JPH01302699A - X-ray generating device - Google Patents

Abstract

PURPOSE:To prevent insulation breakage of an X-ray tube by furnishing X-ray tube voltage restricting elements, which are put in continuity when a voltage exceeding a certain value is going to be impressed on the X-ray tube, absorb the impression energy, and restrict impressed voltage onto the X-ray tube. CONSTITUTION:X-ray tube voltage restricting elements (lightening protector) 17, 18, which are put in continuity when a voltage exceeding a certain value (normally an allowable value) is going to be impressed on an X-ray tube 15, absorb the impression energy, and restrict impressed voltage on the X-ray tube 15, are inserted between the positive and negative electrode sides of the outputs from rectifiers 11, 12 and a grounding terminal and connected parallelly with the X-ray tube 15. Accordingly, when a high voltage exceeding the allowable voltage for X-ray tube 15 is given externally in the event, for ex., of ground discharge to a power supply line, or when any reason has generated an overshoot exceeding the same allowable voltage, the lightening protectors 17, 18 are put in continuity so as to absorb the impressed energy. Thereby the overshoot voltage generated on the output sides of the rectifiers 11, 12 is absorbed to restrict the impressed voltage onto X-ray tube 15, which prevents the tube 15 from insulation breakage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an X-ray generator that generates X-rays by applying a high voltage to an X-ray tube, and particularly relates to an X-ray generator that generates X-rays by applying a high voltage to an The present invention relates to an X-ray generator that limits the voltage within a voltage value.

[Conventional technology]

Conventional X! The 51 generator was constructed as shown in FIG. In FIG. 5, 1 is a power supply terminal, and the X-ray radiation power input from this power supply terminal 1 (LU, LV, LW) is connected to the power supply switch 2 (SU, SV).

SW) is supplied to the autotransformer 3. When the position of the brush (sliding brush) 4 that moves on the sliding coil of the autotransformer 3 is adjusted by the tube voltage adjustment setting device (not shown), the autotransformer 3 A predetermined voltage is output to the output terminal. 5 is a switch circuit for X-ray radiation;
When it is turned on, power is supplied to the high voltage transformer 6 connected to the subsequent stage.

When the switch circuit 5 is turned off, the supply of power to the high voltage transformer 6 is stopped. The high voltage transformer 6 includes a negative winding 7, an iron core 8, and a secondary winding 9.10, and the output voltages of the secondary windings 9 and 10 have a phase difference of 30 degrees. The output voltages thereof are each subjected to full-wave rectification by a rectifier LL12 and then synthesized.

This combined output voltage has a 12-peak rectification type, which reduces pulsation in the output voltage and contributes to improving the X-ray generation efficiency. The full-wave rectified output voltage is applied to the X-ray tube 15 via high-voltage cables 13.14 on the anode and cathode sides, and the X-ray tube 15 with ray tube current
Emit more X-rays.

In such a conventional device, the factor that determines the upper limit of the X-ray tube voltage (hereinafter abbreviated as tube voltage) applied to the X-ray tube 15 is the setting position of the shearing brush 4 of the autotransformer 3. It is. The set position of the brush 4 can be precisely managed by a servo system (not shown) that is driven according to the set output voltage for tube voltage adjustment.

However, such a method using a servo system requires a mechanism such as the use of a motor to drive the brush 4, and therefore high-speed response is not possible. Therefore, for example, when the power line is struck by lightning, the power supply terminal 1 may be suddenly (suddenly)
When a voltage fluctuation occurs, the brush 4 cannot respond instantaneously because the responsiveness of the entire servo system is slow. Therefore, instantaneous voltage fluctuations are input to the high voltage transformer 6 through the switch circuit 5, causing instantaneous voltage fluctuations in the tube voltage. If this voltage fluctuation is a fluctuation in the direction of increasing the tube voltage, there is a possibility that an overshoot voltage will be generated in the X-ray tube 15 and dielectric breakdown of the X-ray tube 15 will occur.

In addition to such electric shocks from the outside, voltage fluctuations that occur internally for some reason may also generate overshoot voltage for the following reasons, which may cause dielectric breakdown of the X-ray tube 15. Therefore, the magnetic coupling between the negative winding 7 and the secondary windings 9 and 10 is poor, and the leakage reactance is large. In addition, the high voltage cable 13.14 on the output side of the rectifier 11.12 has a metal shield on its outer sheath to prevent electric shock, and therefore there is a wire between the core wire of the high voltage cable 13.14 and the ground as shown in FIG. It has a capacitance as shown by the middle broken line. For this reason, the circuit after the high voltage transformer 6 reacts like an equalization circuit, forming a resonant circuit with the capacitance C and the equivalent resistance R of the X-ray tube 15, and is therefore susceptible to sudden fluctuations in the input voltage. On the other hand, transient phenomena such as vibration are likely to occur. Therefore, there is a possibility that an overshoot voltage will be generated in the X-ray tube 15 and dielectric breakdown of the X-ray tube 15 will occur.

[Problem to be solved by the invention]

As described above, conventional devices cannot respond quickly to sudden fluctuations in input voltage, and fluctuations in input voltage tend to affect output voltage, and circuit constants tend to be oscillating. Therefore, there is a problem in that fluctuations in the input voltage affect the output voltage (tube voltage of the X-ray tube 15), causing an overshoot in the X-ray tube voltage and causing dielectric breakdown of the X-ray tube.

An object of the present invention is to effectively absorb such overshoot occurring in the X-ray tube voltage and to prevent dielectric breakdown of the X-ray tube.

[Means to solve the problem]

The above purpose is to provide an X-ray radiation switch circuit that controls the opening and closing of the X-ray radiation power supply, a high-voltage transformer that boosts the output voltage of this X-ray radiation switch circuit, and a rectifier that rectifies the output power of this high-voltage transformer. an X-ray tube to which a high voltage rectified by the rectifier is applied, and a rectifier connected in parallel to the X-ray tube,
This is achieved by providing an X-ray tube voltage limiting element that becomes conductive when a voltage higher than a predetermined value is applied to the X-ray tube, absorbs the applied energy, and limits the voltage applied to the X-ray tube. be done.

Additionally, there is an X-ray radiation switch circuit that controls opening and closing of the X-ray radiation power supply, a high-voltage transformer that boosts the output voltage of this X-ray radiation switch circuit, and a rectifier that rectifies the output voltage of this high-voltage transformer. and an X-ray tube to which a high voltage rectified by this rectifier is applied, and this X-ray tube is connected in parallel, and when a voltage higher than a predetermined value is applied to the X-ray tube, conduction occurs and the voltage is applied. An X-ray tube voltage limiting element that absorbs energy and limits the voltage applied to the X-ray tube, and detects continuity between the X-ray tube voltage limiting element and supplies power for X-ray radiation to the high voltage transformer. This can be achieved more satisfactorily by providing an X-ray radiation power supply cutoff circuit that cuts off the X-ray radiation.

[Effect]

The X-ray tube voltage limiting element is connected in parallel to the X-ray tube, and
When a voltage higher than a predetermined value (usually an allowable value) is applied to the line tube, for example when an electric shock occurs, the overshoot voltage occurs on the output side of the rectifier as the tube becomes conductive and absorbs the applied energy. is absorbed, the voltage applied to the X-ray tube is limited, and dielectric breakdown of the X-ray tube is prevented. Further, the X-ray radiation power supply cutoff circuit detects continuity of the X-ray tube voltage limiting element, that is, application of a voltage equal to or higher than a predetermined value to the X-ray tube, and cuts off the X-ray radiation power supply. When a voltage of a predetermined value or more is applied for a period of time, the X-ray tube voltage limiting element is protected, and dielectric breakdown of the X-ray tube is further prevented.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
The figure is a circuit diagram showing the main parts of a basic configuration example of the X-ray generator according to the present invention, and 6 to 15 in the figure are the same as those in FIG. 5. 17 and 18 become conductive when a voltage higher than a predetermined value (usually an allowable value) is applied to the X-ray tube 15, absorb the applied energy, and limit the voltage applied to the X-ray tube 15. An X-ray tube voltage limiting element, here a lightning arrester, is inserted between the anode and cathode sides of the outputs of the rectifiers 11 and 12 and the ground terminal, and is connected in parallel to the X-ray tube 15.

This lightning arrester 17.18 is connected to the high voltage transformer 6 and the rectifier 1.
It is housed in the same container 16 as 1.12. In this case, the container 16 is filled with insulating oil (not shown) to improve the high voltage insulation of the lightning arrester 17, 18, the high voltage transformer 6, and the rectifier 11, 12 and to dissipate the generated heat.

In such a configuration, if a high voltage higher than the permissible voltage of the X-ray tube 15 is applied from the outside, such as due to a lightning strike to the power supply line, or if an overshoot voltage higher than the permissible voltage of the X-ray tube 15 occurs for some reason. When it occurs, lightning arrester 17.1
8 becomes conductive and absorbs the applied energy. Therefore, the overshoot voltage generated on the output sides of the rectifiers 11 and 12 is absorbed, the voltage applied to the X-ray tube 15 is limited, and dielectric breakdown of the X-ray tube 15 is prevented.

Here, a high-voltage lightning arrester is usually used with a discharge gap connected in series with a current-limiting resistor. According to this, when an impact voltage equal to or higher than the discharge starting voltage is applied to both ends of the discharge gap, a discharge occurs in the discharge gap, and the impact voltage is absorbed. However, when a discharge gap is used, a follow-on current occurs, so a means for blocking the follow-on flow is required. This is because if this follow-on current cannot be blocked, the lightning arrester may be damaged and lose its function as a lightning arrester. Furthermore, it is known that it is difficult for lightning arresters using a discharge gap to limit high voltages at steep wave fronts because there is a delay in the discharge characteristics of the air gap.

Therefore, it is preferable to use an element made of a varistor, particularly a zinc oxide varistor (a varistor whose main component is zinc oxide ZnO) as the structure of the lightning arrester.

Zinc oxide varistors have zinc oxide (ZnO) as the main component, and oxides such as B+ + Pb+ Br, Ba, Co+ Mn are added to this and sintered at high temperature, and electrodes are provided at both ends. Due to the boundary layer of sintered fine particles, the voltage-current characteristics exhibit sharp current rise characteristics. Since this type of sintered element has a structure in which countless fine particles are connected in a network in the sintered body, an element with high withstand voltage can be easily produced by appropriately increasing the number of fine particles connected in series.

The features of the zinc oxide varistor due to this structure are as follows: 1. It has a large surge current withstand capacity. 2. It has a large non-linearity index, so the leakage current is extremely small, and its limiting voltage characteristics are excellent. 3. This is a lightning arrester configuration that has many advantages over discharge gaps, such as: quick response even to surge voltages with steep rises, 4. No follow current, and 5. Any varistor voltage can be obtained. It is an extremely useful element against surge voltages such as overshoot voltages.

By using a lightning arrester made of such a zinc oxide varistor and by detecting the current flowing through the varistor, it is possible to detect the occurrence of overshoot voltage, and to release the overload state of a high voltage transformer, varistor, etc. An example of the configuration of the X-ray generator that makes this possible will be described below with reference to FIG.

To explain by assigning the same reference numerals to the same or equivalent parts as in FIGS. 1 and 5, a lightning arrester 17 made of a zinc oxide varistor is provided between the anode output terminal on the output side of the rectifier 11 and 12 and the ground.
and a current detector 19 are connected in series, and a lightning arrester 1 consisting of a zinc oxide varistor is connected between the cathode output terminal and the ground.
8 and a series circuit of a current detector 20 are connected. The output signals SL and S2 of the current detectors 19 and 20 are input to the continuity state detector 21. When the continuity state detector 21 detects the continuity state of the lightning arrester 17, 18 from the output signals SL and S2, it outputs a continuity state detection signal S3. The continuity state detection signal S3 is sent to the control circuit 22 of the X-ray radiation switch circuit 5.
is man-powered.

When the continuity state detection signal S3 is manually inputted while the X-ray radiation signal S4 is manually inputted, the control circuit 22 sends an X-ray radiation stop signal S5 to the X-ray radiation switch circuit 5, and the high voltage transformer 6 Cut off the power supply to the equipment and stop the X-ray emission.

Here, the varistor voltage of the zinc oxide varistor constituting the lightning arrester 17, 18 is set to be slightly higher than the rated voltage of the X-ray tube 15, etc.

With the above configuration, when an overshoot voltage is generated and a voltage higher than the varistor voltage is applied across the lightning arrester (zinc oxide varistor) 17.18, the lightning arrester 17.18 becomes conductive. When the current is detected by the current detectors 19 and 20, the power supply to the high voltage transformer 6 is cut off, and the overshoot state is released. Note that the energy absorption operation of the overshoot voltage by the lightning arresters 17 and 18 is the same as in the case of FIG. 1.

FIG. 3 shows an example of the structure of a zinc oxide varistor used as a lightning arrester 17, 18. As shown in this figure, the zinc oxide varistor is made up of a necessary number of unit varistors 24 connected in series on an insulating plate 23, and a rectifier 11° is connected so that a high voltage is applied between connection terminals 25 and 26. 12 in parallel. As shown in the figure, by connecting unit varistors 24 having a predetermined varistor voltage in series, it is possible to reduce the varistor voltage of the unit varistors 24 and create the overall varistor voltage with high accuracy. Furthermore, by adjusting the number of unit varistors 24 connected in series, the overall varistor voltage can be adjusted as desired.

As mentioned above, this type of zinc oxide varistor has a large non-linearity index, so the leakage current (current that flows when non-conducting) is extremely small. Heat) loss is small. Furthermore, even if heat is generated due to power loss, since it is immersed in the insulating oil in the container 16, it is efficiently cooled.

Figure 4 shows the current detector 19, 20 and the continuity state detector 21.
FIG. 2 is a diagram showing a specific example of a circuit. In this figure, R1
, R2 are resistors constituting the current detector 19.20, which converts the current flowing through the lightning arrester 17.18 made of a zinc oxide varistor into a voltage and outputs the voltage. This output voltage is op amp 3
1.32 to one input terminal of the comparators 33 and 34. Variable resistors R10 and R12 connected to the other input terminals of the comparators 33 and 34 respectively subtract the voltage level corresponding to the leakage current of the lightning arrester 17.
This is to detect that a large current has flowed through 18. The output signals of comparators 33 and 34 are photocoupler PC
I, manually power the light emitting parts 35 and 36 of PC2. The photocoupler Pct and the output sides of the light receiving sections 37 and 38 of PC2 are connected in common, that is, forming an OR circuit, and are connected to the output terminal A. Therefore, at the output terminal A, there is a lightning arrester 17.
Or when any of 18 becomes conductive, LO
A W level signal (detection signal) is output. The signal S3 from the output terminal A is input to the control circuit 22, which switches off the X-ray radiation switch circuit 5, cuts off the power supply to the high voltage transformer 6, and stops generating the high voltage output. ,X
This prevents dielectric breakdown of the wire tube 15. In addition, R3-R9, R
11, R13 to R16 each represent a resistance, among which R6
is a resistor for inverting the operational amplifier 32 output voltage.

In the above embodiment, the X-ray tube voltage limiting element (surge arrester 17
．． 18) detects continuity and cuts off the supply of the X-ray radiation power source to the high voltage transformer 6;
Although a case has been described in which the current detectors 19, 20, the conduction state detector 21, and the control circuit 22 of the X-ray emission switch circuit 5 are configured, the present invention is not limited to this.

In short, it is sufficient that the configuration is such that the power for X-ray radiation is not supplied to the high voltage transformer 6 from the time when continuity of the X-ray tube voltage limiting element (surge arrester 17, 18) is detected.

〔Effect of the invention〕

According to the present invention, when an overshoot voltage exceeding the permissible value (rated voltage or permissible voltage) of the X-ray tube or the like occurs, the X-ray tube voltage limiting element connected in parallel with the X-ray tube Energy exceeding the permissible value flows, and a voltage exceeding the permissible value is not applied to the X-ray tube, thereby preventing dielectric breakdown of the X-ray tube. Further, by using a varistor, particularly a zinc oxide varistor, as the X-ray tube voltage limiting element, high-speed response is superior to the case where a discharge gap is used. Furthermore, by providing means for detecting the current flowing through the varistor and cutting off the voltage input to the high voltage transformer when an overshoot occurs, the duration of the overshoot state can be made extremely short. Therefore, the loss of the varistor can be reduced, and elements with small loss capacitance can be used.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the main part of a basic configuration example of the device of the present invention, Fig. 2 is a circuit diagram showing the main part of a specific example of the structure of the device of the invention, and Fig. 3 is the circuit diagram shown in Fig. 2. A fourth diagram showing a structural example of a zinc oxide varistor used as a lightning arrester in the device of the present invention.
The figure shows a specific circuit example of the current detector and discharge state detector in the device of the present invention shown in FIG. 2, and FIG. 5 is a circuit diagram of the conventional device. 1--power terminal, 3--auto transformer, 4--brush,
5-X-ray radiation switch circuit, 6-High voltage transformer, 11
．． 12-rectifier, 15-X-ray tube, 17.18--surge arrester (zinc oxide varistor'), 19.20--current detector (resistance), 2t-continuity state detector, 22--control circuit. Figure 4 37.38: Blow

Claims (1)

[Claims] 1. An X-ray radiation switch circuit that controls opening and closing of an X-ray radiation power supply, a high-voltage transformer that boosts the output voltage of this X-ray radiation switch circuit, and a high-voltage transformer that boosts the output voltage of this X-ray radiation switch circuit. A rectifier that rectifies the output voltage, an X-ray tube to which a high voltage rectified by this rectifier is applied, and a parallel connection to this X-ray tube, and when a voltage higher than a predetermined value is applied to the X-ray tube. An X-ray tube voltage limiting element that conducts to the X-ray tube and absorbs the applied energy to limit the voltage applied to the X-ray tube. 2. An X-ray radiation switch circuit that controls opening and closing of the X-ray radiation power supply, a high-voltage transformer that boosts the output voltage of this X-ray radiation switch circuit, and a rectifier that rectifies the output voltage of this high-voltage transformer. and an X-ray tube to which a high voltage rectified by this rectifier is applied, and this X-ray tube is connected in parallel, and when a voltage higher than a predetermined value is applied to the X-ray tube, conduction occurs and the voltage is applied. An X-ray tube voltage limiting element that absorbs energy and limits the voltage applied to the X-ray tube, and detects continuity between this X-ray tube voltage limiting element and supplies power for X-ray radiation to the high voltage transformer. An X-ray generator comprising: an X-ray emission power cutoff circuit that cuts off the power source. 3. The X-ray generator according to claim 1 or 2, wherein the X-ray tube voltage limiting element is an earth arrester. 4. The X-ray generator according to claim 3, wherein the electric arrestor is a zinc oxide varistor.