Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05G—X-RAY TECHNIQUE
  • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
  • H05G1/08—Electrical details
  • H05G1/26—Measuring, controlling or protecting
  • H05G1/54—Protecting or lifetime prediction
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05G—X-RAY TECHNIQUE
  • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
  • H05G1/08—Electrical details
  • H05G1/10—Power supply arrangements for feeding the X-ray tube
  • H05G1/12—Power supply arrangements for feeding the X-ray tube with DC or rectified single-phase AC or double-phase

Definitions

• the invention relates to a high-voltage supply for an X-ray device, which essentially consists of electrical lines which are arranged between a high-voltage circuit and an X-ray tube of the X-ray device.
• X-ray tubes are constructed as high vacuum tubes.
• the high vacuum basically prevents flashovers between the cathode and the anode of the X-ray tube when the X-ray voltage, which is in the kilo-volt range, is applied.
• small amounts of residual gases that contaminate the high vacuum are unavoidable. This applies in particular because gaseous material components escape inside the tube during the operation of the X-ray tube.
• the residual gases can be ionized by the X-ray voltage. The ionization causes a flashover and thus a short circuit within the X-ray tube.
• the temporal profiles of the short-circuit currents and the resulting processes for charge equalization in the lines of the high-voltage supply sometimes have very high slope steepnesses, since they run very quickly.
• the resulting interference spectrum therefore extends into the upper megahertz range and is very broadband.
• the short-circuit and charge equalization currents cause vibrations associated with overvoltages, which decay only very slowly.
• Such interference signals and overvoltages in the high-voltage circuit of the X-ray device can lead to malfunctions in the electronics and the computer device. Component failures also often occur, especially in the high-voltage circuit of the X-ray generator. In addition to downtime during operation and costly damage to the X-ray device, If the disturbances also increase the radiation exposure of the patients to be examined, which have to be examined repeatedly due to system failures.
• the object of the invention is to provide an x-ray device in which interference signals and overvoltages that occur due to short circuits in the x-ray tube are so strongly damped that malfunctions in the electronics and component damage within the x-ray device are avoided.
• the invention solves this problem by means of an X-ray device with the features of the first claim.
• a basic idea of the invention is to dampen vibrations and interference signals in the high-voltage supply of the X-ray device, that is to say between the X-ray generator and the X-ray tube.
• the damping is effected by providing terminating resistors on the high-voltage lines of the high-voltage supply. Attenuation through terminating resistors is particularly uncomplicated and easy to implement.
• An advantageous embodiment of the invention results if the high-voltage lines of the high-voltage supply are not provided with a terminating resistor at both ends, but only at one end, that is to say on one side. Even a one-sided terminating resistor can cause the interference signals to decay sufficiently quickly.
• a particularly advantageous variant of this embodiment results from the fact that the one-sided terminating resistor is arranged on the x-ray tube side of each high-voltage line. This allows the high output impedance of the X-ray generator to be maintained during operation to be maintained.
• the impedance of the terminating resistors is matched to the line impedance of the respective line. Adequate damping results in particular if the impedance of the terminating resistors corresponds to the impedance of the high-voltage lines.
• FIG. 1 shows the basic structure of the high-voltage circuit of an X-ray device according to the prior art. posed.
• a primary voltage generator 3 generates a primary voltage, which is passed on to high-voltage transformers 5 and transformed by them into a high voltage sufficient for the operation of the x-ray tube.
• the high voltage output by the high-voltage transformers 5 is passed on to the components 7, in which a rectifier diode and a smoothing capacitance are indicated, and rectified and smoothed by them.
• the components 7 deliver the high voltage to the damping resistors 9 (R D ).
• the damping resistors 9 (R D ) have the task of largely preventing the X-ray generator 1 from overvoltages and interference signals from the
• the X-ray tube 15 is connected to the X-ray generator 1 by an intermediate high-voltage supply, the high-voltage supply essentially consisting of an anodic coaxial high-voltage line 11 and a cathodic coaxial high-voltage line 13.
• the coaxial structure of the high-voltage lines 11 and 13 is indicated by the drawing as a box instead of a line.
• the anodic high-voltage line 11 connects the output of the X-ray generator 1 to the anode 17 of the X-ray tube 15.
• the cathodic high-voltage line 13 connects the cathode 19 of the X-ray tube 15.
• the X-ray tube 15 can be designed with two beams, ie as a two-focus tube, which is why the cathode 19 is indicated with two coils.
• the two coils of the cathode 19 are supplied with heating current by the heating transformer 21.
• FIG. 2 shows a schematic representation of the high voltage circuit of an X-ray device according to the prior art.
• the X-ray voltage U 0 is generated by the generator 31 and output to the high-voltage lines 11 and 13 via the damping resistors 9 (R D ).
• R D damping resistors 9
• High-voltage lines 11 and 13 apply the voltage to the X-ray tube, which is shown here as load resistor 33 (R L ).
• the high voltage circuit is shown during operation, ie in the steady state.
• the anodic high-voltage line 11 is at its entire length at potential U 0
• the cathodic high-voltage line 13 is at its entire length at -U 0 volts.
• the potential distribution on the anodic high-voltage lines is indicated in FIG. 2 by arrows which are denoted by plus, minus and U 0 .
• the potential drop in the damping resistors 9 (R D ) should be neglected.
• Figure 3 shows the same schematic representation of the high-voltage circuit according to the prior art as the previous Figure 2 with the same reference numerals.
• Figure 3 shows the high-voltage circuit at a different time, namely immediately after a short circuit occurs in the X-ray tube.
• the disappearance of the load resistor 33 (R L ) has the consequence that the voltage on the high-voltage lines 11 and 13 collapses because the charges that are on the high-voltage lines 11 and 13 can flow away via the short circuit in the X-ray tube.
• This type of discharge of a uniformly charged line is a standard problem that is well known in the literature. Approximately, the discharge process can be described in such a way that half of the charges on the line run to the left, the other half of the charges to the right. As a result, waves with half the output voltage, i.e.
• the diverging waves meet impedance jump points on both the left and right.
• the damping resistors 9 R D
• the reflected waves then run back towards each other, meet and run again apart until they again
• the oscillation duration depends on the length of the high-voltage lines 11 and 13, respectively.
• the high-voltage line takes up the voltage over the entire length 0 on, after half of the oscillation period the voltage -U 0 and after three quarters of the oscillation period again the voltage 0 until the oscillation process begins to repeat itself after an entire oscillation period
• FIG. 4 shows the anodic side of a high-voltage circuit of an X-ray device according to the invention with rectification and damping component 7, damping resistor 9 (R D ), coaxial high-voltage line 11 and X-ray tube 15 grounded via the groundings 23.
• This conventional structure is supplemented by the terminating resistor 37 (R A ), which closes the X-ray generator-side end of the high-voltage line 11, and by the terminating resistor 38 (R A ), which closes the X-ray tube-side end of the high-voltage line 11.
• the terminating resistors 37, 38 (R A ) are connected in parallel, that is to say they lie between the respective ends of the high-voltage line 11 and the ground 23. They can be connected by soldering.
• Values of approximately 40 to 50 ohms are customary for the line impedance of the high-voltage lines 11, 13 in the high-voltage circuit of an X-ray device.
• the terminating resistors 39 (R A ) therefore have a value of approximately 45 ohms, since their damping effect becomes optimal if their impedance corresponds to that of the high-voltage lines 11, 13.
• the termination with parallel terminating resistors 37, 38 (R A ) alone would not be applicable in reality, since in the operating state the total operating voltage would be present at the two terminating resistors 37 (R A ) and 38 (R A ) and to ground would decrease, which would lead to permanent and extremely high performance losses.
• the X-ray tube-side terminating resistor 38 (R A ) would be short-circuited by the short circuit in the X-ray tube 15 and would therefore not be able to build up a damping effect.
• high-voltage smoothing capacitances 41 (C H ) are provided, which are connected in series between them and the ground 23.
• the high-voltage smoothing capacitances 41 (C H ) have the task of allowing high-frequency interference signals and overvoltages to pass to ground 23, but to block low-frequency and direct-voltage useful signals. You serve in other words, as a high-pass filter, the frequency of which must be selected so that interference signals can flow to ground, but no power loss occurs with regard to useful signals.
• the high-voltage smoothing capacitances 41 (C H ) also prevent the X-ray tube-side termination resistor 38 (R A ) from being short-circuited by the short circuit in the X-ray tube 15 and therefore remain ineffective. Because of the high frequencies of the interference signals, a high-pass filter with a relatively high cut-off frequency is required, so a value in the order of approximately 50 nano-farads is selected as the capacitance of the high-voltage smoothing capacitances 41 (C H ). For example, ceramic or foil capacitors can be used, which can be connected by soldering.
• FIG. 5 shows a variant of the circuit according to the invention in a departure from the parallel connection of the terminating resistors.
• the rectifier and damping component 7, the coaxial high-voltage line 11 together with groundings 23 and the X-ray tube 15 are shown.
• the terminating resistors 39 (R A ) are also shown, but this time in a serial connection between the high-voltage line 11 and the component 7 and between the high-voltage line 11 and the X-ray tube 15.
• the X-ray generator-side low-ohmic terminating resistor 39 (R A ) replaces the normally provided high-ohmic damping resistor R D , which is the component 7 and the one behind it subsequent other X-ray generator, not shown in FIG. 5, protects against overvoltages.
• the damping resistance R D normally to be provided is of the order of several kilo-ohms
• the terminating resistor 39 (R A ) which is of the order of a few tens of ohms, does not offer the same protection against overvoltages in the X-ray generator 1.
• the X-ray generator 1 would therefore have to be dimensioned sufficiently robust to withstand 15 currents in the kilo-ampere range in the event of a short circuit in the X-ray tube.
• the terminating resistors 39 (R A ) do not have the same impedance as the high-voltage lines 11, 13 to be terminated, but double the impedance or more, that is to say at least 90 ohms. This dimensioning causes a largely aperiodic discharge of the high-voltage lines 11, 13. The aperiodic discharge is gradual and takes longer than the discharge through terminating resistors 39 (R A ) with the optimal impedance of 45 ohms.
• a disadvantage is the higher permanent loss line, which is caused by the drop in high voltage across the terminating resistors 39 (R A ).
• the X-ray tube voltage measured on the X-ray generator side is measured in reverse of the increased voltage drop. However, this can be compensated for by a mathematical correction of the measured value.
• FIG. 6 shows a high-voltage circuit according to the invention which has been improved under the aspects described.
• the terminal resistors is implemented insofar as a compromise in terms, as here, both the anodic high-voltage line 11 and the cathodic high-voltage line 13 39 (R A) each terminated on one side by a terminating resistor.
• the impedance of the terminating resistors 39 (R A ) is approximately the same as the line impedance of the high-voltage lines 11 and 13, that is to say approximately 45 ⁇ .
• FIG. 6 shows the X-ray generator 1, which contains the primary voltage generator 3, the high-voltage transformers 5, the rectifier and damping components 7, the damping resistors 9 (R D ) and the heating current transformer 21.
• the X-ray generator 1 is above the coaxial high-voltage lines 11 and 13 connected to the ground 23 are connected to the X-ray tube 15.
• the terminating resistors 39 (R A ) are arranged in series between the high-voltage lines 11 and 13 and the X-ray tube 15. The only one-sided termination of the high-voltage lines 11 and 13 prevents the occurrence of a permanent vibration when a short circuit occurs in the X-ray tube 15.
• the three terminating resistors on the lines would be connected in parallel to one another, they would also have to have a resistance value three times greater than the simple terminating resistor 39 (R A ), so that the heating current losses would even triple.
• additional filter inductors 40 are therefore introduced instead of terminating resistors.
• These additional filter inductors 40 are designed as current-compensated chokes and are usually connected by soldering. Their task is to block the high-frequency interference signals in the high-voltage line 13, but to let the low-frequency heating current pass. In this respect, they represent low-pass filtering.
• the filter inductors 40 are arranged in series between the X-ray tube 15 and the high-voltage line 13 and the heating current transformer 21 and in parallel with the terminating resistor 39 (R A ).
• the size of the filter inductors 40 is to be dimensioned as a function of the interference signals in the high-voltage line 13 or 11. Since the interference signals are in the megahertz range, the heating current usually in the kilo-hertz range, the filter inductors 40 are to be measured with a size of approximately 50 micro-Henry.
• the filter inductors 40 on the cathodic high-voltage side as a current-compensated choke, so as to further reduce the overall inductance with respect to the heating current, without reducing the filter effectiveness in relation to the high-frequency interference signals.
• FIG. 7 shows a further variant of the invention, which has been significantly changed with regard to the supply of heating current to the cathode.
• FIG. 7 shows the high-voltage circuit with the X-ray generator 1 and the internal assemblies already known from the previous figures.
• the anodic high-voltage line 11 and the cathodic high-voltage line 13 are connected to the X-ray generator 1, which in turn are connected in series with the terminating resistors 39 (R A ).
• the heating current transformer 21 is arranged in the periphery of the X-ray tube 15, for example in the X-ray generator 1 or within the high-voltage tank which surrounds the X-ray tube 15 to protect the environment from high voltage and radiation.
• the heating current transformer 21 in FIG. 7 is arranged inside the X-ray tube 15. As a result, the heating current transformer 21 is decoupled from the front from the disturbance processes in the high-voltage line 13. Therefore, no additional filter inductors for filtering overvoltages or interference signals have to be arranged before the heating power supply.
• FIG. 8 shows a further variant of the high-voltage circuit, in which the high-voltage lines 11 and 13 are also each provided on one side with terminating resistors 39 (R A ).
• Figure 8 shows the X-ray generator 1 with the damping resistors 9 (R D ) and otherwise the same components as in the previous figures.
• the terminating resistors 39 (R A ) are connected to the X-ray generator 1 both on the anodic and on the cathodic side, with which the coaxial high-voltage lines 11 and 13 are in turn connected to respective groundings 23.
• the terminating resistors 39 (R A ) are connected in series between the high-voltage lines 11 and 13 and the X-ray generator 1.
• damping resistors 9 (R D ) are also arranged in the usual way, which are dimensioned in the usual order of magnitude of a few kilo-ohms.
• the terminating resistors 39 (R A ) are therefore provided in addition to the damping resistors 9 (R D ) within the X-ray generator 1.
• High-voltage smoothing capacitances 41 (C H ) are provided between the terminating resistors 39 (R A ) and the damping resistors 9 (R D ) of the X-ray generator 1, generally ceramic or foil capacitors, which are connected by soldering become.
• the high-voltage smoothing capacitances 41 (C H ) are connected to the respective connection point between the damping resistors 9 (R D ) and the terminating resistors 39 (R A ) and to the respective ground 23. They are therefore connected in parallel with the damping resistors 9 (R D ) and in parallel with the terminating resistors 39 (R A ).
• the high-voltage lines 11 and 13 are terminated with the series connection of the respective terminating resistors 39 (R A ) and the respective high-voltage smoothing capacitance 41 (C). So that approximately only the ohmic resistance of the terminating resistors 39 (R A ) contributes to the line impedance, the high-voltage smoothing capacitances 41 (C H ) must be selected large enough to compensate for the compensating processes in the high-voltage lines 11 and 13 to act with low resistance. With the value of approximately 50 nano-farads required for this purpose, this variant of the circuit is of particular interest in X-ray devices in whose high-voltage circuit a large high-voltage smoothing capacitance is provided from the outset.
• FIG. 9 shows a simulation of the voltage profile at the cathode of a conventional high-voltage circuit of an X-ray device, as shown in FIG. 1.
• the cathodic high voltage is plotted over time in FIG. 9, assuming an X-ray typical high voltage of 100 kilovolts.
• a short circuit in the X-ray tube is simulated, which can be clearly recognized by the breakdown of the cathodic voltage.
• the short-circuit starts suddenly and ends just as suddenly at 300 nano-seconds.
• Two voltage curves are shown, one of which is at the beginning of the high-voltage line 13 is tapped, the other at the end of the high-voltage line 13. Strong interference signals can clearly be seen, which continue after the short circuit has ended for a long time and with clear overvoltage peaks. It would not be sensible to operate the X-ray tube during the occurrence of these faults, or component defects could occur.
• FIG. 10 shows the same simulation based on a circuit according to the invention, as shown in FIG. 6.
• the cathodic voltage over time is shown again.
• the two voltage curves again represent the voltage at the beginning or at the end of the high-voltage line 13.
• a short circuit suddenly begins in the X-ray tube, which also ends suddenly at 300 ns.
• overvoltages and interference signals are completely eliminated.
• the cathodic voltage dampened by the terminating resistor and the filter inductances, gradually increases again.
• a point in time that is no longer shown in FIG. 10 the cathode reaches the operating voltage again.
• the X-ray device By introducing terminating resistors, the X-ray device can be largely protected from interference and damage caused by the consequences of a short circuit in the X-ray tube. It is only necessary to accept a short time until the x-ray voltage is reached again after a short circuit in the x-ray tube, so that the operation of the x-ray device can be continued.

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• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• X-Ray Techniques (AREA)
• Apparatus For Radiation Diagnosis (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

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• 2003
  • 2003-01-09 DE DE10300542A patent/DE10300542A1/de not_active Ceased
  • 2003-12-15 EP EP03785820A patent/EP1584220B1/fr not_active Expired - Lifetime
  • 2003-12-15 DE DE50313141T patent/DE50313141D1/de not_active Expired - Lifetime
  • 2003-12-15 ES ES03785820T patent/ES2352431T3/es not_active Expired - Lifetime
  • 2003-12-15 AU AU2003294854A patent/AU2003294854A1/en not_active Abandoned
  • 2003-12-15 AT AT03785820T patent/ATE483350T1/de not_active IP Right Cessation
  • 2003-12-15 WO PCT/EP2003/014257 patent/WO2004064458A2/fr not_active Ceased
• 2005
  • 2005-07-06 US US11/175,708 patent/US7110499B2/en not_active Expired - Fee Related

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