US 2717315 A
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Sept- 6, 1955 A. A. NEMET ET AL X-RAY APPARATUS 2 Sheets-Sheet 1 Filed Nov. 27 1951 Sept. 6, 1955 A. A. NEMET ET AL X-RAY APPARATUS Filed Nov. 27, 1951 2 Sheets-Sheet 2 AM I '* INVENTORS Q. AMT/10mg Anfa/ Nemef Matthew BerindeL BY United States Patent X-RAY APPARATUS Anthony Antal Nemet, Richmond-Surrey, and Matthew Berindei, Cheam-Surrey, England, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application November 27, 1951, Serial No. 258,338
Claims priority, application Great Britain November 28, 1950 3 Claims. (Cl. 250-95) This invention relates to X-ray apparatus of the type having an X-ray tube which, when in operation, takes a heavy current for a short period of time, and relates particularly to high-tension voltage supply arrangements for X-ray apparatus of this type.
The voltage required for the energisation of an X- ray tube for diagnostic radiography are usually of the order of 50 to 120 kv. and with existing arrangements the X-ray exposures are normally taken with heavy currents from the supply mains lasting for a fraction of a second. For chest exposure, the instantaneous power may be of the order of 20-40 kw.
The wiring, not only inside the apparatus but also to the points of supply, must consequently be heavy enough to carry without excessive voltage drop the heavy currents involved. Consequently, in many hospitals, special wiring has to be installed for the operation of the X-ray apparatus. In any event, the power station and the associated transmission system is subjected to instantaneous shocks.
To obviate these difliculties X-ray apparatus has been devised which works on the condenser storage principle, using high-tension condensers and associated high-tension switchgear.
The object of the present invention is to provide means for obviating the difiiculties without the use of hightension condensers.
According to the present invention, an X-ray apparatus having an X-ray tube which, when in operation, takes a heavy current for a short period of time, has the hightension supply for the X-ray tube obtained from the output of an electric generator driven by an electric motor.
Thus, the mains supply is used solely to energise the electric motor which in turn drives the generator from which the power is derived to energize the X-ray tube.
With this arrangement, it is possible to use a relatively small electric motor for example, a squirrel cage or a capacitor type motor, which is incapable of driving the generator at its operating speed when the generator is under load, but is able to run the generator up to speed in a short time when the generator is off lead.
Thus, when it is desired to make an X-ray exposure, the motor is first switched on and when the motor-generator system has run up to full speed, the generator is connected to the load. The kinetic energy of the rotating system is used to supply the heavy load during the operation of the X-ray tube and, although the speed of the generator is slightly reduced by the impressed load, the kinetic energy of the rotating system is sufficient to prevent the speed of the generator, and hence the generator output from being reduced below a satisfactory working value during the period of an exposure.
If desired, the small driving motor may be disconnected from the mains supply before the exposure begins but, even if it remains connected, the increase of power taken from the mains is small, instantaneous peak loads on the supply mains are avoided and a normal wiring installation is adequate to carry the mains current to the motor.
2,717,315 Patented Sept. 6, 1955 The high-tension supply apparatus may be installed separately from the part of an X-ray installation in which the X-ray tube is situated and an X-ray high-tension supply unit according to the invention has a supply obtained from the output of an electric generator driven by an electric motor in the manner described above.
The electric motor may be driven either from a D. C. or an A. C. supply mains.
The generator may be a high-voltage D. C. machine,
but, in general, the generator will be an A. C. machine of relatively low voltage output from which the high-tension supply will be obtained by means of a high-tension transformer and rectifier system. It is preferable, therefore, for the generator to be a high-frequency alternator with an output of 360-400 volts at a frequency of 400 to 500 cycles per second and for the supply to be obtained from the output thereof by Way of at least one transformer and a rectifier. By using a high frequency of the order referred to, instead of a supply frequency of cycles per second, the weight and size aswell as the cost of both the generator and the high-tension transformer can be substantially reduced.
In many cases, it may be sufficient to provide some indication of the generator output which enables the operator of the apparatus to see when the generator has run up to speed before operating the X-ray tube. For example, a voltmeter, a frequency meter or a tachometer may be supplied for this purpose. However, for an apparatus of this kind, it is the usual practice for the period of operation of the X-ray tube to be controlled by a time switch which is pre-set by the operator to give the required exposure time and is switched into operation by the operator when he requires the exposure to begin. For some applications it is preferred to interlock the time switch with the generator output to prevent the commencement of an exposure until the generator has run up to speed.
This may be done by using a control circuit which is dependent upon the voltage of the generator output or its frequency, when the generator is an A. C. machine, or simply by providing a time delay mechanism which prevents the operation of the time switch until the motorgenerator system has had time to run up to speed.
It is preferred, however, to interlock the time switch with the generator output by means of a frequency sensitive circuit which prevents the operation of the X-ray tube until the generator is able to provide the required operating output and hence has reached its normal frequency rating for this purpose.
To this end, the output of the generator may be applied across a network comprising a series resonance circuit tuned to the required frequency and a bridge-connecting rectifier in series, the rectifier output being applied to the input terminals of a magnetic amplifier having a trigger characteristic, the output of which amplifier controls the operation of the time switch.
The filament current of the X-ray tube and that of the high-tension rectifying valves associated with the hightension supply rectifier may be derived in a number of alternative ways. Both may be derived from the local A. C. supply mains using suitable transformers and suitable stabilising arrangements if desired. Alternatively, the filament current of the X-ray tube, which current is more critical, may be obtained from the A. C. supply mains, using a stabilising arrangement, while the rectifying valve filament currents may be taken from the alternator supply of higher frequency. As a further alternative, both may be taken through suitable transformers from the high-frequency alternator supply. However, this last alternative requires a more elaborate stabilising arrangement, particularly because the speed of the alternator will fall when under load and, for this reason, the
high-frequency source will not normally be used for supplying the X-ray tube filament current. A still further arrangement is to use two convertors connected to the supply mains, one for the high-tension supply and one for the filament supplies. This latter arrangement is particularly suitable for an installation intended for operation from a D. C. supply mains.
In order that the invention may readily be carried into effect, two examples will now be described in detail with reference to the accompanying drawings of which:
Figure 1 is a schematic circuit diagram of an X-ray installation the high-tension supply apparatus of which uses a motor energised from an A. C. supply mains coupled to a high-frequency alternator, a voltmeter being provided across the high-frequency supply so that the operator may know when the generator output has risen to its working value and Figure 2 is a schematic circuit diagram of a modified form of X-ray apparatus in which the time switch is interlocked with the generator output by means of a frequency sensitive device.
In the two figures, corresponding components are in dicated by the same reference numerals.
In Figure 1, an electric motor 1 is energised from an A. C. supply mains 42 by way of an isolating switch 2 and is coupled to a high-frequency alternator 3 providing an output at 360 volts, 450 cycles per second A. C. The generator 3 is provided with a voltage stabiliser 4. This may be of any suitable form to provide rapid compensation of the output voltage and a suitable stabiliser of this form is described in British patent specification No. 568,185. This form of stabiliser has a voltage input obtained from connections across the generator output and a load current input derived from the secondary winding of a load current transformer 5. The voltage stabiliser 4 controls the current through the field winding 6 of the generator 3 in order to maintain a substantially constant voltage output when the generator 3 is under load. The output of the generator 3 is con nected across the primary winding of an auto-transformer 7 and the required voltage is taken from the secondary of the auto-transformer 7 at the adjustable tap 8. A voltmeter 9 is connected across the output of the transformer 7 and serves to indicate both when the output is of a required voltage, when the motor-generator 13 has run up to speed, and also, when the adjustable tap 8 has been set, when the motor-generator has attained its working speed after being switched on. The operator may therefore use the reading of this voltmeter to indicate when the X-ray apparatus may properly be brought into operation. The output of the auto-transformer 7 is connected to the poles of an isloating switch 10, it).
A time switch 11, of known form, is used to control the moment when the X-ray tube of the apparatus is brought into operation and the time for which its operation continues. This time switch is energised from an electric supply 39 and controlled by a control switch 13. It operates the isolating switch 719. 10 by means of a relay 12 so connecting the high-frequency supply to the input winding of a hightension transformer 14 or disconnecting it therefrom.
The high-tension transformer 14 has two output windings 15 and 16 connected together at their inner ends through a milliamrneter 17. The outer end of the windings 15, 16 are connected across the input of a bridgeconnected rectifier comprising four rectifying valves 18, 19, 29 and 21 obtaining their filament supplies from four output windings of a filament transformer 22 having its primary connected through a series variable resistance 23 to a supply 24, which may conveniently be the same as the supply mains 42. The output of the bridge-con- 27 which may conveniently be the same as the supplies 42 and 24.
In operation, the motor 1 is connected across the supply mains 42, by closing the switch 2 and the rising electric output voltage is noted from the voltmeter 9. When this has reached a steady value such adjustment of the tapping 8 as may be required may be made otherwise, the time switch, which it is assumed has already been set to provide the correct exposure time, may be switched on by closing switch 13. This causes the switch 10, 19- to be closed and the generator output connected to the hightension transformer 14 and hence the load. The X-ray tube is thus brought into operation and after the requisite exposure time, which is determined by the time switch 11, the switch 10, 10 isautomatically opened by the operation of the time switch and the X-ray tube 25 put out of operation. During the exposure period, a heavy load is imposed on the generator 3 which consequently has a high reaction load placed on it tending to slow it down. However, the kinetic energy of the motor-generator system prevents the slowing down effect from being such as to reduce the generator output below a satisfactory working value during the period of the exposure.
In the modified arrangement shown in Figure 2 a series resonant circuit, comprising a condenser 27, an inductance 28 and a series adjustable resistance 29, which is tuned to the frequency of the output of the generator 3 when it has reached its operating value, is connected in series With a bridge-connected rectifier 30 across the output terminals of the generator 3. The rectified output of the rectifier 30 is connected to the input winding 31 of a magnetic amplifier 32 having two output windings 33, 34. These output windings 33, 34 are connected in series with a bridge-connected rectifier 35 and a solenoid winding of an A. C. relay 36 across an A. C. supply 37, which may conveniently be the same as the A. C. supply 42.
The rectified output of the rectifier 35 is connected across a winding 38 of the magnetic amplifier 32 which provide a measure of reaction and thus provides the magnetic amplifier 32 with a trigger characteristic. The relay 36 operates the control switch 13 of the time switch 11.
When this modified form of the apparatus is operated, the motor 1 is connected to the supply mains 42 as before and it will be assumed that the tapping 8 has been set as required and that the time switch 11 has been adjusted to give the required exposure time. When the motor generator 1, 3 runs up to speed so that the generator output has reached its operating value, the generator output has also reached its nominal frequency rating to which the tuned circuit 27, 28 and 29 is tuned. In this state, an A. C. potential is applied across the bridge rectifier 30 and a D. C. input is provided to the magnetic amplifier 32. Owing to the characteristic of the tuned circuit, it will be appreciated that the input to the magnetic amplifier 32 rises rapidly as the generator runs up to its operating speed. The input to the magnetic amplifier causes an A. C. potential to be applied across the bridge-connected rectifier 35 and the D. C. output of this rectifier applied to the winding 38 supplements the effect of the winding 31 so that a trigger effect is obtained and a sufiiciently high current fiows through the series circuit comprising the windings 33, 3 the bridge-connected rectifier 35 and the relay 36 to operate the relay and hence to close the control switch 13. The time switch 11 is thus put into operation closing the switch 10, 10 and putting the X-ray tube 25 into operation for the required exposure time as in the form of the apparatus previously described.
What we claim is:
1. X-ray apparatus comprising an X-ray tube having a given power rating, a source of high-tension potential connected to said tube, said potential source comprising an electric generator having a power rating of sufficient magnitude to supply said given power to said tube when running substantially at its operating speed, a small electric motor coupled to said generator for driving the same, said motor having a power rating substantially below that of said generator whereby it can only drive said generator at its operating speed when the latter is unloaded, means for separately energizing said motor when said generator is unloaded to bring said generator to its operating speed, and means coupling the output of said generator to said tube only when said generator is running at its operating speed.
2. X-ray apparatus comprising an X-ray tube adapted to take a given power, a source of high-tension potential connected to said tube, said potential source comprising an electric generator having a power rating of sufficient magnitude to supply said given power to said tube when running substantially at its operating speed, a small electric motor coupled to said generator for driving the same, said motor having a power rating substantially be low that of said generator whereby it can only drive said generator at its operating speed when the latter is unloaded, means for separately energizing said motor when said generator is unloaded to bring said generator to its operating speed, time switch means responsive to the speed of said generator coupling the output of said generator to said tube and adapted to be actuated to supply power to the latter only when said generator is running at its operating speed, and a frequency sensitive circuit coupled to the output of said generator and adapted to actuate said switch means only when said generator is running at its operating speed.
3. X-ray apparatus as claimed in claim 2 in which the frequency sensitive circuit includes a series-resonant circuit coupled to said generator and tuned to the frequency produced by said generator when running at its operating speed, a bridge-connected rectifier coupled to said resonant circuit, and a magnetic amplifier having a trigger characteristic connected between said rectifier and said switch means and adapted to actuate the latter.
References Cited in the file of this patent UNITED STATES PATENTS 2,094,141 Zingg Sept. 28, 1937 2,140,707 Lee Dec. 20, 1938 2,488,167 Brown Nov. 15, 1949 2,488,168 Brown Nov. 15, 1949 2,542,638 Desch Feb. 20, 1951