WO2013017569A1 - Method for checking the function of a pressure sensor - Google Patents

Method for checking the function of a pressure sensor Download PDF

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Publication number
WO2013017569A1
WO2013017569A1 PCT/EP2012/064892 EP2012064892W WO2013017569A1 WO 2013017569 A1 WO2013017569 A1 WO 2013017569A1 EP 2012064892 W EP2012064892 W EP 2012064892W WO 2013017569 A1 WO2013017569 A1 WO 2013017569A1
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WO
WIPO (PCT)
Prior art keywords
temperature
electromechanical
electromechanical transducer
measuring
transducers
Prior art date
Application number
PCT/EP2012/064892
Other languages
German (de)
French (fr)
Inventor
Rolf Müller
Markus Messmer
Heinz Walter
Original Assignee
Ifm Electronic Gmbh
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Filing date
Publication date
Application filed by Ifm Electronic Gmbh filed Critical Ifm Electronic Gmbh
Publication of WO2013017569A1 publication Critical patent/WO2013017569A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
    • G01L9/0051—Transmitting or indicating the displacement of flexible diaphragms using variations in ohmic resistance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/028—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure
    • G01D3/036—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure on measuring arrangements themselves
    • G01D3/0365—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure on measuring arrangements themselves the undesired influence being measured using a separate sensor, which produces an influence related signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/08—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K15/00—Testing or calibrating of thermometers
    • G01K15/007—Testing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L27/00—Testing or calibrating of apparatus for measuring fluid pressure
    • G01L27/007—Malfunction diagnosis, i.e. diagnosing a sensor defect
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/02—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning
    • G01L9/025—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning with temperature compensating means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/02—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning
    • G01L9/04—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning of resistance-strain gauges
    • G01L9/045—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning of resistance-strain gauges with electric temperature compensating means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/02—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning
    • G01L9/06—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning of piezo-resistive devices
    • G01L9/065—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning of piezo-resistive devices with temperature compensating means

Definitions

  • the invention relates to a method for checking the function of a
  • a pressure sensor for detecting the pressure prevailing in a medium comprising a pressure measuring cell with an elastic membrane and a temperature sensor for detecting the temperature.
  • the pressure within a medium adjacent to a measuring cell is often to be detected.
  • the measuring cell is part of the
  • Measuring device wherein it has an elastic membrane, one side of which is at least partially in contact with the medium and the other side facing away from the medium.
  • the pressure within the usually gaseous, liquid, pasty or at least free-flowing medium is determined by the fact that the medium deflects the elastic membrane differently depending on the pressure prevailing within the medium.
  • the deflection or reversible deformation of the membrane is converted from an electromechanical transducer, which is deformed with the deflected membrane, into a corresponding one
  • Measurement signal converted i. in a corresponding resistance value
  • the electromechanical transducer is usually a measuring bridge consisting of strain gauges.
  • Measuring cells and measuring devices of this type have been known for a long time and are used, for example, in many areas of process measuring technology for metrological process monitoring. Such measuring devices are produced by the applicant, for example, under the device designations PTxx and PKxx and placed on the market. The measuring ranges are currently usually up to 400 bar.
  • the measuring cells used are often made of metal, in particular of a steel, so that the strain gauges are directly influenced when changing the medium or the ambient temperature due to the good thermal conductivity of metals.
  • the converter is due to the different temperature coefficients of the
  • Strain gauges and / or the thermal deformation of the membrane detected a change in resistance and thus a pressure change whose
  • the actual amount may differ from the measured value. For example. can the actual pressure change will be zero while the meter is a
  • the electromechanical transducer must be temperature compensated, i. the proportion of in the immediate vicinity of the converter
  • a temperature sensor can be provided on the measuring cell.
  • a temperature sensor is preferably an NTC or PTC temperature sensor in question, for example.
  • Pt100 resistance thermometer As a Pt100 resistance thermometer
  • an evaluation unit e.g. one
  • Microcontroller then can mathematically the measured pressure value to the
  • Degradation effects are subject, which can lead to a false measurement of the temperature and thus to an incorrect compensation of the measured pressure value.
  • a reliable temperature measurement is necessary. Especially at
  • a common method for permanently checking the temperature sensor is a redundant design.
  • the measured values of at least two temperature sensors are compared in terms of magnitude and a malfunction is detected with a correspondingly large deviation.
  • a disadvantage of this simple redundant structure is that systematic errors are difficult or impossible to detect.
  • drift and aging effects are subject to a certain degree of randomness, so that it can not be ruled out that both temperature sensors have the same or similar error behavior over time.
  • the magnitude comparison of both temperature readings would not reveal any irregularities in this case.
  • DE 10 2004 035 014 A1 proposes a construction with diverse redundancy.
  • This arrangement includes at least two sensor elements with temperature-dependent impedance, which are integrated thermally coupled within a sensor head. In this case, the temperature-dependent impedances have different temperature / resistance characteristics, so the diversified
  • the object of the invention is to further improve the reliable temperature measurement while taking up space and in particular the manufacturing costs
  • the elastic membrane of the pressure measuring cell on a first and a second electromechanical transducer, wherein the first
  • Temperature characteristics have been adapted to each other. After the difference of the temperature-compensated measured values of the transducers relative to one another has been determined, a faulty function of the temperature measuring transducer and / or of the two electromechanical transducers can be detected if the specified threshold value is significantly exceeded or undershot.
  • the electromechanical transducers thus act indirectly as a temperature element, since they contribute in conjunction with the actual temperature sensor to control its exact measurement.
  • the prerequisite for the method is that two electromechanical transducers, ie strain gauges connected as a measuring bridge, are present on the membrane of the measuring cell and are thus in the same thermal environment. These may, for example, be arranged point-symmetrically or concentrically on the membrane, as described, for example, in the patent application DE102010035862A1.
  • the temperature characteristics of the electromechanical transducers describe the temperature-induced fault influences in different thermal situations, i. the respective percentage deviations of the actual value from the nominal value, wherein the nominal value is a constant resistance value. Due to manufacturing tolerances, these characteristics scatter very much even with identical elements - as in this case the strain gauges. The effect resulting from the scattering of the characteristic curves is ultimately evaluated, as will be described in more detail below. By interconnecting the individual resistors to form an electromechanical transducer or a measuring bridge, the effect resulting from the scattering of the characteristic curves is further enhanced.
  • the essential idea of the invention is therefore that it does not concern the actual measurement result of the temperature sensor to check for plausibility in terms of amount, but to check whether the difference of the compensated Temperature characteristics of both measuring bridges is zero. If there are deviations, it can be due to a faulty temperature compensation and thus to a
  • the method can thus be referred to as a method for self-diagnosis of the pressure measuring cell with regard to the detection of a faulty temperature compensation.
  • a basic requirement of the invention is that the temperature characteristics of both measuring bridges are sufficiently different from one another, the difference being at least 50 ppm, preferably 100, very particularly preferably 200 ppm. The greater the difference between the two characteristics the better the
  • Temperature sensor is disposed in an outer region of the membrane. Since the temperature sensors also respond to the elongation of the membrane surface and change their resistance, it is advantageous to place them at the edge of the membrane, where the change in the membrane surface is the lowest or almost zero.
  • the temperature compensation preferably takes place with the aid of a look-up table which is stored in a microcontroller.
  • Temperature compensation is comparatively high, so it is advantageous to deposit the individual scenarios, at which temperature which resistance value should exist, firmly in lookup tables. These can be stored in memory
  • MicroControllers are stored and are therefore quickly accessible.
  • An alternative here is that in the lookup table to the measured
  • Temperature values of the temperature sensor associated corrected measured values of the electromechanical converter are stored. The factory will be around the
  • the two electromechanical transducers i. the two measuring bridges are diversified, in which they each have a further thermistor component or only one measuring bridge has a further thermistor component.
  • a clear differentiation from the thermistor component is to be achieved, which supplies the data for the temperature compensation of the two measuring bridges Due to a plastic deformation of the membrane, after an offset, they can be mutually eliminated or reduced in amount such that the result is within the permissible range of the evaluation unit and therefore no error can be detected Due to the diverse structure, this case can be ruled out
  • both measuring bridges each have a thermistor component which is connected in parallel or in series with one another Inem the individual resistors can be switched.
  • the thermistors may be the same, but should then be implemented in the positive bridge branch for the first bridge and in the negative bridge for the second bridge. It is more advantageous to provide two different thermistors. At the same temperature influence and different
  • Thermistor devices must therefore necessarily different
  • Resistance elements are structurally adjusted accordingly.
  • the invention can be used in any measuring devices in which at least two
  • Sensors are present whose difference is evaluated to each other and must be temperature compensated for further evaluation. It is conceivable, e.g. the application with flow or flow sensors.
  • Figure 1 is a plan view of an embodiment of a Druckmesszelie for
  • Figure 2 is a side sectional view of a pressure measuring cell according to
  • FIG. 3 shows a diagram with the temperature characteristics of the two measuring bridges and of the temperature sensor in the ideal case
  • FIG. 4 shows a diagram with the temperature-compensated values from FIG. 3,
  • FIG. 5 shows a diagram with the temperature characteristics of the two measuring bridges and of the temperature sensor with 1% drift
  • Figure 6 is a diagram with the temperature-compensated, driftbehafteten
  • Figure 7 is a schematic diagram to illustrate the signal processing within the microcontroller.
  • FIG. 1 shows a plan view of a pressure measuring cell 1 as part of a pressure sensor.
  • Measuring elements are interconnected.
  • Measuring bridge 4 is arranged concentrically around the first measuring bridge 3, is hereby mentioned only by way of example. Of course, the arrangement of the measuring elements also be different from it.
  • 4 is basically the use of strain gauges or resistor paste or piezo elements in question. Strain gauges and piezo elements are well known and require no further design at this point.
  • Piezo elements work piezoelectric and resistor paste based on a piezo-resistive effect.
  • the resistor paste has a binder with a conductive powder whose concentration is a measure of the specific
  • Resistance is.
  • a selection of the measuring elements to be used is carried out due to the different properties of these alternatives, for example in terms of overload and bursting strength, nominal pressure bandwidth, accuracy, design size, weight and signal and not least the expected costs.
  • a pressure is applied to the membrane 2 of the measuring cell 1, this deforms elastically, so that it comes to strains and compressions of the measuring elements, which in turn results in a change in resistance.
  • the resistance changes can be with the help of a resistance measuring bridge, for example as
  • Wheatstone bridge convert into a useful signal in the form of an electrical voltage that will continue to process in an evaluation unit, not shown here as a measure of the applied pressure.
  • the prerequisite for the invention is that a second measuring bridge 4 is present and that its temperature characteristic differs from that of the first measuring bridge 3.
  • a minimum difference of 50ppm should not be undercut. In practice, this is not a problem, because due to lowest manufacturing tolerances or finest differences in the composition of material - to name just a few examples - already sets this distinction.
  • a temperature sensor 5 which is preferably designed as an NTC or PTC temperature sensor, for example.
  • the temperature sensor 5 is arranged in an outer region of the membrane 2, since the temperature sensor 5 also reacts to the expansion or compression of the membrane surface and changes its resistance value. At the edge of the membrane 2, the change of the membrane surface is the lowest or almost zero, so that the influence of the membrane curvature on the measurement result of the temperature sensor 5 is lowest here.
  • FIG. 2 shows the previously described pressure measuring cell 1 as a lateral sectional view. Evident is the concentric arrangement of the measuring elements of the second measuring bridge 4 to the measuring elements of the first measuring bridge 3. At the outer edge of the measuring cell 1, the temperature sensor 5 is arranged. In this profile view, it can be seen that the outer edge region of the measuring cell 1 is made so solid that deformation of the membrane 2 in this region does not occur or is negligible and the actual deformation from the center to at most in the region of the outermost Measuring element of the second measuring bridge 4 extends.
  • FIGS 3 and 4 illustrate the ideal case in which the temperature element functions properly and measures correct temperatures. You can see them
  • Temperature characteristics of the two measuring bridges and of the temperature sensor ie the change of a variable - in this case the resistance value - above the temperature.
  • the characteristic curves S1, S2 of the two measuring bridges are sufficiently different from each other and that of the temperature sensor usually has a strictly monotonous course within the relevant measuring range of about -40X to +125.
  • the monthly temperature is measured and this value is compared with a lookup table stored for each measuring bridge. Further details are given in connection with the description of Fig. 7. In these lookup tables the respective "correct" resistance value is stored for each temperature value, ie the value adjusted for the temperature influence.
  • the look-up tables are described with the specific data of the respective measuring bridges, the error-corrected, ie temperature-compensated, values are now compared - for further details see Fig. 7 - and the difference to each other is formed This difference is shown in Fig. 4. If the temperature sensor correctly and compensation is correct, the difference should be zero over the entire temperature range as shown, or in other words, only if the difference is zero can be concluded that the Temperature sensor measures correctly, correct temperature compensation is done and the measuring bridges measure correctly, which means that the measuring device
  • FIGS. 5 and 6 illustrate the fault case in which the temperature element does not function properly due to aging and / or drift effects and thus does not measure correct temperatures.
  • the temperature characteristics S1, S2 of the two measuring bridges correspond exactly to those of Fig. 3, while the characteristic of the temperature sensor has a drift of 1%, i. the measured temperatures are measured to be too high by 1% in the present example, and this drift effect does not have to be uniform over the entire temperature curve. In the present example, the drift effect increases with increasing temperature. Comparing Figures 3 and 5, the difference is apparently hard to make out, but as seen in Figure 6, this 1% measurement error of the temperature sensor has a corresponding effect on the temperature compensation. The difference of
  • Temperature sensor 5 incorrectly measures and / or the temperature compensation is not correct and / or the measuring bridges 3, 4 are defective. It does not matter to learn the exact error amount. It is primarily important to receive any information that the output pressure value is one
  • FIG. 7 shows a schematic diagram for clarifying the signal processing within the microcontroller.
  • the signals transmitted by the two measuring bridges 3, 4 and the temperature sensor 5 are respectively digitized in the microcontroller in an A / D converter 12 and then the respective lookup table 1 1 supplied.
  • For each bridge a lookup table 1 1 is provided.
  • value pairs are deposited, which consist of a temperature value and the associated resistance. These value pairs are stored in the lookup table during a factory calibration process prior to delivery of the pressure sensor. Due to tolerances in, for example, structure, shape, composition of the individual measuring elements, ie the individual strain gauges are the Each measuring bridge must be adjusted individually, so that in the look-up table an individual data record is stored for the respective measuring bridge.
  • the corresponding value pairs are now retrieved in the lookup tables 1 1 and the stored, error-corrected values are passed on.
  • a downstream comparator unit the difference between the two values is determined relative to one another and this difference is output. In case the difference is zero, the temperature measurement and / or the temperature compensation has been correct. If, however, a value other than zero results here, this is indicated by a signal unit, not shown, as an optical and / or acoustic warning signal.
  • a part of the signal processing can also be carried out analogously, which, for example, brings advantages in terms of the speed of the data processing.
  • the correction values with which the signals of the first and second measuring bridge 3, 4 have to be corrected so that the temperature error is compensated are stored in the lookup tables.
  • the measurement signals of the two bridges are then temperature compensated for the correction value from the lookup tables 1 1 and then also analogously to the comparator unit for subtraction outside the microcontroller 10 analog.

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  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
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  • Measuring Fluid Pressure (AREA)

Abstract

The invention relates to a method for checking the function of a pressure sensor for detecting the pressure in a medium, wherein the pressure sensor comprises a pressure measuring cell having an elastic membrane, on which a first electromechanical transducer and a second electromechanical transducer are arranged, and a temperature sensor for detecting the temperature at the two transducers. The first electromechanical transducer has a first temperature characteristic curve that represents the error influence of the temperature on the measurement result of the first electromechanical transducer, and the second electromechanical transducer has a second temperature characteristic curve that represents the error influence of the temperature on the measurement result of the second electromechanical transducer. The two temperature characteristic curves have been adapted to each other in an adjustment procedure. By calculating the difference between the temperature-compensated measured values, faulty function of the temperature sensor and/or of the electromechanical transducers can be determined if said difference significantly exceeds or falls below a specified threshold value.

Description

Verfahren zur Überprüfung der Funktion eines Drucksensors  Method for checking the function of a pressure sensor
Die Erfindung betrifft ein Verfahren zur Überprüfung der Funktion eines The invention relates to a method for checking the function of a
Drucksensors für die Erfassung des in einem Medium vorherrschenden Drucks, wobei der Drucksensor eine Druckmesszelle mit einer elastischen Membran und einen Temperaturmessaufnehmer zur Erfassung der Temperatur umfasst. A pressure sensor for detecting the pressure prevailing in a medium, the pressure sensor comprising a pressure measuring cell with an elastic membrane and a temperature sensor for detecting the temperature.
Bei der Druckmessung soll häufig der Druck innerhalb eines an eine Messzelle angrenzenden Mediums erfasst werden. Die Messzelle ist Bestandteil des In pressure measurement, the pressure within a medium adjacent to a measuring cell is often to be detected. The measuring cell is part of the
Messgeräts, wobei sie eine elastische Membran aufweist, deren eine Seite zumindest teilweise mit dem Medium in Kontakt steht und deren andere Seite von dem Medium abgewandt ist. Der Druck innerhalb des üblicherweise gasförmigen, flüssigen, pastösen oder zumindest schüttfähigen Mediums wird dadurch ermittelt, dass das Medium die elastische Membran in Abhängigkeit von dem innerhalb des Mediums herrschenden Drucks verschieden stark auslenkt. Die Auslenkung bzw. reversible Deformation der Membran wird von einem elektromechanischen Wandler, der mit der ausgelenkten Membran verformt wird, in ein korrespondierendes Measuring device, wherein it has an elastic membrane, one side of which is at least partially in contact with the medium and the other side facing away from the medium. The pressure within the usually gaseous, liquid, pasty or at least free-flowing medium is determined by the fact that the medium deflects the elastic membrane differently depending on the pressure prevailing within the medium. The deflection or reversible deformation of the membrane is converted from an electromechanical transducer, which is deformed with the deflected membrane, into a corresponding one
Messsignal umgewandelt, d.h. in einen entsprechenden Widerstandswert bzw. Measurement signal converted, i. in a corresponding resistance value or
Spannungs- oder Stromwert. Üblicherweise ist der elektromechanische Wandler eine aus Dehnungsmessstreifen bestehende Messbrücke. Voltage or current value. The electromechanical transducer is usually a measuring bridge consisting of strain gauges.
Messzellen und Messgeräte dieser Art sind seit längerem bekannt und werden beispielsweise in vielen Bereichen der Prozessmesstechnik zur messtechnischen Prozessbeobachtung eingesetzt. Derartige Messgeräte werden von der Anmelderin bspw. unter den Gerätebezeichnungen PTxx und PKxx hergestellt und in Verkehr gebracht. Die Messbereiche gehen derzeit üblicherweise bis 400 bar. Measuring cells and measuring devices of this type have been known for a long time and are used, for example, in many areas of process measuring technology for metrological process monitoring. Such measuring devices are produced by the applicant, for example, under the device designations PTxx and PKxx and placed on the market. The measuring ranges are currently usually up to 400 bar.
Auch bei der Druckmessung der in Rede stehenden Art spielt der Temperatureinfluss auf das Messergebnis eine große Rolle. Die verwendeten Messzellen sind oftmals aus Metall, insbesondere aus einem Stahl, gefertigt, so dass bei Änderung der Mediums- oder der Umgebungstemperatur aufgrund der guten Wärmeleitung von Metallen die Dehnungsmessstreifen unmittelbar beeinflusst werden. Über den Wandler wird aufgrund der unterschiedlichen Temperaturkoeffizienten der Also in the pressure measurement of the type in question, the influence of temperature on the measurement result plays a major role. The measuring cells used are often made of metal, in particular of a steel, so that the strain gauges are directly influenced when changing the medium or the ambient temperature due to the good thermal conductivity of metals. About the converter is due to the different temperature coefficients of the
Dehnungsmessstreifen und/oder der thermischen Verformung der Membran eine Widerstandsänderung und damit eine Druckänderung festgestellt, deren Strain gauges and / or the thermal deformation of the membrane detected a change in resistance and thus a pressure change whose
tatsächlicher Betrag vom gemessenen Wert abweichen kann. Bspw. kann die tatsächliche Druckänderung Null betragen, während das Messgerät eineactual amount may differ from the measured value. For example. can the actual pressure change will be zero while the meter is a
Druckänderung feststellt. Determines pressure change.
Aufgrund dessen muss der elektromechanische Wandler temperaturkompensiert werden, d.h. der Anteil der in der unmittelbaren Umgebung des Wandlers Because of this, the electromechanical transducer must be temperature compensated, i. the proportion of in the immediate vicinity of the converter
herrschenden Temperatur muss aus dem gemessenen Widerstandswert bzw. prevailing temperature must be determined from the measured resistance value or
Spannungs- oder Stromwert herausgerechnet werden, so dass alle Messwerte ohne Temperatureinfluss miteinander vergleichbar sind. Voltage or current value are calculated out, so that all measured values without temperature influence are comparable.
Hierfür kann ein Temperaturmessaufnehmer auf der Messzelle vorgesehen werden. Als Temperaturmessaufnehmer kommt vorzugsweise ein NTC- oder PTC- Temperaturf ühler infrage, bspw. ein als Pt100-Widerstandsthermometer For this purpose, a temperature sensor can be provided on the measuring cell. As a temperature sensor is preferably an NTC or PTC temperature sensor in question, for example. As a Pt100 resistance thermometer
ausgeführtes Thermistorbauelement. In einer Auswerteeinheit, z.B. einem executed thermistor device. In an evaluation unit, e.g. one
MikroController, kann dann rechnerisch der gemessene Druckwert um den Microcontroller, then can mathematically the measured pressure value to the
Fehlereinfluss der Temperatur bereinigt werden. Error influence of the temperature are cleaned up.
Problematisch ist nun allerdings, dass der Temperaturfühler nicht immer zuverlässig misst, bspw. können sich über eine längere Betriebsdauer Alterungserscheinungen einstellen. Insgesamt ist festzustellen, dass Temperaturfühler Drift- und However, the problem now is that the temperature sensor does not always measure reliably, for example, aging can occur over a longer service life. Overall, it can be seen that temperature sensors drift and
Degradationseffekten unterliegen, die zu einer Falschmessung der Temperatur und damit zu einer falschen Kompensation des gemessenen Druckwerts führen können. Um also eine zuverlässige Kompensation der Druckwerte durchzuführen ist eine zuverlässige Temperaturmessung notwendig. Insbesondere bei Degradation effects are subject, which can lead to a false measurement of the temperature and thus to an incorrect compensation of the measured pressure value. In order to perform a reliable compensation of the pressure values, a reliable temperature measurement is necessary. Especially at
sicherheitsorientierten Anwendungen, bei denen es auf eine exakte Messung ankommt, ist eine korrekte Temperaturkompensation zwingend notwendig. For safety-oriented applications where exact measurement is important, correct temperature compensation is essential.
Eine übliche Methode zur permanenten Überprüfung des Temperaturfühlers ist ein redundanter Aufbau. Die Messwerte von zumindest zwei Temperaturfühlern werden betragsmäßig miteinander verglichen und bei entsprechend großer Abweichung wird eine Fehlfunktion erkannt. Ein Nachteil dieses einfachen redundanten Aufbaus ist, dass systematische Fehler nicht oder nur schwer erkannt werden können. Außerdem unterliegen Drift- und Alterungseffekte einer gewissen Zufälligkeit, so dass nicht ausgeschlossen werden kann, dass beide Temperaturfühler über die Zeit ein gleich- oder ähnlich gelagertes Fehlerverhalten aufweisen. Das betragsmäßige Vergleichen beider Temperaturmesswerte würde in diesem Fall keine Unregelmäßigkeiten erkennen lassen. Aus diesem Grund schlägt die DE 10 2004 035 014 A1 einen Aufbau mit diversitärer Redundanz vor. Diese Anordnung beinhaltet mindestens zwei Sensorelemente mit temperaturabhängiger Impedanz, die innerhalb eines Sensorkopfs thermisch gekoppelt integriert sind. Dabei weisen die temperaturabhängigen Impedanzen unterschiedliche Temperatur-/Widerstandskennlinien, um so die diversitäre A common method for permanently checking the temperature sensor is a redundant design. The measured values of at least two temperature sensors are compared in terms of magnitude and a malfunction is detected with a correspondingly large deviation. A disadvantage of this simple redundant structure is that systematic errors are difficult or impossible to detect. In addition, drift and aging effects are subject to a certain degree of randomness, so that it can not be ruled out that both temperature sensors have the same or similar error behavior over time. The magnitude comparison of both temperature readings would not reveal any irregularities in this case. For this reason, DE 10 2004 035 014 A1 proposes a construction with diverse redundancy. This arrangement includes at least two sensor elements with temperature-dependent impedance, which are integrated thermally coupled within a sensor head. In this case, the temperature-dependent impedances have different temperature / resistance characteristics, so the diversified
Redundanz der Fühlerelemente zu gewährleisten. Durch den diversitären Aufbau in Kombination mit einer Redundanz können nun systematische Fehler sowie Drift- und Alterungseffekte zuverlässig erkannt werden. Nachteilig ist allerdings - wie bei jedem redundanten Aufbau - die höheren Herstellkosten, die sich durch die zusätzlichen Bauteile und elektrische Verbindungen ergeben. To ensure redundancy of the sensor elements. Due to the diverse structure in combination with redundancy, systematic errors as well as drift and aging effects can now be reliably detected. However, the disadvantage is - as with any redundant structure - the higher manufacturing costs resulting from the additional components and electrical connections.
Aufgabe der Erfindung ist es, die zuverlässige Temperaturmessung weiter zu verbessern und dabei Platzbedarf und insbesondere die Herstellkosten zu The object of the invention is to further improve the reliable temperature measurement while taking up space and in particular the manufacturing costs
verringern. reduce.
Die aufgezeigte Aufgabe wird erfindungsgemäß gelöst durch ein Verfahren mit den Merkmalen des Anspruchs 1. Vorteilhafte Ausgestaltungen der Erfindung sind in den Unteransprüchen angegeben. The stated object is achieved by a method having the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims.
Erfindungsgemäß weist die elastische Membran der Druckmesszelle einen ersten und einen zweiten elektromechanischen Wandler auf, wobei der erste According to the invention, the elastic membrane of the pressure measuring cell on a first and a second electromechanical transducer, wherein the first
elektromechanische Wandler eine erste, den Fehlereinfluss der Temperatur auf das Messergebnis des ersten elektromechanischen Wandlers repräsentierende electromechanical transducer a first, the error influence of the temperature on the measurement result of the first electromechanical transducer representing
Temperaturkennlinie und der zweite elektromechanische Wandler eine zweite, den Fehlereinfluss der Temperatur auf das Messergebnis des zweiten Temperature characteristic and the second electromechanical transducer a second, the error influence of the temperature on the measurement result of the second
elektromechanischen Wandlers repräsentierende Temperaturkennlinie aufweist. In einer vorher stattgefundenen Abgleichprozedur sind die beiden Having electromechanical transducer representative temperature characteristic. In a previous matching procedure, the two are
Temperaturkennlinien auf einander angepasst worden. Nachdem die Differenz der temperaturkompensierten Messwerte der Wandler zueinander bestimmt wurde, kann bei signifikanter Über- oder Unterschreitung eines vorgegebenen Schwellwertes eine fehlerhafte Funktion des Temperaturmessaufnehmers und/oder der beiden elektromechanischen Wandler erkannt werden. Die elektromechanischen Wandler fungieren somit indirekt auch als Temperaturelement, da sie im Zusammenspiel mit dem eigentlichen Temperaturfühler dazu beitragen, dessen exaktes Messen zu kontrollieren. Voraussetzung für das Verfahren ist, dass zwei elektromechanische Wandler, d.h. als Messbrücke verschaltete Dehnungsmessstreifen, auf der Membran der Messzelle vorhanden sind und sich damit in derselben thermischen Umgebung befinden. Diese können bspw. punktsymmetrisch oder konzentrisch auf der Membran angeordnet sein, wie z.B. in der Patentanmeldung DE102010035862A1 beschrieben. Temperature characteristics have been adapted to each other. After the difference of the temperature-compensated measured values of the transducers relative to one another has been determined, a faulty function of the temperature measuring transducer and / or of the two electromechanical transducers can be detected if the specified threshold value is significantly exceeded or undershot. The electromechanical transducers thus act indirectly as a temperature element, since they contribute in conjunction with the actual temperature sensor to control its exact measurement. The prerequisite for the method is that two electromechanical transducers, ie strain gauges connected as a measuring bridge, are present on the membrane of the measuring cell and are thus in the same thermal environment. These may, for example, be arranged point-symmetrically or concentrically on the membrane, as described, for example, in the patent application DE102010035862A1.
Die Temperaturkennlinien der elektromechanischen Wandler beschreiben dabei die temperaturbedingten Fehlereinflüsse bei unterschiedlichen thermischen Situationen, d.h. die jeweiligen prozentualen Abweichungen des Ist-Wertes vom Soll-Wert, wobei der Soll-Wert ein konstanter Widerstandswert ist. Aufgrund von Fertigungstoleranzen streuen diese Kennlinien auch bei baugleichen Elementen - wie in diesem Fall die Dehnungsmessstreifen - sehr stark. Der durch die Streuung der Kennlinien resultierende Effekt wird letztendlich ausgewertet, wie nachfolgend noch näher beschrieben wird. Durch die Verschaltung der einzelnen Widerstände zu einem elektromechanischem Wandler bzw. einer Messbrücke wird der durch die Streuung der Kennlinien resultierende Effekt noch verstärkt. The temperature characteristics of the electromechanical transducers describe the temperature-induced fault influences in different thermal situations, i. the respective percentage deviations of the actual value from the nominal value, wherein the nominal value is a constant resistance value. Due to manufacturing tolerances, these characteristics scatter very much even with identical elements - as in this case the strain gauges. The effect resulting from the scattering of the characteristic curves is ultimately evaluated, as will be described in more detail below. By interconnecting the individual resistors to form an electromechanical transducer or a measuring bridge, the effect resulting from the scattering of the characteristic curves is further enhanced.
Der temperaturbedingte Fehlereinfluss wird durch die Temperaturkompensation eliminiert, so dass im Ergebnis die Kennlinien der einzelnen Messbrücken The temperature-induced fault influence is eliminated by the temperature compensation, so that in the result the characteristic curves of the individual measuring bridges
idealerweise eine 0%-Abweichung zwischen Ist- und Soll-Wert über den relevanten Temperaturbereich aufweisen. Beide Kennlinien sind damit deckungsgleich bzw. die Differenz beider Kennlinien zueinander beträgt Null. Kleinere Abweichungen von der Deckungsgleichheit fallen unter die Toleranz. Die Differenz zwischen den beiden Kennlinien - bzw. einzelnen Werten auf dieser Kennlinie - wird ermittelt und als Maß für die Fehlererkennung herangezogen. Sollte es hier zu einer signifikanten Überoder Unterschreitung dieses Schwellwerts kommen, also die Differenz ungleich Null sein, würde dies auf eine fehlerhafte Funktion des Temperaturmessaufnehmers und/oder der beiden elektromechanischen Wandler schließen lassen. ideally, have a 0% deviation between actual and setpoint over the relevant temperature range. Both characteristics are thus congruent or the difference between the two characteristics to each other is zero. Minor deviations from the congruence fall below the tolerance. The difference between the two characteristic curves - or individual values on this characteristic curve - is determined and used as a measure for error detection. Should there be a significant overshoot or undershoot of this threshold, so be the difference not equal to zero, this would suggest a faulty function of the temperature sensor and / or the two electromechanical transducer.
Selbstverständlich ist es vorteilhaft, den Schwellwert nicht exakt bei Null anzusetzen sondern einen gewissen Toleranzbereich über- und unterhalb von Null vorzusehen, um geringfügige Abweichungen mit abzudecken, deren Ursache nichts mit einer fehlerhaften Temperaturkompensierung zu tun haben. Of course, it is advantageous not to set the threshold exactly at zero but to provide a certain tolerance range above and below zero in order to cover minor deviations whose cause has nothing to do with a faulty temperature compensation.
Die wesentliche Idee der Erfindung besteht also darin, dass es nicht darum geht, das eigentliche Messergebnis des Temperaturfühlers betragsmäßig auf Plausibilität zu überprüfen, sondern um die Überprüfung, ob die Differenz der kompensierten Temperaturkennlinien beider Messbrücken Null ist. Wenn es hierbei Abweichungen gibt, kann auf eine fehlerhafte Temperaturkompensation und damit auf eine The essential idea of the invention is therefore that it does not concern the actual measurement result of the temperature sensor to check for plausibility in terms of amount, but to check whether the difference of the compensated Temperature characteristics of both measuring bridges is zero. If there are deviations, it can be due to a faulty temperature compensation and thus to a
Fehlfunktion des Temperaturfühlers und/oder der beiden Messbrücken geschlossen werden, ohne dass - wie bei klassischen Redundanzsystemen - der gemessene Wert betragsmäßig als falsch erkannt werden muss. Das erfindungsgemäße Malfunction of the temperature sensor and / or the two measuring bridges are closed without - as in the case of classical redundancy systems - the measured value must be recognized in terms of amount as wrong. The invention
Verfahren kann also als ein Verfahren zur Selbstdiagnose der Druckmesszelle hinsichtlich der Erkennung einer fehlerhaften Temperaturkompensation bezeichnet werden. The method can thus be referred to as a method for self-diagnosis of the pressure measuring cell with regard to the detection of a faulty temperature compensation.
Eine Grundvoraussetzung der Erfindung ist, dass die Temperaturkennlinien beider Messbrücken ausreichend verschieden voneinander sind, wobei der Unterschied wenigstens 50ppm, bevorzugt 100, ganz besonders bevorzugt 200ppm beträgt. Je größer der Unterschied zwischen den beiden Kennlinien desto besser die A basic requirement of the invention is that the temperature characteristics of both measuring bridges are sufficiently different from one another, the difference being at least 50 ppm, preferably 100, very particularly preferably 200 ppm. The greater the difference between the two characteristics the better the
Auswertbarkeit, weil sich bei einer fehlerhaften Temperaturkompensation die Evaluability, because at a faulty temperature compensation the
Kennlinien stark unterschiedlich auseinander bewegen und damit eine deutliche Differenz ungleich Null ergibt. Characteristics vary widely differently and thus results in a significant difference not equal to zero.
Eine vorteilhafte Weiterbildung der Erfindung sieht vor, dass der An advantageous development of the invention provides that the
Temperaturmessaufnehmer in einem äußeren Bereich der Membran angeordnet ist. Da der Temperaturfühler auch auf die Dehnung der Membranoberfläche reagieren und ihren Widerstandswert ändern, ist es vorteilhaft, diese am Rand der Membran zu platzieren, wo die Veränderung der Membranoberfläche am geringsten bzw. nahezu Null ist. Temperature sensor is disposed in an outer region of the membrane. Since the temperature sensors also respond to the elongation of the membrane surface and change their resistance, it is advantageous to place them at the edge of the membrane, where the change in the membrane surface is the lowest or almost zero.
Bevorzugt erfolgt die Temperaturkompensation mit Hilfe einer Lookup-Tabelle, die in einem Mikrocontroller abgelegt ist. Der rechnerische Aufwand bei der The temperature compensation preferably takes place with the aid of a look-up table which is stored in a microcontroller. The arithmetic effort at the
Temperaturkompensation ist vergleichsweise hoch, so dass es vorteilhaft ist, die einzelnen Szenarien, bei welcher Temperatur welcher Widerstandswert vorliegen sollte, fest in Lookup-Tabellen zu hinterlegen. Diese können im Speicher des Temperature compensation is comparatively high, so it is advantageous to deposit the individual scenarios, at which temperature which resistance value should exist, firmly in lookup tables. These can be stored in memory
MikroControllers abgelegt werden und sind daher schnell aufrufbar. Eine Alternative sieht hierbei vor, dass in der Lookup-Tabelle die zu den gemessenen MicroControllers are stored and are therefore quickly accessible. An alternative here is that in the lookup table to the measured
Temperaturwerten des Temperaturfühlers zugehörigen korrigierten Messwerte der elektromechanischen Wandler abgelegt sind. Werkseitig werden die um den Temperature values of the temperature sensor associated corrected measured values of the electromechanical converter are stored. The factory will be around the
Temperatureinfluss bereinigten„richtigen" Messwerte der Wandler in der Lookup- Tabelle abgelegt, so dass dann zu der jeweils herrschenden Temperatur der dazugehörige Spannungswert der Messbrücken entnommen und für die weitere Verarbeitung weitergeleitet werden kann. Eine zweite Alternative sieht dagegen vor, dass in der Lookup-Tabelle nur die zu den gemessenen Temperaturwerten zugehörigen Korrekturwerte abgelegt sind, d.h. die Werte, mit denen die Messwerte der elektromechanischen Wandler zu verrechnen sind, um den„richtigen" Messwert zu erhalten. Die Berechnung der korrigierten Messwerte selbst erfolgt dann außerhalb des Mikrocontrollers auf analoge Weise. Eine analoge Signalverarbeitung kann bspw. Vorteile bei der Schnelligkeit der Datenverarbeitung bringen. Temperature taken adjusted "correct" measured values of the converter stored in the lookup table, so that then taken to the prevailing temperature of the associated voltage value of the measuring bridges and for the other Processing can be forwarded. On the other hand, a second alternative provides that only the correction values associated with the measured temperature values are stored in the look-up table, ie the values with which the measured values of the electromechanical converters are to be calculated in order to obtain the "correct" measured value The corrected measured values themselves are then processed in an analogous manner outside the microcontroller An analog signal processing can, for example, bring advantages in terms of the speed of the data processing.
In einer weiteren bevorzugten Ausführungsform ist vorgesehen, dass die beiden elektromechanischen Wandler, d.h. die beiden Messbrücken, diversitär ausgebildet sind, in dem sie jeweils ein weiteres Thermistorbauelement aufweisen oder nur eine Messbrücke ein weiteres Thermistorbauelement aufweist. Mit dem Zusatz„weiteres" soll an dieser Stelle eine klare Abgrenzung zu dem Thermistorbauelement erreicht werden, das die Daten für die Temperaturkompensation der beiden Messbrücken liefert. Diese Weiterbildung ist für den vergleichsweise seltenen, aber durchaus denkbaren Fall vorgesehen, dass sich verschiedene Fehlereinflüsse, bspw. aufgrund einer plastischen Verformung der Membran, nach einer Verrechnung gegenseitig betragsmäßig eliminieren bzw. soweit reduzieren, dass sich das Ergebnis im zulässigen Bereich der Auswerteeinheit befindet und aufgrund dessen kein Fehler erkannt werden kann. Auch wäre der Fall denkbar, dass die Fertigungstoleranzen der Messbrücken doch geringer sind, so dass die Temperaturkennlinien beider Brücken nicht ausreichend unterschiedlich zu einander sind. Durch den diversitären Aufbau kann dieser Fall ausgeschlossen werden. In der ersten Alternative weisen beide Messbrücken jeweils ein Thermistorbauelement auf, welches parallel oder in Reihe zu einem der Einzelwiderstände geschaltet werden kann. Die Thermistoren können gleich sein, sollten dann aber bei der ersten Messbrücke im positiven Brückenzweig und bei der zweiten Messbrücke im negativen Brückenzweig implementiert sein. Vorteilhafter ist es, zwei unterschiedliche Thermistoren vorzusehen. Bei gleichem Temperatureinfluss und unterschiedlichen In a further preferred embodiment it is provided that the two electromechanical transducers, i. the two measuring bridges are diversified, in which they each have a further thermistor component or only one measuring bridge has a further thermistor component. With the addition "further", a clear differentiation from the thermistor component is to be achieved, which supplies the data for the temperature compensation of the two measuring bridges Due to a plastic deformation of the membrane, after an offset, they can be mutually eliminated or reduced in amount such that the result is within the permissible range of the evaluation unit and therefore no error can be detected Due to the diverse structure, this case can be ruled out In the first alternative, both measuring bridges each have a thermistor component which is connected in parallel or in series with one another Inem the individual resistors can be switched. The thermistors may be the same, but should then be implemented in the positive bridge branch for the first bridge and in the negative bridge for the second bridge. It is more advantageous to provide two different thermistors. At the same temperature influence and different
Thermistorbauelementen müssen sich daher zwingend unterschiedliche Thermistor devices must therefore necessarily different
Temperaturkennlinien ergeben. Gleiches gilt für die zweite Alternative, dass nur eine der Messbrücken ein Thermistorbauelement aufweist. Um die Diagonalspannung nicht zu sehr zu verzerren, können die mit Thermistoren ergänzten Temperature characteristics result. The same applies to the second alternative that only one of the measuring bridges has a thermistor component. In order not to distort the diagonal voltage too much, those with thermistors can be added
Widerstandselemente konstruktiv entsprechend angepasst werden. Abgesehen von Drucksensoren als bevorzugte Anwendung kann die Erfindung bei jeglichen Messgeräten eingesetzt werden, bei denen mindestens zwei Resistance elements are structurally adjusted accordingly. Apart from pressure sensors as a preferred application, the invention can be used in any measuring devices in which at least two
Messaufnehmer vorhanden sind, deren Differenz zueinander auswertbar ist und die zur weiteren Auswertung temperaturkompensiert werden müssen. Denkbar ist z.B. die Anwendung bei Strömungs- bzw. Durchflusssensoren. Sensors are present whose difference is evaluated to each other and must be temperature compensated for further evaluation. It is conceivable, e.g. the application with flow or flow sensors.
Nachfolgend wird die Erfindung im Zusammenhang mit Figuren anhand von The invention will be described in connection with figures with reference to FIG
Ausführungsbeispielen näher erläutert. Embodiments explained in more detail.
Es zeigen: Show it:
Figur 1 eine Draufsicht auf ein Ausführungsbeispiel einer Druckmesszelie zur Figure 1 is a plan view of an embodiment of a Druckmesszelie for
Ausführung des erfindungsgemäßen Verfahrens,  Execution of the method according to the invention,
Figur 2 eine seitliche Schnittdarstellung einer Druckmesszelle gemäß Figure 2 is a side sectional view of a pressure measuring cell according to
Ausführungsbeispiel aus Fig. 1 ,  Embodiment of FIG. 1,
Figur 3 ein Diagramm mit den Temperaturkennlinien der beiden Messbrücken und des Temperaturfühlers im Idealfall, FIG. 3 shows a diagram with the temperature characteristics of the two measuring bridges and of the temperature sensor in the ideal case,
Figur 4 ein Diagramm mit den temperaturkompensierten Werten aus Fig. 3, FIG. 4 shows a diagram with the temperature-compensated values from FIG. 3,
Figur 5 ein Diagramm mit den Temperaturkennlinien der beiden Messbrücken und des Temperaturfühlers mit 1 % Drift, FIG. 5 shows a diagram with the temperature characteristics of the two measuring bridges and of the temperature sensor with 1% drift,
Figur 6 ein Diagramm mit den temperaturkompensierten, driftbehafteten Figure 6 is a diagram with the temperature-compensated, driftbehafteten
Werten aus Fig. 5 und  Values from Fig. 5 and
Figur 7 eine Prinzipskizze zur Verdeutlichung der Signalverarbeitung innerhalb des MikroControllers. Figure 7 is a schematic diagram to illustrate the signal processing within the microcontroller.
In den nachfolgenden Figuren bezeichnen, sofern nicht anders angegeben, gleiche Bezugszeichen gleiche Teile mit gleicher Bedeutung. In the following figures, unless otherwise stated, like reference numerals designate like parts with the same meaning.
Figur 1 stellt eine Draufsicht auf eine Druckmesszelle 1 als Teil eines Drucksensors dar. Zu erkennen sind die auf der Membran 2 angeordneten Messelemente der beiden elektromechanischen Wandler 3, 4, die zu Messbrücken von je vier FIG. 1 shows a plan view of a pressure measuring cell 1 as part of a pressure sensor. The measuring elements of the two electromechanical transducers 3, 4 arranged on the membrane 2, which lead to measuring bridges of four each, can be seen
Messelementen verschaltet sind. Die gezeigte Ausführung, bei der die zweite Measuring elements are interconnected. The shown embodiment, in which the second
Messbrücke 4 konzentrisch um die erste Messbrücke 3 angeordnet ist, ist hierbei nur beispielhaft erwähnt. Selbstverständlich kann die Anordnung der Messelemente auch verschieden davon sein. Für die Messelemente der beiden Messbrücken 3, 4 kommt grundsätzlich die Verwendung von Dehnungsmessstreifen oder Widerstandspaste oder Piezoelementen infrage. Dehnungsmessstreifen und Piezoelemente sind hinlänglich bekannt und bedürfen an dieser Stelle keiner weiteren Ausführung. Measuring bridge 4 is arranged concentrically around the first measuring bridge 3, is hereby mentioned only by way of example. Of course, the arrangement of the measuring elements also be different from it. For the measuring elements of the two measuring bridges 3, 4 is basically the use of strain gauges or resistor paste or piezo elements in question. Strain gauges and piezo elements are well known and require no further design at this point.
Piezoelemente arbeiten piezo-elektrisch und Widerstandspaste auf Basis eines piezo-resistiven Effekts. Die Widerstandspaste weist ein Bindemittel mit einem leitfähigen Pulver auf, dessen Konzentration ein Maß für den spezifischen Piezo elements work piezoelectric and resistor paste based on a piezo-resistive effect. The resistor paste has a binder with a conductive powder whose concentration is a measure of the specific
Widerstand ist. Je nach Anwendungsfall erfolgt eine Auswahl der einzusetzenden Messelemente aufgrund der unterschiedlichen Eigenschaften dieser Alternativen, bspw. hinsichtlich Überlast- und Berstdruck-Festigkeit, Nenndruckbandbreite, Genauigkeit, Bauformgröße, Gewicht sowie Signalhub und nicht zuletzt auch die zu erwartenden Kosten. Resistance is. Depending on the application, a selection of the measuring elements to be used is carried out due to the different properties of these alternatives, for example in terms of overload and bursting strength, nominal pressure bandwidth, accuracy, design size, weight and signal and not least the expected costs.
Wenn an der Membran 2 der Messzelle 1 ein Druck anliegt, verformt sich diese elastisch, so dass es zu Dehnungen und Stauchungen der Messelemente kommt, was wiederum in einer Widerstandsänderung resultiert. Die Widerstandsänderungen lassen sich mit Hilfe einer Widerstandsmessbrücke, beispielsweise als If a pressure is applied to the membrane 2 of the measuring cell 1, this deforms elastically, so that it comes to strains and compressions of the measuring elements, which in turn results in a change in resistance. The resistance changes can be with the help of a resistance measuring bridge, for example as
Wheatstonesche Messbrücke, in ein Nutzsignal in Form einer elektrischen Spannung umsetzen, das in einer hier nicht dargestellten Auswerteeinheit als Maß für den anliegenden Druck weiter verarbeiten wird. Wheatstone bridge, convert into a useful signal in the form of an electrical voltage that will continue to process in an evaluation unit, not shown here as a measure of the applied pressure.
Voraussetzung für die Erfindung ist, dass eine zweite Messbrücke 4 vorhanden ist und dass deren Temperaturkennlinie sich von der der ersten Messbrücke 3 unterscheidet. Ein minimaler Unterschied von 50ppm sollte nicht unterschritten werden. In der Praxis ist dies kein Problem, weil sich aufgrund von geringsten Fertigungstoleranzen oder feinste Unterschiede in der Materialzusammensetzung - um nur einige Beispiel zu nennen - bereits diese Unterscheidung einstellt. The prerequisite for the invention is that a second measuring bridge 4 is present and that its temperature characteristic differs from that of the first measuring bridge 3. A minimum difference of 50ppm should not be undercut. In practice, this is not a problem, because due to lowest manufacturing tolerances or finest differences in the composition of material - to name just a few examples - already sets this distinction.
Ebenfalls auf der Membran 2 angeordnet ist ein Temperaturmessaufnehmer 5, der vorzugsweise als NTC- oder PTC- Temperaturfühler ausgeführt ist, bspw. ein als Pt100-Widerstandsthermometer ausgeführtes Thermistorbauelement. Also disposed on the membrane 2 is a temperature sensor 5, which is preferably designed as an NTC or PTC temperature sensor, for example. A designed as a Pt100 resistance thermometer thermistor device.
Vorteilhafterweise ist der Temperaturmessaufnehmer 5 in einem äußeren Bereich der Membran 2 angeordnet, da der Temperaturfühler 5 auch auf die Dehnung bzw. Stauchung der Membranoberfläche reagiert und seinen Widerstandswert ändert. Am Rand der Membran 2 ist die Veränderung der Membranoberfläche am geringsten bzw. nahezu Null, so dass der Einfluss der Membranwölbung auf das Messergebnis des Temperaturfühlers 5 hier am geringsten ist. Advantageously, the temperature sensor 5 is arranged in an outer region of the membrane 2, since the temperature sensor 5 also reacts to the expansion or compression of the membrane surface and changes its resistance value. At the edge of the membrane 2, the change of the membrane surface is the lowest or almost zero, so that the influence of the membrane curvature on the measurement result of the temperature sensor 5 is lowest here.
In Figur 2 ist die zuvor beschriebene Druckmesszelle 1 als seitliches Schnittbild dargestellt. Zu erkennen ist die konzentrische Anordnung der Messelemente der zweiten Messbrücke 4 um die Messelemente der ersten Messbrücke 3. Am äußeren Rand der Messzelle 1 ist der Temperaturfühler 5 angeordnet. In dieser Profilansicht ist zu erkennen, dass der äußere Randbereich der Messzelle 1 derart massiv ausgeführt ist, dass eine Verformung der Membran 2 in diesem Bereich nicht erfolgt bzw. zu vernachlässigbar ist und sich die eigentliche Verformung von der Mitte bis maximal in den Bereich des äußersten Messelements der zweiten Messbrücke 4 erstreckt. FIG. 2 shows the previously described pressure measuring cell 1 as a lateral sectional view. Evident is the concentric arrangement of the measuring elements of the second measuring bridge 4 to the measuring elements of the first measuring bridge 3. At the outer edge of the measuring cell 1, the temperature sensor 5 is arranged. In this profile view, it can be seen that the outer edge region of the measuring cell 1 is made so solid that deformation of the membrane 2 in this region does not occur or is negligible and the actual deformation from the center to at most in the region of the outermost Measuring element of the second measuring bridge 4 extends.
Im Folgenden wird anhand der Figuren 3-7 die Funktionsweise des In the following, with reference to the figures 3-7, the operation of the
erfindungsgemäßen Verfahrens erläutert. inventive method explained.
Die Figuren 3 und 4 stellen den Idealfall dar, bei dem das Temperaturelement einwandfrei funktioniert und korrekte Temperaturen misst. Zu sehen sind die Figures 3 and 4 illustrate the ideal case in which the temperature element functions properly and measures correct temperatures. You can see them
Temperaturkennlinien der beiden Messbrücken und des Temperaturfühlers, d.h. die Veränderung einer Größe - in vorliegenden Fall des Widerstandswertes - über der Temperatur. Die Kennlinien S1 , S2 der beiden Messbrücken sind ausreichend verschieden von einander und die des Temperaturfühlers hat üblicherweise einen streng monotonen Verlauf innerhalb des relevanten Messbereichs von ca. -40X bis +125 . Mit Hilfe des Temperaturfühlers wird die mo mentane Temperatur gemessen und dieser Wert mit jeweils einer für jede Messbrücke hinterlegten Lookup-Tabelle abgeglichen. Näheres dazu folgt im Zusammenhang mit der Beschreibung von Fig. 7. In diesen Lookup-Tabellen ist zu jedem Temperaturwert der jeweils„richtige" Widerstandswert hinterlegt, d.h. den um den Temperatureinfluss bereinigten Wert. In einer Abgleichprozedur, die werkseitig vor Auslieferung der Messzelle erfolgt, werden die Lookup-Tabellen mit den spezifischen Daten der jeweiligen Messbrücken beschrieben. Die fehlerbereinigten, d.h. temperaturkompensierten Werte werden nun miteinander verglichen - Näheres dazu siehe Fig. 7 - und die Differenz zueinander gebildet. Diese Differenz ist in Fig. 4 dargestellt. Wenn der Temperaturfühler richtig misst und eine korrekte Kompensation erfolgt, sollte die Differenz wie abgebildet über den gesamten Temperaturbereich Null sein. Oder anders ausgedrückt: Nur wenn die Differenz Null ist, kann daraus geschlossen werden, dass der Temperaturfühler richtig misst, eine korrekte Temperaturkompensation erfolgt ist und die Messbrücken richtig messen, was bedeutet, dass die am Messgerät Temperature characteristics of the two measuring bridges and of the temperature sensor, ie the change of a variable - in this case the resistance value - above the temperature. The characteristic curves S1, S2 of the two measuring bridges are sufficiently different from each other and that of the temperature sensor usually has a strictly monotonous course within the relevant measuring range of about -40X to +125. With the help of the temperature sensor, the monthly temperature is measured and this value is compared with a lookup table stored for each measuring bridge. Further details are given in connection with the description of Fig. 7. In these lookup tables the respective "correct" resistance value is stored for each temperature value, ie the value adjusted for the temperature influence. the look-up tables are described with the specific data of the respective measuring bridges, the error-corrected, ie temperature-compensated, values are now compared - for further details see Fig. 7 - and the difference to each other is formed This difference is shown in Fig. 4. If the temperature sensor correctly and compensation is correct, the difference should be zero over the entire temperature range as shown, or in other words, only if the difference is zero can be concluded that the Temperature sensor measures correctly, correct temperature compensation is done and the measuring bridges measure correctly, which means that the measuring device
ausgegebenen Druckwerte keinen temperaturbedingten Fehler enthalten. output pressure values do not contain a temperature-related error.
Die Figuren 5 und 6 stellen den Fehlerfall dar, bei dem das Temperaturelement aufgrund von Alterungs- und/oder Drifteffekten nicht einwandfrei funktioniert und damit keine korrekten Temperaturen misst. Die Temperaturkennlinien S1 , S2 der beiden Messbrücken entsprechen exakt denen aus Fig. 3, während die Kennlinie des Temperaturfühlers eine Drift von 1 % aufweist, d.h. die gemessenen Temperaturen werden im vorliegenden Beispiel um 1 % zu hoch gemessen, und dieser Drifteffekt muss nicht über den gesamten Temperaturverlauf gleichmäßig sein. Im vorliegenden Beispiel nimmt der Drifteffekt mit zunehmender Temperatur zu. Beim Vergleich der Figuren 3 und 5 ist der Unterschied augenscheinlich kaum auszumachen, aber wie in Fig. 6 zu sehen, hat dieser 1 %-ige Messfehler des Temperaturfühlers entsprechende Auswirkungen auf die Temperaturkompensation. Die Differenz der FIGS. 5 and 6 illustrate the fault case in which the temperature element does not function properly due to aging and / or drift effects and thus does not measure correct temperatures. The temperature characteristics S1, S2 of the two measuring bridges correspond exactly to those of Fig. 3, while the characteristic of the temperature sensor has a drift of 1%, i. the measured temperatures are measured to be too high by 1% in the present example, and this drift effect does not have to be uniform over the entire temperature curve. In the present example, the drift effect increases with increasing temperature. Comparing Figures 3 and 5, the difference is apparently hard to make out, but as seen in Figure 6, this 1% measurement error of the temperature sensor has a corresponding effect on the temperature compensation. The difference of
temperaturkompensierten Werte beider Messbrücken ist ungleich Null - im Temperature compensated values of both measuring bridges are not equal to zero - im
vorliegenden Fall kleiner Null. Auf diese Weise ist feststellbar, dass der present case less than zero. In this way it can be stated that the
Temperaturfühler 5 fehlerhaft misst und/oder die Temperaturkompensation nicht korrekt ist und/oder die Messbrücken 3, 4 defekt sind. Dabei spielt es keine Rolle, den exakten Fehler betragsmäßig zu erfahren. Wichtig ist vorrangig, überhaupt eine Information darüber zu erhalten, dass der ausgegebene Druckwert einen Temperature sensor 5 incorrectly measures and / or the temperature compensation is not correct and / or the measuring bridges 3, 4 are defective. It does not matter to learn the exact error amount. It is primarily important to receive any information that the output pressure value is one
temperaturbedingten Fehler enthält. Insbesondere bei Anlagen, die Vorgaben der Funktionalen Sicherheit unterliegen sollen, sind derartige fehlerbehaftete Messwerte zu vermeiden. contains temperature-related errors. In particular in the case of systems which are to be subject to the requirements of functional safety, such erroneous measured values are to be avoided.
Figur 7 stellt eine Prinzipskizze zur Verdeutlichung der Signalverarbeitung innerhalb des Mikrocontrollers dar. Die jeweils von den beiden Messbrücken 3, 4 sowie dem Temperaturfühler 5 übermittelten Signale werden in dem MikroController jeweils in einem A/D-Wandler 12 digitalisiert und dann der jeweiligen Lookup-Tabelle 1 1 zugeführt. Für jede Messbrücke ist je eine Lookup-Tabelle 1 1 vorgesehen. In dieser Lookup-Tabelle 1 1 sind Wertepaare hinterlegt, die aus einem Temperaturwert und dem dazugehörigen Widerstandswert bestehen. Diese Wertepaare werden bei einem Abgleichvorgang im Werk vor Auslieferung des Drucksensors in der Lookup-Tabelle gespeichert. Aufgrund von Toleranzen in bspw. Aufbau, Form, Zusammensetzung der einzelnen Messelemente, d.h. der einzelnen Dehnungsmessstreifen sind die Messbrücken jeweils individuell abzugleichen, so dass in der Lookup-Tabelle ein für die jeweilige Messbrücke individueller Datensatz gespeichert ist. 7 shows a schematic diagram for clarifying the signal processing within the microcontroller. The signals transmitted by the two measuring bridges 3, 4 and the temperature sensor 5 are respectively digitized in the microcontroller in an A / D converter 12 and then the respective lookup table 1 1 supplied. For each bridge a lookup table 1 1 is provided. In this lookup table 1 1 value pairs are deposited, which consist of a temperature value and the associated resistance. These value pairs are stored in the lookup table during a factory calibration process prior to delivery of the pressure sensor. Due to tolerances in, for example, structure, shape, composition of the individual measuring elements, ie the individual strain gauges are the Each measuring bridge must be adjusted individually, so that in the look-up table an individual data record is stored for the respective measuring bridge.
Zu von den drei A/D-Wandlern 12 empfangenen Daten werden nun in den Lookup- Tabellen 1 1 die dazugehörigen Wertepaare herausgesucht und die hinterlegten, fehlerbereinigten Werte weitergegeben. In einer nachgeschalteten Vergleichereinheit wird die Differenz der beiden Werte zueinander ermittelt und dieser Differenzbetrag ausgegeben. Im Falle, dass die Differenz Null ist, ist die Temperaturmessung und/oder die Temperaturkompensation korrekt gewesen. Sollte sich hier aber ein Wert ungleich Null ergeben, wird durch eine nicht dargestellte Signaleinheit als optisches und/oder akustisches Warnsignal darauf hingewiesen. For data received from the three A / D converters 12, the corresponding value pairs are now retrieved in the lookup tables 1 1 and the stored, error-corrected values are passed on. In a downstream comparator unit, the difference between the two values is determined relative to one another and this difference is output. In case the difference is zero, the temperature measurement and / or the temperature compensation has been correct. If, however, a value other than zero results here, this is indicated by a signal unit, not shown, as an optical and / or acoustic warning signal.
Alternativ zu der in Figur 7 dargestellten Ausführungsform - jedoch nicht dargestellt - kann ein Teil der Signalverarbeitung auch analog erfolgen, was bspw. Vorteile bei der Schnelligkeit der Datenverarbeitung bringt. In diesem Fall sind in den Lookup- Tabellen nur die Korrekturwerte hinterlegt, mit denen die Signale der ersten und zweiten Messbrücke 3, 4 korrigiert werden müssen, damit der Temperaturfehler kompensiert ist. In einem Zwischenschritt vor der Differenzbildung werden dann außerhalb des Mikrocontrollers 10 analog die Messsignale der beiden Brücken um den Korrekturwert aus den Lookup-Tabellen 1 1 temperaturkompensiert und dann ebenfalls analog der Vergleichereinheit zur Differenzbildung zugeführt. As an alternative to the embodiment illustrated in FIG. 7, but not shown, a part of the signal processing can also be carried out analogously, which, for example, brings advantages in terms of the speed of the data processing. In this case, only the correction values with which the signals of the first and second measuring bridge 3, 4 have to be corrected so that the temperature error is compensated are stored in the lookup tables. In an intermediate step before the difference formation, the measurement signals of the two bridges are then temperature compensated for the correction value from the lookup tables 1 1 and then also analogously to the comparator unit for subtraction outside the microcontroller 10 analog.

Claims

Patentansprüche claims
1 . Verfahren zur Überprüfung der Funktion eines Drucksensors für die Erfassung des in einem Medium vorherrschenden Drucks, wobei der Drucksensor eine Druckmesszeiie (1 ) mit einer elastischen Membran (2), auf der ein erster und ein zweiter elektromechanischer Wandler (3, 4) angeordnet sind, und einen Temperaturmessaufnehmer (5) zur Erfassung der an den beiden Wandler (3, 4) herrschenden Temperatur umfasst, 1 . Method for checking the function of a pressure sensor for detecting the pressure prevailing in a medium, wherein the pressure sensor comprises a pressure measuring cell (1) with an elastic membrane (2) on which a first and a second electromechanical transducer (3, 4) are arranged, and a temperature measuring transducer (5) for detecting the temperature prevailing at the two transducers (3, 4),
wobei der erste elektromechanische Wandler (3) eine erste, den  wherein the first electromechanical transducer (3) comprises a first, the
Fehlereinfluss der Temperatur auf das Messergebnis des ersten  Error influence of the temperature on the measurement result of the first
elektromechanischen Wandlers repräsentierende Temperaturkennlinie (S1 ) und der zweite elektromechanische Wandler (4) eine zweite, den  Temperature characteristic (S1) representing the electromechanical transducer and the second electromechanical transducer (4) a second, the
Fehlereinfluss der Temperatur auf das Messergebnis des zweiten  Error influence of the temperature on the measurement result of the second
elektromechanischen Wandlers repräsentierende Temperaturkennlinie (S2) aufweist,  having a temperature characteristic (S2) representing the electromechanical transducer,
in einer Abgleichprozedur die beiden Temperaturkennlinien (S1 , S2) auf einander angepasst worden sind  in an adjustment procedure, the two temperature characteristics (S1, S2) have been adapted to each other
und wobei die Differenz der temperaturkompensierten Messwerte der beiden Wandler (3, 4) zueinander bestimmt und bei signifikanter Über- oder  and wherein the difference between the temperature-compensated measured values of the two transducers (3, 4) is determined relative to one another and at a significant overshoot or
Unterschreitung eines vorgegebenen Schwellwertes eine fehlerhafte Funktion des Temperaturmessaufnehmers (5) und/oder der beiden  Falling below a predetermined threshold, a faulty function of the temperature measuring transducer (5) and / or the two
elektromechanischen Wandler (3, 4) erkannt wird.  electromechanical transducer (3, 4) is detected.
2. Verfahren nach Anspruch 1 , 2. The method according to claim 1,
dadurch gekennzeichnet, dass der Temperaturmessaufnehmer (5) in einem äußeren Bereich der Membran (2) angeordnet ist.  characterized in that the temperature sensor (5) is arranged in an outer region of the membrane (2).
3. Verfahren nach Anspruch 1 oder 2, 3. The method according to claim 1 or 2,
dadurch gekennzeichnet, dass die Temperaturkompensation mit Hilfe einer Lookup-Tabelle (1 1 ) erfolgt, die vorzugsweise in einem Mikrocontroller (10) abgelegt ist. characterized in that the temperature compensation by means of a look-up table (1 1), which is preferably stored in a microcontroller (10).
4. Verfahren nach Anspruch 3, 4. The method according to claim 3,
dadurch gekennzeichnet, dass in der Lookup-Tabelle (11 ) die zu den gemessenen Temperaturwerten zugehörigen korrigierten Messwerte der elektromechanischen Wandler (3, 4) abgelegt sind.  characterized in that the corrected measured values of the electromechanical transducers (3, 4) associated with the measured temperature values are stored in the look-up table (11).
5. Verfahren nach Anspruch 3, 5. The method according to claim 3,
dadurch gekennzeichnet, dass in der Lookup-Tabelle (11 ) die zu den gemessenen Temperaturwerten zugehörigen Korrekturwerte abgelegt sind, mit denen die Messwerte der elektromechanischen Wandler (3, 4) zu verrechnen sind, wobei die Berechnung der korrigierten Messwerte der elektromechanischen Wandler (3, 4) außerhalb des Mikrocontrollers (10) auf analoge Weise erfolgt.  characterized in that the correction values associated with the measured temperature values are stored in the look-up table (11), with which the measured values of the electromechanical transducers (3, 4) are to be calculated, the calculation of the corrected measured values of the electromechanical transducers (3, 4) takes place in an analogous manner outside the microcontroller (10).
6. Verfahren nach einem der vorherigen Ansprüche, 6. The method according to any one of the preceding claims,
dadurch gekennzeichnet, dass die beiden elektromechanischen Wandler (3, 4) diversitär ausgebildet sind, in dem beide elektromechanischen Wandler (3, 4) jeweils ein weiteres Thermistorbauelement aufweisen oder nur ein elektromechanischer Wandler (3, 4) ein weiteres Thermistorbauelement aufweist.  characterized in that the two electromechanical transducers (3, 4) are diversified, in which both electromechanical transducers (3, 4) each have a further thermistor component or only one electromechanical transducer (3, 4) has a further thermistor component.
PCT/EP2012/064892 2011-08-01 2012-07-30 Method for checking the function of a pressure sensor WO2013017569A1 (en)

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