Housing for a high-voltage tank, high-voltage tank for high-voltage generation and method for operating a high-voltage tank

Abstract

Housing for a high-voltage tank for high-voltage generation, comprising a tank (1) open on one side and a circuit board cover (2) closing the tank (1), characterized by: - at least one strain gauge (4) which is arranged on or in the circuit board cover (2) in such a way that it is stretched or compressed when the circuit board cover (2) is deformed due to pressure.

Description

Field of the invention

[0001] The invention relates to a housing for a high-voltage generation tank. The housing has a tank that is open on one side and a circuit board cover that closes the tank. The invention also relates to a high-voltage tank for a high-voltage generation system with such a housing. The invention also relates to an associated method for operating a high-voltage tank. Background of the invention

[0002] When generating X-rays, a high-voltage tank (also abbreviated as HVT) is required to generate the high voltage for the X-ray tube. The HVT is often designed as a tank with a metallic housing filled with a liquid insulating medium. This allows the high voltages required to generate X-rays to be achieved in a small installation space. Due to its high heat capacity, the liquid insulating medium, such as insulating oil, absorbs the resulting heat loss from the electrical components and distributes it through convection when temperatures differ. This causes the insulating oil to heat up and expand.

[0003] Common mineral insulating oils have a thermal expansion coefficient of 700–950 ppm / K. Since the insulating oil is incompressible, a design to compensate for the volume change (e.g., an expansion vessel, pressure equalization tank) of the insulating oil in the X-ray tube and HVT is required. Elastic expansion tanks are well-known. Typically, a so-called expansion tank is made from an oil-resistant membrane material (nitrile, silicone, etc.) with insulating properties. The pressure of the expanding insulating oil deforms and compresses the membrane, thus ensuring pressure equalization.

[0004] This compensation mechanism prevents internal pressures in the HVT tank during temperature fluctuations, although in practice, of course, only limited expansion volumes can be provided. However, if the existing electronic temperature sensors fail or the function of the diaphragm is disrupted or limited (e.g., due to incorrect basic settings or aging effects that lead to stiffening of the compensation diaphragm), pressures in the tank can become so high that the tank can burst. Therefore, according to the Pressure Vessel Ordinance, oil-filled tanks must be able to withstand three times the potentially occurring pressure, at least for a short time.

[0005] When using a thin-walled deep-drawn vessel with a flat circuit board cover including electrical interface functions (power supply lines, measuring signals, connection technology, etc.), even a slight overpressure inside the vessel (especially due to heat generation) can trigger deformations of the vessel.

[0006] The functionality of the HVT is endangered by the following risks: - Shear forces that can cause lasting damage to the seals; leakage of insulating oil may occur. - If other safety functions fail (membranes, temperature sensors), internal pressures can build up until the boiler bursts. - Even slight mechanical stresses can impair or permanently damage parts of the interface function of the circuit board cover. - Leakage test of the high voltage generating device to ensure that no loss of insulating oil can occur over its lifetime, with three times the maximum operating pressure.

[0007] Excessively high pressures can be detected using a pressure sensor that directly measures the pressure in the boiler. However, the pressure sensor must be fed with external air pressure at the rear (relative pressure measurement), which is why the pressure sensor must be embedded in the boiler wall, which requires an additional opening and complex wiring.

[0008] Alternatively, the absolute pressure of the insulating oil in the closed tank can be measured, but this requires two sensors: one for the insulating oil and a second for the surrounding atmosphere. This leads to calibration and accuracy problems in the manufacture of a high-voltage generation tank.

[0009] For safety reasons, an additional pressure switch is usually integrated for emergency shutdown (= an additional opening in the boiler wall). However, the pressure switch is a mechanical component with correspondingly high pressure tolerances for the switching torque. Furthermore, mechanical pressure switches are only suitable for a minimum pressure difference of approximately 0.5 bar.

[0010] The published patent application DE 21 48 768 C discloses an arrangement for measuring high voltages, wherein strain gauges are formed in an electrode and in a crystal in a housing, with the aid of which strain gauges a deformation of the crystal caused by high voltage can be detected.

[0011] Utility model DE 20 2016 000 716 U1 discloses a housing consisting of a vessel-shaped container and a circuit board cover for a high-voltage generator. The housing is filled with insulating oil. Summary of the invention

[0012] It is an object of the invention to provide a housing for a high-voltage tank, a high-voltage tank and a method for operating a high-voltage tank which can detect pressure changes inside the housing.

[0013] According to the invention, the stated object is achieved with the housing, the high-voltage tank, and the method for operating a high-voltage tank of the independent patent claims. Advantageous further developments are specified in the dependent claims.

[0014] Since the mechanical stability of a circuit board cover is significantly lower than that of the vessel in the housing of a high-voltage tank, the pressure differences inside the housing initially manifest themselves as deformation on the circuit board cover (in the case of overpressure, as an outward bulge, in the case of negative pressure, as an inward bulge). According to the invention, this deformation is directly recorded using a strain gauge (SG) and used for monitoring or shutdown.

[0015] For this purpose, the strain gauge can be glued to the outside of the circuit board cover or integrated into the cover. The strain gauge exhibits a resistance that is dependent on pressure or deformation. A downstream measuring circuit, for example, in the form of a half- or full-bridge (e.g., a Wheatstone bridge), can record the changes in the resistance of the strain gauge due to mechanical deformation.

[0016] The invention claims a housing for a high-voltage tank for high-voltage generation, comprising a tank open on one side and a circuit board cover closing the tank, wherein at least one strain gauge is arranged on or in the circuit board cover in such a way that it is stretched or compressed upon pressure-induced deformation of the circuit board cover.

[0017] In a further development, the pan is a Gastronorm container. Gastronorm is a container system used worldwide that allows for easy exchange of food containers through the use of standardized sizes and is used in food processing plants and commercial kitchens. Using a Gastronorm container is a cost-effective alternative for a thermoformed pan.

[0018] The invention offers the advantage that an inadmissible pressure in a housing for a high-voltage tank can be determined in a simple and reliable manner.

[0019] In a further development, an insulating oil can be present inside the housing.

[0020] In a further development, the housing can have a measuring circuit which is designed to detect resistance changes of the strain gauge.

[0021] In a further embodiment, the measuring circuit can have a Wheatstone bridge circuit.

[0022] In a further embodiment, an electrical safety circuit electrically connected to the measuring circuit can be provided, which is designed to switch off high voltage generation when a predeterminable limit value of a change in resistance of the strain gauge is reached.

[0023] The invention also claims a high-voltage tank for high-voltage generation comprising a high-voltage transformer arranged inside a housing according to the invention.

[0024] The invention also claims a method for operating a high-voltage tank according to the invention, wherein the high-voltage generation is switched off when the strain gauge is stretched or compressed exceeding a predeterminable limit value.

[0025] Further features and advantages of the invention will become apparent from the following explanations of an embodiment using schematic drawings.

[0026] They show: Fig. 1: an oblique view of a housing with strain gauges, Fig. 2: a cross-section of a housing with a curved circuit board cover with strain gauges and Fig. 3: a block diagram of a circuit arrangement for determining an overpressure in a housing. Detailed description of an embodiment

[0027] Fig. Figure 1 shows an oblique view of a housing of a high-voltage tank for high-voltage generation. The housing has a vessel 1 that is open at the top and sealed pressure-tight by a circuit board cover 2. Inside the housing, among other things, is the high-voltage transformer in insulating oil 3. A strain gauge 4 is glued to the circuit board cover 2 and is connected to a measuring circuit (not shown). Fig. 1, there is no excessive overpressure in the housing. The circuit board cover 2 is flat and not curved or deformed. The pressure equalizing diaphragms 7 are not stressed.

[0028] Fig. 2 shows a cross section through a housing according to Fig. 1, whereby the insulating oil 3 inside the tank 1 has expanded due to an increase in temperature and has already completely compressed the compensating diaphragms 7. The pressure inside the housing is so great that the circuit board cover 2 is bulged outward, thereby stretching the strain gauge 4. The change in resistance caused by the expansion can be determined using the measuring circuit (not shown).

[0029] The measuring circuit, featuring AD converters / FPGAs and associated software, can determine the baseline state and record and evaluate any changes. Before damage-relevant deformations can occur, the high-voltage generation can be shut down using the safety circuit. This can, for example, reduce the internal temperature, which leads to increased pressure, among other things. In the rare event of aging-related membrane failure, this damage can be detected before the insulating oil can leak from the housing. This must be avoided at all costs due to the environmental impact of the insulating oil.

[0030] The deformation of the circuit board cover 2 and its determination with the strain gauge 4 were experimentally recorded for a 3.2 mm thick circuit board cover 2. This shows an approximately parabolic relationship between the strain of the strain gauge 4 and the force on the circuit board cover 2.

[0031] Fig. 3 shows a block diagram of a circuit arrangement for determining an overpressure in a housing according to the Fig. 1 and Fig.2. A strain gauge 4 is mounted on the circuit board cover 2 of a housing and is electrically connected to the measuring circuit 5. The measuring circuit can have a Wheatstone bridge for evaluation. The measuring circuit 5 is connected to a safety circuit 6, which ensures that the high-voltage generation is shut off if a preset pressure in the tank 1 is exceeded. This allows the insulating oil to cool and the pressure to decrease. A high-voltage transformer 8 is located inside the tank 1. All of this together forms part of a high-voltage tank 9 for an X-ray tube 10.

[0032] The HVT typically also contains an oil temperature sensor. Since pressure and temperature are inevitably related after the vessel 1 is closed, the PT curve (i.e., the change in strain gauge 4 as a function of oil temperature) can be recorded in a calibration step (e.g., during the required test of the vessel 1) and continuously monitored during subsequent operation. This allows not only oil loss due to a leak in the HVT to be detected (the pressure would be too low for the current temperature), but also gas formation due to arcing in the oil (the gas would cause the pressure to be too high for the current temperature). These two problems have not yet been detectable using conventional technology (temperature or pressure switches).

[0033] Although the invention has been illustrated and described in detail by the embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention. List of reference symbols 1 boiler 2 circuit board covers 3 Insulating oil 4 strain gauges 5 Measuring circuit 6 Safety circuit 7 Compensating membrane 8 High-voltage transformer 9 High-voltage tank 10 X-ray tubes

Claims

[1] Housing for a high-voltage tank for high-voltage generation, comprising a tank (1) open on one side and a circuit board cover (2) closing the tank (1), characterized by : - at least one strain gauge (4) which is arranged on or in the circuit board cover (2) in such a way that it is stretched or compressed when the circuit board cover (2) is deformed due to pressure. [2] Housing according to claim 1, characterized by : - insulating oil (3) arranged inside the housing. [3] Housing according to claim 1 or 2, characterized by that the boiler (1) is a Gastronorm container. [4] Housing according to one of the preceding claims, characterized by : - a measuring circuit (5) designed to detect changes in resistance of the strain gauge (4). [5] Housing according to claim 4, characterized by that the measuring circuit (5) has a Wheatstone bridge circuit. [6] Housing according to claim 4 or 5 characterized by : - a safety circuit (6) electrically connected to the measuring circuit (5) and designed to switch off high voltage generation when a predeterminable limit value of a change in resistance of the strain gauge (4) is reached. [7] High-voltage tank (9) for high-voltage generation, comprising a high-voltage transformer (7) arranged inside a housing according to one of the preceding claims. [8] Method for operating a high-voltage tank (9) according to claim 7, characterized by that if the strain gauge (4) is stretched or compressed beyond a preset limit value, the high voltage generation is switched off.

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