing throu h the winding 16 is due to the con]oint e ect of the respective windings 11 and 31, which act alike in phase.

lf, now, by turning of the screw 34, the position of the compensator be properly adjusted relatively to the transformer 6, the leakage of' magnetic flux from the core 32 through the closed core of the transformer 6 is just enough to superpose, on the flux in the transformer core, so much ener y as will tend to minimize the ultimate e ect of a drop in the voltage of the primary winding 11. Thus the fluxpassing from the core 32 and finding its way through the secondary winding 16 is substantially constant. The result is that the temperature of the cathode 5, and consequently the current passing through the X-ray tube, is also substantiallyA constant.

In some instances Iprefer to use, as the low tension transformer, the device 6 shown in Figure 3. Here I place a winding 31 upon the closed core of the transformer, and provide a sliding contact 35 for varyi the effective number of turns of this win ing. The wires 33 are for the pu ose -of energizing the winding 31", and use in the same manner as the wires 30, 33 above described.

T-he operator by actuating the sliding contact 35 can increase or diminish the number of effective turns of the winding 31, and by so doing can regulate the uantity of magnetic flux generated by t e winding 31. Thus the winding 31l and its sliding'contact 35 are an equivalent for the winding 31 and its adjustable core tute a compensator as the term is used in the foregoing description.

In order to keep the cathode current substantially constant, it is desirable that the flux developed by the winding 31 be very large with respect to that developed by the winding 11.

The switch 27 being closed, the high-tension transformer 7 and the low-tension transformer 6 are energized. Currents induced in the secondary winding 24 pa through the wires 22, 23 to the rectifying device 8, and thence the rectified currents pass through the wires 20, 21 to the X-ray tube 4 through which they pass in a unitary direction indicated by the signs plus and minus. The rectifying device 8 is not in all instances essential, as a Coolidge tube is itself a rectifier under most conditions normally obtaining in practice.

Currents induced in the secondary winding 16 pass through the wire 17, the cathode 5 and wires 18 and 19, thus heating the cathode 5.

32, and together consti- -its magnetic flux exerts a considerable infiuence upon the transformer 6 Whenever the tube is operated. i

The current supplied to the heating circuit by the low-tension transformer 6 is thus maintained substantially constant, and as a consequence the temperature of the cathode remains fixed, and the current through the X-ray tube is maintained substantially constant.

To obtain the best results the operator can make proper adjustment as above described, and this may be done with either of the two'forms of compensator 'shown respectively in Fi 'res 2 and 3. Y

I do not llmit myself to the precise mechanism shown, as variations therefrom can be made within the scope of my claim.

The combination of an ,X-ray tube provided with a cathode to be heated, a transformer connected with said cathode in order to heat said cathode by supplying currents thereto, avtransformer connected with said X-ray. tube for the purpose of exciting the latter, a circuit connected with said last mentioned transformer in order to energize said last mentioned transformer, and electromagnetic inechanism energized by said circuit, said electromagnetic mechanism being so positioned and arranged relatively to said irst mentioned transformer that the magnetic flux of said electromagnetic mechanism reaches directly said first mentioned transformer. and modifies the magnetic ux thereof.

CHARLES FAYER.

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