Pressure sensor for determining the initial pressure of a process medium

Abstract

The invention relates to a pressure sensor (1) for determining a first pressure (p1) of a process medium (2) with - a housing (3) for receiving a pressure sensor (4), - the pressure sensor (4) with a first surface (5) and a second surface (6), which is arranged in the housing (3), wherein the first surface (5) is arranged on the process medium side and can be subjected to the first pressure (p1) of the process medium (2), wherein the second surface (6) can be subjected to a second pressure (p2), - a sealing element (7) which is designed and arranged in such a way that it seals a back space (8) between the pressure sensor (4) and the housing (3) to the process medium (2), - a first electrode (9) and a second electrode (10) which are arranged in the rear space (8), wherein the first electrode (9) is designed as a comb electrode, - a monitoring unit (11) which is configured to apply an electrical excitation signal to the first electrode (9) and to receive an electrical reception signal from the second electrode (10), wherein the monitoring unit (11) is further configured to determine a phase shift between the electrical excitation signal and the electrical reception signal and to detect a leakage based on the phase shift.

Description

[0001] The invention relates to a pressure sensor for determining a first pressure of a process medium.

[0002] In pressure measurement technology, absolute pressure, differential pressure, and gauge pressure sensors are known. Absolute pressure sensors determine the prevailing pressure of a process medium absolutely, i.e., relative to a vacuum, while differential pressure sensors determine the difference between two different pressures of the process medium or media. With gauge pressure sensors, the pressure of the process medium to be measured is determined relative to a reference pressure, where the prevailing atmospheric pressure in the vicinity of the gauge serves as the reference pressure.

[0003] Pressure sensors have a pressure-sensitive measuring element, the so-called pressure sensor, on whose first and second surfaces pressure is applied. In the case of relative or absolute pressure sensors, the pressure of the process medium to be measured acts on the first surface of the pressure sensor, while an absolute or reference pressure acts on the second surface. In the case of differential pressure sensors, a first and a second pressure of the process medium are applied to each surface. The measuring element bends depending on the relative pressure, which is the difference between the pressures applied to the two surfaces. This bending is converted by an electronic unit into an electrical signal dependent on the relative pressure, which is then available for further processing or evaluation. A distinction is made, among other things, between capacitive and piezoresistive pressure sensors.A large number of such pressure sensors are manufactured and distributed by companies of the Endress+Hauser Group.

[0004] A typical pressure sensor comprises, for example, a base body and a ceramic measuring diaphragm, which is pressure-tightly connected to the base body by means of an active brazing alloy, forming a measuring chamber. Furthermore, the pressure sensor usually includes a transducer for converting a pressure-dependent deformation of the measuring diaphragm into a primary electrical signal, as well as a primary signal path extending through the base body. The transducer can be, for example, a capacitive or a resistive transducer. The primary signal path usually includes at least one electrical feedthrough through the base body. Silicon chips, which are typically bonded to a silicon substrate, are also known as pressure sensors instead of ceramic ones.

[0005] Ceramic pressure sensors, in particular, are often installed in the housing of the pressure sensor using a sealing element. If this sealing element leaks, the process medium can penetrate the housing and cause the pressure sensor to fail.

[0006] To detect such a leak, leakage holes are currently installed in the area of ​​the sealing element, allowing the process medium to escape through the housing in the event of a leak. The escaped process medium is then visible to service personnel. However, such leakage holes necessitate regular on-site inspection of the pressure sensor.

[0007] It is therefore an object of the present invention to provide a pressure sensor in which a leakage of the sealing element is detected in a simple manner.

[0008] According to the invention, the problem is solved by a pressure sensor for determining a first pressure of a process medium with - a housing for a pressure sensor, - the pressure sensor with a first surface and a second surface, which is arranged in the housing, wherein the first surface is arranged on the process medium side and can be subjected to the first pressure of the process medium, wherein the second surface can be subjected to a second pressure, - a sealing element which is designed and arranged in such a way that it seals a gap between the pressure sensor and the housing to the process medium, - a first electrode and a second electrode, which are arranged in the rear space, wherein the first electrode is designed as a comb electrode, - a monitoring unit configured to apply an electrical excitation signal to the first electrode and to receive an electrical reception signal from the second electrode, wherein the monitoring unit is further configured to determine a phase shift between the electrical excitation signal and the electrical reception signal and to detect a leakage based on the phase shift.

[0009] According to the invention, two electrodes are inserted into a rear compartment of the pressure sensor. This rear compartment corresponds to a space between the pressure sensor and the housing. The first electrode is supplied with an electrical excitation signal by the monitoring unit. The second electrode receives the excitation signal emitted by the first electrode, which is received by the monitoring unit as an electrical signal. The electrical excitation signal interacts with a medium between the first and second electrodes. If the sealing element is intact, air or another predetermined medium is present between the two electrodes. As soon as the sealing element becomes leaky and process medium enters the space between the two electrodes, a phase shift of the electrical excitation signal occurs, which is determined by the monitoring unit.In this way, the monitoring unit can detect whether a leak is present. The first electrode and / or the second electrode are designed, in particular, as a conductor track or microstrip. An electrode with a comb-like structure is called a comb electrode. The precise design of the comb-like structure is particularly related to the frequency of the excitation signal.

[0010] In a further training, the second electrode is applied in the form of a metallic coating in the rear area. Such a metallic coating can be easily applied, for example, to the pressure sensor, especially to a base body of the pressure sensor, or to the housing.

[0011] In one embodiment, the first electrode and / or the second electrode are arranged in the area of ​​the sealing element. The first electrode and / or the second electrode can be located on the sealing element itself or adjacent to the sealing element. In this way, the ingress of process medium into the back chamber can be detected at an early stage. The first electrode and / or the second electrode are located in an area of ​​the sealing element facing away from the process medium.

[0012] In another embodiment, the first electrode and / or the second electrode are applied to the pressure sensor and / or the housing. Both electrodes can be applied to either the pressure sensor or the housing. Alternatively, one electrode can be applied to the pressure sensor and the other to the housing.

[0013] Further training stipulates that the pressure sensor must have at least one mounting element designed to hold the pressure sensor in a predetermined position.

[0014] Advantageously, the first electrode and / or the second electrode are mounted on the mounting element or at least partially embedded in it. If only one of the two electrodes is mounted on or at least partially embedded in the mounting element, the other electrode can be located, for example, on the pressure sensor, the housing, or in the area of ​​the sealing element.

[0015] In one embodiment, the housing has a mounting surface for receiving the pressure sensor.

[0016] Another configuration involves using a high-frequency electrical excitation signal. A high-frequency signal is specifically defined as a signal with a frequency in the MHz to GHz range.

[0017] The invention will be further described using the following figures. Fig. 1-5 will be explained. They show: Fig. 1: a first embodiment of the pressure sensor according to the invention. Fig. 2: a second embodiment of the pressure sensor according to the invention. Fig. 3: a third embodiment of the pressure sensor according to the invention. Fig. 4: a fourth embodiment of the pressure sensor according to the invention. Fig. 5: a fifth embodiment of the pressure sensor according to the invention.

[0018] Fig. Figure 1 shows a first embodiment of a pressure sensor 1 according to the invention, comprising a ceramic pressure sensor 4 and a housing 3 for mounting the pressure sensor 4, for example, in a container wall, a pipe wall, or another part of a process plant. The housing 3 has, by way of example, a sleeve 20 with a longitudinal axis A and a radially inwardly projecting end contact surface 13.

[0019] The pressure sensor 4 comprises, for example, a pressure-dependent, elastically deformable measuring diaphragm 4b, which is arranged on a ceramic base body 4a. The measuring diaphragm 4b and base body 4a can be made of ceramic, e.g., aluminum oxide (Al₂O₃), and are pressure-tightly connected to each other, enclosing a pressure chamber 14. The edge of the measuring diaphragm 4b can be connected to the edge of the base body 4a, for example, by means of active brazing 15 or in another way, e.g., by glass brazing. The measuring diaphragm 4b has a first surface 5 and a second surface 6. The first surface 5 can be subjected to the first pressure p₁ of the process medium 20. The second surface 6 can be subjected to a second pressure p₂. The pressure sensor 4 shown can be designed as an absolute pressure sensor. In this case, the pressure chamber 14 enclosed under the measuring diaphragm 4b is evacuated, and the second pressure corresponds to a vacuum pressure.Alternatively, the pressure sensor 4 can be designed as a reference pressure sensor by supplying a reference pressure, e.g. atmospheric pressure, to the pressure chamber 14 via a bore (not shown) passing through the base body 4a.

[0020] The pressure sensor 4 has an electromechanical transducer for detecting pressure-dependent deformation of the measuring diaphragm 4b. The transducer can be designed as a capacitive transducer with at least one capacitor, wherein the capacitor has a capacitance that varies depending on the pressure-induced deflection of the measuring diaphragm 4b. The at least one capacitor is formed by a measuring electrode 16 mounted on the base body 4a facing the measuring diaphragm 4b and a counter electrode 17 mounted on an end face of the base body 4a facing the measuring diaphragm 4b. The pressure-dependent capacitance of the capacitor is detected by measuring electronics (not shown) which are connected to the measuring electrode 16 and the counter electrode 17. The measuring electronics can be configured to convert the capacitance into a pressure-dependent measurement signal and make it available for further evaluation and / or processing.

[0021] The pressure sensor 4 rests on the contact surface 13 at its edge via a sealing element 7, for example, an O-ring or a sealing ring. A space 8 formed between the housing 3 and the pressure sensor 4 is sealed by the sealing element 7. The pressure sensor 4 can be fixed by means of a threaded ring 16 to prevent axial movement of the pressure sensor 4. The first electrode 9, which is designed as a comb electrode, and the second electrode 10 are arranged in the space 8. A monitoring unit 11 (see figure) Fig. 5) is configured to apply an electrical excitation signal, in particular a high-frequency signal, to the first electrode 10 and to receive an electrical reception signal from the second electrode 10. Depending on the medium between the first electrode 9 and the second electrode 10, a phase shift occurs between the electrical excitation signal and the electrical reception signal. The phase shift results in particular from a change in the effective dielectric constant in the region of the first electrode 9 and / or the second electrode 10 due to the entry of process medium 20 into the back chamber 8. Based on the phase shift between the electrical excitation signal and the electrical reception signal, a leak can be detected by the monitoring unit 11.

[0022] The first electrode 9 and the second electrode 10 can be arranged at different positions in the rear space 8. As shown in Fig. As shown in Figure 1, for example, one of the two electrodes can be located in the area of ​​the sealing element 7 and the other electrode can be placed on the housing 3. Alternatively, as shown in Figure 1, the electrodes can be located on the housing 3. Fig. As shown in Figure 2, one of the two electrodes is located on the housing 3 and the other on the pressure sensor 4. The two electrodes can also be located in the area of ​​the sealing element 7 and on the pressure sensor 4, as shown in Figure 2. Fig. 3 shown. Of course, it is also possible that both electrodes 9, 10 are applied to the housing 3 or the pressure sensor 4 (cf. Fig. 4) The first electrode 9 and / or the second electrode 10 can, for example, be applied as a metallic coating or in the form of a circuit board or a microstrip in the rear space 8. It is advantageous if the first electrode 9 and / or the second electrode 10 are arranged at a short distance from the sealing element 7 in order to detect a leak at an early stage.

[0023] The pressure sensor 1 can further comprise a mounting element 12, as shown in Fig. Figure 5 shows a mounting element 12, which serves to hold the pressure sensor 4 in a predetermined position. For example, the mounting element 12 prevents movement of the pressure sensor 4 in an axial or radial direction. In this case, the first electrode 9 and / or the second electrode 10 can also be mounted on the mounting element 12 or at least partially embedded in it. Mounting one of the two electrodes 9, 10 on or near the mounting element 12 can be combined with other possible arrangements of the electrodes 9, 10. Reference symbol list 1 pressure sensor 2 Process medium 3 cases 4 pressure sensor 4a Basic body 4b Measuring membrane 5 first area 6 second area 7 Sealing element 8 Backcourt 9 first electrode 10 second electrode 11 Monitoring unit 12 Mounting element 13 Contact surface 14 Pressure chamber 15 joint 16 Measuring electrode 17 Counter electrode 18 Introduction opening 19 Edge area 20 Sheath sleeve 21 Threaded ring

Claims

[1] Pressure sensor (1) for determining a first pressure (p1) of a process medium (2) with - a housing (3) for accommodating a pressure sensor (4), - the pressure sensor (4) having a first surface (5) and a second surface (6), which is arranged in the housing (3), wherein the first surface (5) is arranged on the process medium side and can be subjected to the first pressure (p1) of the process medium (2), wherein the second surface (6) can be subjected to a second pressure (p2), - a sealing element (7) which is designed and arranged in such a way that it seals a rear space (8) between the pressure sensor (4) and the housing (3) to the process medium (2), - a first electrode (9) and a second electrode (10) which are arranged in the rear space (8), wherein the first electrode (9) is designed as a comb electrode, - a monitoring unit (11) which is designed to apply an electrical excitation signal to the first electrode (9) and to receive an electrical reception signal from the second electrode (10), wherein the monitoring unit (11) is further designed to determine a phase shift between the electrical excitation signal and the electrical reception signal and to detect a leakage based on the phase shift. [2] Pressure sensor (1) according to claim 2, wherein the second electrode (10) is applied in the form of a metallic coating in the rear space (8). [3] Pressure sensor (1) according to one of claims 1-2, wherein the first electrode (9) and / or the second electrode (10) are arranged in the region of the sealing element (7). [4] Pressure transducer (1) according to one of claims 1-3, wherein the first electrode (9) and / or the second electrode (10) are applied to the pressure sensor (4) and / or the housing (3). [5] Pressure transducer (1) according to one of claims 1-4, wherein the pressure transducer (1) has at least one holding element (12) which is designed to hold the pressure sensor (4) at a predetermined position. [6] Pressure sensor (1) according to claim 5, wherein the first electrode (9) and / or the second electrode (10) are applied to the support element (12) or at least partially introduced into the support element (12). [7] Pressure transducer (1) according to one of claims 1-6, wherein the housing (3) has a support surface (13) for receiving the pressure sensor (4). [8] Pressure sensor (1) according to one of claims 1-7, wherein the electrical excitation signal is a high-frequency signal.

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