DE102019133808A1 - Pressure sensor for determining a differential or relative pressure variable - Google Patents

Abstract

Pressure sensor (1) for determining a differential or relative pressure variable, comprising: - a differential or relative pressure transducer (20) for determining a differential or relative pressure variable, - an absolute pressure transducer (70) for determining an absolute pressure variable, - a diaphragm seal (30), - a signal processing unit which is set up to carry out a self-monitoring function of the pressure sensor on the basis of an absolute pressure variable and / or its time derivative and a differential or relative pressure variable and / or its time derivative.

Description

The invention relates to a pressure sensor for determining a differential or relative pressure variable.

Pressure sensors are used to record pressures and are used in industrial measurement technology. Depending on the application, differential pressure sensors or relative pressure sensors are used. For example, they are used for level measurement or for flow measurement. When measuring the fill level, for example, the difference between a first pressure acting at the bottom of a container and a second pressure prevailing above the filling material is measured. The difference is proportional to a level-dependent hydrostatic pressure in the container and thus to the level. In flow measurement, for example, a flow resistance is inserted into a line and a difference between a first high-pressure side pressure prevailing upstream of the resistor and a second low-pressure side pressure prevailing downstream of the resistor is determined by means of a differential pressure sensor. This differential pressure is a measure of the flow through the line.

In pressure measurement technology, so-called semiconductor pressure transducers, e.g. silicon chips with doped resistance elements, are often used as pressure-sensitive elements. Corresponding differential pressure transducers typically have a measuring membrane, one side of which is exposed to a first pressure and the second side of which is subjected to a second pressure during measuring operation. The acting pressures cause a resulting deflection of the measuring membrane, which corresponds to the differential or relative pressure to be measured. Semiconductor pressure transducers are usually very sensitive and are therefore not directly exposed to a medium whose pressure is to be recorded. Instead, diaphragm seals filled with a transmission fluid are connected upstream.

For this purpose, diaphragm seals regularly have a massive, typically multi-part diaphragm seal body on which at least one separating membrane is arranged on the outside. The separating membrane closes off a pressure receiving chamber which is connected via a pressure-communicating path to a pressure chamber in which the differential or relative pressure transducer is arranged in such a way that the pressure applied to this separating membrane is fed to a first side of the measuring membrane.

In the event that the pressure sensor is a differential pressure sensor, two separating membranes can be provided. The second separating membrane is also arranged on the outside parallel and opposite to the first separating membrane on the pressure transmitter body. The second separating membrane closes off a second pressure receiving chamber via which the pressure applied to this separating membrane is fed to a second side of the measuring membrane by means of a second pressure-communicating path. The differential pressure transducer can thus determine the differential pressure variable on the basis of the two pressures supplied.

In the event that the pressure sensor is a relative pressure sensor, the second side of the measuring membrane can be supplied with a second pressure, for example via a capillary. The relative pressure transducer can thus determine the relative pressure variable on the basis of the two pressures supplied.

When using such pressure sensors in industrial measurement technology, for example in an automation system in order to execute or control / monitor a process, they must be checked regularly and, if necessary. must be maintained, as these lose their measuring accuracy as the service life progresses.

To do this, the process is usually stopped or interrupted. Then the pressure sensors are removed, checked and, if necessary. waited. The short-term interruption of the process, however, means a system standstill, which, depending on the process being carried out, is associated with considerable costs for the system operator.

It is therefore an object of the invention to propose a pressure sensor which can be checked in a simpler manner.

The object is achieved according to the invention by the pressure sensor according to claim 1 and the pressure measuring arrangement according to claim 7.

• - ein Differenz- oder Relativdruckmesswandler mit einer ersten Messmembran und einer ersten Schaltung zum Wandeln einer druckabhängigen Verformung der ersten Messmembran in die Differenz- oder Relativdruckgröße,
• - einen Absolutdruckmesswandler mit einer zweiten Messmembran und einer zweiten Schaltung zum Wandeln einer druckabhängigen Verformung der zweiten Messmembran in eine Absolutdruckgröße, wobei der Absolutdruckmesswandler separat zu dem Differenz- oder Relativdruckmesswandler ausgebildet ist,
• - einen Druckmittler mit einem Druckmittlerkörper in dem sich eine mit einer Übertragungsflüssigkeit gefüllte Druckkammer befindet, in der ein Füllkörper mit zwei Aussparung angeordnet ist, um Hohlräume zwischen Wänden der Druckkammer und den in den Aussparungen angeordneten Differenz- oder Relativdruckmesswandler und Absolutdruckmesswandler auszufüllen, wobei sich ein erster und ein zweiter druckkommunizierender Pfad jeweils zwischen einer ersten Öffnung und einer zweiten Öffnung durch den Druckmittlerkörper erstrecken, wobei zumindest eine der beiden ersten Öffnungen mit einer ersten Trennmembrane verschlossen ist, die mit einem ersten Druck eines Mediums beaufschlagbar ist, um den ersten Druck in den ersten Pfad einzuleiten, wobei zumindest der erste Pfad mit der Übertragungsflüssigkeit gefüllt ist und an einer der zweiten Öffnungen in der Druckkammer mündet, so dass die erste Messmembran des Differenz- oder Relativdruckmesswandlers auf einer ersten Messmembranseite mit dem ersten Druck beaufschlagt ist und eine zweite Messmembranseite der ersten Messmembran über den zweiten Pfad mit einem an der anderen der beiden ersten Öffnungen herrschendem zweiten Druck beaufschlagt ist, so dass die Verformung der zweiten Messmembran die Absolutdruckgröße repräsentiert;
• - eine Signalverarbeitungseinheit, die dazu eingerichtet ist, anhand der Absolutdruckgröße und/oder deren zeitlicher Ableitung und der Differenz- oder Relativdruckgröße und/oder deren zeitlicher Ableitung eine Selbstüberwachungsfunktion des Drucksensors durchzuführen.

The pressure sensor according to the invention for determining a differential or relative pressure variable, comprising:

• - a differential or relative pressure transducer with a first measuring membrane and a first circuit for converting a pressure-dependent deformation of the first measuring membrane into the differential or relative pressure variable,
• - An absolute pressure transducer with a second measuring membrane and a second circuit for converting a pressure-dependent deformation of the second measuring membrane into an absolute pressure variable, the absolute pressure transducer being designed separately from the differential or relative pressure transducer,
• - A diaphragm seal with a diaphragm seal body in which there is a pressure chamber filled with a transmission fluid, in which a filling body with two recesses is arranged to fill cavities between the walls of the pressure chamber and the differential or relative pressure transducer and absolute pressure transducer arranged in the recesses, with a first and a second pressure-communicating path each extend between a first opening and a second opening through the pressure transmitter body, wherein at least one of the two first openings is closed with a first separating membrane to which a first pressure of a medium can be applied to the first pressure in the initiate first path, wherein at least the first path is filled with the transmission fluid and opens at one of the second openings in the pressure chamber, so that the first measuring membrane of the differential or relative pressure transducer on a first measuring membrane side with the first D. jerk is applied and a second measuring membrane side of the first measuring membrane is acted upon via the second path with a second pressure prevailing at the other of the two first openings, so that the deformation of the second measuring membrane represents the absolute pressure variable;
• a signal processing unit which is set up to carry out a self-monitoring function of the pressure sensor on the basis of the absolute pressure variable and / or its time derivative and the differential or relative pressure variable and / or its time derivative.

According to the invention, it is proposed that, in addition to the differential or relative pressure transducer for determining the differential or relative pressure, an absolute pressure transducer for determining an absolute pressure is also integrated in a pressure sensor. The two pressure transducers are designed separately from one another, i.e. as two different units. For example, the two pressure transducers, in the event that they are designed as semiconductor pressure transducers, are formed on different substrates. Due to the separate design, mutual influencing of the two pressure transducers can be reduced. According to the invention, it is further proposed that self-monitoring of the pressure sensor is carried out by means of the two detected pressure variables.

$$mit\gamma ={\left({\gamma }_1,{\gamma }_2,\dots ,{\gamma }_n\right)}_{n\in N}\in Rund\phi ={\left({\phi }_1,{\phi }_1,\dots ,{\phi }_m\right)}_{m\in N}\in R$$

wobei Pabs die Absolutdruckgröße, ΔP_abs eine gemessene Druckänderung der Absolutdruckgröße, P_ret die Differenz- oder Relativdruckgröße, ΔP_rel eine gemessene Druckänderung der Differenz- oder Relativdruckgröße und γ, φ jeweils ein Set von feststehende Koeffizienten (γ₁, γ₂,..., γ_n) bzw. (φ₁, φ₂, ... , φ_m) sind, welche Koeffizienten vorzugweise während der Fertigung des Drucksensor festgelegt worden sind.An advantageous embodiment of the pressure sensor according to the invention can provide that the signal processing unit executes the following equation or an equation derived therefrom in order to detect the faulty first and / or second measuring membrane: $$f\left({\mathrm{P.}}_{abs},\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t},t,\gamma \right)=G\left({\mathrm{P.}}_{rel},\frac{\mathrm{\Delta }{\mathrm{P.}}_{rel}}{\mathrm{\Delta }t},t,\phi \right)$$

$$mit\gamma ={\left({\mathrm{<figure-callout\; id="1"\; label="\gamma "\; filenames="DE102019133808A1\_0015.png,DE102019133808A1\_0016.png"\; state="\{\{state\}\}">\gamma </figure-callout>}}_1,{\gamma }_2,...,{\gamma }_n\right)}_{n\in N}\in \mathrm{R.}und\phi ={\left({\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102019133808A1\_0015.png,DE102019133808A1\_0016.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1,{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102019133808A1\_0015.png,DE102019133808A1\_0016.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1,...,{\phi }_m\right)}_{m\in N}\in \mathrm{R.}$$

where Pabs is the absolute pressure variable, ΔP _{abs is} a measured pressure change in the absolute pressure variable, P _{ret is} the differential or relative pressure variable, ΔP _{rel is} a measured pressure change in the differential or relative pressure variable and γ, φ is a set of fixed coefficients (γ ₁ , γ ₂ , .. ., γ _n ) and (φ ₁ , φ ₂ , ..., φ _m ) are which coefficients have preferably been established during the manufacture of the pressure sensor.

wobei ΔP_abs eine gemessene Druckänderung der Absolutdruckgröße über eine Zeiteinheit Δt, ΔP_Rel eine gemessene Druckänderung der Differenz- oder Relativdruckgröße über die Zeiteinheit Δt und φ₀, φ₀ feststehende Koeffizienten sind, welche Koeffizienten vorzugweise während der Fertigung des Drucksensor festgelegt worden sind, und wobei die Signalverarbeitungseinheit ferner dazu eingerichtet ist, die Koeffizienten Δγ und Δφ so anzupassen, dass die Gleichung erfüllt ist und basierend auf der Anpassung der Koeffizienten Δγ und Δφ eine fehlerhafte erste und/oder zweite Messmembran erkennt.In particular, the advantageous embodiment of the pressure sensor according to the invention can provide that the self-monitoring function includes the detection of a faulty first and / or second measuring membrane. In particular, the embodiment can provide that the signal processing unit executes the following equation to identify the faulty first and / or second measuring membrane: $$\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t}\right|\cdot \left({\gamma }_0\pm \mathrm{\Delta }\gamma \right)=\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{\mathrm{R.}el}}{\mathrm{\Delta }t}\right|\cdot \left({\phi }_0\pm \mathrm{\Delta }\phi \right),\left({\gamma }_0,{\phi }_0,\mathrm{\Delta }\gamma ,\mathrm{\Delta }\phi \right)\in \mathrm{R.}$$

where ΔP _{abs is} a measured pressure change in the absolute pressure variable over a unit of time Δt, ΔP _{Rel is} a measured pressure change in the differential or relative pressure variable over the time unit Δt and φ ₀ , φ _{0 are} fixed coefficients, which coefficients are preferably determined during the manufacture of the pressure sensor, and wherein the signal processing unit is further set up to adapt the coefficients Δγ and Δφ in such a way that the equation is fulfilled and recognizes a faulty first and / or second measuring membrane based on the adaptation of the coefficients Δγ and Δφ.

wobei ΔP_abs eine gemessene Druckänderung der Absolutdruckgröße über eine Zeiteinheit Δt, ΔP_Rel eine gemessene Druckänderung der Differenz- oder Relativdruckgröße über die Zeiteinheit ist und die Signalverarbeitungseinheit dazu eingerichtet ist, in dem Fall, dass die Gleichung erfüllt ist, einen konstanten Messbetrieb festzustellen und in dem Fall, dass die Gleichung nicht erfüllt ist, einen Drift der ersten und/oder zweiten Messmembran zu erkennen.A further advantageous embodiment of the pressure sensor according to the invention can provide that the self-monitoring function includes the detection of a drift in the first and / or second measuring membrane. In particular, the embodiment can provide that, in order to detect the drift of the first and / or second measuring membrane, the signal processing unit checks, preferably continuously during a measuring operation, whether the following equation is fulfilled: $$\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t}\right|\cong \left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{\mathrm{R.}el}}{\mathrm{\Delta }t}\right|\cong 0$$

where ΔP _{abs is} a measured pressure change in the absolute pressure variable over a time unit Δt, ΔP _{Rel is} a measured pressure change in the differential or relative pressure variable over the time unit and the signal processing unit is set up to determine a constant measuring operation in the event that the equation is fulfilled and in in the event that the equation is not fulfilled, a drift of the first and / or second measuring membrane can be recognized.

A further advantageous embodiment of the pressure sensor according to the invention can provide that the differential or relative pressure transducer and the absolute pressure transducer are designed as semiconductor pressure transducers, in particular as silicon-chip pressure transducers, each of which is designed on a different substrate.

wobei Pabs die durch den Absolutdruckmesswandler ermittelte Absolutdruckgröße, P_Bereich,rel ein Messbereich des Differenz- oder Relativdruckmesswandlers und ξ_0, Δξ feststehende Koeffizienten sind, welche Koeffizienten vorzugweise während der Fertigung des Drucksensor festgelegt worden sind, wobei in dem Fall, dass die Gleichung nicht erfüllt ist, die Aussage über die mögliche Abweichung der beiden Größen getroffen wird.The invention further relates to a pressure measuring arrangement, comprising a pressure sensor according to one of the configurations described above, a measuring tube, a diaphragm arranged in the measuring tube through which the medium flows, and a valve arrangement, with a pressure prevailing in the flow direction of the medium in front of the diaphragm being the first pressure for the pressure sensor is supplied and wherein the valve arrangement is designed such that in a first valve position the second pressure directed via the second path corresponds to a pressure of the medium prevailing in the flow direction behind the orifice and in a second valve position the second pressure directed via the second path corresponds to an ambient pressure of an environment corresponds, wherein the signal processing unit is further set up to compare the differential or relative pressure variable and the absolute pressure variable in the second valve position with one another and based thereon to make a statement about a possible deviation of the two variables en. In particular, it can be provided that the signal processing unit is also set up to check in the second valve position whether the following equation is fulfilled: $${\mathrm{P.}}_{abs}\cdot \left({\xi }_0\pm \mathrm{\Delta }\xi \right)={\mathrm{P.}}_{\mathrm{B.}ereicH,rel}{\xi }_0,\mathrm{\Delta }\xi \in \mathrm{R.}$$

where Pabs is the absolute pressure value determined by the absolute pressure transducer, P _{range, rel} a measuring range of the differential or relative pressure _{transducer and ξ 0,} Δξ are fixed coefficients, which coefficients have preferably been specified during the manufacture of the pressure sensor, in which case the equation is not met, the statement about the possible deviation of the two variables is made becomes.

• 1: einen Schnitt durch ein erstes Ausführungsbeispiel eines erfindungsgemäßen Drucksensors zum Bestimmen einer Differenzdruckgröße,
• 2: einen Schnitt durch ein zweites Ausführungsbeispiel eines erfindungsgemäßen Drucksensors zum Bestimmen einer Relativdruckgröße, und
• 3: eine Druckmessanordnung mit einem Drucksensor und einer Ventilanordnung.

The invention is explained in more detail with reference to the following drawings. It shows:

• 1 : a section through a first embodiment of a pressure sensor according to the invention for determining a differential pressure variable,
• 2 : a section through a second embodiment of a pressure sensor according to the invention for determining a relative pressure variable, and
• 3rd : a pressure measuring arrangement with a pressure sensor and a valve arrangement.

1 shows a section through a first embodiment of a pressure sensor according to the invention. This includes a diaphragm seal 30th with a diaphragm seal body made up of several parts 31a , 31b , 31c and a differential pressure transducer 20th as well as an absolute pressure transducer 70 . In which in 1 The pressure sensor shown is therefore a differential pressure sensor. The two pressure sensor elements are designed as semiconductor pressure transducers, both of which are designed separately from one another as each independent sensor element.

In the in 1 The example shown is a substantially massive block 31a made of a metal, in particular made of a steel or stainless steel, and a carrier body 31b as a carrier for the two pressure transducers 20th , 70 serves. The massive block 31a has a first separating membrane on a side face 37a also a first separating membrane on and on a side surface opposite the first side surface 37b on. The first two separating membranes 37a and 37b each close a pressure receiving chamber integrated into the massive block on the outside 38a , 38b from. In the actual measuring operation, it acts on that of the massive block 31a remote side of the first separating membrane 37a a first print from a medium p1 or on those of the massive block 31a remote side of the other first separating membrane 37b a second print also derived from the medium p2 . The two pressures p1 and p2 are via a first and a second pressure-communicating path, respectively 34a , 34b to the differential pressure transducer 20th guided. In the in 1 The illustrated embodiment, both pressure-communicating paths are filled with a pressure transmission fluid, so that these are also referred to below as hydraulic paths. The first hydraulic path 34a extends from a first opening 35a a first pressure receiving chamber 38a through the massive block 31a via a capillary tube system 31c to a second opening 36a in the carrier body 31b . Via the second opening 36a the first hydraulic path opens 34a thus in one in the carrier body 31b integrated pressure chamber 32 who have favourited the first print p1 a front 21a a first measuring membrane 21 of the differential pressure transducer 20th feeds. Both the pressure chamber 32 as well as the first hydraulic path 34a are for transmitting the corresponding pressure with a transmission fluid 39 filled.

To the volume of the transmission fluid 39 in the pressure chamber 32 to keep it as low as possible, the differential pressure sensor 1 also one in the pressure chamber 32 introduced packing 33 on. Through the packing 33 there are cavities between the walls of the pressure chamber and the pressure transducers 20th , 70 each in a recess of the packing 33 are filled in.

The second hydraulic path 34b extends from the first opening 35b a second pressure receiving chamber 38b again through the massive block 31a via a capillary tube system 31c to a second opening 36b in the carrier body 31b . The second opening 36b is such in the support body 31b provided that the via the second hydraulic path 34b transmitted second pressure p2 a back 21b the first measuring membrane 21 of the differential pressure transducer 20th is fed. To do this is the second hydraulic path 34b also with the transmission fluid 39 filled.

Through the one at the front 21a the first measuring membrane 21 attached first print p1 and the one at the back 21b the first measuring membrane 21 attached second print p2 experiences the first measuring membrane 21 a pressure-dependent deflection. The pressure-dependent deflection can in turn, for example, through in the first measuring membrane 21 integrated piezoresistive elements are recorded by measuring technology, so that a differential pressure variable is generated by a first circuit 22nd can be determined for converting the pressure-dependent deflection. Alternatively, instead of the piezoresistive elements, capacitive elements can also be used to measure the pressure-dependent deflection.

About the pressure chamber 32 will also be the first print p1 also on a front 71a a second measuring membrane 71 of the absolute pressure transducer. A pressure chamber (vacuum chamber) adjoins a rear side of the second measuring membrane, which is closed off by the second measuring chamber, so that the second measuring membrane has one of the first pressure p1 dependent deflection, which in turn is measured by a second circuit 72 can be recorded in order to determine an absolute pressure measured variable. The absolute pressure transducer is thus only able to handle one of the two pressures originating from a medium p1 or p2 in contact. This measured pressure p1 or p2 is used according to the invention as a reference pressure for the differential pressure variable of the differential pressure transducer.

2 shows a section through a second embodiment of a pressure sensor according to the invention, which is designed as a relative pressure sensor. The structure of the relative pressure sensor and the in 1 The differential pressure sensors shown are basically the same with the exception that the relative pressure sensor does not have two first separating membranes, but only one (single) first separating membrane. A first pressure originating from a medium acts on the first separating membrane p1 which is also fed to the pressure chamber via the first hydraulic path (filled with a transmission fluid). The second pressure is via a second pressure communicating path extending from a first port 35b to a second opening 36b in the carrier body 31b extends, transferred. In the in 2 illustrated embodiment, which is a relative pressure sensor, the second pressure-communicating path is not filled with a pressure transmission fluid, but is formed by a tube, in particular a capillary tube, which has the first opening 35b to an ambient pressure as the second pressure p2 is led. The second opening 36b is in turn such in the carrier body 31b provided that the one via the second path 34b transmitted second pressure p2 a back 21b the first measuring membrane 21 of the differential pressure transducer 20th is fed.

Through the one at the front 21a the first measuring membrane 21 attached first print p1 and the one at the back 21b the first measuring membrane 21 attached second print p2 (Ambient pressure) experiences the first measuring membrane 21 a pressure-dependent deflection. The pressure-dependent deflection can in turn, for example, through in the first measuring membrane 21 integrated piezoresistive elements are recorded by measuring technology, so that a relative pressure variable is determined by a first circuit 22nd can be determined for converting the pressure-dependent deflection. Alternatively, instead of the piezoresistive elements, capacitive elements can also be used to measure the pressure-dependent deflection.

About the pressure chamber 32 will also be the first print p1 also on a front 71a a second measuring membrane 71 of the absolute pressure transducer 70 guided. A vacuum chamber, which is closed by the second measuring chamber, adjoins a rear side of the second measuring membrane, so that the second measuring membrane has one of the first pressure p1 dependent deflection, which in turn is measured by a second circuit 72 can be detected in order to determine an absolute pressure quantity. The absolute pressure transducer is therefore only in contact with the first pressure originating from the medium. This pressure is used as a reference pressure for the relative pressure variable of the differential pressure transducer.

Both the in 1 differential pressure sensor shown as well as the one in 2 Relative pressure sensor shown also has a signal processing unit 80 to which the pressure variable (differential pressure variable or relative pressure variable) and the absolute pressure variable detected by the respective pressure transducer are supplied. The signal processing unit can comprise a microprocessor, for example. The pressure sizes can be via electrical lines 81 from the first and second electrical circuits 22nd and 72 to the signal processing unit 80 be led.

The signal processing unit is according to the invention 80 set up to execute a self-monitoring function based on the differential or relative pressure variable and the absolute pressure variable.

$$mit\gamma ={\left({\gamma }_1,{\gamma }_2,\dots ,{\gamma }_n\right)}_{n\in N}\in Rund\phi ={\left({\phi }_1,{\phi }_2,\dots ,{\phi }_m\right)}_{m\in N}\in R$$

The self-monitoring function can initially provide for the detection of a faulty first and / or second measuring membrane. In principle, the invention is based on the consideration that in the event that a faulty first and / or second measuring membrane is present, the following equation is not fulfilled: $$f\left({\mathrm{P.}}_{abs},\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t},t,\gamma \right)=G\left({\mathrm{P.}}_{rel},\frac{\mathrm{\Delta }{\mathrm{P.}}_{rel}}{\mathrm{\Delta }t},t,\phi \right)$$

$$mit\gamma ={\left({\mathrm{<figure-callout\; id="1"\; label="\gamma "\; filenames="DE102019133808A1\_0015.png,DE102019133808A1\_0016.png"\; state="\{\{state\}\}">\gamma </figure-callout>}}_1,{\gamma }_2,...,{\gamma }_n\right)}_{n\in N}\in \mathrm{R.}und\phi ={\left({\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102019133808A1\_0015.png,DE102019133808A1\_0016.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1,{\phi }_2,...,{\phi }_m\right)}_{m\in N}\in \mathrm{R.}$$

wobei ΔP_abs eine gemessene Druckänderung der Absolutdruckgröße über eine Zeiteinheit Δt, ΔP_Rel eine gemessene Druckänderung der Differenz- oder Relativdruckgröße über die Zeiteinheit Δt und φ₀, γ₀ feststehende Koeffizienten sind. Die Koeffizienten sind vorzugweise während der Fertigung des Drucksensor festgelegt worden. Während des eigentlichen Messbetriebs passt die Signalverarbeitungseinheit 80 die Koeffizienten Δγ und Δφ so an, dass die Gleichung erfüllt ist. Basierend auf der Anpassung der Koeffizienten Δγ und Δφ kann die Signalverarbeitungseinheit 80 eine fehlerhafte erste und/oder zweite Messmembran erkennen. In anderen Worten, die Selbstüberwachungsfunktion basiert auf einer Anpassung von den Koeffizienten φ₀, γ₀, die bspw. in der Fertigung oder Produktion des Drucksensors festgelegt worden sind, durch die Koeffizienten Δγ und Δφ. In dem Fall, dass eine Änderung der Koeffizienten Δγ und Δφ zu groß sein sollte, kann die Signalverarbeitungseinheit 80 eine Fehlermeldung ausgeben, dass eine der beiden Messmembrane fehlerhaft ist.For example, the following equation can be carried out by the signal processing unit: $$\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t}\right|\cdot \left({\gamma }_0\pm \mathrm{\Delta }\gamma \right)=\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{rel}}{\mathrm{\Delta }t}\right|\cdot \left({\phi }_0\pm \mathrm{\Delta }\phi \right),\left({\gamma }_0,{\phi }_0,\mathrm{\Delta }\gamma ,\mathrm{\Delta }\phi \right)\in \mathrm{R.}$$

where ΔP _{abs is} a measured pressure change in the absolute pressure variable over a time unit Δt, ΔP _{Rel is} a measured pressure change in the differential or relative pressure variable over the time unit Δt and φ ₀ , γ _{0 are} fixed coefficients. The coefficients have preferably been established during manufacture of the pressure sensor. The signal processing unit fits during the actual measuring operation 80 the coefficients Δγ and Δφ in such a way that the equation is satisfied. Based on the adaptation of the coefficients Δγ and Δφ, the signal processing unit 80 detect a faulty first and / or second measuring membrane. In other words, the self-monitoring function is based on an adaptation of the coefficients φ ₀ , γ ₀ , which have been established, for example, in the manufacture or production of the pressure sensor, by the coefficients Δγ and Δφ. In the event that a change in the coefficients Δγ and Δφ should be too great, the signal processing unit can 80 output an error message that one of the two measuring diaphragms is defective.

The self-monitoring function can furthermore include the detection of a drift in the first and / or second measuring membrane. For this purpose, the signal processing unit continuously checks the following equation derived from equation (1) during the actual measuring operation: $$\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t}\right|\cong \left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{\mathrm{R.}el}}{\mathrm{\Delta }t}\right|\cong 0$$

In the event that the measured pressure change of the differential or relative pressure variable over the time unit Δt and / or the measured pressure change of the absolute pressure variable over a time unit Δt falls below a specified tolerance limit supplied to the pressure sensor, the signal processing unit is set up to determine a constant measuring operation. In the event that the measured pressure change of the differential or relative pressure variable over the time unit Δt and / or the measured pressure change of the absolute pressure variable over a time unit Δt is above the tolerance limit, the signal processing unit is set up to add a drift to the first and / or second measuring membrane detect. In the event that the signal processing unit detects a drift in the first and / or second measuring membrane, an error message can also be output.

The self-monitoring functions described above can be performed by the signal processing unit 80 can be carried out during operation, ie without interrupting the process.

Pressure sensors according to the first and / or second exemplary embodiment can usually be found in pressure measuring arrangements for determining a flow rate of a medium. 3rd shows a corresponding pressure measuring arrangement. In addition to the pressure sensor, the pressure measuring arrangement also comprises an orifice plate introduced into a measuring tube and a valve arrangement 91, 92, 93

The valve arrangement is designed in such a way that, in a first valve position, the valve via the second path ( 34b ) directed second pressure ( p2 ) a pressure of the medium prevailing downstream of the orifice in the direction of flow and in a second valve position the pressure via the second path ( 34b ) directed second pressure ( p2 ) corresponds to an ambient pressure of an environment.

The signal processing unit 80 can also be set up to compare the difference variable and the absolute pressure variable in the second valve position with one another and to make a statement about a possible deviation based thereon.

List of reference symbols

1

Differential pressure sensor

20th

Differential or relative pressure transducer

21

First measuring membrane

21a

First side of the first measuring membrane

21b

Second side of the first measuring membrane

22nd

First circuit for converting the pressure-dependent deformation of the first measuring membrane into a differential or relative pressure variable

30th

Diaphragm seal

31a

Massive block of the diaphragm seal body

31b

Carrier body

31c

Capillary tube system

32

Pressure chamber

33

Packing

34a

First pressure communicating path

34b

Second pressure communicating path

35a, 35b

First opening

36a, 36b

Second opening

37a, 37b

First separating membrane

38a, 38b

First pressure receiving chamber

39

Pressure transmission fluid

70

Absolute pressure transducer

71

Second measuring membrane

71a

First side of the second measuring membrane

72

Second circuit for converting the pressure-dependent deformation of the measuring membrane into an absolute pressure variable

80

Signal processing unit

81

Electric lines

91

First valve

92

Second valve

93

Third valve

100

cover

200

Measuring tube

p1

First print

p2

Second print

PRel

p1-p2

P area, rel

Measuring range of the differential or relative pressure transducer

Claims (9)

Pressure sensor (1) for determining a differential or relative pressure variable, comprising: - a differential or relative pressure transducer (20) with a first measuring membrane (21) and a first circuit (22) for converting a pressure-dependent deformation of the first measuring membrane (21) into the Differential or relative pressure variable, - an absolute pressure transducer (70) with a second measuring membrane (71) and a second circuit (72) for converting a pressure-dependent deformation of the second measuring membrane (71) into an absolute pressure variable, the absolute pressure transducer being separate from the differential or relative pressure transducer - a diaphragm seal (30) with a diaphragm seal body (31a, 31b, 31c) in which there is a pressure chamber (32) filled with a transmission fluid (39) and in which a filling body (33) with two recesses is arranged to Cavities between the walls of the pressure chamber (32) and the differential or relative pressure transducer (20) and the absolute pressure transducer arranged in the recesses pressure transducers (70), a first and a second pressure-communicating path (34a, 34b) each extending between a first opening (35a, 35b) and a second opening (36a, 36b) through the pressure transmitter body (31a, 31b, 31c) , wherein at least one of the two first openings (35a) is closed with a first separating membrane (37a) to which a first pressure (p1) of a medium can be applied in order to introduce the first pressure (p1) into the first path (34a), wherein at least the first path (34a) is filled with the transmission fluid (39) and opens at one of the second openings (36a) in the pressure chamber (32), so that the first measuring membrane (21) of the differential or relative pressure transducer is on a first measuring membrane side (21a) is acted upon by the first pressure and a second measuring membrane side (21b) of the first measuring membrane (21) is acted upon via the second path (34b) with a second pressure (p2) prevailing at the other of the two first openings (35b) so that the deformation of the first measuring membrane represents the differential or relative pressure variable between the first pressure (p1) and the second pressure (p2), the second measuring membrane (71) of the absolute pressure transducer (70) on a first measuring membrane side (71a) ) the first pressure is applied so that the deformation of the second measuring membrane (71) represents the absolute pressure variable; - a signal processing unit which is set up to carry out a self-monitoring function of the pressure sensor at least on the basis of the absolute pressure variable and / or its time derivative and the differential or relative pressure variable and / or its time derivative. Pressure sensor after Claim 1 , wherein the self-monitoring function comprises the detection of a faulty first and / or second measuring membrane. Pressure sensor according to one of the preceding claims, wherein the signal processing unit executes the following equation or an equation derived therefrom in order to identify the faulty first and / or second measuring membrane: $$f\left({\mathrm{P.}}_{abs},\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t},t,\gamma \right)=G\left({\mathrm{P.}}_{rel},\frac{\mathrm{\Delta }{\mathrm{P.}}_{rel}}{\mathrm{\Delta }t},t,\phi \right)$$

$$mit\gamma ={\left({\gamma }_1,{\gamma }_2,...{\gamma }_n\right)}_{n\in N}\in \mathrm{R.}und\phi ={\left({\phi }_1,{\phi }_2,...,{\phi }_m\right)}_{m\in N}\in \mathrm{R.}$$

where P _{abs is} the absolute pressure variable, ΔP _{abs is} a measured pressure change in the absolute pressure variable, P _{rel is} the differential or relative pressure variable, ΔP _{rel is} a measured pressure change in the differential or relative pressure variable and φ _m , n is a set of fixed coefficients, which coefficients are preferably used during production of the pressure sensor have been set. Pressure sensor according to the preceding claim, wherein the signal processing unit executes the following equation to identify the faulty first and / or second measuring membrane: $$\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t}\right|\cdot \left({\gamma }_0\pm \mathrm{\Delta }\gamma \right)=\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{\mathrm{R.}el}}{\mathrm{\Delta }t}\right|\cdot \left({\phi }_0\pm \mathrm{\Delta }\phi \right),\left({\gamma }_0,{\phi }_0,\mathrm{\Delta }\gamma ,\mathrm{\Delta }\phi \right)\in \mathrm{R.}$$

where ΔP _{abs is} a measured pressure change in the absolute pressure variable over a unit of time Δt, ΔP _{Rel is} a measured pressure change in the differential or relative pressure variable over the time unit Δt and φ ₀ , γ _{0 are} fixed coefficients, which coefficients are preferably determined during the manufacture of the pressure sensor, and wherein the signal processing unit is further set up to adapt the coefficients Δγ and Δφ in such a way that the equation is fulfilled and recognizes a faulty first and / or second measuring membrane based on the adaptation of the coefficients Δγ and Δφ. Pressure sensor according to one of the preceding claims, wherein the self-monitoring function comprises the detection of a drift in the first and / or second measuring membrane. Pressure sensor according to the preceding claim, wherein, in order to detect the drift of the first and / or second measuring membrane, the signal processing unit checks, preferably continuously during a measuring operation, whether the following equation is fulfilled: $$\left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{abs}}{\mathrm{\Delta }t}\right|\cong \left|\frac{\mathrm{\Delta }{\mathrm{P.}}_{\mathrm{R.}el}}{\mathrm{\Delta }t}\right|\cong 0$$

where ΔP _{abs is} a measured pressure change in the absolute pressure variable over a time unit Δt, ΔP _{Rel is} a measured pressure change in the differential or relative pressure variable over the time unit and the signal processing unit is set up to determine a constant measuring operation in the event that the equation is fulfilled and in in the event that the equation is not fulfilled, a drift of the first and / or second measuring membrane can be recognized. Pressure sensor according to one of the preceding claims, wherein the differential or relative pressure transducer and the absolute pressure transducer are designed as semiconductor pressure transducers, in particular as silicon-chip pressure transducers, which are each formed on a different substrate. Pressure measuring arrangement, comprising a pressure sensor according to one of the preceding claims, a measuring tube (200), a diaphragm (100) arranged in the measuring tube (200) through which the medium flows and a valve arrangement (91, 92, 93), wherein a pressure prevailing in the flow direction of the medium in front of the orifice (100) is supplied to the pressure sensor (1) as the first pressure (p1) and wherein the valve arrangement (91, 92, 93) is designed in this way is that in a first valve position the second pressure (p2) passed via the second path (34b) is a pressure of the medium prevailing downstream of the orifice in the direction of flow and in a second valve position the second pressure (p2) passed via the second path (34b) corresponds to an ambient pressure of an environment, wherein the signal processing unit is also set up to compare the differential or relative pressure variable and the absolute pressure variable at the second valve position with one another and based thereon to make a statement about a possible deviation of the two variables. Pressure measuring arrangement according to the preceding claim, wherein the signal processing unit is further configured to check in the second valve position whether the following equation is fulfilled: $${\mathrm{P.}}_{abs}\cdot \left({\xi }_0\pm \mathrm{\Delta }\xi \right)={\mathrm{P.}}_{\mathrm{B.}ereicH,rel}{\xi }_0,\mathrm{\Delta }\xi \in \mathrm{R.}$$

where Pabs is the absolute pressure variable determined by the absolute pressure transducer, P _{range, rel is} a measuring range of the differential or relative pressure _{transducer and ξ 0} Δξ are fixed coefficients, which coefficients are preferably determined during the manufacture of the pressure sensor, in the event that the equation is not fulfilled is, the statement is made about the possible discrepancy between the two quantities.

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