US2835823A - Diagnostic x-ray apparatus - Google Patents

Description

May 20, 1958 J. FRANSEN DIAGNOSTIC X-RAY APPARATUS Filed March 15, 1954 EJ iim MA A l\ A F mvsmok JACOBUS r-wuxueuzu BY AGENT DIAGNOSTIC X-RAY APPARATUS .lacobus Fransen, Eiudhoven, Netherlands, assignor, by mesne assignments, to North American lfhilips Com pany, Inc, New York, N. Y., a corporation of Helm ware Application March 15, 1954, Serial No. 416,il56 Ciairns priority, application Netherlands March 21, 1953 2 Claims. (Cl. 250-95) The present invention relates to X-ray apparatus.

Diagnostic X-ray apparatus have been designed in a manner such that the X-ray tube is loaded automatically with a power varying with the choice of the exposure time. However, it is not always possible to obtain the best image quality with the aid of such apparatus. With the large variety of objects of which radiographs are taken a difficulty often arises. Due to the limitation of the number of adjusting positions which is inherent in prior forms of apparatus, it has not been possible to adjust the loading of the X-ray tube to any desired product of milliamperes and seconds. Particularly in the range of short operational periods, frequently only an approximation of the most favourable load for the image quality can be attained.

This disadvantage is least troublesome, if the X-ray tube is fed by direct current and if a time switch is used which operates very accurately. The measures required for this purpose render the apparatus complicated and costly and it is doubtful whether the advantage of better quality of the radiographs obtainable in certain cases pays for the additional effort and expense.

. In the much simpler X-ray apparatus, with alternatingcurrent supply and monoor biphase rectification of the tube voltage, the stated disadvantage is aggravated in that the ray output of the X-ray tube in the range of short operational times of one or a few periods of the alternating current is not proportional to the exposure time. Due to the sinusoidal nature of the alternating current, the exposure intensity during these short periods is closely dependent upon the instant when the load is switched on and off. Thus the advantage of an accurately operating time switch which permits the switching on and oil of the tube load at any desired instant, is lost for a great part. A further disadvantage of making radiographs with short exposure times by means of an apparatus having automatic adjustment of the tube load occurs with small objects which require a low tube load. In these cases it is often impossible to adjust the required low value of the product of milliamperes and seconds to obtain an image of good quality.

The invention has for its object to avoid these disadvantages and relates to a measure to increase the service ability of a diagnostic X-ray apparatus with alternatingcurrent supply, in which the X-ray tube is automatically loaded by a power varying with the choice of the exposure time for veiy short exposure radiographs. According to the invention, in the range comprising time adjustments of only a few periods of the alternating current, the time switch is designed to be such that the successive values of the operational times differ by an integral number of one half periods, each adjustable time value being associated with two or more positions of the selector. In each of these positions the load of the X-ray tube is different; in one of the positions the maximum permissible power corresponding to the load capacity of the X-ray atent 2,835,823 Patented May 20, 1958 ICC tube is supplied to the X-ray tube, and in the other positions a lower power may be supplied to the X-ray tube.

A few load stages may be added, the exposure time remaining constant, without requiring fundamental modifications of the construction of the time switch, and in the X-ray apparatus only a few additional tappin'gs on the adjusting resistor for the filament current would be required.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing in which the single figure is a schematic diagram of an embodiment of X-ray apparatus in accordance with the present invention.

The X-ray tube 1 is fed via the secondary Winding 2 of the high-voltage transformer 3. The high voltage is fed directly to the cathode and the anode of the X-ray tube, but the invention also applies to apparatus in which the voltage is rectified.

The cathode of the X-ray tube is fed via the secondary Winding 4 of the filament-current transformer 5.

The alternating supply current is fed to the primary winding 6 of the transformer 3 for high voltage through the adjusting transformer 7 and the voltage control 8. This control is termed the kilovolt-selector.

The primary winding 9 of the filament current transformer 5 receives current traversing a smaller or greater part of the control resistor 10. The value of the resistor it) part connected in series with the winding is determined by the adjustment of the filament-current control 11. This control may, as is shown in the figure, occupy sixteen positions; it is actuated by means of the time-adjusting member 12.

The time switch comprises a transformer, the primary winding 13 of which is connected to the power supply voltage. The secondary winding 14 serves to feed the anode circuit of the control-tube 15 and for charging the capacitor 16. This capacitor is charged by means of a rectifier 17, for example a gas-filled discharge tube. The filament cathode of the control tube is fed from part of the winding 14. The control-tube is preferably a gasfilled tube having a filament cathode.

The current circuit of the winding 6 of the high-voltage transformer 3, which circuit is to be automatically interrupted and closed, includes a bipolar switch 18, which is actuated by the magnet coil 19. This magnet coil is included in the anode circuit of the discharge tube 15.

The capacitor 16 is included in the charging circuit, which is traversed by the current which flows from a tapping 20 of the transformer Winding 14, to the capacitor 16, from which the current flows through the switching arm 12 of the time-adjusting member and the switched-in part of the control-resistor 21, via the rectifier 17, back to the winding 14.

The grid 22 of the tube 15' is connected to one terminal of the capacitor 16. When the capacitor is not charged, the grid potential exceeds the maximum value at which tube 15 becomes conductive. The anode current of the tube is then permitted to flow and the switch 18 is closed. As the charge of the capacitor continues, its voltage increases and hence the potential of the grid connected to the negative terminal of the capacitor 16 decreases. After some time, which depends on the position of the switching arm 12, the grid voltage is so low that the tube 15 becomes non-conductive and the switch 18 is opened.

The time-adjusting member has as many positions as the filament-current control 11. A variation in position of the switch 12 is not always attended with a variation in time. In the position shown the smallest part of the control-resistor 21 is shunted out of the circuit so that the capacitor 1a is charged within a minimum time. In the two next following positions the same resistor does not vary.

7 In the position shown, the filament-current control 11 includes such a part of the control resistor 10 in the filament current circuit that the X-ray tube load is smaller than'the maximum permissible power at the adjusted time, it being for example 66% thereof. In the second position the resistor is decreased and the load is adjusted to for example 80% of the permissible value. In the subsequent position the smallest part of the resistor is included and the load is raised to the maximum permissible value. 1

At the transition to the next following position of the time switch a greater resistor part is included in the charging circuit of the capacitor 16, so that the switching time is increased. In this position, the filamentcurrent control 11 decreases the load by switching on a larger part of the control resistor 10, i. e. to a value whichis lower than the load permissible at the adjusted time. Only in the next-following position of the time switch, in which the duration of the load is not varied, the X-ray tube is fully loaded.

At the transition to the next-following time adjustment an additional load stage is added.

If the next following resistor stages of the time switch are chosen to be such that they together'constitute a geometrical progression, increasing the adjustable times each'time by the difference between the successive stages is invariably greater than half a period of the alternating current if the minimum switching time is adjusted to 0.02 sec.; with the half periods there is no need for further control. The division of the resistor 10 is therefore such that at the further adjustments the 'X-ray tube is constantly fully loaded.

With a suitable choice of the decreased loads, the ar- .rangement may be such that for the intermediate positions use is made of tappi'ngs already required for the adjustments of longer exposures, at which the X-ray tube is fully loaded. In this case, it is sufficient to provide a few additional connections with the filament- .current control.

The instant of switching on the tube load is determined by the change-over of the switch 23, which connects thecapacitor 16 to the tapping 20 of the winding 14-, in one-position, and short-circuits said capacitor, in the other position.

Withthe adjustment of the load of the X-ray tube,

the tube voltage applied may at the same time be observed.

"This may be simply realized by providing an adjusting transformer 26, the secondary winding of which is conhected in series with the filament-current resistor 10. iV Vith the aid of the switching arm 24 a larger or smaller part of the primary winding is switched in. The switching arm 24 is coupled with the kilovolt-selector 8, so that with a decrease in tube voltage the voltage induced inthe filament-current circuit is higher than if the tube voltage is adjusted to a higher value.

While the invention has been described by means of a specific example and ma specific embodiment, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. X-ray apparatus comprising an X-ray tube, means for supplying energy to said tube from a source of alternating current, means including a time switch having a plurality of contacts for varying the time intervals during which energy is supplied to said tube from said source, the time intervals in the range of only a few periods of the voltage from the source of alternating current having successive values differing by an integral number of one-half periods of said voltage, a switching device having a plurality of contact points for supplying different loads to said X-ray tube, means for coupling said time switch to said switching device to produce simultaneous adjustment thereof, and means for interconnecting several of the contact points of said time switch in a manner whereby when said switching device is in one of a plurality of selected positions the time of application of the load to said X-ray tube through the said switching device is the same as the time of application of a different load to the said X-ray tube when the said switching device is in another of said selected positions, the said time of application approximating a few periods of said alternating current voltage.

2. X-ray apparatus comprising an X-ray tube having a cathode, means for supplying energy to said tube from a source of alternating current, means including a time switch for varying the time intervals during which energy is supplied to said tube from said source, said time switch having a plurality of contacts, the time intervals in the range of only a few periods of the voltage from the source of alternating current having successive values differing by an integral number of one-half periods of said voltage, a switching device comprising a plurality of contact points and a resistor having a plurality of taps thereon connected to the said contact points to apply voltages having different values across said cathode,

means for coupling said time switch to said switching device to produce simultaneous adjustment thereof, and means for interconnecting several of the contact points of said time switch in a manner whereby when said switching device is in one of a plurality of selected positions the time of application of the voltage across said cathode through the said switching device is the same as the time of application of a different voltage across the said cathode when the said switching device is in another of said selected positions, the said time of application approximating a few periods of said alternating current voltage.

References Cited in the file of this patent UNITED STATES PATENTS 2,365,554 Jeans Dec. 19, 1944 2,379,125 Weisglass June 26, 1945 2,573,029 Kuhlman Oct. 30, 1951

Images