PRESSURE MEASURING DEVICE FOR USE IN EXPLOSION-HAZARDOUS ENVIRONMENTS

Description

[0001] The invention relates to a pressure measuring device for detecting the pressure of a medium inside a container or pipeline in a potentially explosive atmosphere.

[0002] Pressure gauges or pressure sensors are used in many industrial sectors for pressure measurement. They essentially consist of a process connection and a housing. The process connection serves to connect the measuring device to the container holding the medium to be measured and to accommodate a pressure sensor, such as a piezoresistive or capacitive sensor, which acts as a transducer for the process pressure. The housing contains evaluation electronics for signal processing and has a connector that supplies power to the measuring device and allows the generated measurement signals to be accessed for further processing in a higher-level control unit, such as a PLC.

[0003] Capacitive measuring cells consist of a compact unit with a ceramic base and a membrane, with a spacer ring, e.g., a glass solder ring, positioned between the base and the membrane. The resulting cavity between the base and membrane allows the membrane to move longitudinally in response to pressure. Electrodes are located on the underside of the membrane and on the opposite upper side of the base, together forming a measuring capacitor. Pressure causes the membrane to deform, resulting in a change in the capacitance of the measuring capacitor.

[0004] Special requirements apply to pressure gauges intended for use in potentially explosive atmospheres. For this purpose, directives have been issued under the designation ATEX – derived from the French term for explosive atmospheres: ATmosphères Explosibles – which regulate the placing on the market of explosion-proof electrical and mechanical equipment, components, and protective systems. An example of such a pressure gauge is disclosed in EP 2913651 B1.

[0005] A key component of these guidelines is the definition of zones, which define specific hazard areas. This results in a strict and defined demarcation between the individual zones. For example, if a pressure gauge is used to measure pressure within a potentially explosive atmosphere, the gauge will, on the one hand, be in contact with the critical hazard area, while on the other hand, parts of the gauge will also be located outside the critical zone. This means that within the gauge itself, there is at least one transition from one zone to another, which poses a particular challenge for relative pressure gauges, as an air passage is necessary to equalize the pressure between the measuring cell and the atmosphere. This requires design measures to achieve this separation in accordance with the guidelines.

[0006] Document US 5,287,746 A discloses a modular pressure transmitter with a flame-retardant head. The head has a passage through which a second, flame-retardant section is formed as a long, narrow channel. This channel runs through a monolithic part of the head and is intended to prevent flame propagation between the process fluid and the interior of the transmitter.

[0007] Document US 2005 / 0172738 A1 discloses a process seal for a transmitter and a method for its attachment. To prevent measurement errors caused by welding distortion, the sealing ring is pre-tensioned during welding to the housing. This ensures that an inner annular shoulder of the seal remains in contact with the separating diaphragm even in the unloaded, assembled state, thus reducing the introduction of stresses during assembly.

[0008] Document US 2022 / 0099516 A1 discloses an enclosure arrangement for a field device that enables explosion-proof mounting of a transparent window without the use of potting compound. The arrangement uses a retaining ring that is screwed into the enclosure lid to clamp the transparent window against a flange of the lid. This purely mechanical clamping creates a multi-stage, tortuous flame path between the components that meets explosion protection requirements.

[0009] The object of the invention is to propose a pressure measuring device in which zone separation and thus a guideline-compliant demarcation to a danger zone is realized in a simple manner.

[0010] The problem is solved according to the invention by a pressure measuring device having the features of claim 1 or claim 2. Advantageous embodiments of the invention are specified in the dependent claims.

[0011] The invention relates to a pressure measuring device with a pressure measuring cell arranged in a process connection. The pressure measuring cell is preferably designed as a capacitive pressure measuring cell, is made of a ceramic material, and consists of a base body and a membrane. In addition to capacitive pressure measuring cells, the invention also includes piezoresistive pressure measuring cells.

[0012] Preferably, the pressure measuring cell is axially clamped in the process connection between a process-side retaining element and a threaded ring resting on the base body. The retaining element is designed as a circumferential, inwardly directed metallic sealing rib, which preferably has spring-elastic properties. Advantageously, a sealing element is arranged between the inwardly projecting area of ​​the retaining element and the pressure measuring cell or the diaphragm to prevent the measuring medium from penetrating into the interior of the measuring device.

[0013] The core of the invention is the realization that the zone separation required by the ATEX directives, in particular between Zone 0 and Zone 1, is achieved by a partition wall having an external thread and screwed into a corresponding internal thread located on the inside of the housing or the process connection. Zone 0 is defined as an area in which a hazardous explosive atmosphere, consisting of a mixture of air and flammable gases, vapors, or mists, is present continuously, for long periods, or frequently, and Zone 1 is defined as an area in which a hazardous explosive atmosphere, consisting of a mixture of air and flammable gases, vapors, or mists, may occasionally form during normal operation.

[0014] The invention further assumes that the pressure measuring cell is arranged on the process side and is therefore located in the critical danger zone as a result of the zone separation realized by the partition wall.

[0015] To avoid pipe penetrations or similar air passages through the partition that would require special sealing, in one alternative the air passage runs via the threaded connection formed between the partition and the inside of the housing or process connection. In a second alternative, the partition has a longitudinal through-hole with an internal thread, and the air passage then runs via the threaded connection formed between this through-hole and a threaded stud screwed into it.

[0016] In addition to zone separation, the ATEX directives also require that this air passage in the zone transition area be flame-resistant, which is achieved through a specific diameter-to-length ratio of a corresponding duct or similar. The invention fulfills this requirement in a simple manner, since the necessary length is provided by the air passage through the threaded connection, while maintaining a comparatively small diameter.

[0017] As a result of the invention, the membrane of the pressure measuring cell is now connected to the atmosphere in accordance with the guidelines via the interior of the measuring instrument housing, one of the aforementioned threaded connections, and the vent opening on the outside of the housing. Advantageously, the threaded connection to the pressure measuring cell is connected by at least one capillary tube, so that pressure equalization does not have to occur via a mere volume equalization of the interior of the measuring instrument housing, but rather via a continuous connection from the membrane of the pressure measuring cell to the vent opening on the outside of the housing.

[0018] The partition wall is preferably made at least partially of metal, although other materials such as glass or ceramic or a combination thereof are also possible, such as an outer ring made of metal and a middle part made of glass or ceramic.

[0019] In a preferred embodiment of the invention, the partition wall is formed by the threaded ring that is already present, which axially clamps the pressure measuring cell together with the holding element arranged on the process side.

[0020] In a further preferred embodiment of the invention, means for inductive energy transfer, comprising at least two coils, are arranged on the partition. This makes it possible to transfer energy for operating the pressure sensor and an electrical signal representing the pressure detected by the pressure sensor—i.e., a voltage signal, current signal, or modulated signal—from one zone to another without having to run electrical conductors through the partition in a sealed and code-compliant manner. A metallic partition offers a further advantage, as the often-perceived disadvantage of inductive signal or energy transfer through a metal wall is advantageous in this case, since otherwise, code-compliant limiting elements such as chokes or similar devices would be necessary.

[0021] The advantage of the invention is therefore that a guideline-compliant zone separation can be created through simple design measures. The invention is explained in more detail below with reference to exemplary embodiments and the drawings.

[0022] They show schematically: Figure 1 shows a pressure measuring device according to the invention, Figure 2 shows a longitudinal section through the process connection of a first embodiment of the pressure measuring device according to the invention, Figure 3 shows a longitudinal section through the process connection of a second embodiment of the pressure measuring device according to the invention, Figure 4 shows a longitudinal section through the process connection of a third embodiment of the pressure measuring device according to the invention, and Figure 5 shows a longitudinal section through the process connection of an embodiment of the pressure measuring device according to the invention not covered by the claims, which does not fall within the scope of protection of the claims.

[0023] In the following description of preferred embodiments, identical reference numerals denote identical or comparable components.

[0024] In Figur 1 Figure 1 shows a perspective view of a pressure measuring device 1 according to the invention. A housing 4 is mounted on a process connection 2. The pressure measuring device 1 is connected via the process connection 2 to a container containing the medium to be measured, i.e., a pipeline, a tank, or the like. This connection is usually made by means of a flange molded onto the container or a corresponding adapter. The housing 4 has a display and control unit, which displays the measurement results and allows the operator to make various settings, such as setting a switching point or displaying the measured values ​​in different units of measurement.However, the invention also includes so-called transmitter devices, which do not have any display or control unit and merely output an analog voltage or current signal corresponding to the measurement result, which is evaluated in a higher-level control unit.

[0025] A connector 8 is located on the side of the housing 4. This connector supplies power to the pressure gauge 1 and acts as an electronic interface, providing the generated measurement signals for further processing by the aforementioned control unit, e.g., a PLC. A vent 6c is also located on the side of the housing 4. This vent allows pressure equalization between the pressure measuring cell 3 and the environment for the purpose of relative pressure measurement.

[0026] In Figur 2 Figure 1 shows a longitudinal section through the process port 2 of a first embodiment of the pressure measuring device 1 according to the invention. The housing 4 is mounted directly onto the process port 2 and preferably welded together. The core element of the pressure measuring device 1 is a capacitive pressure measuring cell 3 with a diaphragm 3a and a base body 3b. The operating principle of such pressure measuring cells is well known and therefore requires no further explanation. On the process side, the pressure measuring cell 3 rests with its diaphragm 3a on a circumferential retaining element 10 designed as a sealing rib. On the opposite side of the pressure measuring cell 3, a screwed-in threaded ring 5a is supported on the base body 3b, so that the pressure measuring cell 3 is axially clamped firmly between the threaded ring 5a and the sealing rib 10.Advantageously, the threaded ring 5a does not rest fully on the base body 3b, but rather has corresponding recesses so that it only bears on the base body 3b in spaced-apart areas. To prevent the measuring medium from penetrating the interior of the housing 4, a sealing element 20 is arranged between the inwardly projecting area of ​​the retaining element 10 and the pressure measuring cell 3 or the diaphragm 3a. The measurement signals from the pressure measuring cell 3 are transmitted via an electrical conductor (not shown) to an electronic unit located in the housing 4 of the measuring device 1, where they are further processed and analyzed.

[0027] To achieve the aforementioned pressure equalization between the pressure measuring cell 3 and the environment, the base body 3b of the pressure measuring cell 3 has a vent channel 6a, so that the interior space between the diaphragm 3a and the base body 3b is connected to the interior space of the measuring instrument housing 4 via this vent channel 6a. Since the interior space of the measuring instrument housing 4 is connected via the Fig. 1 Since the vent opening 6c shown is connected to the environment, a relative pressure measurement is therefore possible.

[0028] For the use of measuring device 1 in a potentially explosive atmosphere, certain structural precautions must be taken in accordance with the relevant ATEX directives. A key part of these directives is the definition of different hazard zones within measuring device 1 and a strict and defined demarcation of these zones from one another. This zone separation is described in the Fig. 2 In the first embodiment shown, this is achieved by a partition 5. This partition 5 separates the process-side Zone 0, in which a hazardous explosive atmosphere consisting of a mixture of air and flammable gases, vapors, or mists is constantly, frequently, or for long periods of time present, from Zone 1 in the rear compartment of the pressure gauge 1, in which a hazardous explosive atmosphere consisting of a mixture of air and flammable gases, vapors, or mists may occasionally form during normal operation.

[0029] However, since a hermetic separation of these two zones is not possible due to the aforementioned need for pressure equalization, and a simple, guideline-compliant through-hole through the partition 5 would be too complex, the air passage runs from the vent 6a in the pressure measuring cell 3 via the threaded connection 6b formed between the partition 5 and the inside of the housing to the vent opening 6c. The threaded connection 6b easily achieves the length-to-diameter ratio required by the guidelines, so that the air passage at the boundary between the two zones exhibits the required flame penetration resistance.

[0030] Furthermore, means for inductive energy transfer in the form of two coils 7 are indicated in the center of the partition 5. This makes it possible to transfer energy to operate the pressure measuring cell 3 and an electrical signal representing the pressure detected by the pressure measuring cell 3 from one zone to the other, without having to run electrical cables through the partition in a sealed and guideline-compliant manner.

[0031] The second embodiment of the invention, which is described in Fig. 3 The image shown essentially corresponds to that of the Fig. 2 , so that, to avoid repetition, we can refer to the explanations regarding Fig. 2 Reference is made to the above. The difference lies in the fact that a separate partition wall has been omitted here, and instead the threaded ring 5a, which is already present due to the axial clamping of the pressure measuring cell 3, is designed to function as a partition wall 5 and establish the required zone separation. Accordingly, the air then passes through the threaded connection 6b formed between the threaded ring 5a and the inside of the housing to the vent opening 6c. A connection between the vent channel 6a and the threaded connection 6b is provided by the previously mentioned recesses in the threaded ring 5a.

[0032] The third embodiment of the invention, which is described in Fig. 4 The diagram shown differs from the previous ones in that the threaded connection 6b is now connected to the vent channel 6a by a capillary tube 6d. Above the partition 5, another capillary tube 6d is indicated, which is then connected to the vent opening 6c on the outside of the housing 4 (not shown). In this way, pressure equalization does not occur via a simple volume equalization of the interior of the measuring instrument housing 4, but via a continuous connection from the diaphragm 3a of the pressure measuring cell 3 to the vent opening 6c. The two capillary tubes 6d are each connected to the top and bottom of the partition, respectively, by a coupling element that provides fastening and the necessary sealing. This connection is such that a direct connection is established between the capillary tube 6d and the threaded connection 6b, as shown in the diagram. Fig. 4 can be seen from this.

[0033] An embodiment of the invention not covered by the claims, which is described in Fig. 5 The diagram shown differs from the previous ones in that the threaded connection 6b is no longer formed by the partition 5 and the inside of the housing 4, but by a threaded stud 9, which is screwed into a through-hole 9a provided for this purpose in the partition 5. The threaded stud 9 can, for example, be designed as a setscrew. The partition 5 can then be, as shown in Fig. 5 As shown, the partition is arranged on the process connection 2, between the process connection 2 and the housing 4. However, it is also conceivable that the partition is welded into the housing 4. Furthermore, in this embodiment as well, the connection between the pressure measuring cell 3 and the threaded pin 9, as well as between the threaded pin 9 and the vent opening 6c on the outside of the housing 4 (not shown), is realized by means of a capillary tube 6d. However, a [context missing] is also conceivable. Fig. 2 and 3 known volume compensation. Reference symbol list

[0034] 1 Pressure gauge 2 Process connection 3 Pressure measuring cell 3a Membrane 3b Base body 4 Housing 5 Partition 5a Threaded ring 6a Vent channel 6b Threaded connection 6c Vent opening 6d Capillary tube 7 Means of inductive energy transfer; coil 8 Plug connection 9 Threaded pin, setscrew 9a Through hole 10 Retaining element, sealing rib 20 Sealing element

Claims

1. Pressure measuring device (1) for recording the pressure of a medium inside a container or pipeline in a potentially explosive environment, the device having a pressure measuring cell (3) comprising a membrane (3a), a process connection (2) accommodating the pressure measuring cell (3), a housing (4), mounted on the process connection (2), for accommodating means for electronic signal processing, and a flameproof air passage (6a, 6b, 6c, 6d) which enables pressure compensation between the pressure measuring cell (3) and the environment for the purpose of measuring relative pressure, wherein a partition (5, 5a) is arranged inside the housing (4), which partition extends perpendicularly to the longitudinal axis of the pressure measuring device (1) and by means of which partition the interior of the housing is divided into two regions and a first zone facing the process is separated from a second zone in accordance with the ATEX directives, wherein the pressure measuring cell (3) is arranged in the first zone, wherein the partition (5, 5a) either has a circumferentially arranged external thread and is screwed into the housing (4), which has a corresponding internal thread, or has a longitudinally oriented through-hole (9a), which has an internal thread and into which a threaded stud (9) is screwed, wherein the flameproofing of the air passage (6a, 6b, 6c, 6d) is achieved by the air passage (6a, 6b, 6c, 6d) extending at least partially over the threaded connection (6b) formed either between the partition (5, 5a) and the inside of the housing or between the partition (5, 5a) and the threaded stud.

2. Pressure measuring device (1) for recording the pressure of a medium inside a container or pipeline in a potentially explosive environment, the device having a pressure measuring cell (3) comprising a membrane (3a), a process connection (2) accommodating the pressure measuring cell (3), a housing (4), mounted on the process connection (2), for accommodating means for electronic signal processing, and a flameproof air passage (6a, 6b, 6c, 6d) which enables pressure compensation between the pressure measuring cell (3) and the environment for the purpose of measuring relative pressure, wherein a partition (5, 5a) is arranged inside the process connection (2), which partition extends perpendicularly to the longitudinal axis of the pressure measuring device (1) and by means of which partition the interior of the process connection is divided into two regions and a first zone facing the process is separated from a second zone in accordance with the ATEX directives, wherein the pressure measuring cell (3) is arranged in the first zone, wherein the partition (5, 5a) has a circumferentially arranged external thread and is screwed into the process connection (2), which has a corresponding internal thread, wherein the flameproofing of the air passage (6a, 6b, 6c, 6d) is achieved by the air passage (6a, 6b, 6c, 6d) extending at least partially over the threaded connection (6b) formed between the partition (5, 5a) and the interior of the process connection.

3. Pressure measuring device (1) according to claim 1 or 2, wherein the pressure measuring cell (3) is designed as a capacitive pressure measuring cell (3) and consists of a main body (3b) in addition to the membrane (3a).

4. Pressure measuring device (1) according to claim 3, wherein the partition (5) is formed by a threaded ring (5a) which rests on the main body (3b) of the pressure measuring cell (3).

5. Pressure measuring device (1) according to claim 3 or 4, wherein the air passage (6a, 6b, 6c, 6d) also extends through a vent channel (6a) in the main body (3b) of the pressure measuring cell (3) in addition to the threaded connection (6b).

6. Pressure measuring device (1) according to claim 5, wherein the air passage (6a, 6b, 6c, 6d) is further formed by at least one capillary tube (6d) which connects the threaded connection (6b) to the vent channel (6a) in the main body (3b) of the pressure measuring cell (3).

7. Pressure measuring device (1) according to any of the preceding claims, wherein the process connection (2) comprises a retaining element (10) on which the pressure measuring cell (3) rests with its membrane side (3a) in an inwardly projecting region so that the pressure measuring cell (3) is axially clamped in conjunction with the threaded ring (5) resting on the main body (3b).

8. Pressure measuring device (1) according to claim 7, wherein a sealing element (20) is arranged between the inwardly projecting region of the retaining element (10) and the pressure measuring cell (3) to prevent the measuring medium from entering the interior of the housing (4).

9. Pressure measuring device (1) according to any of the preceding claims, wherein the first zone is designed as zone 0 and the second zone as zone 1 or the first zone as zone 1 and the second zone as zone 2 in accordance with the ATEX directives.

10. Pressure measuring device (1) according to any of the preceding claims, wherein means for inductive energy transmission are arranged on the partition (5, 5a), which have at least two coils (7) and are suitable for transmitting, through the partition (5, 5a), energy to operate the pressure measuring cell (3) and a pressure recorded by the pressure measuring cell (3) as an electrical signal.