Pressure transducer for determining a first pressure of a process medium

Abstract

The invention relates to a pressure transducer (1) intended for determining a first pressure (p1) of a process medium (2) and having - a housing (3) for receiving a pressure sensor (4), - the pressure sensor (4), which has a first area (5) and a second area (6) and is located in the housing (3), wherein the first area (5) is on the pressure-medium side and can be subjected to the first pressure (p1) of the process medium (2) and wherein the second area (6) can be subjected to a second pressure (p2), - a sealing element (7), which is designed and located in such a way that it seals off from the process medium (2) a rear space (8) between the pressure sensor (4) and the housing (3), - a first electrode (9) and a second electrode (10), which are located in the rear space (8), wherein the first electrode (9) is designed as a comb-shaped 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 also designed to determine a phase shift between the electrical excitation signal and the electrical reception signal and, on the basis of the phase shift, to detect a leakage.

Description

[0001] Pressure sensor for determining a first pressure of a process medium

[0002] The invention relates to a pressure sensor for determining a first pressure of a process medium.

[0003] 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, with the atmospheric pressure prevailing in the vicinity of the gauge pressure sensor serving as the reference pressure.

[0004] Pressure transducers have a pressure-sensitive measuring element, the so-called pressure sensor, with a pressure applied to its first and second surfaces. In the case of relative or absolute pressure transducers, the pressure of the process medium to be determined 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 transducers, a first pressure and a second pressure of a process medium are applied to both surfaces. The measuring element bends depending on the existing relative pressure, which is calculated from 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 between capacitive and piezoresistive pressure sensors, among others.A large number of such pressure sensors are manufactured and distributed by companies in the Endress+Hauser Group.

[0005] A generic 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 typically includes a transducer for converting a pressure-dependent deformation of the measuring diaphragm into an electrical primary signal, as well as a primary signal path extending through the base body. The transducer can be a capacitive or resistive transducer, for example. The primary signal path usually includes at least one electrical feedthrough through the base body. Instead of ceramic pressure sensors, silicon chips, which are usually bonded to a silicon substrate, are also known as pressure sensors.

[0006] Ceramic pressure sensors, in particular, are often installed in the housing of the pressure transducer using a sealing element. If the sealing element leaks, the process medium can penetrate the housing and cause the pressure transducer to fail.

[0007] To detect such leaks, leak holes are currently installed near the sealing element, allowing the process medium to escape through the housing in the event of a leak. The leaked process medium is then visible to service personnel. However, such leak holes require regular on-site inspection of the pressure transducer.

[0008] It is therefore an object of the present invention to provide a pressure measuring sensor in which a leakage of the sealing element is determined in a simple manner.

[0009] According to the invention, the object is achieved by a pressure sensor for determining a first pressure of a process medium with

[0010] - a housing for accommodating a pressure sensor,

[0011] - the pressure sensor having 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 such that it seals a rear space between the pressure sensor and the housing to the process medium,

[0012] - a first electrode and a second electrode arranged in the rear space, wherein the first electrode is designed as a comb electrode,

[0013] - a monitoring unit which is designed 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 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.

[0014] According to the invention, two electrodes are inserted into a rear chamber of the pressure sensor. The rear chamber corresponds to a space between the pressure sensor and the housing. The first electrode is subjected to an electrical excitation signal by means of 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 reception signal. The electrical excitation signal interacts with a medium between the first electrode and the second electrode. 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 a space between the two electrodes, a phase shift of the electrical excitation signal occurs, which is determined by means of 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 referred to as a comb electrode. The precise design of the comb-like structure is particularly related to the frequency of the excitation signal. In one development, the second electrode is applied in the form of a metallic coating in the rear space. Such a metallic coating can be easily applied, for example, to the pressure sensor, in particular to a base body of the pressure sensor, or to the housing.

[0015] In one embodiment, the first electrode and / or the second electrode are arranged in the region of the sealing element. The first electrode and / or the second electrode can be arranged on the sealing element itself or adjacent to the sealing element. In this way, the ingress of process medium into the rear chamber can be detected at an early stage. The first electrode and / or the second electrode are located in a region of the sealing element facing away from the process medium.

[0016] In a further 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 the pressure sensor or the housing. One electrode can also be applied to the pressure sensor and the other to the housing.

[0017] A further development provides that the pressure sensor has at least one holding element which is designed to hold the pressure sensor in a predetermined position.

[0018] Advantageously, the first electrode and / or the second electrode are mounted on the support element or at least partially incorporated into the support element. If only one of the two electrodes is mounted on or at least partially incorporated into the support element, the other electrode can be mounted, for example, on the pressure sensor or on the housing or in the region of the sealing element.

[0019] In one embodiment, the housing has a support surface for accommodating the pressure sensor. Another embodiment provides for the electrical excitation signal to be a high-frequency signal. A high-frequency signal is particularly referred to as a signal with a frequency in the MHz to GHz range.

[0020] The invention will be explained further with reference to the following figures 1-5. They show:

[0021] Fig. 1 : a first embodiment of the pressure sensor according to the invention.

[0022] Fig. 2: a second embodiment of the pressure sensor according to the invention.

[0023] Fig. 3: a third embodiment of the pressure sensor according to the invention.

[0024] Fig. 4: a fourth embodiment of the pressure sensor according to the invention.

[0025] Fig. 5: a fifth embodiment of the pressure sensor according to the invention.

[0026] Fig. 1 shows a first embodiment of a pressure transducer 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 comprises, for example, a jacket sleeve 20 with a longitudinal axis A and a radially inwardly projecting terminal support surface 13.

[0027] 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 one another by 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 soldering. 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 beneath 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 in that a reference pressure, e.g. an atmospheric pressure, is supplied to the pressure chamber 14 via a bore (not shown) leading through the base body 4a.

[0028] The pressure sensor 4 has an electromechanical transducer for detecting a 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 can be varied depending on the pressure-induced deflection of the measuring diaphragm 4b. The at least one capacitor is formed by a measuring electrode 16 applied to the side of the measuring diaphragm 4b facing the base body 4a and a counter electrode 17 applied to an end face of the base body 4a facing the measuring diaphragm 4b. The pressure-dependent capacitance of the capacitor is detected via measuring electronics (not shown) connected to the measuring electrode 16 and the counter electrode 17. The measuring electronics can be designed to convert the capacitance into a pressure-dependent measurement signal and to provide it for further evaluation and / or processing.

[0029] The pressure sensor 4 rests on the bearing surface 13 via a sealing element 7, for example an O-ring or a seal. A rear chamber 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 rear chamber 8. A monitoring unit 11 (see Fig. 5) is designed 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 results 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 as a result of process medium 20 entering the rear chamber 8. Based on the phase shift between the electrical excitation signal and the electrical reception signal, a leak can be detected by means of the monitoring unit 11.

[0030] The first electrode 9 and the second electrode 10 can be arranged at different positions in the rear chamber 8. As shown in Fig. 1, for example, one of the two electrodes can be applied in the region of the sealing element 7 and the other electrode on the housing 3. Alternatively, as shown in Fig. 2, one of the two electrodes can be applied to the housing 3 and the other to the pressure sensor 4. The two electrodes can also be applied in the region of the sealing element 7 and on the pressure sensor 4, as shown in Fig. 3. Of course, it is also possible for both electrodes 9, 10 to be applied to the housing 3 or the pressure sensor 4 (cf. Fig. 4). The first electrode 9 and / or the second electrode 10 can be applied in the rear chamber 8, for example, as a metallic coating or in the form of a circuit board or a microstrip.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.

[0031] The pressure sensor 1 can further comprise a mounting element 12, as shown in Fig. 5, which serves to hold the pressure sensor 4 in a predetermined position. For example, the mounting element 12 blocks movement of the pressure sensor 4 in the 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 incorporated into the mounting element 12. The attachment of one of the two electrodes 9, 10 on or at the mounting element 12 can be combined with other possible arrangements of the electrodes 9, 10.

[0032] List of reference symbols

[0033] 1 pressure sensor

[0034] 2 Process medium

[0035] 3 housings

[0036] 4 Pressure sensor

[0037] 4a Basic body

[0038] 4b Measuring membrane

[0039] 5 first area

[0040] 6 second area

[0041] 7 Sealing element

[0042] 8 backcourt

[0043] 9 first electrode

[0044] 10 second electrode

[0045] 11 Monitoring unit

[0046] 12 Supporting element

[0047] 13 Support surface

[0048] 14 pressure chamber

[0049] 15 joint

[0050] 16 measuring electrode

[0051] 17 Counter electrode

[0052] 18 Inlet opening

[0053] 19 Marginal area

[0054] 20 jacket sleeve

[0055] 21 threaded ring

Claims

Patent 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) 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 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 sensor (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 sensor (1) according to one of claims 1 - 4, wherein the pressure sensor (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 sensor (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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