Pressure measuring cell with activation device and method for operating a pressure measuring cell

Abstract

The invention relates to a pressure measuring cell with a base body (18) and with a membrane (14), wherein the membrane (14) is designed to bulge depending on an applied pressure, and with measuring electronics (38), wherein the pressure measuring cell (10) has an activation device (36) which converts the pressure-induced movement of the membrane (14) into an electrical impulse to activate the measuring electronics (36). The invention also relates to a method for operating a pressure measuring cell (10).

Description

[0001] The invention relates to a pressure measuring cell according to claim 1. The invention further relates to a method for operating a pressure measuring cell according to claim 9.

[0002] Pressure measuring cells are available in a wide variety of designs from the state of the art. Pressure measuring cells are differentiated according to the underlying measuring principle, the materials oriented toward the process, and whether absolute or relative pressures are measured.

[0003] One of the measuring principles is based on a change in capacitance, whereby a change in pressure causes a deformation of a diaphragm, resulting in a change in capacitance. In resistive pressure sensors, the deformation of a diaphragm is detected using strain gauges, for example, and the pressure is determined from a change in the resistance of the strain gauges. Piezoresistive pressure sensors use pressure sensors with piezoelectric properties.

[0004] The distinction based on the materials oriented towards the process, i.e., the materials that come into contact with the process environment and the process media, is usually made between metallic and ceramic pressure measuring cells, with the former having a metallic and the latter a ceramic membrane on the side facing the process.

[0005] Whether absolute or relative pressures can be measured usually depends on whether a second pressure, e.g. ambient pressure, is applied to the back of the membrane, or whether the back of the membrane is evacuated.

[0006] Pressure sensors are used in a wide variety of processes and systems, sometimes even at locations far removed from control rooms and higher-level units. It is therefore desirable to provide self-contained pressure sensors that consume as little energy as possible.

[0007] Based on this, the underlying object of the present invention is to provide a pressure measuring cell that requires particularly little energy. Furthermore, a method for operating a pressure measuring cell is to be provided, which allows the pressure measuring cell to be operated in a particularly energy-efficient manner.

[0008] The object is achieved according to the invention with the features of the independent claims. Further practical embodiments and advantages are described in conjunction with the dependent claims.

[0009] The pressure measuring cell according to the invention comprises a base body and a membrane. In this case, the membrane and the base body are made of ceramic. The membrane is attached to the base body, particularly with its circumferential edge, and a cavity is formed between the membrane and the base body. The membrane is designed to bulge in response to pressure applied to it.

[0010] The pressure sensor also includes measuring electronics. These electronics serve, in particular, to acquire one or more measured values ​​and also to process and transmit at least one of these measured values.

[0011] In particular, the pressure sensor is a capacitive pressure sensor. This means that the pressure applied to the diaphragm and the resulting curvature of the diaphragm are determined capacitively. For this purpose, the diaphragm and the base body each have an electrode on their facing sides, which together form a parallel-plate capacitor. Depending on the curvature of the diaphragm, the distance between the plates changes, resulting in a capacitance that depends on the applied pressure and is measured by the electronics.

[0012] According to the invention, the pressure measuring cell has an activation device which converts the pressure-induced movement of the membrane into an electrical pulse to activate the measuring electronics. Overall, the activation device converts a mechanical pulse into an electrical pulse. This electrical pulse can be either a current or a voltage.

[0013] The electrical pulse is used to activate the measuring electronics. In particular, the measuring electronics can be completely deactivated, and only when a pressure change and the associated movement or curvature of the diaphragm occur is an electrical pulse generated, which is used to activate the measuring electronics. Because the measuring electronics are largely deactivated, the pressure measuring cell according to the invention can be operated with particularly low energy consumption.

[0014] In particular, the pressure measuring cell is a self-contained pressure measuring cell. Self-contained means that the pressure measuring cell is not connected to an external power source via a cable or line. In particular, the pressure measuring cell also has no wired communication connection. The pressure measuring cell is equipped with a battery and / or accumulator that supplies the measuring electronics with power when activated.

[0015] In particular, the activation device is electrically connected to a drive input of a transistor. The transistor is part of the measurement electronics. When the measurement electronics are deactivated, the transistor is in the off state. The transistor is then cut off and does not conduct current between its source and drain. If a current or voltage is applied to the drive input (i.e., to the gate, for example, in the case of a MOSFET or IGBT, or to the base in the case of a bipolar transistor) by means of the activation device, the transistor switches on, current can flow, and the measurement electronics are powered. The transistor is typically a MOSFET or an IGBT. An advantage of this type of transistor is that it cuts off even at low or no input voltage and exhibits very low input leakage currents.

[0016] The activation unit generates voltages in the range of 0.1 V to 0.6 V or – modulated by a resistor – currents in the nA to µA range. These voltages or currents are sufficient to switch a transistor from an off state to an on state. Alternatively, a voltage below the threshold voltage can be continuously applied to the control input, and the additional voltage generated by the activation unit can then switch the transistor on.

[0017] In a practical embodiment, the activation device comprises a permanent magnet connected to the membrane, which is located at least partially within a coil. In order to induce a high voltage with the smallest possible magnetic field strength, the permanent magnet is arranged directly within the coil. If necessary, a dielectric can also be arranged between the coil and the permanent magnet. As the membrane moves when pressure changes, the permanent magnet connected to the membrane moves within the coil, generating a voltage in the coil. This voltage can then be used to activate the measuring electronics.

[0018] Instead of the coil, a Hall sensor, a reed sensor and / or a Wiegand coil can also be used to generate a voltage by means of the moving permanent magnet.

[0019] Alternatively or additionally, the activation device can include a capacitor, wherein a first electrode of the capacitor is connected to the diaphragm. A second electrode is, in particular, fixed to the base body. The diaphragm, moving in response to pressure changes, also moves the first electrode relative to the second electrode. The plate separation of the capacitor changes, and a charging or discharging current flows accordingly. This current can be used, as described above, in particular to switch a control input and thus to activate the measuring electronics.

[0020] To increase the capacitor area and thus the amount of charge, the capacitor plates can have comb-like structures, or several capacitors can be connected in series.

[0021] In particular, the first electrode can be directly connected to the membrane, and the second electrode can be mounted on the base body. The electrodes are specifically arranged on the surfaces of the membrane and the base body that face each other. The first and second electrodes are, in particular, the electrodes of the capacitive pressure sensor for detecting the measured value and thus the pressure applied to the membrane. The existing structures can therefore be used to form the activation device.

[0022] It is also conceivable that the activation device incorporates a piezoelectric element directly connected to the membrane. Compression or extension of the piezoelectric element through movement of the membrane can generate an electrical pulse, which is then used to activate the measuring electronics.

[0023] In another practical embodiment of the pressure measuring cell, the activation device comprises a bolt extending from the diaphragm, with the permanent magnet or the first electrode or a piezoelectric element arranged at the end of the bolt facing away from the diaphragm. The bolt serves as a connecting piece between the diaphragm and the permanent magnet or the first electrode. The bolt can be formed as a single piece.

[0024] It is also conceivable for the bolt to have a lever to increase the resulting travel length. One end of the lever would then be connected to the diaphragm, and the other end to the permanent magnet or the first electrode. A small movement of the diaphragm would cause a larger change in the travel distance at the other end by means of the lever.

[0025] In particular, the bolt extends through the base body, so that the permanent magnet or the first electrode or a piezo element is arranged on the rear side of the base body, facing away from the membrane. In particular, the bolt is arranged centrally on the membrane.

[0026] In particular, it can be provided that the first capacitor plate is displaceable relative to the second capacitor plate, so that the first and second capacitor plates can move relative to each other and thus the common sectional area can be reduced or enlarged.

[0027] In another practical embodiment, the coil is integrated into the base body. The coil can be arranged in a bore in the base body or completely embedded within the base body, e.g., embedded in a ceramic base body.

[0028] The invention also relates to a method for operating a pressure measuring cell, in particular a pressure measuring cell as described above. A movement induced by a pressure change on the diaphragm is converted into an electrical pulse. The electrical pulse is then used to activate the measuring electronics.

[0029] As already described above, the method according to the invention allows a pressure measuring cell to be operated in a particularly energy-efficient manner. It can even be a self-contained pressure measuring cell. The measuring electronics can be completely switched off. Pressure changes and movement of the diaphragm are then used to generate an activation signal for the measuring electronics.

[0030] In particular, a pressure measurement is performed after the measuring electronics are activated. This means that whenever the measuring electronics are activated by a pressure change, this pressure change can then be measured and processed immediately afterward. The energy to power the measuring electronics is then supplied primarily by a rechargeable battery or a battery.

[0031] After the measuring electronics have been activated and a measured value has been acquired and processed, the measuring electronics can be deactivated again, particularly after a certain period of time in which no further activation signal has been detected (and accordingly no further movement of the diaphragm and thus a constant pressure or a change below or above a defined threshold value).

[0032] Further practical embodiments and advantages are described below in conjunction with the figures. They show: Fig. 1 a pressure measuring cell according to a first embodiment in a schematic representation in cross section, Fig. 2 a pressure measuring cell according to a second embodiment in a schematic representation in cross section, Fig. 3 a pressure measuring cell according to a third embodiment in a schematic representation in cross section, Fig. 4 an activation device according to the first embodiment in Fig. 1 with a part of a measuring electronics, and Fig. 5 a flow chart for a method for operating a pressure measuring cell.

[0033] In Fig. 1 shows a first embodiment of a pressure measuring cell 10 according to the invention. The pressure measuring cell 10 is a capacitive pressure measuring cell

[0034] The pressure measuring cell 10 comprises a membrane 14. The membrane 14 is attached to a base body 18 in an outer edge region via a glass seam 16. The glass seam 16 spaced the membrane 14 and the base body 18 from each other. A cavity 20 is formed between the membrane 14 and the base body 18.

[0035] A channel 22 runs through the base body 18, through which the cavity 20 is connected to the environment. The pressure measurement cell 10 is used to measure the pressure relative to the ambient pressure. It is also conceivable to not provide a channel 22 in order to measure an absolute pressure with the pressure measurement cell 10.

[0036] The membrane 14, with its upper side facing away from the cavity 20, faces a medium, e.g., a container (not shown), and bulges depending on the pressure ratio between ambient pressure and process pressure. The initial position of the membrane 14 is indicated by the dashed line.

[0037] In order to dissipate the pressure from the curvature of the membrane 14, the mutually facing surfaces of the membrane 14 and the base body 18 are provided with a metallic coating, each forming an electrode 24, 26. The contact between the electrodes 24, 26 is made via bores 28, 30 in the base body 18. A capacitance C mess measured, which changes depending on the distance between the electrodes 24, 26, or the curvature of the membrane 14.

[0038] In addition, a reference electrode 32 is formed by means of a metallic coating on the base body 18. The reference electrode 32 serves to detect any measurement errors or malfunctions of the pressure measuring cell 10 via a capacitance C ref to detect. The reference electrode 32 is contacted via a bore 34 in the base body 18.

[0039] In the present case, the pressure measuring cell 10 has an activation device 36 which is connected to a measuring electronics 38 (a section of which is shown in Fig. 4 shown) is connected.

[0040] In this first embodiment of the pressure measuring cell 10, the activation device 36 has a permanent magnet 40 connected to the diaphragm 14, which is arranged in a coil 42 at its end facing away from the diaphragm 14.

[0041] The permanent magnet 40 is connected to the diaphragm 14 via a bolt 44. The bolt 44 extends from the diaphragm 14 through a bore 46 in the base body 18.

[0042] When the membrane 14 moves, the permanent magnet 40 is moved through the coil 42 via the bolt 44, thus inducing a voltage in the coil 42.

[0043] In Fig. 4 shows part of a measuring electronics 38. In Fig. 4 shows that coil 42 is connected to a control input (gate) 48 of a transistor 50. If a voltage is induced in coil 42, it is then applied between gate 48 and drain 49, and transistor 50 is turned on. A current can flow through transistor 50 from source 51 to drain 49, and the measuring electronics 38 are activated.

[0044] If the modulation of the gate 48 is not to be voltage-controlled but current-controlled, then a resistor 52 can be connected in series (shown here with a dashed line).

[0045] In the following, the same reference numerals are used to describe further embodiments for identical or at least functionally equivalent components as for the description of the first embodiment.

[0046] In Fig. Figure 2 shows a second embodiment of a pressure measuring cell 10. This embodiment differs from the first embodiment in the design of the activation device 36.

[0047] The activation device 36 here comprises a capacitor with a first electrode 54 and a second electrode 56. The first electrode 54 is connected to the movable membrane 14, and the second electrode 56 is arranged stationary relative to the base body 18. As in the first embodiment, the first electrode 54 is only indirectly connected to the membrane 14: via the bolt 44, which extends from the center of the membrane 14 through the base body 18.

[0048] When the membrane 14 bulges, the bolt 44 moves, and thus the first electrode 54 moves relative to the second electrode 56. Depending on whether the plate separation between the first electrode 54 and the second electrode 56 increases or decreases, charges flow in or out. This charging or discharging current is used to activate the measuring electronics 38.

[0049] In Fig. Figure 3 shows a third embodiment of a pressure measuring cell 10, wherein the activation device 36 comprises a capacitor with a first electrode 54 and a second electrode 56. In contrast to the second embodiment, here the first electrode 54 is directly connected to the membrane 14 and the second electrode 56 is directly connected to the base body 18 and correspond to the electrodes 24 and 26 for acquiring the measured value. Fig. Figure 5 shows a flowchart for a procedure for operating a pressure measuring cell 10. In step S1 the process is started and

[0050] In step S2, a pressure change occurs and the membrane 14 moves, thereby generating an electrical impulse from the mechanical movement via the activation device 36 and activating the measuring electronics 38.

[0051] In step S3, the measuring electronics 38 are activated and a measurement is performed. For the capacitive pressure measuring cell 10, the capacitance is determined as a measure of the curvature and the applied pressure.

[0052] In step S4, after a specific time interval, it is checked whether another activation signal has been received from the activation device within that interval (y), and if so, a measurement is recorded again according to step S3. If no further activation is detected in step S4 (n), the procedure starts again from S1. List of reference symbols 10 pressure measuring cell 14 Membran 16 glass seam 18 basic bodies 20 cavity 22 channels 24 Electrode 26 Electrode 28 bore 30 holes 32 Reference electrode 34 Hole 36 Activation device 38 Measuring electronics 40 permanent magnet 42 coil 44 bolts 46 Hole 48 Control input, Gate 49 Drain 50 transistors 51 Source 52 resistance 54 first electrode 56 second electrode

Claims

[1] Pressure measuring cell with a base body (18) and with a membrane (14), wherein the membrane (14) is designed to bulge depending on an applied pressure, and with measuring electronics (38), characterized by that the pressure measuring cell (10) has an activation device (36) which converts the pressure-induced movement of the membrane (14) into an electrical pulse for activating the measuring electronics (36). [2] Pressure measuring cell according to the preceding claim, characterized by that the pressure measuring cell (10) is a self-contained pressure measuring cell. [3] Pressure measuring cell according to one of the preceding claims, characterized by that the activation device (36) is connected to a control input (48) of a transistor (50). [4] Pressure measuring cell according to one of the preceding claims, characterized bythat the activation device (36) has a permanent magnet (40) connected to the membrane (14), which is located at least partially within a coil (42). [5] Pressure measuring cell according to one of the preceding claims, characterized by that the activation device (36) comprises a capacitor with a first electrode (54) and a second electrode (56), wherein the first electrode (54) is connected to the membrane (14). [6] Pressure measuring cell according to the preceding claim, characterized by that the first electrode (54) is an electrode directly connected to the membrane (14) and the second electrode (56) is an electrode arranged on the base body (18). [7] Pressure measuring cell according to one of the preceding claims, characterized bythat the activation device (36) has a bolt (44) extending from the membrane (14), and wherein the permanent magnet (40) or the first electrode (54) is arranged at the end of the bolt (44) facing away from the membrane (14). [8] Pressure measuring cell according to the preceding claim, characterized by that the bolt (44) extends through the base body (18). [9] Method for operating a pressure measuring cell (10) according to one of the preceding claims, characterized by that a movement of the membrane (14) induced by a pressure change is converted into an electrical pulse and the electrical pulse is used to activate a measuring electronics (38). [10] Method according to the preceding claim, characterized by that a pressure measurement is carried out following the activation of the measuring electronics (38).

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