DE102020121581A1 - differential pressure sensor - Google Patents

Abstract

Differential pressure sensor (1) for determining the differential pressure of two pressures (p1, p2) with a measuring mechanism (2) and a converter chamber (3), with a coplanar double diaphragm system with two double diaphragms ( 4a, 4b) and wherein a differential pressure measuring cell (12) with a pressure-sensitive element (13) is arranged in the converter chamber (3), the two double membranes (4a, 4b) each consisting of a separating membrane (5a, 5b) and an in In the direction of the pressure effect, there are overload diaphragms (6a, 6b) arranged behind the separating diaphragm (5a, 5b), with a first pressure chamber (7a) between the first separating diaphragm (5a) and the first overload diaphragm (6a) and between the first overload diaphragm (6a) and a first additional pressure chamber (8a) is formed in the base body (9), with a second pressure chamber (7b) between the second separating membrane (5b) and the second overload membrane (6b) and between the second A second additional pressure chamber (8b) is formed in the overload diaphragm (6b) and the base body (9), with the first additional pressure chamber (8a) or the second additional pressure chamber (8b) being assigned a first connecting capillary (10a) or a second connecting capillary (10b). and wherein the first pressure chamber (7a) or the second pressure chamber (7b) is assigned a first auxiliary capillary (11a) or a second auxiliary capillary (11b), with a pressure-transmitting coupling between the first auxiliary capillary (11a) and the second connecting capillary (10b) or between the second auxiliary capillary (11b) and the first connecting capillary (10a) in the measuring mechanism (2), and wherein the two pressures (p1, p2) via the connecting capillary (10a, 10b) - against one-sided overpressure protected - are transmitted hydraulically to the differential pressure measuring cell (12).

Description

The invention relates to a coplanar differential pressure sensor for determining the differential pressure of two pressures. The differential pressure sensor according to the invention is preferably used in the field of automation technology.

Differential pressure gauges are used in particular for the continuous measurement of pressure differences in measurement media, e.g. in liquids, vapours, gases and dust. For example, the level of a medium in a container or the flow of a medium through a pipe can be determined from the differential pressure.

A silicon chip is usually used as the pressure-sensitive element. In order to achieve good measuring sensitivity, a differential pressure sensor preferably works in a range that is close to a critical limit value for the pressure (nominal pressure). If the critical limit is exceeded, there is a risk that the chip will be destroyed. Since silicon chips, in particular, have a relatively low overload resistance, overload protection is usually assigned to a differential pressure sensor. This is preferably designed in such a way that it affects the measurement sensitivity and the measurement accuracy of the pressure-sensitive element as little as possible.

From the DE 3 222 620 A1 a pressure difference measuring device has become known which has a pressure measuring transducer device protected against overload. The measuring device has a central receiving body which forms an antechamber on two opposite sides between a membrane bed and a separating membrane. In the receiving body, an additional chamber is provided behind the side facing away from the membrane bed, which is delimited by a prestressed overload membrane. Inside the receiving body there is also a measuring chamber, which is divided into two sub-chambers by the pressure sensor device. Each of the two partial chambers of the measuring chamber is connected to one of the two antechambers via a respective connecting channel. Each of the two connecting channels is connected to one of the two additional chambers via an additional channel.

If the device is exposed to a differential pressure below or in the range of the nominal differential pressure value, then this differential pressure is transmitted to the pressure sensor device via the connecting channels. The additional membranes develop a small effect, which is negligible in a first approximation. If the pressure difference exceeds the nominal pressure difference value by a predetermined value as a result of an overload, the pressure transmitter liquid located below it is pressed into the antechamber assigned to it on the high-pressure side of the separating membrane. The liquid that is pushed out reaches the auxiliary diaphragm on the low-pressure side via the connection channel and the auxiliary channel, causing it to lift. Thus, in the event of an overload, the liquid that is pressed out on the high-pressure side under the separating diaphragm is under the lifting additional diaphragm on the low-pressure side. Consequently, an overload of the pressure sensor device is avoided. In the case of the German patent application, the converter chamber is integrated into the measuring mechanism.

From the WO 2018/165122 A1 a coplanar differential pressure sensor has become known in which the pressure inputs with separating diaphragm and overload diaphragm are arranged in one plane - namely in the end area facing the process - and not on opposite, parallel planes as in the aforementioned German patent application. It is a so-called double membrane system. The advantage of double membrane systems lies in the significantly lower oil volume that is required for the hydraulic operation of the differential pressure sensor. In addition, the pressure-loaded center membrane weld can be dispensed with here, so that the measuring mechanism can be made in one piece. As in the previously mentioned patent application, the overload protection is also arranged in the measuring mechanism in this known solution, ie the crossed capillaries are located in the measuring mechanism. The converter chamber is placed directly on the measuring mechanism or integrated into the measuring mechanism.

The known solutions have several disadvantages: Since the crossed hydraulic pressure feedthroughs are arranged in the measuring mechanism, e.g. in the known coplanar design, for the purpose of oil filling, externally exposed bores are required, which are closed after filling. The closure areas are potential corrosion weak points. In addition, the holes are quite long, which has a negative impact on manufacturing costs. Long bores also inevitably require a larger oil volume, which in turn makes it difficult to implement overload protection in the measuring mechanism. Since defined distances between the pressure ducts must be maintained, there are limits to minimizing the dimensions of the measuring unit.

The object of the invention is to propose a pressure sensor with overload protection and reduced oil volume. At this point, the term "oil volume" is chosen because it is the hydraulic transmission fluid usually an almost incompressible oil, for example a silicone oil.

The object is achieved by a coplanar differential pressure sensor for determining the differential pressure of two pressures with a measuring mechanism and a converter chamber, a coplanar double diaphragm system with two double diaphragms being provided on or in an end region of the measuring mechanism facing the process. A differential pressure measuring cell with a pressure-sensitive element is arranged in the converter chamber. The two double diaphragms each consist of a separating diaphragm and an overload diaphragm arranged behind the separating diaphragm in the direction of the pressure effect, with a first pressure chamber being formed between the first separating diaphragm and the first overload diaphragm and a first additional pressure chamber being formed between the first overload diaphragm and the base body. A second pressure chamber is formed between the second separating membrane and the second overload membrane and a second additional pressure chamber is formed between the second overload membrane and the base body, with the first additional pressure chamber or the second additional pressure chamber being assigned a first connecting capillary or a second connecting capillary, the connecting capillaries being separated from the Guide the measuring mechanism to the converter chamber. A first auxiliary capillary or a second auxiliary capillary is assigned to the first pressure chamber or the second pressure chamber, with a pressure-transmitting coupling being arranged between the first auxiliary capillary and the second connecting capillary or between the second auxiliary capillary and the first connecting capillary in the measuring unit, and wherein the two pressures are transmitted hydraulically to the differential pressure measuring cell via the corresponding auxiliary and connecting capillaries - protected against overpressure.

• - Das Messwerk ist einteilig ausgestaltet.
• - Das Messwerk hat einen relativ einfachen und in weiten Teilen symmetrischen Aufbau.
• - Messwerk und Wandlerkammer sind voneinander abgesetzt; Messwerk und Wandlerkammer sind nur über die beiden Verbindungsleitungen gekoppelt, so dass sich eine gute mechanische und thermische Entkopplung zwischen Messwerk und Wandlerkammer erreichen lässt.
• - Die Kreuzung der Hilfskapillaren mit den Verbindungskapillaren erfolgt im Messwerk, also sehr nahe am Messort des Drucks.
• - Ein einseitig auftretender Überdruck auf der Hochdruckseite wird auf die Rückseite der Überlastmembrane/Zusatzmembrane der Niederdruckseite und parallel über die Verbindungsleitungen zur Wandlerkammer geleitet. Wandlerkammer und Überlastmembrane liegen druckdynamisch parallel.
• - Die Länge der Verbindungskapillaren ist größer als die Länge der Hilfskapillaren und der Teilstücke der Verbindungskapillaren des Überlastschutzes, was eine schnelle Reaktionszeit des Überlastschutzes sicherstellt.
• - Aufgrund der geringen Kapillarlängen ist der Ölverbrauch gering.
• - Kosteneinsparung beim Messwerk, insbesondere durch Materialeinsparung (kleine Dimensionen) und infolge einer vereinfachten Fertigung und Bearbeitung, da die Anzahl der Kapillaren gering ist; die Kapillaren können z.B. kostengünstig durch Bohren oder Erodieren hergestellt werden;
• - Die Befüllung des hydraulischen Systems erfolgt über das Messwerk.

The solution according to the invention has the following advantages:

• - The measuring mechanism is designed in one piece.
• - The measuring mechanism has a relatively simple and largely symmetrical structure.
• - Measuring mechanism and converter chamber are separated from each other; Measuring mechanism and converter chamber are only coupled via the two connecting lines, so that good mechanical and thermal decoupling can be achieved between the measuring mechanism and converter chamber.
• - The crossing of the auxiliary capillaries with the connection capillaries takes place in the measuring unit, i.e. very close to the measuring point of the pressure.
• - An overpressure occurring on one side on the high-pressure side is routed to the rear of the overload diaphragm/additional diaphragm on the low-pressure side and parallel via the connecting lines to the converter chamber. In terms of pressure dynamics, the converter chamber and overload diaphragm are parallel.
• - The length of the connection capillaries is greater than the length of the auxiliary capillaries and the sections of the connection capillaries of the overload protector, which ensures a fast response time of the overload protector.
• - Due to the short capillary lengths, the oil consumption is low.
• - Cost savings in the measuring mechanism, in particular through material savings (small dimensions) and as a result of simplified manufacture and processing, since the number of capillaries is small; the capillaries can be produced inexpensively, for example, by drilling or eroding;
• - The hydraulic system is filled via the measuring unit.

It is preferably provided that the measuring mechanism and the converter chamber are not only separate components, but that the measuring mechanism and the converter chamber are also spatially separated or spaced apart from one another. As a result, the measuring mechanism and the measuring unit in the converter chamber are mechanically decoupled from one another. The separation is of course designed to be pressure-resistant and gas-tight. Due to the reduced oil volume, the measurement error caused by the temperature gradient is lower. Furthermore, due to the smaller oil volume, smaller membranes are also possible, which is important for realizing a coplanar sensor. Small membranes, on the other hand, are required for effective overload protection. This is very important for the realization of the coplanar sensor, since it enables small measuring ranges. In turn, small measuring ranges allow the activation or deflection of the membranes to be kept low, which is associated with smaller measuring errors.

In general it can be said that to protect the pressure-sensitive element against overpressure, the invention ensures that overpressure occurring on one side on the coplanar double membrane system is limited when it reaches the pressure-sensitive element such that destruction of the pressure-sensitive element is ruled out.

According to one embodiment of the differential pressure sensor according to the invention, the overload membranes are prestressed in such a way that they rest in a form-fitting or non-positive manner and essentially over the entire surface on the base body and only then stand out from the base body when a specified critical limit pressure is exceeded. This ensures that the overload or overpressure protection is only activated when the pressure to be measured is so high that there is a risk of the pressure-sensitive element being destroyed. In one embodiment, a capillary can be provided in the membrane bed or in the bearing surface of the overload membrane. A process membrane / separating membrane, which can be used, inter alia, in connection with the solution according to the invention is, for example, in US 10,656,039 B2 described.

As a result of the full-surface and preferably form-fitting contact of the overload membranes on the measuring unit, the measured pressure reaches the pressure chambers, the correspondingly coupled auxiliary and connecting capillaries to the corresponding additional pressure chamber and to the plus or minus side of the pressure-sensitive element. In terms of pressure dynamics, the overload membranes and the pressure-sensitive element are parallel. The deflection of the overload diaphragms is forcibly prevented up to a specified value as a result of their prestressing or is so small that it can be neglected. The preload is designed in such a way that it is larger than the measuring range of the differential pressure sensor. In particular, it is ensured that this condition applies throughout the lifetime of the differential pressure sensor, so that aging effects cannot have a negative impact on the measurement performance.

The pressure-sensitive element receives the pressure information for the positive side via the second pressure chamber, the second auxiliary capillary and the first connecting capillary coupled to it. The pressure-sensitive element receives the pressure information for the minus side via the first pressure chamber, the first auxiliary capillary and the second connecting capillary coupled to it. Due to the parallel connection, the pressures applied to the sides of the pressure-sensitive element also act on the back of the corresponding overload diaphragms. The pressure-sensitive element deflects according to the applied differential pressure. Incidentally, the effect of the parallel paths via the additional pressure chambers is almost negligible due to the prestressed and essentially form-fitting contact of the overload membranes on the housing of the measuring unit.

The prestressing of the overload diaphragms ensures that they are only deflected when a critical overpressure occurs on one of the double diaphragms, which would entail the risk of destroying the pressure-sensitive element. For example, as soon as a critical overpressure occurs at the second separating diaphragm, the second separating diaphragm is moved against the second overload diaphragm until it is in contact with the overload diaphragm. When the pretension of the first overload membrane is exceeded, it is deflected and the transmission fluid pushed out of the second pressure chamber is pushed into the first additional pressure chamber via the second auxiliary capillary and the first connecting capillary coupled to it. The pressure in the first additional pressure chamber and in the first pressure chamber that is operatively connected to it increases. This continues until the hydraulic fluid is shifted from the high-pressure side to the low-pressure side. The hydraulic pressure in the measuring unit can then no longer rise and the pressure limitation, i.e. the overpressure protection, takes effect.

One embodiment provides that the measuring mechanism is arranged in a process connection, with the process connection having a diameter in the area facing the process that is larger than the diameter in the area facing away from the process, in which it is connected to a housing connection for pressure, gas and and/or is connected in a liquid-tight manner.

In addition, it is proposed that the auxiliary capillaries in the measuring mechanism and the connecting capillaries in the measuring mechanism and in the converter chamber are capillary bores and/or capillary tubes. In particular, the connecting capillaries between the measuring mechanism and the converter chamber are aligned essentially parallel to the longitudinal axis of the measuring mechanism. Alternatively, of course, it is also possible for the capillaries to be arranged at an angle of less than 90°, preferably less than 45°, to the longitudinal axis of the measuring unit or the differential pressure sensor. Furthermore, it is provided that the connecting capillaries in the area between the measuring unit and the converter chamber are designed as capillary tubes which open pressure-tight, non-positively and gas-tight into the capillary bores in the measuring unit or in the converter chamber. Due to the separation of measuring mechanism and converter chamber, it is also possible in a simple manner to implement an electrically insulated separation between the two components—measuring mechanism and converter chamber. More on that later.

The converter chamber can be of any shape, as long as it is compact. Preferably, the transducer chamber has a cube shape, or a cylindrical shape, or a cylindrical shape with flattened opposing portions. At its end area facing the process, there are two connecting capillaries which—as already mentioned—are preferably arranged parallel to one another.

In order to ensure that an overload is limited before it reaches the pressure-sensitive element, an advantageous embodiment of the differential pressure sensor according to the invention proposes that the connecting capillaries and/or the auxiliary capillaries be designed and/or dimensioned in such a way that an overpressure that is above the predetermined critical limit pressure compensated by the overload protection before the overpressure is transmitted to the differential pressure measuring cell. In order to additionally protect the pressure-sensitive element against pressure peaks, dynamic brakes are built into the connecting lines/connecting capillaries between the measuring mechanism and the converter chamber, according to one embodiment of the differential pressure measuring transducer. The dynamic brakes are flow resistances, eg sintered metal inserts. The dynamic brakes can also be designed in such a way that they also assume the function of explosion protection.

Furthermore, it is provided that the auxiliary capillaries in the measuring chamber in a first section are led out of the corresponding pressure chamber essentially parallel to the longitudinal axis of the differential pressure sensor and in a second section are led with a change of direction of approximately 90° to the corresponding connecting capillaries.

An embodiment of the differential pressure sensor according to the invention proposes that the hydraulic system of the differential pressure sensor has two filling bores in extension of the auxiliary capillaries running in the second section for the purpose of filling with a hydraulic fluid. After filling with the hydraulic fluid, each of the filling bores is closed in a pressure-tight and gas-tight or at least liquid-tight manner with a closure element. For example, the closure element is a ball that is pressed into the bore and then caulked. It is also possible to weld the closure element in the bore. The closure elements are preferably arranged as close as possible to the crossing points of the auxiliary capillaries with the connecting capillaries. This has the advantage that the filling quantity of transmission fluid in the hydraulic system is reduced. If the sealing element is located far outside, i.e. close to the outer wall of the process connection, the required amount of transmission liquid can be reduced by inserting filling elements, e.g. filling rods, into the filling bores.

The filling bores run either in the area of the process connection facing the process - which requires longer lateral bores due to the larger diameter, or in the area of the process connection facing away from the process - whereby the lateral bores are smaller, while the auxiliary bores are longer.

The connection capillaries can also be designed in such a way that they electrically insulate the converter chamber from the measuring unit. The electrical insulation of the converter chamber from the measuring mechanism is preferably carried out via additional elements. These can be arranged in the measuring mechanism in the pressure path and/or in the capillaries and/or in the converter chamber in the transition from the connecting capillaries to the converter chamber. An additional insulating element can be, in particular, a ceramic insulating body or an insulating glazing. The connection must be gas-tight, either as a soldered connection or as a glazing. As stated, the electrical insulators can be provided in the converter chamber and/or in the measuring mechanism and/or between the measuring mechanism and the converter chamber. In particular, the electrical insulators can also be integrated as intermediate pieces in the connecting capillaries designed as capillary tubes.

• - Guarding für besseres EMV (elektromagnetisches Verhalten);
• - Geringerer bzw. kein Fremdspannungseinfluss;
• - Möglichkeit einen kapazitiven Siliziumchip einzusetzen, bei dem das Guarding eine Voraussetzung ist, dass nur geringere Störkapazitäten auftreten;
• - Das bislang erforderliche isolierende Element z.B. ein Keramiksockel, ein Glassockel oder eine ausreichend isolierende Klebung in der Wandlerkammer kann entfallen; Bei einer bevorzugten Ausgestaltung des erfindungsgemäßen Differenzdrucksensor wird das drucksensitive Element, üblicherweise ein Silizium-Chip, bevorzugt auf einen Silizium-Sockel aufgebracht. Nimmt man einen Silizium-Sockel anstelle des sonst üblichen Glassockels, so lässt sich ein günstigeres thermisches Verhalten (T-Hysterese) und ein geringerer statischer Druckfehler erreichen. Erklärung: Der E-Modul von Glas ist verschieden von dem E-Modul von Silizium. Bei Glas tritt eine größere Verformung und somit ein größerer Fehler infolge eines statischen Drucks auf als bei Silizium. Da Silizium jedoch kein Isolator ist, sondern eine gewisse Leitfähigkeit aufweist, sind für den sicheren elektrischen Betrieb Mindestisolationsstrecken erforderlich. Diese können z.B. durch in die Verbindungsleitungen eingesetzte keramische Isolierkörper und/oder entsprechend ausgestaltete Dynamikbremsen realisiert werden.
• - Der volle oder partielle Ex-Schutzverguss in der Wandlerkammer, der bislang bei Differenzdrucksensoren erforderlich war, kann entfallen. Bislang wurde der Verguss genutzt, um die Mindestabstände der stromführenden Elemente zum Massepotential möglichst gering halten zu können. Diese Abstandsreduzierung kann bei der Ausgestaltung der Erfindung entfallen, wo die Isolationselemente in den Verbindungskapillaren angeordnet sind. Zwecks Erzielung einer sicheren elektrischen Isolierung können die erforderlichen Mindestabstände um einiges kleiner ausfallen als beiden bislang bekannt gewordenen Lösungen. Auch lassen sich diese Mindestabstände ohne großen Aufwand erreichen.

This makes it possible to separate earth and ground (circuit zero point; Ue = reference point of the electrical supply = ground) and to achieve the following advantages for the current feedthrough:

• - Guarding for better EMC (electromagnetic behavior);
• - Lower or no external voltage influence;
• - Possibility to use a capacitive silicon chip, in which the guarding is a prerequisite that only low interference capacitances occur;
• - The previously required isolating element, for example a ceramic base, a glass base or a sufficiently insulating bond in the converter chamber, can be omitted; In a preferred embodiment of the differential pressure sensor according to the invention, the pressure-sensitive element, usually a silicon chip, is preferably applied to a silicon base. If a silicon base is used instead of the usual glass base, a more favorable thermal behavior (T hysteresis) and a lower static pressure error can be achieved. Explanation: The modulus of elasticity of glass is different from the modulus of elasticity of silicon. Glass suffers from greater deformation and thus greater error due to static pressure than silicon. However, since silicon is not an insulator but has a certain conductivity, there are minimum insulation distances for safe electrical operation necessary. These can be implemented, for example, by using ceramic insulating bodies in the connecting lines and/or correspondingly designed dynamic brakes.
• - The full or partial explosion protection potting in the converter chamber, which was previously required for differential pressure sensors, can be omitted. So far, encapsulation has been used in order to be able to keep the minimum distances between the current-carrying elements and the ground potential as small as possible. This reduction in distance can be omitted in the embodiment of the invention where the insulation elements are arranged in the connecting capillaries. In order to achieve reliable electrical insulation, the required minimum distances can turn out to be somewhat smaller than in the two solutions that have been known hitherto. These minimum distances can also be achieved without great effort.

Furthermore, it is provided that the electrical connecting pins or connecting lines from the electrical converter are routed in a gas-tight manner through one of the end regions of the converter chamber facing away from the process in the direction of an electronic circuit board. This is preferably done via glass bushings. Because the transducer chamber is electrically isolated from the movement, the glass feedthrough PINs can be smaller and therefore have a higher throughput. The aim is in particular to achieve a pressure resistance that is greater than 1280 bar. Smaller PINs/encapsulation elements also allow more PINs to be accommodated in the same space. This may also mean that less oil volume is required.

In order to increase the measurement accuracy, the converter chamber is designed in such a way that the same transmission liquid or oil volumes are present on the low-pressure side (-) and the high-pressure side (+). The oil volumes on the high-pressure and low-pressure side can be equalized, for example, by creating a corresponding additional volume by enlarging or lengthening one of the bores.

In order to record and subsequently compensate for the influence of the static pressure on the measured values of the differential pressure sensor, a corresponding pressure-sensitive element for measuring the static pressure is provided in the converter chamber. In order to keep the oil volume as small as possible, the pressure-sensitive element for measuring the differential pressure and the pressure-sensitive element for measuring the static pressure are stacked one on top of the other. This is where the advantage of the previously mentioned smaller PINs comes into play: since the PINs are smaller, the four additional PINs, which provide the measured values of the static pressure element, can be accommodated in the converter chamber without having to enlarge it . The arrangement of the PINs is dealt with in more detail below in the description of the figures.
However, it is also possible to arrange the pressure-sensitive element for measuring the differential pressure and the pressure-sensitive element for measuring the static pressure next to one another.

• 1a: eine schematische Darstellung einer ersten Ausgestaltung des erfindungsgemäßen Differenzdruckmessaufnehmers,
• 1b: eine Verdeutlichung der Wirkung des Überlastschutzes bei dem in 1a gezeigten Differenzdruckmessaufnehmer,
• 2a: eine schematische Darstellung einer zweiten Ausgestaltung des erfindungsgemäßen Differenzdruckmessaufnehmers,
• 2b: eine Verdeutlichung der Wirkung des Überlastschutzes bei dem in 2a gezeigten Differenzdruckmessaufnehmer,
• 2c: eine Skizze der Arbeitsweise des koplanaren Differenzdruckmessaufnehmers im Messbetrieb,
• 2d: eine Skizze der Arbeitsweise des koplanaren Differenzdruckmessaufnehmers im Überlastfall,
• 3a: eine perspektivische Ansicht des in 2a gezeigten koplanaren Differenzdruckmessaufnehmers,
• 3b: eine Draufsicht auf die Unterseite (Kennzeichnung C) des in 2a gezeigten koplanaren Differenzdruckmessaufnehmers,
• 3c: einen Schnitt durch die in 2a gezeigte Variante des Differenzdruckmessaufnehmers im Bereich der ersten Verbindungskapillaren,
• 3d: einen Schnitt durch die in 2a gezeigte Variante des Differenzdruckmessaufnehmers im Bereich der zweiten Verbindungskapillaren,
• 4: eine perspektivische Darstellung der Stromdurchführung,
• 4a: eine Explosionsdarstellung einer bevorzugten Ausgestaltung der Wandlerkammer mit Stromdurchführung,
• 5: unterschiedliche Darstellungen vorteilhafter Varianten, wie die elektrische Isolierung zwischen Messwerk und Wandlerkammer erreicht wird,
• 6: unterschiedliche Ansichten und Schnitte durch eine Wandlerkammer mit einer Einheit zur Kompensation des statischen Drucks,
• 7: die Schaltung der elektrischen Anschlüsse von Differenzdruckmesszelle und statischer Druckmesszelle, und
• 8: einen Längsschnitt durch einen schematisch dargestellten Differenzdruckmesssaufnehmer, und
• 9: eine Draufsicht auf einen Füllkörper, bei dem die Druckmesszelle und die Druckmesszelle für den statischen Druck in einer Ebene angeordnet sind.

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

• 1a : a schematic representation of a first embodiment of the differential pressure sensor according to the invention,
• 1b : a clarification of the effect of the overload protection at the in 1a shown differential pressure sensor,
• 2a : a schematic representation of a second embodiment of the differential pressure sensor according to the invention,
• 2 B : a clarification of the effect of the overload protection at the in 2a shown differential pressure sensor,
• 2c : a sketch of the mode of operation of the coplanar differential pressure sensor in measurement mode,
• 2d : a sketch of the operation of the coplanar differential pressure sensor in the event of an overload,
• 3a : a perspective view of the in 2a shown coplanar differential pressure sensor,
• 3b : a plan view of the underside (marking C) of the in 2a shown coplanar differential pressure sensor,
• 3c : a cut through the in 2a shown variant of the differential pressure sensor in the area of the first connection capillaries,
• 3d : a cut through the in 2a shown variant of the differential pressure sensor in the area of the second connection capillaries,
• 4 : a perspective view of the current bushing,
• 4a : an exploded view of a preferred embodiment of the converter chamber with current feedthrough,
• 5 : different representations of advantageous variants, such as electrical insulation is reached between the measuring mechanism and the converter chamber,
• 6 : different views and sections through a converter chamber with a static pressure compensation unit,
• 7 : the wiring of the electrical connections of the differential pressure measuring cell and the static pressure measuring cell, and
• 8th : a longitudinal section through a differential pressure measuring sensor shown schematically, and
• 9 : a plan view of a packing in which the pressure measuring cell and the pressure measuring cell for the static pressure are arranged in one plane.

In 1 a shows the course of the connecting capillaries 10a, 10b and the auxiliary capillaries 11a, 11b and their coupling according to a first embodiment of the differential pressure sensor 1 according to the invention. The differential pressure sensor 1 is used to determine the differential pressure of two pressures p1, p2. The measurement of the differential pressure of two pressures p1, p2, for example in a pipe, is used to determine the flow rate. A further application of a differential pressure measuring sensor 1 is, for example, determining the fill level of a fluid medium located in a tank.

The differential pressure sensor 1 consists of a measuring unit 2 and a converter chamber 3. A coplanar double membrane system with two double membranes 4a, 4b is provided on or in an end region of the measuring unit 2 facing the process. The measuring unit 2 is arranged in the process connection 21 . A differential pressure measuring cell 12 with a pressure-sensitive element 13 is arranged in the converter chamber 3 . The converter chamber 3 is located in the housing adapter 22. In the case shown, the converter chamber 3 and measuring mechanism 2 are separated from one another.

The two double diaphragms 4a, 4b each consist of a process diaphragm 5a, 5b or a separating diaphragm 5a, 5b and an overload diaphragm 6a, 6b arranged behind the separating diaphragm 5a, 5b in the direction of the pressure effect. A first pressure chamber 7a is formed between the first separating membrane 5a and the first overload membrane 6a and a first additional pressure chamber 8a or overpressure chamber 8a is formed between the first overload membrane 6a and the base body 9 . Furthermore, a second pressure chamber 7b is formed between the second separating membrane 5b and the second overload membrane 6b and a second additional pressure chamber 8b or a second overpressure chamber 8b is formed between the second overload membrane 6b and the base body 9 .

The first additional pressure chamber 8a is assigned a first connecting capillary 10a and the second additional pressure chamber 8b is assigned a second connecting capillary 10b. A first auxiliary capillary 11a is assigned to the first pressure chamber 7a. A second auxiliary capillary 11b is assigned to the second pressure chamber 7b. The pressure-transmitting coupling/crossing between the first auxiliary capillary 11a and the second connecting capillary 10b or between the second auxiliary capillary 11b and the first connecting capillary 10a is implemented in the measuring mechanism 2 according to the invention.
The pressure transmission and the limitation of the overpressure to a level that does not damage or destroy the pressure-sensitive element 13 work in parallel in the solution according to the invention, with pressure-dynamics ensuring that the overpressure peÜL is limited before it reaches the pressure measuring cell 12. The overpressure peÜL is limited via a correspondingly predetermined prestressing of the overload diaphragms 6a, 6b. These are prestressed in such a way that during normal measuring operation they rest almost completely and form-fitting on the housing of the base body 9 and only lift off from the base body 9 when the specified critical limit pressure is exceeded. The integrity of the pressure-sensitive element is ensured up to this limit pressure.

1b shows the in 1a illustrated configuration of a differential pressure sensor 1 in the case of overload or excess pressure. In the case shown, an overpressure peÜL occurs on one side on the right-hand separating diaphragm 5b. Without the protection device according to the invention, the overpressure peÜL would be transferred to the pressure-sensitive element 13 . Due to the one-sided overload, there is a risk that the silicon chip will be destroyed.

According to the invention, this danger is averted by a bypass. The bypass consists of the auxiliary capillaries 11a, 11b, which intersect with the connecting capillaries 10a, 10b in the measuring unit 2 and direct the pressure or any excess pressure that occurs to the back of the overload membranes 6a, 6b. The path that the overpressure PeÜL takes through the capillary system is in 2 B symbolized by arrows: The excess pressure PeÜL is hydraulically transmitted via the auxiliary capillary 11b to the connecting capillary 10a and from there to the back of the overload membrane 6a of the first double membrane 4a.

If an overpressure PeÜL occurs at the right-hand separating membrane 5b, then the overpressure PeÜL is increased via the pressure chamber 7b to the overload transfer membrane 6b. Since this is already applied to the housing 9, the pressure does not reach the pressure-sensitive element 13 via the connecting capillary 10b. The overpressure PeÜL is routed via the pressure chamber 7b, the auxiliary capillary 11b, the connecting capillary 10a, the additional pressure chamber 8a and the overload membrane 6a to the pressure chamber 7a. Overload diaphragm 6a and separating diaphragm 5a are deflected and the additional pressure chamber 8a and the pressure chamber 7a absorb the transfer fluid 16 displaced from the high-pressure side 4b until the separating diaphragm 5b rests on the overpressure diaphragm 6b. A further increase in pressure is then no longer possible. At the same time, the pressure, which is always below the critical limit value, is also applied to the plus side of the pressure-sensitive element 13 .

In order to have an even greater certainty that the overpressure is limited before it reaches the sensitive area of the pressure chip (usually also a membrane), the connecting capillaries 10a, 10b, like the auxiliary capillaries 11a, 11b, preferably have appropriately adapted capillary geometries, which are directed in the direction of the pressure sensitive chip 13 perform a braking function. In particular, the connecting and auxiliary capillaries 10a, 10b, 11a, 11b, which are usually designed as bores, in the measuring mechanism 2 and in the converter chamber 3 are suitably dimensioned in terms of length and diameter. In the case shown, upstream dynamic brakes 18a, 18b and possibly 20a, 20b are additionally provided. These are preferably arranged in the capillary tubes 17a, 17b, which open into the capillary bores 10a, 10b of the measuring mechanism 2. Additionally or alternatively, dynamic brakes 20a, 20b are used in the connecting capillaries 10a, 10b of the converter chamber 3. These delay the transmission of the pressure, in particular an overpressure peÜL, and also protect the pressure-sensitive element 13 from pressure peaks occurring in the process.

The dynamic brakes 18a, 18b, 20a, 20b can be sintered metal inserts. If the differential pressure sensor 1 is used in an area at risk of explosion, the dynamic brakes 18a, 18b, 20a, 20b are made of a non-conductive material. In this case, the dynamic brakes 18a, 18b, 20a, 20b then fulfill a dual function: delayed transmission of the pressure and explosion protection, which is designed according to the required type of explosion protection.

The figures 2a and 2 B largely correspond to those in figures 1a and 1b shown embodiment of the differential pressure sensor according to the invention 1. The main difference is in the arrangement of the filling holes 14a, 14b. The capillary system of the differential pressure sensor 1 is filled with transmission liquid 16 via these filling bores 15a, 15b. The filling bores 14a, 14b run laterally in the process connection 21 or in the measuring unit 2. In the configurations shown, the filling bores 14a, 14b run parallel to the base of the process connection 21. The position is chosen so that the oil volume required for filling is as small as possible.

For this reason, the closure elements 15a, 15b are also provided as close as possible to the crossing points of the capillaries 10a, 10b, 11a, 11b. Incidentally, this configuration is good in the 3c and 3d to see. The embodiment is preferred in which the closed filling bores 14a, 14b end in the rear space of the sensor and there preferably within the housing adapter 22. Due to this arrangement in the interior of the differential pressure sensor 1, the filling bores 14a, 14b—behind the closure elements 15a, 15b—are protected against corrosion. Furthermore, the corresponding areas of the filling bores 14a, 14b can also be cast to the outside; However, this is due to the position of the filling bores 14a, 14b closed off from the outside space in the case of the embodiment shown in FIGS 2a and 2 B configuration shown is not absolutely necessary.

A preferably spherical closure element 15a, 15b is provided as a pressure-tight, gas-tight or at least liquid-tight closure, which is pressed into the filling bore 14a, 14b and then caulked.

In principle, other methods for closing the openings are also available. However, welding is regarded as critical insofar as negative repercussions on the defined properties of the transmission liquid 16 can occur as a result of the temperature increase.

In the figures 2c and 2d the operation of the coplanar double membrane system 4 is shown in more detail. The figures 2c and 2d refer to those in the figures 2a or. 2 B illustrated embodiment of the differential pressure sensor according to the invention 1. 2c shows the mode of operation of the coplanar membrane system 4 in regular measurement operation and in the initial stage when an overpressure PeÜL occurs. The overload diaphragms 6a, 6b are in full contact with the base body 9 of the measuring mechanism 2. The system is largely form-fitting, the overload diaphragms 6a, 6b are correspondingly prestressed. The measured pressure p1, p2 reaches the back of the additional d pressure chambers 8a, 8b and parallel to the converter chamber 3 or to the pressure-sensitive measuring element 13.

The overload diaphragms 6a, 6b and the measuring element 13 are hydraulically parallel, so the same pressure acts on both. At the overload diaphragms 6a, 6b and the measuring element 13, the differential pressure dp is formed from p ₁ -p ₂ . The pressure-sensitive measuring element 13 deflects depending on the differential pressure. Since the overload membranes 6a, 6b are prestressed, their deflection is prevented up to a specified value. Of course, the bias is also larger than the measuring range.

The pressure-sensitive measuring element 13 receives the pressure information for the plus side (+) via the pressure chamber 7b and the connecting capillaries 11b, 10a. The pressure information for the minus side (-) of the pressure-sensitive measuring element 13 is transmitted via the pressure chamber 7a and the connecting capillaries 11a, 10b. The effect of the parallel paths via the additional pressure chambers 8a, 8b is almost negligible due to the preloaded and approximately form-fitting contact of the overload membranes 6a, 6b on the base body 9 of the measuring unit 2.

2d shows the mode of operation of the coplanar membrane system 4 in the event of an overload, ie when a one-sided overpressure PeÜL occurs on the right-hand side of the differential pressure sensor 1 at the separating membrane 5b. The pressure in the pressure chamber 7b increases under the effect of the overpressure PeÜL. Since the overload membrane 6b rests against the base body 9, a pressure increase in the additional pressure chamber 8b is not possible. The pressure reaches the node (2) via the pressure chamber 7b, the connecting capillary 11b and acts via the connecting capillary 10a on the plus side (+) of the pressure-sensitive measuring element 13 and parallel on the back of the overload diaphragm 6a facing away from the process. If the pressure exceeds the preload of the overload membrane 6a, the latter is deflected and the additional pressure chamber 8a can absorb the oil 16 which is displaced from the pressure chamber 7b. The pressure in the additional pressure chamber 8a and the subsequent pressure chamber 7a increases continuously. The overload diaphragm 6a and the separating diaphragm 5a are deflected in the direction of the process. This process only ends when all the oil 16 has been displaced from the pressure chamber 7b and the separating membrane 5b comes to rest on the overload membrane 6b supported on the base body 9 of the measuring unit 2. As soon as this condition is reached, the pressure inside the hydraulic system cannot rise any further: the pressure limitation, ie the overload protection, unfolds its effect.

In the 3a-3d are different views of an embodiment of the differential pressure sensor 1 according to the invention to see, in large parts of the figures 2a and 2 B correspond to the configuration shown. 3a shows a perspective view, 3b a top view of the underside of the in 2a shown coplanar differential pressure sensor 1, 3c a longitudinal section through the in 2a shown variant of the differential pressure sensor 1 in the first connecting capillaries 10a and 3d a longitudinal section through the in 2a shown variant of the differential pressure sensor 1 in the region of the second connecting capillaries 10b. If the differential pressure measuring sensor according to the invention is to be used in an area at risk of explosion, the Exd implementation can take place via a suitable connection/design between the process connection 21 and the housing adapter 22 . Individually or in combination, the following are possible: an Exd weld, an Exd gap or an Exd thread.

4 shows a schematic representation of the converter chamber 3 with the two connecting capillaries 10a, 10b. The pressures p1, p2 applied to the separating membranes 5a, 5b are transmitted hydraulically to the pressure-sensitive element 15 via the connecting capillaries 10a, 10b. The pressure p1 is on the minus side, the pressure p2 on the plus side. In this configuration, two vertical (ie parallel to the longitudinal axis of the differential pressure sensor 1) bores and one horizontal bore are required in the converter chamber 3 . It may also make sense to have two filling and closure accesses to make filling easier. The dynamic brakes that may be provided can make filling more difficult or greatly increase the filling times.

4a shows an exploded view of a cube-shaped configuration of the differential pressure measuring cell 12 and visualizes how the individual components of the differential pressure measuring cell 12 and the current bushing 23 are arranged in the converter chamber 3 . An insulating base 31, such as a ceramic base or a glass base, is bonded to the bottom surface of a recess in the transducer chamber 3 with a suitable adhesive 30. FIG. The pressure measuring cell 12 , which preferably has a silicon chip as the pressure-sensitive element 13 , is connected to the ceramic base 31 by means of an adhesive 32 . For the purpose of minimizing the required volume of oil or the volume of the transmission liquid 16, a filling body 33 is provided, which encloses the pressure measuring cell 12 as closely as possible in the side area. The filling body 33 is closed with a cover 34 . The converter chamber 3 is closed to the outside with a sealing cap 34 for the current feedthrough 23 . The isolation of the Sil ziumchips 13 takes place via the insulating base 31, which has a thickness d≥0.5 mm, for example for explosion protection reasons. Furthermore, the filling body 33 with the cover 34, which is made of a suitable plastic, for example, insulates the silicon chip 13 and its bond connections 24. The connecting capillaries 10a, 10b designed as capillary tubes 17 are shown below.

5 shows different representations of advantageous variants of how the electrical insulation between measuring unit 2 and converter chamber 3 can be realized via insulation elements 25, preferably insulation tubes 25, adapted in or on the capillary tubes. Incidentally, in these configurations, the ceramic base 31 glued in place in the converter chamber 3, as described above, can be dispensed with. The electrical insulation between the measuring mechanism 2 and the converter chamber 3 takes place in the area of the capillary tubes 17 between the corresponding connecting capillaries 10a, 10b or at the transition of the capillary tubes 17 to the measuring mechanism 2 or to the converter chamber 3.

As in the illustration on the left 5 can be seen, the electrically insulating ceramic tubes 25 in the converter chamber 3 ( 5a) , in the intermediate area between converter chamber 3 and measuring unit 2 ( 5c ) or in measuring element 2 ( 5b) be executed. The insulation preferably achieves potential isolation from ground or the internal ground. This is required for Ex ia safety level and electrical safety. The alternative that the Ex isolation can also be achieved by appropriate design of the dynamic brakes 18a, 18b has already been mentioned above. The differential pressure measuring sensor 1 according to the invention can also be used in potentially explosive areas. To do this, it must meet the ex d safety requirements, for which additional safety measures are required.

6 shows a converter chamber 3 or its components and different sections through the converter chamber 3. In this embodiment, a measuring cell 27 is also provided for determining the static pressure. In 6a the power feedthrough 23 is shown with an advantageous arrangement of the connection pins 26 for the differential pressure measuring cell 14 with the pressure-sensitive element 13 and the measuring cell 27 arranged above it for determining the static pressure. The PINs 26 are preferably found symmetrically in the edge area of the two pressure measuring cells 12, 27, which are preferably stacked one on top of the other. However, it can also be an advantage to position at least one PIN asymmetrically in order to make subsequent processing, for example soldering on the circuit board, safer later in the process (poka-yoke principle). Either the PINs 26 all end in one plane or in parallel planes. Two pins 1.1, 1.2 of the eight pins 26 ( 7c ) can be used without insulation, e.g. B. soldered, since they are on ground / housing potential.

PINS 2 and 3 could be electrically connected together, i.e. in a common PIN, to potential ( 7b) . The electrical insulation then preferably takes place via a glazing. If the ground PINS 1.1, 1.2, which correspond to PINS 1, 8, and PINS 2, 3 for the power supply are combined, the two bridges are connected in parallel to the power supply. This circuit is shown in 7c .

In order to meet the requirements of electrical safety and for use in hazardous areas, all PINs 26 are arranged or spaced such that there is sufficient dielectric strength both from PIN 26 to PIN 26 and from PIN 26 to the housing/ground of the converter chamber 3 is. Since the oil volume is all the smaller, the smaller the interior space of the converter chamber 3 is dimensioned, the interior space preferably has a diameter of <10 mm, in particular <8 mm.

6b shows a longitudinal section through the pressure measuring cells 12, 27 stacked one on top of the other. The power feedthrough 23 is designed to be pressure-resistant and gas- or liquid-resistant. The PINs 26 are either soldered or glazed. Alternatively they are pressed in or impulse welded. Only the ground PINS are arranged in the housing without insulation, all others must be insulated. This is possible if the housing is isolated and connected to the measuring unit via the capillaries. Otherwise, all PINs (including the ground PINS) must be electrically isolated.

In order to minimize the oil volume required, the differential pressure measuring cell 12 with the bonding wires 24 is embedded as closely as possible in the filling body 33 and the filling body cap 37 . The packing cap 37 has a recess for receiving the chip/static pressure cell 27 . The sealing cap 35 follows an insulating film 29. 6c shows a cross section in the area of the differential pressure measuring cell 12, while 6d shows a section in the area of the chip 27 for measuring the static pressure.

In the figures 7a , 7b and 7c the circuits for the previously mentioned arrangements of the PINs 26 are shown. The differential pressure (1.2) and the static pressure (1.1) are measured via two resistance bridges. The measured values are sent to an electronic circuit board 36 for further processing. 7a shows the principle Connection diagram of the two Si chips 13, 27. In order to be able to operate the circuit completely independently, eight PINs 26 are required; minimum are six PINs 26 ( 7b) necessary. 7c shows a circuit with 7 PINs 26. This interim solution has a separate plus supply, but a common ground. The advantage of using a smaller number of PINs 26 is clearly that space can be saved. The PINs 26 for the ground connection can also be implemented as a direct connection between the corresponding PIN 26 or the corresponding PINs 26 and the conductive housing (metal housing). The connection can be made by soldering, pressing in or welding.

• (2), (3): PINs 26 für den Anschluss der Versorgungsspannung,
• (4), (5): PINs 26 für das Brückenausgangssignal der statischen Druckmesszelle 27,
• (6), (7): PINs 26 für das Brückenausgangssignal der Differenzdruckmesszelle 14,
• 1 = (1.1): Versorgungsspannungs-Minusanschluss (Masse),
• 8 = (1.2): Versorgungsspannungs-Minusanschluss (Masse).

Below is the function of each in 7 shown PINs 26 listed:

• (2), (3): PINs 26 for connecting the supply voltage,
• (4), (5): PINs 26 for the bridge output signal of the static pressure measuring cell 27,
• (6), (7): PINs 26 for the bridge output signal of the differential pressure measuring cell 14,
• 1 = (1.1): supply voltage minus connection (ground),
• 8 = (1.2): supply voltage minus connection (ground).

As already described above, a common PIN 26 can also be used for the ground connection.

• ① Innenvolumen, das ev. mit einem Verguss ausgefüllt ist
• ② Schweißung zwischen Gehäuseadapter 22 und Messwerk 2
• ③ Druckzuführung Wandlerkammer 3 - Messwerk 2
• ④ Druckzuführung zur Wandlerkammer 3
• ⑤ Stromdurchführung 23 mit PIN/Einglasung
• ⑥ Ölverschluss 20
• ⑧ Trennung zwischen Gehäuse und Sensorrückraum 16
• ⑨ Exd-Gewinde Gehäuse-Sensor, z.B. über ein Second Containment und/oder einen Verguss
• ⑩ Verschlusskappe 35 Stromdurchführung 23 (GDF)

8th shows a longitudinal section through a differential pressure measuring sensor 1 shown schematically 8th lists the different zones AG to which the differential pressure sensor 1 is exposed. Since the zones in 8th are listed by name, they will not be repeated here. The encircled numbers schematically document components that characterize the basic structure of the differential pressure sensor 1 according to the invention:

• ① Inner volume that may have been filled with encapsulation
• ② Welding between housing adapter 22 and measuring mechanism 2
• ③ Pressure supply converter chamber 3 - measuring unit 2
• ④ Pressure supply to converter chamber 3
• ⑤ Power feedthrough 23 with PIN/glazing
• ⑥ Oil cap 20
• ⑧ Separation between the housing and the rear of the sensor 16
• ⑨ Exd thread housing sensor, eg via a second containment and/or encapsulation
• ⑩ Closing cap 35 power feedthrough 23 (GDF)

9 shows a plan view of a packing 33 in which the pressure measuring cell 12 and the pressure measuring cell 27 for the static pressure are arranged in one plane. The distances between the pins - can be seen in the 9 only the recesses 38 for the pins from the power feedthrough - are chosen so that a galvanic isolation is ensured.

Reference List

1

differential pressure sensor

2

measuring mechanism

3

converter chamber

4

double membrane system

4a, 4b

first double diaphragm, second double diaphragm

5a, 5b

first separating diaphragm, second separating diaphragm

6a, 6b

first overload diaphragm, second overload diaphragm

7a, 7b

first pressure chamber, second pressure chamber

8a, 8b

first additional pressure chamber, second additional pressure chamber

9

body

10a, 10b

first connection capillary, second connection capillary

11a, 11b

first auxiliary capillary, second auxiliary capillary,

12

differential pressure measuring cell

13

pressure-sensitive differential pressure element

14a, 14b

filling hole

15a, 15b

closure element

16

Transmission Fluid / Hydraulic Fluid / Oil

17a, 17b

capillary tubes

18a, 18b

dynamic brake

19

intermediate area

20a, 20b

dynamic brake

21

process connection

22

housing adapter

23

current feedthrough

24

bond connection

25

isolation tube

26

pin code

27

Measuring cell for determining the static pressure

28

Packing cap with recess

29

Insulation film / PTFE film

30

Adhesive for gluing the insulation base (ceramic base)

31

ceramic base

32

Adhesive for gluing the pressure measuring cell

33

random packing

34

packing cover

35

Closing cap for power feedthrough

36

electronics board

37

fill cap

38

Recess for pin

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 3222620 A1 [0004]
• WO 2018/165122 A1 [0006]
• US 10656039 B2 [0013]

Claims (19)

Differential pressure sensor (1) for determining the differential pressure of two pressures (p1, p2) with a measuring unit (2) and a converter chamber (3), with a coplanar double membrane system (4) on or in an end area of the measuring unit (2) facing the process two double membranes (4a, 4b) are provided and a differential pressure measuring cell (12) with a pressure-sensitive element (13) is arranged in the converter chamber (3), the two double membranes (4a, 4b) each consisting of a separating membrane (5a, 5b) and an overload membrane (6a, 6b) arranged behind the separating membrane (5a, 5b) in the direction of the pressure effect, with a first pressure chamber (7a) between the first separating membrane (5a) and the first overload membrane (6a) and between the first overload membrane ( 6a) and the base body (9) a first additional pressure chamber (8a) is formed, wherein between the second separating membrane (5b) and the second overload membrane (6b) a second pressure chamber (7b) and between the z wide overload membrane (6b) and the base body (9), a second additional pressure chamber (8b) is formed, with the first additional pressure chamber (8a) being assigned a first connecting capillary (10a), with the second additional pressure chamber (8b) being assigned a second connecting capillary (10b). a first auxiliary capillary (11a) is assigned to the first pressure chamber (7a), and a second auxiliary capillary (11b) is assigned to the second pressure chamber (7b), a pressure-transmitting coupling between the first auxiliary capillary (11a) and the second Connecting capillary (10b) or between the second auxiliary capillary (11b) and the first connecting capillary (10a) in the measuring unit (2) is arranged, and the two pressures (p1, p2) via the corresponding auxiliary and connecting capillaries (10a, 10b , 11a, 11b) - protected against overpressure on one side - are transmitted hydraulically to the differential pressure measuring cell (12). differential pressure sensor claim 1 , wherein the overload membranes (6a, 6b) are prestressed in such a way that they rest against the base body (9) and only lift off from the base body (9) when a predetermined critical limit pressure is exceeded. differential pressure sensor claim 1 or 2 , wherein the measuring mechanism (2) is arranged in a process connection (21), the process connection (21) in the area facing the process having a diameter which is larger than the diameter in the area facing away from the process, in which it is connected to a housing connection (22) is pressure-tight, gas-tight and/or liquid-tight. Differential pressure sensor according to one or more of the preceding claims, wherein the auxiliary capillaries (11a, 11b) in the measuring mechanism (2) and the connecting capillaries (10a, 10b) in the measuring mechanism (2) and in the converter chamber (3) are capillary bores and/or or capillary tubes. Differential pressure sensor according to one or more of the preceding claims, wherein the connecting capillaries (10a, 10b) between the measuring mechanism (2) and the converter chamber (3) run essentially parallel to the longitudinal axis of the measuring mechanism (2), and the connecting capillaries (10a, 10b) between the measuring mechanism (2) and the converter chamber (3) being designed as capillary tubes (17a, 17b) in an intermediate region between the measuring mechanism (2) and the converter chamber (3). Differential pressure sensor according to one or more of Claims 1 until 5 , wherein the connecting capillaries (10a, 10b) and/or the auxiliary capillaries (11a, 11b) are designed and/or dimensioned in such a way that an overpressure (peÜL) above the predetermined critical limit pressure is limited by means of the overload protection before the overpressure the differential pressure measuring cell (12) is transmitted. Differential pressure sensor according to one or more of Claims 1 until 6 wherein in the pressure paths (10a, 10b; 17a, 17b) at least one pressure dynamic brake (18a, 18b) is inserted in each of the connecting capillaries (10a, 10b) and/or capillary tubes (17a, 17b). Differential pressure sensor according to one or more of the preceding claims, wherein the auxiliary capillaries (11a, 11b) are led out of the corresponding pressure chamber (7a, 7b) in a first section essentially parallel to the longitudinal axis (L) of the differential pressure sensor (1) and in a second section with a change of direction of approximately 90° to the corresponding connecting capillaries (10b, 10a). differential pressure sensor claim 8 , two filling bores (14a, 14b) for filling the hydraulic system of the differential pressure sensor (1) with a hydraulic fluid (16) being provided as an extension of the auxiliary capillaries (11a, 11b) running in the second section, the filling bores (14a, 14b) each being of a closure element (15a, 15b) after being filled with the hydraulic fluid (16) in a pressure-tight and gas-tight or at least liquid-tight manner. Differential pressure sensor according to one or more of the preceding claims, wherein filling holes (14a, 14b) run either in the area of the process connection (21) facing the process or in the area of the process connection (21) facing away from the process, so that filling holes (14a, 14b) are protected against corrosion are arranged within the housing adapter. Differential pressure sensor according to one or more of the preceding claims, wherein electrical connection pins (26) are guided in a gas-tight manner through one of the end regions of the converter chamber (3) facing away from the process in the direction of an electronic circuit board (36). Differential pressure sensor according to one or more of the preceding claims, electrical insulators being provided in the connecting capillaries (10a, 10b, 17a, 17b) which electrically insulate the converter chamber (3) from the measuring unit (2). differential pressure sensor claim 12 or any of the preceding Claims 1 - 11 , wherein the connecting capillaries (10a, 10b, 17a, 17b) are provided at least in sections with an electrical insulator (25), in particular a ceramic insulating body or an insulating glazing, and/or via a gas-tight connection in the corresponding capillaries of the measuring unit (2) and/or the converter chamber (3) or the capillary tubes 17a, 17b). Differential pressure sensor according to one or more of the preceding claims, wherein the electrical insulators (25) are provided in the converter chamber (3) and/or in the measuring mechanism (2) and/or in the space between the measuring mechanism (2) and the converter chamber (3). Differential pressure sensor according to one or more of the preceding claims, wherein the electrical insulators (25) are each integrated as intermediate pieces in the connecting capillaries (10a, 10b) designed as capillary tubes (17a, 17b). Differential pressure sensor according to one or more of the preceding claims, wherein the pressure-sensitive element (13) is a silicon chip, and wherein the differential pressure (p2-p1) is determined using a capacitive or resistive measuring method or resonator. Differential pressure sensor according to one or more of the preceding claims, wherein the converter chamber (3) is designed in such a way that the same transmission liquid volumes are present on the low-pressure side (-) and the high-pressure side (+). Differential pressure sensor according to one or more of the preceding claims, wherein a pressure-sensitive element (27) for measuring the static pressure is provided in the converter chamber (3). Differential pressure sensor according to one or more of the preceding claims, wherein the pressure-sensitive element (13) for measuring the differential pressure (dp) and the pressure-sensitive element (27) for measuring the static pressure (pstat) are stacked on top of one another or arranged next to one another in the converter chamber (3). .

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