WO2021047896A1 - Absolute pressure gauge having a relative-measurement pressure measurement cell - Google Patents

Absolute pressure gauge having a relative-measurement pressure measurement cell Download PDF

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Publication number
WO2021047896A1
WO2021047896A1 PCT/EP2020/073635 EP2020073635W WO2021047896A1 WO 2021047896 A1 WO2021047896 A1 WO 2021047896A1 EP 2020073635 W EP2020073635 W EP 2020073635W WO 2021047896 A1 WO2021047896 A1 WO 2021047896A1
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Prior art keywords
pressure
measuring
housing
measurement
measuring device
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PCT/EP2020/073635
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German (de)
French (fr)
Inventor
Heinz Walter
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Ifm Electronic Gmbh
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Publication of WO2021047896A1 publication Critical patent/WO2021047896A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
    • G01L19/14—Housings
    • G01L19/148—Details about the circuit board integration, e.g. integrated with the diaphragm surface or encapsulation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L15/00—Devices or apparatus for measuring two or more fluid pressure values simultaneously

Definitions

  • the invention relates to a measuring device for detecting the absolute pressure of a medium adjoining the pressure measuring device.
  • Pressure measuring devices or pressure sensors are used in many industrial sectors for measuring pressure. They often have a pressure measuring cell as a transducer for the process pressure and evaluation electronics for signal processing. Typical pressure measuring cells measure the pressure either capacitively or resistively.
  • Typical capacitive pressure measuring cells consist of a compact unit with a ceramic base body and an elastic membrane, an annular joint, typically a glass solder ring, being arranged between the base body and the membrane.
  • the resulting cavity between the base body and the diaphragm - also referred to as the measuring chamber - enables the diaphragm to move longitudinally as a result of the influence of pressure.
  • electrodes are provided which together form a measuring capacitor.
  • the effect of pressure causes deformation of the membrane, which results in a change in the capacitance of the measuring capacitor. With the help of an evaluation unit, the change in capacitance is recorded and converted into a pressure reading.
  • a capacitive pressure measuring device is known, for example, from DE 102010 062622 A1.
  • resistively measuring pressure cells record the deflection of the membrane with the help of electromechanical transducers, for example by means of strain gauges, which are deformed with the deflected membrane and convert the deflection into a corresponding resistance value or voltage or current value.
  • Such pressure measuring cells are available both in one piece in the form of a monolith, but also in two pieces with a base body and a thin membrane.
  • a resistive pressure measuring device is known, for example, from DE 102010035862 A1.
  • the so-called process connection is located on the lower part of the measuring device, through which the measuring device is connected to a container or pipe carrying the medium.
  • these pressure gauges are used for monitoring or control of processes. They are therefore often connected to higher-level control units (PLC) via a plug connection.
  • PLC higher-level control units
  • pressure measuring devices used in process measurement technology are provided to measure a relative pressure, that is to say the output of the pressure values recorded by the pressure measuring cell in relation to the ambient or atmospheric pressure.
  • a relative pressure that is to say the output of the pressure values recorded by the pressure measuring cell in relation to the ambient or atmospheric pressure.
  • atmospheric pressure in the room, which enables the longitudinal mobility of the measuring membrane of the measuring cell as a result of the influence of pressure.
  • this is the aforementioned measuring chamber between the base body and the membrane.
  • resistively measuring pressure measuring cell this is usually the entire interior of the housing of the measuring device, provided the measuring cell is not encapsulated.
  • the measuring devices that measure a relative pressure have a pressure compensation device that includes an opening of whatever type.
  • This opening can be arranged in the housing wall, as disclosed, for example, in DE 102013 200840 A1 by the applicant, or also in the plug connection, as known from DE 102012201 018 A1 by the applicant.
  • the measuring devices must be cleaned frequently in order to maintain hygienic conditions, which is done, for example, by means of a high pressure or steam jet.
  • DE 10232028 B4 proposes, for example, to provide an opening in the housing wall which is closed with a liquid-repellent and gas-permeable segment in order to achieve pressure equalization between the interior of the housing and the external environment of the housing.
  • the segment consists of a film, for example a plastic film, or a membrane, for example made of PTFE.
  • DE 19708 116 A1 proposes the use of a breathable and waterproof film, such as are known, for example, under the name Goretex® or Sympatex®.
  • the object of the invention is to propose an absolute pressure measuring device that can be produced simply and inexpensively.
  • the core of the invention is the use of a conventional, relatively measuring pressure measuring cell that does not require an evacuated cavity, as well as a barometric air pressure transducer that records the internal pressure within the measuring device housing, which also acts on the second side of the measuring membrane facing away from the medium.
  • a processing unit is also provided that increases the relative pressure measured value at the output of the evaluation electronics by the internal housing pressure recorded by the barometric air pressure transducer.
  • the measuring device can thus provide a measured value, for example via a cable connection, which is independent of external pressure conditions.
  • Both the pressure measuring cell and the barometric air pressure transducer can be manufactured or procured inexpensively, among other things because no special structural requirements have to be placed on the barometric air pressure transducer if it is located inside the measuring device housing and thus against external, in particular mechanical influences of a process environment is protected. Furthermore, no special requirements have to be placed on the measuring device housing or the connection between the measuring device housing and the process connection, e.g. with regard to tightness, since the barometric air pressure transducer immediately detects pressure changes inside the measuring device housing and calculates them accordingly with the measurement results of the relatively measuring pressure measuring cell . It is particularly advantageous to design the barometric air pressure transducer as an SMD component, since these components are available very inexpensively.
  • FIG. 1 an electronic pressure measuring device
  • FIG. 2 shows a cross section through the pressure measuring device.
  • FIG. 1 shows an electronic pressure measuring device 1 for use in process measurement technology, which is manufactured and sold by the applicant under the designation PNxxxx.
  • the measuring device 1 consists essentially of a housing 2, which is divided into an upper part 3 and a lower part 4.
  • the lower part 4, also referred to as a process connection on the one hand includes the sensor unit 10 (not shown) in the form of a pressure measuring cell and on the other hand enables the mechanical connection of the measuring device 1 with the container or pipe containing the medium.
  • the evaluation electronics 30 (not shown), which are provided for evaluating and processing the measurement signals supplied by the sensor unit 10, which can then be picked up via the plug connection 8 and, for example, forwarded to a PLC.
  • the measuring device 1 is operated via the operating elements 7, i.e. a parameterization or a setting of essential key data, such as the switching points, is carried out.
  • the respective actions are displayed to the user via the display 6.
  • FIG. 2 shows a very schematic representation of a cross section through the measuring device 1 together with a representation of a conventional capacitive, Relatively measuring pressure measuring cell 10.
  • the pressure measuring cell 10 consists essentially of a base body 12 and a measuring membrane 11.
  • the structure and mode of operation of such pressure measuring cells is well known, for example from EP 2606330 B1 of the applicant.
  • a capacitive pressure measuring cell 10 is shown as an example in FIG. 2, the invention can also be implemented with a resistive pressure measuring cell, as is known, for example, from DE 102010035862 B4 by the applicant.
  • the housing 2 of the measuring device 1 essentially contains the electronic units, consisting of evaluation electronics 30 and a processing unit 40, which is preferably designed as a microcontroller.
  • the pressure measuring cell 10 is connected to the interior of the housing 2 via a ventilation channel 13, i.e. the same pressure pi is applied to the side of the measuring membrane 11 facing away from the medium that also prevails in the interior of the housing 2.
  • a ventilation channel 13 i.e. the same pressure pi is applied to the side of the measuring membrane 11 facing away from the medium that also prevails in the interior of the housing 2.
  • the measuring device 1 does not have such a pressure compensation opening in the housing 2.
  • the pressure pi in the interior of the housing 2 can change permanently, primarily due to temperature influences, which must be taken into account in terms of measurement technology.
  • a barometric air pressure transducer 20 is provided in the interior of the housing 2, which is preferably arranged as an SMD component on the same circuit carrier as the evaluation electronics 30 and the processing unit 40.
  • An example of such a barometric air pressure transducer 20 is the Bosch BME280.
  • the relative pressure measured value at the output of the evaluation electronics 30 is increased by the measured internal pressure value pi of the housing recorded by the barometric air pressure transducer 20 and is made available at the indicated plug connection 8 for further processing.
  • the housing 2 of the measuring device 1 therefore does not have to be be hermetically sealed. Every change in pressure inside the housing 2 is detected by the barometric air pressure transducer 20 and taken into account by the processing unit 40 when calculating the process pressure.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Fluid Pressure (AREA)

Abstract

The invention relates to a measuring device for measuring the absolute pressure of a medium in a container, having at least one process connection (3) comprising a relative-measurement pressure measurement cell (10), and a housing (2) placed on the process connection (3), in the interior chamber of which an evaluating electronics unit (30) for evaluating and processing a measurement signal generated by the pressure measurement cell (10) is arranged. In order to to make the measurement device simple and cost-effective to produce, according to the invention the housing (2) comprises a processing unit (40) and a barometric air pressure converter (20) for detecting the housing interior pressure pI prevailing in the interior of the housing (2), in addition to the evaluation electronics unit (30), and, in the processing unit (40), the relative pressure measurement value at the output of the evaluation electronics unit (30) is increased by the housing interior pressure pI detected by the barometric air pressure converter (20).

Description

Absolutdruckmessgerät mit einer relativ messenden DruckmesszelleAbsolute pressure measuring device with a relative measuring pressure measuring cell
Die Erfindung betrifft ein Messgerät zur Erfassung des Absolutdrucks eines an das Druckmessgerät angrenzenden Mediums. The invention relates to a measuring device for detecting the absolute pressure of a medium adjoining the pressure measuring device.
Druckmessgeräte bzw. Drucksensoren werden in vielen Industriebereichen zur Druckmessung eingesetzt. Sie weisen häufig eine Druckmesszelle, als Messwandler für den Prozessdruck, und eine Auswerteelektronik zur Signalverarbeitung auf. Typische Druckmesszellen erfassen den Druck entweder kapazitiv oder resistiv.Pressure measuring devices or pressure sensors are used in many industrial sectors for measuring pressure. They often have a pressure measuring cell as a transducer for the process pressure and evaluation electronics for signal processing. Typical pressure measuring cells measure the pressure either capacitively or resistively.
Typische kapazitive Druckmesszellen bestehen aus einer kompakten Einheit mit einem keramischen Grundkörper und einer elastischen Membran, wobei zwischen dem Grundkörper und der Membran eine ringförmige Fügestelle, typischerweise ein Glaslotring, angeordnet ist. Der sich dadurch ergebende Hohlraum zwischen Grundkörper und Membran - auch als Messkammer bezeichnet - ermöglicht die längsgerichtete Beweglichkeit der Membran infolge eines Druckeinflusses. An der Unterseite der Membran und an der gegenüberliegenden Oberseite des Grundkörpers sind jeweils Elektroden vorgesehen, die zusammen einen Messkondensator bilden. Durch Druckeinwirkung kommt es zu einer Verformung der Membran, was eine Kapazitätsänderung des Messkondensators zur Folge hat. Mit Hilfe einer Auswerteeinheit wird die Kapazitätsänderung erfasst und in einen Druckmesswert umgewandelt. Ein kapazitives Druckmessgerät ist bspw. aus der DE 102010 062622 A1 bekannt. Typical capacitive pressure measuring cells consist of a compact unit with a ceramic base body and an elastic membrane, an annular joint, typically a glass solder ring, being arranged between the base body and the membrane. The resulting cavity between the base body and the diaphragm - also referred to as the measuring chamber - enables the diaphragm to move longitudinally as a result of the influence of pressure. On the lower side of the membrane and on the opposite upper side of the base body, electrodes are provided which together form a measuring capacitor. The effect of pressure causes deformation of the membrane, which results in a change in the capacitance of the measuring capacitor. With the help of an evaluation unit, the change in capacitance is recorded and converted into a pressure reading. A capacitive pressure measuring device is known, for example, from DE 102010 062622 A1.
Demgegenüber erfassen resistiv messende Druckmesszellen die Auslenkung der Membrane mithilfe von elektromechanischen Wandlern, bspw. mittels Dehnungsmessstreifen, der mit der ausgelenkten Membran verformt wird und die Auslenkung in einen entsprechenden Widerstandswert bzw. Spannungs- oder Stromwert umwandelt. Derartige Druckmesszellen gibt es sowohl einstückig in Form eines Monoliths, aber auch zweistückig mit einem Grundkörper und einer dünnen Membrane. Ein resistives Druckmessgerät ist bspw. aus der DE 102010035862 A1 bekannt. On the other hand, resistively measuring pressure cells record the deflection of the membrane with the help of electromechanical transducers, for example by means of strain gauges, which are deformed with the deflected membrane and convert the deflection into a corresponding resistance value or voltage or current value. Such pressure measuring cells are available both in one piece in the form of a monolith, but also in two pieces with a base body and a thin membrane. A resistive pressure measuring device is known, for example, from DE 102010035862 A1.
Am Unterteil des Messgeräts befindet sich der sogenannte Prozessanschluss, durch den das Messgerät mit einem das Medium führenden Behälter oder Rohr verbunden ist. In der Regel dienen diese Druckmessgeräte zur Überwachung oder Steuerung von Prozessen. Sie sind deshalb häufig über einen Steckeranschluss mit übergeordneten Steuereinheiten (SPS) verbunden. The so-called process connection is located on the lower part of the measuring device, through which the measuring device is connected to a container or pipe carrying the medium. As a rule, these pressure gauges are used for monitoring or control of processes. They are therefore often connected to higher-level control units (PLC) via a plug connection.
Typischerweise sind in der Prozessmesstechnik eingesetzte Druckmessgeräte dafür vorgesehen, einen Relativdruck zu messen, also die Ausgabe der von der Druckmesszelle erfassten Druckwerte in Relation zum Umgebungs- bzw. Atmosphärendruck. Dabei ist es insbesondere erforderlich, dass in dem Raum Atmosphärendruck herrscht, der die längsgerichtete Beweglichkeit der Messmembran der Messzelle infolge eines Druckeinflusses ermöglicht. Bei einer kapazitiven Messzelle ist das die zuvor erwähnte Messkammer zwischen Grundkörper und Membran. Bei einer resistiv messenden Druckmesszelle ist das zumeist der gesamte Gehäuseinnenraum des Messgeräts, sofern die Messzelle nicht gekapselt ist. Typically, pressure measuring devices used in process measurement technology are provided to measure a relative pressure, that is to say the output of the pressure values recorded by the pressure measuring cell in relation to the ambient or atmospheric pressure. In this case, it is particularly necessary that there is atmospheric pressure in the room, which enables the longitudinal mobility of the measuring membrane of the measuring cell as a result of the influence of pressure. In the case of a capacitive measuring cell, this is the aforementioned measuring chamber between the base body and the membrane. In the case of a resistively measuring pressure measuring cell, this is usually the entire interior of the housing of the measuring device, provided the measuring cell is not encapsulated.
Dementsprechend weisen die Messgeräte, die einen Relativdruck messen, eine Druckausgleichsvorrichtung auf, die eine wie auch immer geartete Öffnung umfasst. Diese Öffnung kann in der Gehäusewandung angeordnet sein, wie bspw. in der DE 102013 200840 A1 der Anmelderin offenbart, oder auch im Steckeranschluss, wie aus der DE 102012201 018 A1 der Anmelderin bekannt. Dabei müssen die Messgeräte zur Einhaltung hygienischer Bedingungen jedoch häufig gereinigt werden, was bspw. mittels eines Hochdruck- oder Dampfstrahlers erfolgt. Accordingly, the measuring devices that measure a relative pressure have a pressure compensation device that includes an opening of whatever type. This opening can be arranged in the housing wall, as disclosed, for example, in DE 102013 200840 A1 by the applicant, or also in the plug connection, as known from DE 102012201 018 A1 by the applicant. In this case, however, the measuring devices must be cleaned frequently in order to maintain hygienic conditions, which is done, for example, by means of a high pressure or steam jet.
Aus dem Stand der Technik sind hierfür einteilige Barrieren in Form von Folien oder Membrane bekannt. Die DE 10232028 B4 schlägt bspw. vor, in der Gehäusewand eine Öffnung vorzusehen, welche mit einem flüssigkeitsabweisenden sowie gasdurchlässigen Segment abgeschlossen ist, um einen Druckausgleich zwischen dem Innenraum des Gehäuses und der äußeren Umgebung des Gehäuses zu erreichen. Das Segment besteht dabei aus einer Folie, bspw. einer Kunststofffolie, oder einer Membran, bspw. aus PTFE. Die DE 19708 116 A1 schlägt diesbezüglich vor, eine atmungsaktive und wasserdichte Folie zu verwenden, wie sie zum Beispiel unter dem Namen Goretex® oder Sympatex® bekannt sind. For this purpose, one-piece barriers in the form of foils or membranes are known from the prior art. DE 10232028 B4 proposes, for example, to provide an opening in the housing wall which is closed with a liquid-repellent and gas-permeable segment in order to achieve pressure equalization between the interior of the housing and the external environment of the housing. The segment consists of a film, for example a plastic film, or a membrane, for example made of PTFE. In this regard, DE 19708 116 A1 proposes the use of a breathable and waterproof film, such as are known, for example, under the name Goretex® or Sympatex®.
Unter bestimmten Bedingungen können diese Folien und Membrane technologisch an ihre Grenzen kommen und müssen vor Verschmutzung sowie dem Einfluss der Reinigungsstrahler geschützt werden. In solchen Fällen bietet sich der Einsatz von Druckmessgeräten an, die einen Absolutdruck messen, also den Druck im Vergleich zu einem Vakuum als Referenzpunkt, weil diese Messgeräte keine Öffnung als Druckausgleichsvorrichtung benötigen. Derartige Messgeräte sind jedoch vor allem wegen der speziellen Druckmesszellen mit einer evakuierten Kavität sehr aufwendig in der Herstellung und ihr Einsatz daher für vergleichsweise einfache Anwendungen zumeist unwirtschaftlich. Under certain conditions, these foils and membranes can reach their technological limits and must be protected from contamination and the influence of cleaning emitters. In such cases, it is advisable to use pressure measuring devices that measure an absolute pressure, i.e. the pressure in comparison to a vacuum as a reference point, because these measuring devices do not require an opening as a pressure compensation device. Such measuring devices, however, are very expensive to manufacture, primarily because of the special pressure measuring cells with an evacuated cavity, and their use is therefore mostly uneconomical for comparatively simple applications.
Aufgabe der Erfindung ist es, ein Absolutdruckmessgerät vorzuschlagen, das einfach und preisgünstig herstellbar ist. The object of the invention is to propose an absolute pressure measuring device that can be produced simply and inexpensively.
Nach der Erfindung wird diese Aufgabe durch ein Druckmessgerät mit den Merkmalen des Anspruchs 1 gelöst. Vorteilhafte Ausgestaltungen der Erfindung sind in den Unteransprüchen angegeben. According to the invention, this object is achieved by a pressure measuring device with the features of claim 1. Advantageous refinements of the invention are given in the subclaims.
Kern der Erfindung ist die Verwendung einer herkömmlichen, relativ messenden Druckmesszelle, die keine evakuierte Kavität benötigt, sowie eines barometrischen Luftdruckwandlers, der den Innendruck innerhalb des Messgerätegehäuses erfasst, der auch auf die vom Medium abgewandte zweite Seite der Messmembran einwirkt. Neben der Auswerteelektronik zur Auswertung und Verarbeitung des von der Druckmesszelle generierten Messsignals ist noch eine Verarbeitungseinheit vorgesehen, die den Relativdruckmesswert am Ausgang der Auswerteelektronik um den vom barometrischen Luftdruckwandler erfassten Gehäuseinnendruck erhöht. Im Ergebnis kann das Messgerät damit bspw. über einen Kabelanschluss einen Messwert zur Verfügung stellen, der unabhängig von äußeren Druckbedingungen ist.The core of the invention is the use of a conventional, relatively measuring pressure measuring cell that does not require an evacuated cavity, as well as a barometric air pressure transducer that records the internal pressure within the measuring device housing, which also acts on the second side of the measuring membrane facing away from the medium. In addition to the evaluation electronics for evaluating and processing the measurement signal generated by the pressure measuring cell, a processing unit is also provided that increases the relative pressure measured value at the output of the evaluation electronics by the internal housing pressure recorded by the barometric air pressure transducer. As a result, the measuring device can thus provide a measured value, for example via a cable connection, which is independent of external pressure conditions.
Sowohl die Druckmesszelle als auch der barometrische Luftdruckwandler sind dabei jeweils preisgünstig herstellbar bzw. zu beschaffen, u.a., weil an den barometrischen Luftdruckwandler keine besonderen baulichen Anforderungen gestellt werden müssen, wenn er sich innerhalb des Messgerätegehäuses befindet und damit vor äußeren, insbesondere mechanischen Einflüssen einer Prozessumgebung geschützt ist. Des Weiteren müssen auch an das Messgerätegehäuse sowie an die Verbindung zwischen Messgerätegehäuse und Prozessanschluss keine besonderen Anforderungen, bspw. hinsichtlich der Dichtigkeit gestellt werden, da durch den barometrischen Luftdruckwandler Druckveränderungen im Inneren des Messgerätegehäuses sofort erfasst und entsprechend mit den Messergebnissen der relativ messenden Druckmesszelle verrechnet wird. Besonders vorteilhaft ist dabei, den barometrischen Luftdruckwandler als SMD- Bauteil auszuführen, da diese Bauteile sehr preisgünstig erhältlich sind. Both the pressure measuring cell and the barometric air pressure transducer can be manufactured or procured inexpensively, among other things because no special structural requirements have to be placed on the barometric air pressure transducer if it is located inside the measuring device housing and thus against external, in particular mechanical influences of a process environment is protected. Furthermore, no special requirements have to be placed on the measuring device housing or the connection between the measuring device housing and the process connection, e.g. with regard to tightness, since the barometric air pressure transducer immediately detects pressure changes inside the measuring device housing and calculates them accordingly with the measurement results of the relatively measuring pressure measuring cell . It is particularly advantageous to design the barometric air pressure transducer as an SMD component, since these components are available very inexpensively.
Mit der Erfindung ist es nun möglich, auf sehr einfache Weise ein Druckmessgerät ohne Druckausgleichsöffnung herzustellen und damit weitgehend unabhängig von äußeren Bedingungen zu betreiben. With the invention it is now possible in a very simple manner to produce a pressure measuring device without a pressure compensation opening and thus to operate it largely independently of external conditions.
Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen unter Bezugnahme auf die Zeichnungen näher erläutert. The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawings.
Es zeigen schematisch: They show schematically:
Figur 1 ein elektronisches Druckmessgerät; FIG. 1 an electronic pressure measuring device;
Figur 2 einen Querschnitt durch das Druckmessgerät. FIG. 2 shows a cross section through the pressure measuring device.
Bei der nachfolgenden Beschreibung der bevorzugten Ausführungsformen bezeichnen gleiche Bezugszeichen gleiche oder vergleichbare Komponenten. In the following description of the preferred embodiments, the same reference symbols designate the same or comparable components.
In Figur 1 ist ein elektronisches Druckmessgerät 1 für den Einsatz in der Prozessmesstechnik abgebildet, das von der Anmelderin unter der Bezeichnung PNxxxx hergestellt und vertrieben wird. Das Messgerät 1 besteht im Wesentlichen aus einem Gehäuse 2, das sich unterteilt in ein Oberteil 3 und ein Unterteil 4. Das Unterteil 4, auch als Prozessanschluss bezeichnet, umfasst zum einen die Sensoreinheit 10 (nicht gezeigt) in Form einer Druckmesszelle und ermöglicht zum anderen die mechanische Verbindung des Messgeräts 1 mit dem das Medium enthaltenen Behälter oder Rohr. Im Gehäuse 2 befindet sich die Auswerteelektronik 30 (nicht gezeigt), die zur Auswertung und Aufbereitung der von der Sensoreinheit 10 gelieferten Messsignale vorgesehen ist, welche dann über den Steckeranschluss 8 abgegriffen und bspw. an eine SPS weitergeleitet werden können. FIG. 1 shows an electronic pressure measuring device 1 for use in process measurement technology, which is manufactured and sold by the applicant under the designation PNxxxx. The measuring device 1 consists essentially of a housing 2, which is divided into an upper part 3 and a lower part 4. The lower part 4, also referred to as a process connection, on the one hand includes the sensor unit 10 (not shown) in the form of a pressure measuring cell and on the other hand enables the mechanical connection of the measuring device 1 with the container or pipe containing the medium. In the housing 2 there is the evaluation electronics 30 (not shown), which are provided for evaluating and processing the measurement signals supplied by the sensor unit 10, which can then be picked up via the plug connection 8 and, for example, forwarded to a PLC.
Auf dem Oberteil 3 aufgesetzt ist ein Gehäusekopf 5, der u.a. eine Anzeigevorrichtung 6 und Bedienelemente 7 aufweist. Über die Bedienelemente 7 wird das Messgerät 1 bedient, d.h. eine Parametrierung oder eine Einstellung von wesentlichen Eckdaten, wie bspw. den Schaltpunkten vorgenommen. Die jeweiligen Aktionen werden dem Benutzer über die Anzeige 6 angezeigt. A housing head 5, which, among other things, has a display device 6 and operating elements 7, is placed on the upper part 3. The measuring device 1 is operated via the operating elements 7, i.e. a parameterization or a setting of essential key data, such as the switching points, is carried out. The respective actions are displayed to the user via the display 6.
Figur 2 zeigt in einer sehr schematischen Darstellung einen Querschnitt durch das Messgerät 1 zusammen mit einer Darstellung einer herkömmlichen kapazitiven, relativ messenden Druckmesszelle 10. Die Druckmesszelle 10 besteht im Wesentlichen aus einem Grundkörper 12 und einer Messmembran 11. Der Aufbau und die Funktionsweise derartiger Druckmesszellen ist hinlänglich bekannt, bspw. aus der EP 2606330 B1 der Anmelderin. Auch wenn in Fig. 2 eine kapazitive Druckmesszelle 10 beispielhaft dargestellt ist, lässt sich die Erfindung genauso auch mit einer resistiven Druckmesszelle realisieren, wie sie bspw. aus der DE 102010035862 B4 der Anmelderin bekannt ist. Figure 2 shows a very schematic representation of a cross section through the measuring device 1 together with a representation of a conventional capacitive, Relatively measuring pressure measuring cell 10. The pressure measuring cell 10 consists essentially of a base body 12 and a measuring membrane 11. The structure and mode of operation of such pressure measuring cells is well known, for example from EP 2606330 B1 of the applicant. Even if a capacitive pressure measuring cell 10 is shown as an example in FIG. 2, the invention can also be implemented with a resistive pressure measuring cell, as is known, for example, from DE 102010035862 B4 by the applicant.
Das Gehäuse 2 des Messgeräts 1 beinhaltet im Wesentlichen die Elektronikeinheiten, bestehend aus einer Auswerteelektronik 30 und einer Verarbeitungseinheit 40, welche vorzugsweise als Mikrocontroller ausgebildet ist. Über einen Entlüftungskanal 13 ist die Druckmesszelle 10 mit dem Innenraum des Gehäuses 2 verbunden, d.h. an der dem Medium abgewandten Seite der Messmembran 11 liegt der gleiche Druck pi an, der auch im Innenraum des Gehäuses 2 herrscht. Auf diese Weise wird bei einem Relativdruckmessgerät mittels einer Öffnung in der Gehäusewand ein Druckausgleich zwischen dem Gehäuseinnenraum und der Umgebung erreicht, so dass an der Messmembran auch Atmosphärendruck anliegt. Wie bereits eingangs beschrieben können diese Druckausgleichsöffnungen, insbesondere die die Öffnungen bedeckende Folien und Membrane, unter bestimmten Bedingungen technologisch an Grenzen kommen.The housing 2 of the measuring device 1 essentially contains the electronic units, consisting of evaluation electronics 30 and a processing unit 40, which is preferably designed as a microcontroller. The pressure measuring cell 10 is connected to the interior of the housing 2 via a ventilation channel 13, i.e. the same pressure pi is applied to the side of the measuring membrane 11 facing away from the medium that also prevails in the interior of the housing 2. In this way, in a relative pressure measuring device, pressure equalization between the housing interior and the surroundings is achieved by means of an opening in the housing wall, so that atmospheric pressure is also applied to the measuring membrane. As already described at the outset, these pressure compensation openings, in particular the foils and membranes covering the openings, can reach their technological limits under certain conditions.
Das erfindungsgemäße Messgerät 1 weist keine solche Druckausgleichsöffnung im Gehäuse 2 auf. Infolge dessen kann sich der Druck pi im Innenraum des Gehäuses 2 permanent verändern, vor allem durch Temperatureinflüsse, was entsprechend messtechnisch berücksichtigt werden muss. H ierfür ist im Innenraum des Gehäuses 2 ein barometrischer Luftdruckwandler 20 vorgesehen, welcher vorzugsweise als SMD-Bauteil auf demselben Schaltungsträger wie die Auswerteelektronik 30 und die Verarbeitungseinheit 40 angeordnet ist. Ein Beispiel für einen solchen barometrischen Luftdruckwandler 20 ist der Bosch BME280. The measuring device 1 according to the invention does not have such a pressure compensation opening in the housing 2. As a result of this, the pressure pi in the interior of the housing 2 can change permanently, primarily due to temperature influences, which must be taken into account in terms of measurement technology. For this purpose, a barometric air pressure transducer 20 is provided in the interior of the housing 2, which is preferably arranged as an SMD component on the same circuit carrier as the evaluation electronics 30 and the processing unit 40. An example of such a barometric air pressure transducer 20 is the Bosch BME280.
In der Verarbeitungseinheit 40 wird dann - angedeutet durch die Pfeile - der Relativdruckmesswert am Ausgang der Auswerteelektronik 30 um den vom barometrischen Luftdruckwandler 20 erfassten Gehäuseinnendruckmesswert pi erhöht und wird an dem angedeuteten Steckeranschluss 8 zur weiteren Verarbeitung zur Verfügung gestellt. Das Gehäuse 2 des Messgeräts 1 muss deswegen auch nicht hermetisch dicht sein. Jede Druckveränderung im Inneren des Gehäuses 2 wird von dem barometrischen Luftdruckwandler 20 erfasst und durch die Verarbeitungseinheit 40 bei der Berechnung des Prozessdruckes entsprechend berücksichtigt. In the processing unit 40 - indicated by the arrows - the relative pressure measured value at the output of the evaluation electronics 30 is increased by the measured internal pressure value pi of the housing recorded by the barometric air pressure transducer 20 and is made available at the indicated plug connection 8 for further processing. The housing 2 of the measuring device 1 therefore does not have to be be hermetically sealed. Every change in pressure inside the housing 2 is detected by the barometric air pressure transducer 20 and taken into account by the processing unit 40 when calculating the process pressure.
Bezugszeichenliste List of reference symbols
1 Messgerät 1 measuring device
2 Gehäuse 2 housings
3 Oberteil 3 top
4 Unterteil, Prozessanschluss 4 lower part, process connection
5 Gehäusekopf 5 housing head
6 Anzeige 6 display
7 Bedienelemente 7 controls
8 Steckeranschluss 8 plug connection
10 Druckmesszelle 10 pressure measuring cell
11 Messmembran 11 measuring membrane
12 Grundkörper 12 base bodies
13 Entlüftungskanal 13 ventilation duct
20 barometrischer Luftdruckwandler 30 Auswerteelektronik 20 barometric air pressure transducer 30 evaluation electronics
40 Verarbeitungseinheit 40 processing unit

Claims

Patentansprüche Claims
1. Messgerät zur Messung des Absolutdrucks eines Mediums in einem Behältnis, mit zumindest einem eine relativ messende Druckmesszelle (10) umfassenden Prozessanschluss (3) und einem auf den Prozessanschluss (3) aufgesetzten Gehäuse (2), in dessen Innenraum eine Auswerteelektronik (30) zur Auswertung und Verarbeitung eines von der Druckmesszelle (10) generierten Messsignals angeordnet ist, wobei die Druckmesszelle (10) eine auslenkbare Messmembran (11) umfasst, deren erste Seite zumindest teilweise mit dem Medium in Kontakt steht und deren von dem Medium abgewandten zweiten Seite mit dem Gehäuseinnenraum in Kontakt steht und einen elektromechanischen Wandler aufweist, der eine vom auf die Messmembran (11) einwirkenden Druck p abhängige Durchbiegung der Messmembran (11) in eine elektrische Größe umwandelt, wobei das Gehäuse (2) neben der Auswerteelektronik (30) noch eine Verarbeitungseinheit (40) sowie einen barometrischen Luftdruckwandler (20) zur Erfassung des im Inneren des Gehäuses (2) herrschenden und auf die vom Medium abgewandte zweite Seite der Messmembran (11) einwirkenden Gehäuseinnendrucks pi umfasst, und in der Verarbeitungseinheit (40) der Relativdruckmesswert am Ausgang der Auswerteelektronik (30) um den vom barometrischen Luftdruckwandler (20) erfassten Gehäuseinnendrucks pi erhöht wird. 1. Measuring device for measuring the absolute pressure of a medium in a container, with at least one process connection (3) comprising a relatively measuring pressure measuring cell (10) and a housing (2) placed on the process connection (3), in the interior of which there is evaluation electronics (30) is arranged for evaluating and processing a measurement signal generated by the pressure measuring cell (10), the pressure measuring cell (10) comprising a deflectable measuring membrane (11) whose first side is at least partially in contact with the medium and whose second side facing away from the medium is in contact with is in contact with the interior of the housing and has an electromechanical converter which converts a deflection of the measuring membrane (11), which is dependent on the pressure p acting on the measuring membrane (11), into an electrical quantity, the housing (2) also having an electrical variable in addition to the evaluation electronics (30) Processing unit (40) and a barometric air pressure transducer (20) for detecting the inside of the housing ( 2) the prevailing internal pressure pi of the housing acting on the second side of the measuring membrane (11) facing away from the medium, and in the processing unit (40) the relative pressure measured value at the output of the evaluation electronics (30) is increased by the internal pressure of the housing pi recorded by the barometric air pressure transducer (20) .
2. Messgerät nach Anspruch 1 , dadurch gekennzeichnet, dass der barometrische Luftdruckwandler (20) als SMD-Bauteil ausgeführt ist. 2. Measuring device according to claim 1, characterized in that the barometric air pressure transducer (20) is designed as an SMD component.
PCT/EP2020/073635 2019-09-09 2020-08-24 Absolute pressure gauge having a relative-measurement pressure measurement cell WO2021047896A1 (en)

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