Method and device for evaluating the measurement signals from a capacitive pressure measurement cell

Abstract

The invention relates to a method for determining the measuring capacitance (Cp) of a capacitive pressure measurement cell (1) that determines the pressure of a process medium within a specified pressure measurement range, wherein: an AC voltage signal is applied to a passive electronic filter (16) formed with the measuring capacitance (Cp) of the capacitive pressure measurement cell (1); the voltage of the input signal (Uref) on the input side upstream of the passive electronic filter (16) is ascertained and the voltage of the output signal (Umeas) on the output side downstream of the electronic passive filter (16) is ascertained; and the measuring capacitance (Cp) of the pressure measurement cell (1) is ascertained on the basis of at least one of the characteristics of the output signal (Umeas) with regard to the input signal (Uref).

Description

[0001] Method and device for evaluating the measuring signals of a capacitive pressure measuring cell

[0002] The invention relates to a method and a device for evaluating the measurement signals of a pressure measuring cell, in particular a capacitive pressure measuring cell.

[0003] Capacitive pressure sensors are used to measure the pressure of a medium in industrial measurement and automation technology. They can be designed as absolute pressure sensors, gauge pressure sensors, or differential pressure sensors. Ceramic pressure sensors, in which at least the measuring diaphragm is made of ceramic, have the advantage of being placed in direct contact with the medium due to their excellent chemical and mechanical properties. This eliminates the need for a diaphragm seal, which is required for metal measuring diaphragms and in which the pressure to be measured is transferred to the measuring diaphragm via an incompressible fluid. Ceramic pressure sensors are developed, offered, and distributed by the Endress+Hauser Group.

[0004] DE 102015105057 A1 discloses a pressure sensor with a ceramic measuring diaphragm. The outer edge of the measuring diaphragm is connected to the outer edge of a face of the pressure sensor body facing the measuring diaphragm via an active brazing joint, forming a pressure chamber. Under the influence of pressure, a pressure-dependent deformation of the measuring diaphragm occurs. The pressure-dependent deflection of the ceramic measuring diaphragm is recorded by an electromechanical transducer.

[0005] For this purpose, a membrane electrode is arranged on the side of the measuring diaphragm facing the base body, and a base body electrode is arranged on the end face of the base body facing the measuring diaphragm. Both electrodes form a plate capacitor. A capacitive measurement signal is evaluated to determine the pressure. The membrane electrode and the base body electrode are preferably made of semiconducting, doped tantalum oxide, especially semiconducting, doped tantalum pentoxide.

[0006] A special ASIC design is preferred for pressure measurement. The charge of an internal reference capacitance in the ASIC is transferred to the measurement capacitance provided by the pressure measuring cell. This results in a voltage that corresponds to the ratio of the measurement capacitance to the reference capacitance—the process is similar to a switched-capacitor method. The resulting voltage is digitized using a high-precision ADC in the ASIC and then evaluated. A disadvantage of this conventional solution is that the ADC is very complex to implement. Furthermore, the voltage or amplitude measurement is sometimes susceptible to external interference.

[0007] The invention is based on the object of proposing a method for evaluating the measurement signals of a pressure measuring cell, in particular a ceramic pressure measuring cell, as well as a corresponding device for carrying out the method, wherein the method and device are characterized by a high level of security against external interference.

[0008] The problem is solved with regard to the method for determining the measuring capacitance of a pressure measuring cell, in particular a capacitive pressure measuring cell which determines the pressure of a process medium within a predetermined pressure measuring range, by the following features: a passive electronic filter, formed with the measuring capacitance of the pressure measuring cell, is subjected to an alternating voltage signal; the voltage of the input signal is determined on the input side before the passive electronic filter and the voltage of the output signal is determined on the output side after the passive electronic filter; the measuring capacitance of the pressure measuring cell is then determined based on at least one of the characteristics of the output signal with respect to the input signal.

[0009] The advantages of the solution according to the invention compared to known solutions consist in particular in a reduction in complexity and increased fault tolerance.

[0010] Preferably—but by no means exclusively—the frequency of the input signal is in the range of 1 kHz to 4 MHz. The input signal provided by the function generator is preferably a sine signal.

[0011] According to a further development of the method according to the invention, a first-order low-pass filter is used as the passive electronic filter, which is formed from the measuring capacitance of the pressure measuring cell and a known resistance. The phase shift and / or the amplitude of the input signal and output signal are used as the characteristic of the passive electronic filter.

[0012] In one embodiment, the passive electronic filter, in particular the first-order low-pass filter, is designed such that the output signal within the specified pressure measurement range has a frequency that lies in the frequency range in which the phase shift of the output signal is frequency-dependent. Additionally or alternatively, the passive electronic filter, in particular the first-order low-pass filter, is designed such that the output signal within the specified pressure measurement range has a frequency that lies in the frequency range in which the amplitude of the output signal exhibits a clear frequency dependence.

[0013] It is considered to be further developing and advantageous in connection with the invention if the known method of quadrature demodulation is used to determine the phase shift between the two measurement signals and / or an amplitude change of the output signal with respect to the input signal.

[0014] Quadrature demodulation is a modulation method known from the prior art in which amplitude and phase modulation are combined. Both analog and digital methods based on quadrature demodulation are used, with digital quadrature demodulation being used in conjunction with the solution according to the invention. Two measurement signals are required to detect the phase, with the first measurement signal having a phase shift of +90°. The second measurement signal has a phase shift of 0° compared to the first measurement signal. Many possibilities for generating the two measurement signals have become known from the prior art. For example, a table in a memory with a 16-point cosine signal is used as the measurement signal. To generate a sine signal, simply read from the 4th position with modulo 16. The measurement signal is then sampled at 16 times the frequency.

[0015] The quadrature demodulation method, also called the I&Q method (In-Phase & Quadrature method), is a way to obtain and evaluate both amplitude and phase information. For this purpose, the two measurement signals are each split into two paths: one demodulation path is performed with the original phase position (in-phase) and produces the so-called I data; the second path is performed with a reference frequency phase-shifted by 90° and produces the Q data (quadrature). I and Q are then calculated using an angular function. Using quadrature demodulation, the susceptibility to interference (external interference) of the inventive method for determining the measurement capacitance can be significantly reduced. The reason for this is that in quadrature demodulation only one spectral component is evaluated. The other spectral components are not considered.This indirectly filters out or ignores all interference that is not in the spectral component under consideration. Only the interference that is precisely in this one spectral component remains, which significantly reduces the interference. Furthermore, in connection with the invention, a bandpass filter is used instead of a 1st order low-pass filter. In this case, the measuring capacitance - and thus the influence of the pressure of the medium on the measuring diaphragm of the pressure measuring cell - is determined via the resonance frequency of the bandpass filter. The oscillating circuit consists successively of the measuring capacitance and the reference capacitance, a known electrical resistance and the known inductance of a coil. In contrast to the 1st order low-pass filter, there is a larger phase shift of a maximum of 180°. The phase shift and, if applicable, the amplitude change are determined as before using a preferably digital IQ demodulation.

[0016] An interesting embodiment of the method according to the invention proposes that the passive electronic filter be subjected to alternating voltage signals that have successive, discrete frequencies. Thus, the passive electronic filter is subjected to a frequency sweep, or frequency search, and the frequency at which the amplitude or phase shift undergoes the optimal change in the current measurement situation is determined based on the frequency sweep.

[0017] Furthermore, it is advantageous not to determine the pressure based on a single value of the measuring capacitance, but to evaluate several output signals successively and determine the measuring capacitance or the pressure of the medium using a mathematical combination, e.g., averaging. In this context, it should be considered to determine the measuring capacitance of the capacitive pressure measuring cell by averaging the capacitance values ​​measured at successive (sweep) different, discrete frequencies.

[0018] When describing the state-of-the-art of a ceramic pressure sensor, it was already mentioned that these typically provide two output signals: a measured value for the measuring capacitance and a measured value for the reference capacitance. The advantage of this solution is that common-mode interference affecting both capacitance values ​​simultaneously can be easily eliminated by calculating the difference.

[0019] In connection with the invention, it is considered advantageous when providing a measurement signal and a reference signal from the pressure measuring cell if the input signals and the output signals are evaluated in parallel in an evaluation cycle. It goes without saying that the signals can also be evaluated sequentially, i.e. one after the other. One embodiment of a device for determining the pressure within a predetermined pressure measuring range via the measurement capacitance and optionally the reference capacitance of a capacitive pressure measuring cell, which is suitable for carrying out the method according to the invention, has the following components: a passive electronic filter which uses the measurement capacitance orif present - the reference capacitance of the pressure measuring cell is formed, a function generator which generates alternating voltage signals, preferably sinusoidal signals, with at least one predetermined frequency and makes the alternating voltage signals available as input signals to the passive electronic filter, at least one analog-digital converter which digitizes corresponding input signals and output signals of the passive electronic filter, a control-evaluation unit which serves to determine the pressure of the medium on the basis of the measuring capacitance and, if applicable, the reference capacitance of the capacitive pressure measuring cell.

[0020] For example, the frequency of the AC signal is in the range of 1 kHz to 4 MHz. An optimal frequency for the AC signal is preferably determined using a frequency sweep.

[0021] Measuring the phase response of a first-order low-pass or bandpass filter to determine the measurement capacitance and, if applicable, the reference capacitance has the advantage that a time measurement replaces the voltage measurement, thus providing temporal resolution instead of amplitude resolution. The accuracy of the two analog-to-digital converters is therefore less important, and more cost-effective analog-to-digital converters with lower resolution can be used. Furthermore, the phase measurement is less susceptible to interference than an amplitude measurement if quadrature demodulation is used for phase determination.

[0022] As already described above, the passive electronic filter is either a first-order low-pass or a band-pass filter. In both cases, the phase shift and / or the amplitude change between the input and output signals is preferably determined using quadrature demodulation.

[0023] The evaluation of the measurement and reference signals from a suitably designed ceramic pressure measuring cell is carried out via a circuit arrangement that determines the measurement and reference capacitances either in parallel, i.e. simultaneously, or alternately, i.e. sequentially. In the case of parallel determination of the measurement and reference capacitances, the circuit consists of two first-order low-pass filters that share the same function generator and the same reference potential (reference ground). The circuit design corresponds to a so-called bridge circuit. Here, the voltage is not measured relative to ground (single-ended), but rather between the two bridge branches. Thus, a differential voltage is measured, which in the bridge circuit is referred to as the bridge voltage.By measuring the difference between the voltages across the two capacitors (measuring capacitor and reference capacitor), common-mode interference, i.e. interference that affects both capacitances equally, can be eliminated.

[0024] If only a 1st order low-pass filter is used, the measurement capacitance and reference capacitance are determined sequentially.

[0025] The invention is explained in more detail with reference to the following figures. They show:

[0026] Fig. 1 : a schematic representation of an apparatus for carrying out the method according to the invention,

[0027] Fig. 2a: a first embodiment of a circuit suitable for carrying out the method according to the invention,

[0028] Fig. 2b: a second embodiment of a circuit suitable for carrying out the method according to the invention

[0029] Fig. 2c: a third embodiment of a circuit suitable for carrying out the method according to the invention

[0030] Fig. 3: a schematic representation of the functional dependence of the amplitude of an alternating voltage signal on the frequency when passing through a first-order low-pass filter,

[0031] Fig. 4: a schematic representation of the functional dependence of the phase shift of an AC signal on the frequency when passing through a first-order low-pass filter,

[0032] Fig. 5: a schematic representation of the functional dependence of the amplitude of an alternating voltage signal on the frequency when passing through a bandpass filter, Fig. 6: a schematic representation of the functional dependence of the phase of an alternating voltage signal on the frequency when passing through a bandpass filter,

[0033] The ceramic pressure measuring cell 1 shown in Fig. 1 comprises a base body 3, on whose surface facing the process medium a circular disk-shaped measuring diaphragm 2, made of aluminum oxide, for example, is arranged. The base body 3 and the measuring diaphragm 2 are preferably joined together using an active brazing alloy 4 in a vacuum process. The distance between the measuring diaphragm 2 and the base body 3 is adjusted by the material thickness of the active brazing alloy 4.

[0034] Between the measuring membrane 2 and the base body 3, a reference pressure chamber 5 is formed by the pressure-tight connection by means of the joint 4, which in the illustrated reference pressure measuring cell can be pressurized with atmospheric pressure or with a reference pressure via a supply channel 6 - a bore in the base body 3.

[0035] In the case of an absolute pressure sensor, the reference pressure chamber 5 would be evacuated, the through-hole would be missing or would be pressure-tight.

[0036] The surface of the measuring diaphragm 2 facing the base body 3 has a metallic electrode 7, which is electrically connected to the active brazing alloy of the joint 4. Opposite, on the base body 3, there is an electrode arrangement comprising a second centrally arranged circular electrode 8a and an insulated annular electrode 8b surrounding the central electrode. The three electrodes 7, 8a, 8b are contacted via metallic pins, e.g., tantalum pins 10, 11, 12, which are fixed and sealed by means of an active brazing alloy in through-holes extending from the rear of the base body 3 into the interior of the pressure measuring cell 1. The electrodes 7, 8a, 8b are electrically connected to an evaluation circuit 13.In order to increase the capacitances Cp, Cr between the first electrode 7 and the counter electrodes 8a, 8b, a carrier layer 9, e.g. made of glass, is applied between the surface of the base body 3 facing the measuring membrane and the electrodes 8a, 8b.

[0037] Since the pressure-dependent deformation of the measuring diaphragm 2 is greater in its central region than in its peripheral region, the measuring capacitance Cp between the second electrode 8a and the first electrode 7 exhibits a greater pressure dependence than the reference capacitance Cr between the third electrode 8b and the first electrode 7. By comparing the capacitances Cp and Cr, the temperature-related cross-sensitivity of the pressure measuring cell can be minimized. Furthermore, common-mode interference, which affects both capacitances equally, can be eliminated. Fig. 2a shows a first embodiment of a circuit suitable for implementing the method according to the invention. The components for generating the input signals and for evaluating the input signals Uref and output signals Umeas are preferably arranged on an electronic chip 13.Essential components of the electronic chip 13 are: a function generator 14, which generates alternating voltage signals, preferably sinusoidal signals, of a desired frequency, two analog-to-digital converters ADC1, ADC2, which transform the analog input signals Uref and the analog output signals Umeas of the 1st order low-pass filter 17 into digital signals, and a microprocessor 15. Instead of the two analog-to-digital converters ADC1, ADC2, an analog-to-digital converter ADC with an upstream switch or a multiplexer can also be used. The function generator 14 generates input signals Uref with at least one predetermined frequency. This can be determined, for example, via a frequency search. Preferably - but by no means exclusively - the frequency of the input signal Uref is in the range from 1 kHz to 4 MHz. The input signals Uref are applied to the input of a 1st order low-pass filter 17. The 1st order low-pass filterOrder 17 has a given resistance R and as capacitance the measuring capacitance Cp and Z or - if present - the reference capacitance Cr of the pressure measuring cell 1.

[0038] The input signal Uref is fed to the low-pass filter 17. The input signal Uref is branched off before the 1st order low-pass filter 17, fed to the first analog-to-digital converter ADC1 and digitized. At the output of the 1st order low-pass filter 17, the corresponding output signal Umeas is tapped and fed to the second analog-to-digital converter ADC2 and also digitized. The digitized input signal Uref and the corresponding digitized output signal Umeas are transmitted to the microprocessor 15 for further processing. In particular, the microprocessor 15 determines the measuring capacitance Cp of the pressure measuring cell 1 based on a comparison of at least one of the characteristics of the input signal Uref and the output signal Umeas. Typically, the reference capacitance Cr of the pressure measuring cell 1 is also taken into account for the evaluation for the reasons already mentioned.Depending on the evaluation method, the parameters are the phase shift and / or the amplitude change of the input signal Uref and the output signal Umeas. Quadrature demodulation is preferably used in conjunction with the invention.

[0039] Depending on the embodiment of the invention, the function generator 14—as already mentioned—generates input signals Uref with successive discrete frequencies, a so-called frequency sweep or a frequency search. A frequency sweep can be used to find the frequency at which the evaluation, under the given measurement conditions, can access an optimal phase shift and / or optimal amplitude change between the input signal Uref and the output signal Umeas. Using the optimal frequency found via the frequency sweep, the function generator 14 subsequently generates the input signal Uref. In the circuit shown in Fig. 2a, the measuring capacitance Cp and the reference capacitance Cr for the evaluation of the medium pressure are each determined sequentially, i.e., one after the other.

[0040] Fig. 3 shows a schematic representation of the functional dependence of the amplitude of an AC signal on the frequency when passing through a 1st order low-pass filter (amplitude response): In the lower frequency range, the amplitude A shows no dependence on the frequency f (the frequencies are passed through unattenuated), whereas in a given middle frequency range it exhibits a clear frequency dependence in the double-logarithmic representation shown here. Higher frequencies are blocked. In order to achieve a measuring effect, the frequency of the input signal Uref must be selected such that the amplitude A changes as a function of the measuring capacitance Cp. In principle, the frequency dependence of AC signals through a 1st order low-pass filter is well known from the state of the art.

[0041] The same applies to the phase response of an alternating voltage signal Uref passing through a first-order low-pass filter. This is shown schematically in Fig. 4. The phase scale is semilog.

[0042] Fig. 2b shows a second embodiment of a circuit suitable for implementing the method according to the invention. The structure of the electronic chip 13 is the same as in Fig. 2a. Instead of a first-order low-pass filter, this embodiment uses an RLC bandpass filter 18, which is composed of a predetermined resistance R, the respective measuring capacitance Cp or the respective reference capacitance Cr, and the predetermined inductance L of a coil. In the embodiment shown, the measuring capacitance Cp and the reference capacitance Cr for evaluating the pressure of the medium are each determined sequentially, i.e., one after the other. In principle, all types of bandpass filters can be used in conjunction with the invention. In Fig. 2b, an RLC parallel bandpass filter is integrated into the circuit. It is also possible to use two RC filters for the bandpass filter: a high-pass and a low-pass. Suitable circuits are known to those with specialist qualifications.

[0043] In the illustrated embodiment, the measurement capacitance Cp and reference capacitance Cr are determined via the phase shift of the resonant frequency fres. While a maximum phase shift of 90° occurs between the input signal Uref and the output signal Umeas when using a first-order low-pass filter, a stronger phase shift of a maximum of 180° occurs with the bandpass filter 19. As in the previously mentioned embodiment with a first-order low-pass filter 17, the phase shift is detected via digital quadrature demodulation, which is performed in the microprocessor 15.

[0044] Fig. 5 shows a schematic representation of the functional dependence of the amplitude A of an alternating voltage signal on the frequency f when passing through a bandpass filter 19. Fig. 6 shows a schematic representation of the functional dependence of the phase of an alternating voltage signal on the frequency f when passing through a bandpass filter 19.

[0045] Fig. 2c shows a third embodiment of a circuit suitable for implementing the method according to the invention. The circuit is comparable to the circuit shown in Fig. 2a, except that here the measuring capacitance Cp and the reference capacitance Cr of the pressure measuring cell 1 are not determined sequentially and thus offset in time, but simultaneously or in parallel. For this purpose, two first-order low-pass filters 17a, 17b are formed, which are simultaneously or in parallel supplied with the input signal Uref provided by the function generator 14.

[0046] The first 1st order low-pass filter 17a comprises a predetermined resistor R1 and the capacitor with the current measuring capacitance Cp of the pressure measuring cell; the second 1st order low-pass filter 17b comprises the predetermined resistor R2 and the capacitor with the current reference capacitance Cr of the pressure measuring cell 1. The two low-pass filters 17a, 17b share not only the function generator 14, but also the reference potential or the reference ground; the two low-pass filters 17a, 17b are components of a so-called bridge circuit. The output voltage Umeas is not measured with respect to ground potential (single-ended) here, but with respect to the ground between the two bridge branches, which is why it is also referred to as a bridge voltage in this context. It is therefore a differential measurement.The bridge voltage results from the difference between the voltages across both capacitors with capacitances Cp and Cr, which in turn has the advantage of automatically eliminating common-mode interference. List of reference symbols.

[0047] 1 pressure measuring cell

[0048] 2 measuring membrane

[0049] 3 basic bodies

[0050] 4 joint

[0051] 5 Reference pressure chamber

[0052] 6 Feed channel for reference pressure

[0053] 7 Electrode on measuring membrane

[0054] 8a, 8b Electrode on base body

[0055] 9 Carrier layer

[0056] 10 Electrode

[0057] 11 Electrode

[0058] 12 Electrode

[0059] 13 Evaluation unit

[0060] 14 Function generator

[0061] 15 microprocessor

[0062] 16 electronic, passive filter

[0063] 17 low-pass filter

[0064] 17a first low pass

[0065] 17b second low pass

[0066] 18 bandpass

[0067] 19 Bridge circuit

[0068] 20 Reference potential

[0069] Cp measuring capacity

[0070] Cr reference capacity

[0071] Uref input signal

[0072] Umea's output signal

[0073] R electrical resistance

[0074] R1 electrical resistance

[0075] R2 electrical resistance

[0076] L Inductance

[0077] Umea's measuring voltage

[0078] Uref reference voltage

[0079] ADC1 Analog-ZDigital Converter

[0080] ADC2 Analog-ZDigital Converter

Claims

Patent claims 1 . Method for determining the measuring capacitance (Cp) of a capacitive pressure measuring cell (1) which determines the pressure of a process medium within a predetermined pressure measuring range, wherein a passive electronic filter (16), formed with the measuring capacitance (Cp) of the capacitive pressure measuring cell (1), is subjected to an alternating voltage signal, wherein the voltage of the input signal (Uref) is determined on the input side before the passive electronic filter (16) and the voltage of the output signal (Umeas) is determined on the output side after the electronic, passive filter (16), and wherein the measuring capacitance (Cp) of the pressure measuring cell (1) is determined on the basis of at least one of the characteristics of the output signal (Umeas) with respect to the input signal (Uref).

2. Method according to claim 1, wherein the phase shift and / or the amplitude of the input signal (Uref) and the output signal (Umeas) is used as the characteristic of the passive electronic filter (16).

3. Method according to claim 1 or 2, wherein a first-order low-pass filter (17) is used as the passive electronic filter (16), which is designed such that the output signal (Umeas) has a frequency within the predetermined pressure measuring range which lies in the frequency range in which the phase shift of the output signal (Umeas) is frequency-dependent.

4. Method according to claim 1, 2 or 3, wherein a first-order low-pass filter (17) is used as the passive electronic filter (16), which is designed such that the output signal (Umeas) has a frequency within the predetermined pressure measuring range which lies in the frequency range in which the amplitude of the output signal (Umeas) is frequency-dependent.

5. Method according to one or more of claims 1-4, wherein quadrature demodulation is used to determine the phase shift between the output signal (Umeas) and the input signal (Uref) and / or an amplitude change of the output signal (Umeas) with respect to the input signal (Uref).

6. Method according to claim 1 or 2, wherein a bandpass filter (18) is used as the passive electronic filter (16) and wherein the measuring capacitance (Cp) is determined via the resonance frequency of the bandpass filter (18).

7. Method according to one or more of the preceding claims, wherein the passive electronic filter (16) is supplied with alternating voltage signals (Uref) which have successively different, discrete frequencies (sweep).

8. The method according to claim 7, wherein the measuring capacitance (Cp) of the capacitive pressure measuring cell (1) is determined by averaging the capacitance values ​​determined at the successively different, discrete frequencies.

9. Method according to one or more of the preceding claims, wherein, in the event that the pressure measuring cell (1) provides at least two output signals (Umeasl, Umeas2) for determining the measuring capacitance (Cp) and a reference capacitance (Cr) of the pressure measuring cell (1), the output signals (Umeasl, Umeas2) are serially evaluated in an evaluation cycle.

10. Method according to one or more of the preceding claims, wherein, in the event that the pressure measuring cell (1) provides at least two output signals (Umeasl, Umeas2) for determining the measuring capacitance (Cp) and a reference capacitance (Cr) of the pressure measuring cell (1), the output signals (Umeasl, Umeas2) are evaluated in parallel in an evaluation cycle.

11. Device for determining the pressure within a predetermined pressure measuring range via the measuring capacitance (Cp) of a capacitive pressure measuring cell (1), wherein a passive electronic filter (16) is provided which is formed using the measuring capacitance (Cp) of the pressure measuring cell (1), wherein a function generator (14) is provided which generates alternating voltage signals (Uref) of at least one predetermined frequency and makes the alternating voltage signals available as input signals (Uref) to the passive electronic filter (16), wherein at least one analog-to-digital converter (ADC) is provided which digitizes corresponding input signals (Uref) and output signals (Umeas) of the low-pass filter (16), and wherein a control / evaluation unit (13) is provided which uses a method as described in one or more of claims 1-10 to determine the measuring capacitance of the capacitive pressure measuring cell (1).

12. Device according to claim 11, wherein the frequency of the input signal or input signals (Uref) is preferably in the range from 1 kHz to 4 MHz.

13. Device according to claim 11 or 12, wherein the passive electronic filter (16) is a 1st order low-pass filter (17) or a band-pass filter (18).

14. Device according to one or more of claims 11-13, wherein the pressure measuring cell (1) is designed to provide two capacitance values ​​(Cp, Cr) for determining the pressure: a measuring capacitance (Cp) and a reference capacitance (Cr).

15. Device according to claim 14, wherein a circuit arrangement (19) for determining the measuring capacitance (Cp) and the reference capacitance (Cr) consists of a bridge circuit (20) consisting of a first 1st order low-pass filter (17a), which comprises the measuring capacitance (Cp) as a measuring capacitor, and a second 1st order low-pass filter (17b), which comprises the reference capacitance (Cr) as a reference capacitor, wherein the first low-pass filter (17a) and the second low-pass filter (17b) use the same reference potential and are each supplied with an AC voltage signal (Uref) by the function generator (14) simultaneously.

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