Pressure measuring cell with evaluation electronics and 4mA to 20mA interface.

Abstract

The present invention relates to a pressure measuring cell, comprising a pressure sensor and evaluation electronics integrated in the pressure measuring cell, characterized in that the pressure measuring cell is provided with a 4 mA to 20 mA interface dedicated to energy supply.

Description

[Technical field]

[0001] The invention relates to a pressure measuring cell with integrated evaluation electronics and a 4 mA to 20 mA interface for energy supply. [Background technology]

[0002] For example, pressure measuring cells are known in the prior art which detect the change in pressure due to the deformation of a membrane and the change in capacitance this deformation brings about. Pressure measuring cells of this kind are called capacitive pressure measuring cells. Furthermore, there are resistive or piezoresistive pressure measuring cells which detect the deformation of a membrane by means of a strain gauge and determine the pressure by the change in resistance of the strain gauge, as well as piezoelectric pressure measuring cells which determine the pressure using the piezoelectric effect.

[0003] Pressure measuring cells are differentiated by the material used for the process, i.e. the material in contact with the process environment and the process medium, and generally differ between metallic and ceramic, one with a metallic membrane and the other with a ceramic membrane. For technical reasons of production and measurement, the substrate of the pressure measuring cell is often made of the same material as the membrane. For technical reasons of production and measurement, connections between identical or similar materials are often easier to manufacture than connections between different materials. For technical reasons of measurement, it is advantageous to use materials with similar, or ideally identical, thermal expansion coefficients.

[0004] Whether absolute or relative pressure can be measured depends on whether a second pressure, e.g., an external pressure, is applied to the rear side of the membrane, or whether the rear side of the membrane is free.

[0005] The evaluation electronics for the sensor signals from the sensors of the pressure measuring cell are located for the most part outside the housing of the pressure measuring cell and are contacted by plated through holes leading to the outside, which means that the signal path from the sensor to the evaluation electronics is relatively long and the signal-to-noise ratio is not optimal: if the signal-to-noise ratio is too high, the sensor signals will be distorted and the accuracy will be reduced.

[0006] The invention is therefore based on the object of providing a pressure measuring cell in which the measurement settings are optimized, improving the input signal quality at the evaluation part compared to the prior art.

[0007] According to the invention, the above object is achieved by the subject matter and the method having the features of the independent patent claims. Further advantageous and practical embodiments are described in conjunction with the dependent claims.

[0008] It should be noted that the features recited individually in the claims may be combined in any combination that is technically reasonable (e.g., across categories such as method and apparatus) to represent further embodiments of the invention. This specification, particularly in conjunction with the figures, further illustrates and specifies the features of the invention.

[0009] It should also be noted that the conjunction "and / or" as used herein, although it is placed between and connects two features, is always interpreted such that in a first embodiment of the subject matter of the present invention, only the first feature may be present, in a second embodiment, only the second feature may be present, and in a third embodiment, both the first and second features may be present.

[0010] The pressure measuring cell according to the invention comprises a pressure sensor and evaluation electronics integrated in the pressure measuring cell, the pressure measuring cell being provided with a 4 mA to 20 mA interface dedicated to the energy supply.

[0011] Evaluation electronics integrated in the pressure measuring cell is understood to mean that the evaluation electronics is part of the pressure measuring cell and can be arranged, for example, in the housing of the pressure measuring cell. It is also conceivable that the evaluation electronics is arranged inside the housing, in which the pressure sensor is also arranged. However, the evaluation electronics can also be arranged outside the housing, since the signal paths can be kept short as well. A further option is to arrange the evaluation electronics between two housing parts of the pressure measuring cell, for example between a substrate and a closing element or between two separate closing elements. Integrated evaluation electronics is characterized in that the evaluation electronics belongs to the pressure measuring cell and is not accommodated, for example, in a different housing remote from the sensor. Due to the evaluation electronics being integrated in the pressure measuring cell, signal processing takes place in the pressure measuring cell, rather than in a conventional external electronic circuit.

[0012] The evaluation electronics are preferably joined to the pressure measuring cell or its housing by adhesive bonding, however other joining methods are also possible, e.g. glass solder, solder, welding, form-fit bonding, etc.

[0013] The evaluation electronics are arranged in or on the housing of the pressure measuring cell, so that they are in any case close to the sensor, which allows for a very short signal path between the sensor chip and the evaluation electronics. The signal path is, for example, made of bond wires, which may improve the signal-to-noise ratio and, as a result, the signal quality. Due to the short signal path, a faster and more direct reaction rate can also be achieved. Contact with the outside can be made, for example, by through-plated holes extending from the housing of the pressure measuring cell. If the evaluation electronics are arranged directly in the measurement chamber, they are likewise connected to the pressure sensor via bond wires.

[0014] A further advantage of integrated evaluation electronics is that the pressure measuring cell outputs the same signal as the measured value, regardless of the measurement principle, e.g. resistive or capacitive, since the evaluation electronics can already process the output signal of the pressure sensor and output a measured value for pressure.

[0015] The pressure measuring cell is supplied with energy by a current signal of 4 mA to 20 mA via a two-wire cable, and no additional supply line is required other than the two-wire cable. In order to minimize the cost of wiring and installation, and to minimize safety measures when used in, for example, an explosion-proof area, it is not preferable to prepare an additional power cable.

[0016] The transmission of the measured value signal of the pressure measuring cell to, for example, a higher-level unit is performed according to the known 4 mA to 20 mA standard, in which case a 4 mA to 20 mA current loop or a two-wire cable is formed between the pressure measuring cell and the higher-level unit. In addition to the analog transmission of signals, the units connected as described above can send further information to the higher-level unit and receive further information from the higher-level unit according to various other protocols, in particular digital protocols. Examples include the HART protocol and the ProfibusPA protocol.

[0017] Advantageous configurations and variants of the invention emerge from the dependent claims and the following description, in which the features recited individually are in any technically reasonable combination possible and can also be combined with the features recited below, representing further advantageous variants of the design of the invention.

[0018] In one embodiment of the pressure measuring cell, the pressure measuring cell is characterized in that the evaluation electronics is an ASIC. ASIC stands for application-specific integrated circuit. It may be constructed as a stand-alone module and applied or integrated in a displacer. ASIC is a low-energy processor and consumes low power, so that an energy supply of 4 mA to 20 mA is sufficient to operate the pressure measuring cell. For this purpose, leakage currents are prevented and circuit components, such as controllers and memories, are in standby as often as possible.

[0019] The operating voltage of the ASIC is preferably limited to 2.1 V, more preferably 1.6 V, and even more preferably 1.2 V. Limiting the operating voltage of the ASIC conserves energy and minimizes electrical losses. To achieve these specifications, a special 90 nm semiconductor manufacturing process is used to manufacture the ASIC, which allows the circuit to operate at a low voltage.

[0020] The evaluation electronics are arranged to electrically insulate the pressure sensor from electrical terminals of the pressure measurement cell, the electrical terminals being electrical terminals leading to the outside of the pressure measurement cell.

[0021] A further embodiment of the pressure measuring cell is characterized in that the evaluation electronics of the pressure measuring cell comprise a temperature sensor for detecting the temperature of the pressure measuring cell.

[0022] The advantage of placing the evaluation electronics inside the pressure measuring cell is that it is thermally coupled to the pressure measuring cell. Temperature variations can thus be detected by the pressure sensor, which cause material expansion and lead to a change in pressure inside the sensor. The evaluation electronics can therefore perform temperature compensation by means of the measured temperature and output a corrected measured value. Furthermore, the measured temperature allows conclusions to be drawn about process parameters, so that the process itself can be optimized.

[0023] It is likewise conceivable that the evaluation electronics of the pressure measuring cell are set in such a way that the evaluation electronics can calibrate the pressure measuring cell, such that by means of the integrated evaluation electronics the pressure measuring cell or its pressure sensor can be checked and possibly recalibrated by applying a defined pressure and temperature, without the need for further calibration devices.

[0024] A further embodiment of the pressure measuring cell is characterized in that the evaluation electronics are SIL2 certified.

[0025] The SIL standard (Safety Integrity Level) according to safety standard EN61508 defines four clearly distinguished levels which specify the requirements regarding the safety integrity of the safety functions assigned to E / E / PE safety-related systems. Safety integrity level 4 represents the highest safety integrity and safety integrity level 1 represents the lowest.

[0026] Another embodiment of the pressure measuring cell is characterized in that the evaluation electronics has a measurement frequency of at least 1 Hz with an accuracy of at least 19 bits. A low measurement frequency of 1 Hz and a low resolution in the measurement range allow energy savings during the measurement.

[0027] The evaluation electronics preferably have a measurement frequency of at least 1 kHz with an accuracy of at least 12 bits. The higher the measurement frequency and the higher the accuracy, the more energy is required for the pressure measurement cell. For an energy supply of 4 mA to 20 mA, the evaluation electronics are therefore designed in an energy-saving manner in order to enable measurements in the measurement frequency range of 1 kHz with an accuracy of 12 bits without imposing unnecessary constraints on the energy supply.

[0028] When using a metallic pressure measuring cell, it comprises a substrate and a metal membrane arranged on the substrate, with a membrane chamber formed between the membrane and the substrate, and a pressure sensor arranged in a sensor chamber of the substrate, between which a connecting duct is formed, the chamber being filled with a diaphragm sealing medium for transmitting the pressure acting on the membrane. Since the volume of the diaphragm sealing medium should be kept as low as possible, in this type of pressure measuring cell a displacer is arranged in the sensor chamber. In one embodiment of this type of pressure measuring cell, the evaluation electronics are arranged in the displacer.

[0029] The evaluation electronics are arranged on the displacer. The connection between the evaluation electronics and the displacer preferably consists of an adhesive bond. In this case, the adhesive bond is preferably adapted to the largely different thermal expansion coefficients of the displacer and the evaluation electronics. Most preferably, an adhesive layer compensates for the length differences occurring in this case, withstands the shear forces occurring and ensures a robust fastening. Alternatively, the evaluation electronics can be applied directly to the displacer in the form of a conductive track. Pressure measuring cells with displacers functionalized in this way have a particularly small installation space.

[0030] The evaluation electronics can thus be attached to the displacer near the sensor chip. The evaluation electronics is thus located close to the sensor and the signal path between the sensor chip and the evaluation electronics is very short. The signal path is for example constructed using bond wires, which improves the signal quality by improving the signal-to-noise ratio. The shorter signal path also results in a faster response time. The contact with the outside world can be made for example by contacts passing through the displacer and the closing element and electrically connected to the evaluation electronics by bond wires on the upper side of the displacer.

[0031] The pressure measuring cell can be set up to operate according to a capacitive or resistive measuring principle.

[0032] A capacitive pressure measuring cell has two electrodes which together form an electric capacitor, one of the electrodes being arranged on the membrane. A change in pressure acting on the membrane changes the distance between the electrodes and thus the capacitance of the capacitor. The capacitance of the capacitor is detected by the evaluation electronics and the pressure can be derived from the capacitance.

[0033] In resistive pressure measuring cells, for example, a strain gauge is used on the membrane, the resistance of which changes when pressure acting on the membrane deforms it. It is also possible to use piezoresistive pressure sensors, which also change their resistance when deformed under the influence of pressure.

[0034] The placement of the evaluation electronics in the pressure measurement cell exposes it to process temperatures depending on the application, and therefore in one embodiment the operating temperature of the pressure measurement cell is set to up to 150°C.

[0035] In one embodiment, the operating temperature of the pressure measuring cell is preferably set to up to 200°C.

[0036] Electronic circuits are often sensitive to high temperatures, so that the pressure measuring cell with the evaluation electronics is constructed to operate normally even at operating temperatures of, for example, 150° C. or 200° C., since the temperature acting directly on the evaluation electronics is compensated for and a corrected measured value is output.

[0037] In another embodiment, the pressure measuring cell is a pressure measuring cell measuring absolute pressure, i.e. the pressure measurement is performed with respect to a vacuum reference level.

[0038] Alternatively, the pressure measuring cell may be designed to measure relative pressure, in which case pressure can be applied not only to the side of the membrane of the pressure sensor facing the process, but also to the underside of the membrane, for example the underside of the membrane is exposed to ambient pressure and a pressure relative to said ambient pressure can be measured. In this case the pressure measuring cell may have a closing element with a through opening for pressure compensation and a constant pressure can be applied to the backside of the membrane.

[0039] The method for producing a pressure measuring cell with evaluation electronics integrated in the pressure measuring cell according to the invention is characterized in that the pressure measuring cell is supplied with energy by an interface of 4 mA to 20 mA.

[0040] Further practical embodiments are explained below with reference to the drawings. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 shows the evaluation electronics integrated on a displacer and a metallic pressure measuring cell with a two-wire energy supply according to the 4 mA to 20 mA standard. [Diagram 2] FIG. 2 shows a metallic pressure measuring cell with evaluation electronics integrated in the closure element of the pressure measuring cell. [Diagram 3] FIG. 3 shows a metallic pressure measuring cell with evaluation electronics integrated outside the pressure measuring cell. [Figure 4] FIG. 4 shows a metallic pressure measuring cell with evaluation electronics integrated in a recess in the base of the pressure measuring cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] In the figures, unless otherwise specified, identical components or components having the same function and corresponding to each other are provided with the same reference numerals.

[0043] 1 shows a cross-sectional view of an exemplary embodiment of a pressure measuring cell 1 according to the present application with integrated evaluation electronics 62 and a two-wire energy supply. The pressure measuring cell 1 shown is a metallic pressure measuring cell 1 for measuring relative pressure, which in this design has a pressure compensation opening 72.

[0044] The pressure measuring cell 1 basically has a single substrate 3 , a metal film 5 arranged on the front side of the substrate 3 in the axial direction A, and a pressure sensor 7 arranged in a sensor chamber 71 formed in the substrate 3 .

[0045] The sensor chamber 71 is fluidly coupled via a communication channel 9 to a membrane chamber 51 disposed between the substrate 3 and the membrane 5 .

[0046] The sensor chamber 71 is closed towards the rear by a closure element 80. The closure element 80 has a through-plated hole 79 for a 4 mA to 20 mA energy supply. The evaluation electronics 62 are in contact with the outside via the through-plated hole 79.

[0047] The pressure sensor 7 is arranged in the sensor chamber 71. The pressure sensor 7 has a sensor chip 73 as a pressure-sensitive element, which is arranged in the closure element 80 by means of a sensor carrier 75. The sensor chip 73 is connected to the evaluation electronics 62 by means of an electrical connection 63 configured as a bond wire.

[0048] Ambient or reference pressure is applied to the rear part of the membrane of the sensor chip 73 via a pressure compensation line 72 which passes through a closure element 80 and leads to the rear side of the sensor chip 73. The reference pressure can be a vacuum so that absolute pressure measurements are possible.

[0049] In the exemplary embodiment shown in Fig. 1, the closure element 80 further comprises a filling opening 11 in which a pipe section is arranged, by means of which a diaphragm sealing medium 13, for example a synthetic oil, can be filled into the sensor chamber 71, the communication channel 9 and the membrane chamber 51. For the sake of clarity, the diaphragm sealing medium 13 has not yet been provided in Fig. 1.

[0050] The membrane 5 in this embodiment of the exemplary embodiment is joined to the substrate 3 by a perimeter joint 57, in this case a weld. The membrane 5 in such a cross-section has a wavy surface contour designed to correspond to the surface contour of the wall of the substrate 3 facing the membrane 5. This wavy surface contour 55 makes the membrane 5 flexible in the axial direction A, while having maximum stiffness in the radial direction R.

[0051] The surface contour 55 of the membrane 5 is transferred from the substrate 3 to the membrane 5 during the manufacture of the pressure measuring cell 1. Thus, after the membrane 5 has been fixed to the substrate 3, it is subjected to an overpressure from the front and moulds to the membrane bed formed by the substrate 3.

[0052] The displacer 61 is disposed within the sensor chamber 71 and occupies a substantial portion of the sensor chamber 71 that is to be filled with the diaphragm sealing medium 13. In this way, the volume of the mainly flat area that is filled with the diaphragm sealing medium 13 is reduced. In this exemplary embodiment, the displacer 61 is substantially rotationally symmetrical, but may deviate from this, for example, due to recesses for providing for filling of the sensor chamber 71 via the filling opening 11.

[0053] The evaluation electronics 62 are arranged on the displacer 61. The evaluation electronics can be surface mounted by adhesive bonding. The evaluation electronics 62 are arranged in direct proximity to the sensor chip 73 and are connected by bond wires 63. The bond wires 63 are very short compared to external connections such as through-plated holes 79, which results in a low signal-to-noise ratio, which is particularly advantageous for the signal quality of the sensor chip. Furthermore, the evaluation electronics 62 consists of a temperature chip which detects the actual temperature of the diaphragm sealing medium 13, thus allowing a temperature compensation of the output pressure measurement signal.

[0054] Energy is supplied to the pressure measuring cell 1 or the evaluation electronics 62 by a current signal of 4 mA to 20 mA via a two-wire cable 81, and no additional supply lines are required other than the two-wire cable 81. At the same time, measurement value signals are transmitted from the pressure measuring cell 1 to the upper unit via the two-wire cable 81. The pressure measuring cell 1 and the upper unit are connected by the two-wire cable 81.

[0055] 2 shows a metallic pressure measuring cell 1 similar to FIG. 1, but in which the evaluation electronics 62 are integrated into a closure element 80 of the pressure measuring cell 1. For this purpose, the closure element 80 is designed in two parts and forms a cavity for accommodating the evaluation electronics 62.

[0056] The evaluation electronics 62 are electrically connected by plated through holes 79. Contact to the sensor chip 73 is made by bond wires 63 connected to plated through holes 79 on the top side of the displacer 61. The evaluation electronics 62 are in contact with the outside world by a two-wire energy supply. The evaluation electronics 62 are connected via a two-wire cable 81 as in FIG. 1.

[0057] 3 shows a metallic pressure measuring cell 1 similar to FIG. 1, but with the evaluation electronics 62 integrated on the outside of the pressure measuring cell 1. The evaluation electronics 62 is mounted from the outside on a closure element 80 and is electrically connected to the sensor chip 73 therein by means of plated-through holes 79 and bond wires 63. The evaluation electronics 62 itself is supplied with energy by a two-wire cable 81.

[0058] Figure 4 is similar to figure 1, but shows a metallic pressure measuring cell 1 in which the evaluation electronics 62 are integrated into a recess in the substrate 3 of the pressure measuring cell 1. The recess is in the substrate 3 of the pressure sensor 1, in which the evaluation electronics 62 are fixed by adhesive bonding.

[0059] The two-wire energy supply is connected to the evaluation electronics 62 by plated through holes 79 or a two-wire cable 81. The evaluation electronics 62 is then connected to the sensor chip 73 by bond wires 63. [Explanation of symbols]

[0060] 1 Pressure measuring cell 3 Base 5 membrane 7 Pressure Sensor 9 Connecting Channels 11 Filling opening 13 Diaphragm sealing medium 51 Membrane Chamber 55 Surface Contour 57 Joint 61 Displacer 62 Evaluation Electronics 63 Bond Wire 71 Sensor Chamber 72 Pressure Compensation 73 Sensor Chip 75 Sensor carrier 79 Plated Through Holes 80 Closure elements 81 Two-wire cable A axis direction R Radial direction

Claims

1. A pressure measuring cell (1) having a pressure sensor (7) and evaluation electronics (62) integrated into the pressure measuring cell (1), The pressure measuring cell is provided with an interface of 4 mA to 20 mA dedicated to energy supply. Pressure measuring cell (1).

2. In the pressure measuring cell (1) according to claim 1, The evaluation electronic device (62) is an ASIC. Pressure measuring cell (1).

3. In the pressure measuring cell (1) according to claim 1, The evaluation electronics (62) preferably comprises a temperature sensor for detecting the temperature of the diaphragm sealing medium (13). Pressure measuring cell (1).

4. In the pressure measuring cell (1) according to claim 1, the evaluation electronics (62) are configured so that the evaluation electronics (62) can calibrate the pressure measuring cell (1). Pressure measuring cell (1).

5. In the pressure measuring cell (1) according to claim 1, The evaluation electronics (62) is SIL2 certified. Pressure measuring cell (1).

6. In the pressure measuring cell (1) according to claim 1, The evaluation electronics (62) have a measurement frequency of at least 1 Hz with an accuracy of at least 19 bits, preferably the evaluation electronics (62) have a measurement frequency of at least 1000 Hz with an accuracy of at least 12 bits. Pressure measuring cell (1).

7. The pressure measuring cell (1) according to claim 1, The pressure measuring cell (1) is provided with a displacer (61) in which the evaluation electronic device (62) is arranged. Pressure measuring cell (1).

8. In the pressure measuring cell (1) according to claim 1, the pressure measuring cell (1) is configured to operate according to a capacitive or resistive measuring principle; Pressure measuring cell (1).

9. In the pressure measuring cell (1) according to claim 1, The operating temperature of the pressure measuring cell (1) is set to 150°C, preferably 200°C. Pressure measuring cell (1).

10. The pressure measuring cell (1) according to claim 1, The pressure measuring cell (1) is a pressure measuring cell (1) that measures absolute pressure. Pressure measuring cell (1).

11. The pressure measuring cell (1) according to any one of claims 1 to 9, The pressure measuring cell (1) is a pressure measuring cell (1) that measures relative pressure. Pressure measuring cell (1).

12. A method for manufacturing a pressure measuring cell (1) comprising a membrane (5) and a pressure sensor (7) filled with a diaphragm sealing medium (13) that transmits the pressure acting on the membrane (5) to the pressure sensor (7), wherein evaluation electronics (62) are integrated into the pressure measuring cell (1), The pressure measuring cell (1) is powered by a 4mA to 20mA interface. A method for manufacturing a pressure measuring cell (1).

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