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WO2010054676A1 - Convertisseur manométrique pour l'instrumentation des procédés et procédé de mesure de la pression - Google Patents

Convertisseur manométrique pour l'instrumentation des procédés et procédé de mesure de la pression Download PDF

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Publication number
WO2010054676A1
WO2010054676A1 PCT/EP2008/009621 EP2008009621W WO2010054676A1 WO 2010054676 A1 WO2010054676 A1 WO 2010054676A1 EP 2008009621 W EP2008009621 W EP 2008009621W WO 2010054676 A1 WO2010054676 A1 WO 2010054676A1
Authority
WO
WIPO (PCT)
Prior art keywords
pressure
temperature
medium
membrane
evaluation device
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2008/009621
Other languages
German (de)
English (en)
Inventor
Herbert Schorb
Stefan Von Dosky
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Siemens Corp
Original Assignee
Siemens AG
Siemens Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG, Siemens Corp filed Critical Siemens AG
Priority to PCT/EP2008/009621 priority Critical patent/WO2010054676A1/fr
Publication of WO2010054676A1 publication Critical patent/WO2010054676A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
    • G01L11/004—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by the use of counterbalancing forces
    • G01L11/006—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by the use of counterbalancing forces hydraulic or pneumatic counterbalancing forces
    • 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

Definitions

  • the invention relates to a pressure transmitter for process instrumentation with a pressure sensor with a membrane, on one side of the pressure to be measured and on the other side a reference pressure are guided, and with at least one sensor element for detecting a deflection of the membrane according to the preamble of claim 1 and a method for pressure measurement with such a pressure transducer.
  • Transmitters are used to record process variables, such as temperature, pressure, flow rate, level, density or gas concentration of a medium.
  • process variables such as temperature, pressure, flow rate, level, density or gas concentration of a medium.
  • actuators By means of actuators, the process flow can be influenced as a function of detected process variables in accordance with a strategy predetermined, for example, by a control station.
  • actuators may be mentioned a control valve, a heater or a pump.
  • pressure transmitters are essential sensory components in the context of automated production processes. With regard to an optimal plant behavior and a permanently high product quality, high-quality transducers are necessary, which provide long-term stable and low error measured values even under extreme conditions.
  • a SITRANS P pressure transmitter for process instrumentation which has sensor elements arranged on a membrane for detecting the membrane deflection as a result of the applied pressure and for generating a measurement signal representing this pressure , wherein an evaluation device determines a measured value of the pressure as a function of the measuring signal.
  • the determined pressure value is compared with a reference pressure value, for which purpose the pressure signal representing the measurement signal is evaluated.
  • This measurement signal usually produces material voltage-dependent, piezoresistive resistances, which are interconnected in a Wheatstone bridge.
  • a disadvantage is that the measurement results over a longer periods due to aging effects of the piezoresistive resistors and the membrane or due to outgassing of a filling oil in a measuring chamber which is provided for transmission of the process pressure to be measured to the membrane, drift and after some time, the accuracy requirements are no longer sufficient, so that recalibration measures are required.
  • the invention has for its object to provide a pressure transducer for process instrumentation, which is characterized by improved long-term stability and thus can be operated longer without recalibration. Another object is to find a suitable method of pressure measurement with such a pressure transducer.
  • the pressure transmitter for process instrumentation of the type mentioned in the characterizing part of claim 1 features on.
  • the invention has the advantage that it can be integrated in a simple manner into a pressure transmitter with a micromechanically produced silicon diaphragm which carries a piezoresistive bridge circuit for detecting the diaphragm deflection.
  • a micromechanically produced silicon diaphragm which carries a piezoresistive bridge circuit for detecting the diaphragm deflection.
  • Such a structure is used for example in the known pressure transmitter SITRANS P.
  • SITRANS P On one side of the membrane of the pressure to be measured, on the other side a reference pressure of a reference pressure chamber is performed.
  • the reference pressure chamber is now filled with a medium whose pressure has a known temperature dependence.
  • the deflection of the membrane can be detected by the piezoresistive measuring resistors of the bridge circuit.
  • the deflection of the diaphragm can, of course, be measured using inductive, capacitive or optical transducers.
  • the medium is brought in the reference pressure chamber by means of a temperature change to that temperature at which the membrane is in a predetermined position, which is preferably free of mechanical stresses.
  • the resulting temperature is precisely measured, for example, with a thermocouple or a temperature-dependent resistor.
  • the pressure to be measured On the physical relationship between the pressure of the medium in the reference pressure chamber and its temperature, which ultimately depends only on the physical properties of the medium, the pressure to be measured, which can also be referred to as system or process pressure, determined and abandonedge - ben. If the reference pressure chamber is designed to be diffusion-tight, then the amount of medium located in the reference pressure chamber does not change over the service life of the pressure transmitter and there is no contamination of the medium either instead of. Since the measurement of the system pressure essentially depends only on the long-term stability of the medium in the reference pressure chamber and the accuracy of the temperature measurement, which can also be performed very long-term stable, the new pressure transducer is characterized by a comparatively good long-term stability with relatively little technical effort for his Realization off.
  • Membrane - as already indicated above - is designed as a piezoresistive full bridge circuit, the bridge voltage is used as a position signal, and also if the value zero of the bridge voltage is used as the predetermined value of the position signal, which is achieved by means of the temperature setting, this has the advantage that also the sensor element is characterized by an excellent long-term stability. For example, if the individual resistors of the bridge circuit experience a drift due to aging effects, this does not affect a shift in the zero position of the bridge voltage, since all measuring resistors of the circuit are exposed to the same influences and thus experience the same drift. In addition, for the realization of the sensor element for detecting the diaphragm deflection no redesign of a conventional membrane is required, as used for example in the pressure transmitter SITRANS P.
  • the membrane can be in the state of a pressure equilibrium between the two membrane sides at the predetermined value of the position signal substantially.
  • the membrane is free of mechanical stresses and aging phenomena, for example material fatigue. These then do not lead to a drift of the membrane layer in the equilibrium state. This further improves the long-term stability of the pressure transmitter.
  • the reference pressure chamber is filled with a medium which, at the operating temperature of the pressure measuring partly in the gaseous and partly in the liquid state of aggregation.
  • the vapor pressure is the pressure of the vaporous phase of a substance when the liquid and gaseous phases are in equilibrium.
  • the vapor pressure of a pure substance is only dependent on its temperature. When the temperature or volume changes, so much of the substance evaporates or condenses, until at equilibrium the vapor pressure again reaches the saturation vapor pressure.
  • even small leaks in the reference pressure chamber are therefore tolerable, as long as there is still a two-phase mixture of the medium in the chamber.
  • the pressure sensor with the novel measuring principle can be used as a reference for calibrating a pressure sensor, which performs the pressure measurement according to a conventional principle.
  • both pressure sensors are subjected to the same system pressure and the pressure sensor, which operates according to the conventional principle, is calibrated with the aid of the long-term stable measuring signal of the reference pressure sensor with a new measuring principle, in particular if a constant system pressure is present for a certain period of time.
  • FIG. 1 shows a schematic representation of a pressure sensor of a pressure transducer
  • FIG. 2 is a block diagram of a pressure transmitter
  • FIG. 3 shows a block diagram for explaining the temperature setting
  • FIG. 4 shows a flowchart of the pressure measurement
  • a pressure sensor 1 for a pressure transducer comprises, according to FIG. 1, a silicon membrane 2 which is arranged on a substrate 3.
  • a system pressure P acts, on the other side a reference pressure, which is generated by a medium 5, 6 in a reference pressure chamber 4.
  • a part 5 of the medium is in the gaseous state, a part 6 in the liquid state.
  • measuring resistors 7 doped in the upper side of the diaphragm are used, which are electrically connected to form a Wheatstone full bridge.
  • the reference pressure in the reference pressure chamber 4 corresponds to the saturation vapor pressure of the medium and is therefore almost exclusively dependent on the temperature of the medium.
  • a control signal u is given to the two connections of the heater 8.
  • a temperature signal T is generated, which corresponds to the temperature of the medium. So that the medium remains as permanently as possible in the reference pressure chamber 4, this is made almost diffusion-tight.
  • FIG. 2 the basic interconnection of the pressure sensor 1 with an evaluation device 20 of a pressure transmitter 24 is shown.
  • the system pressure P is guided as a physical variable to be measured.
  • the pressure sensor 1 transmits to the evaluation device 20 a displacement signal x representing the deflection of the diaphragm 2 (FIG. 1), which in the illustrated embodiment corresponds to the bridge voltage and the temperature signal T representing the fluid temperature.
  • the evaluation device 20 determines based on these signals x and T in a manner to be described in more detail later, a temperature control signal u, in the pressure sensor 1 for controlling a
  • Heating and possibly also for controlling a cooling for the medium in the reference pressure chamber is used.
  • a value of the system pressure P to be measured is determined in the evaluation device 20 on the basis of a vapor pressure curve stored in a memory 21 and, for example, via a fieldbus or a fourth to 20 mA interface 22 to a programmable logic controller or a control station for further processing in a process plant, in which the pressure transmitter 24 is used issued.
  • a suitably programmed microcomputer 23 is present, which performs the necessary calculations, inter alia, to specify the temperature control signal u or to determine the pressure measurements.
  • control variable x the position signal repre- senting the deflection is used, which corresponds to the bridge voltage of the bridge circuit located on diaphragm 2 (FIG. 1).
  • a control deviation is determined, which is on a controller 30, such as a PID controller, out. This provides a default value of the temperature control signal u, with which a temperature actuator 31 is driven for heating or cooling.
  • a member 32 in the control loop according to FIG. 3 represents means for detecting the temperature T of the medium and the sensor element for detecting the deflection of the diaphragm and for generating the displacement signal representing the position signal x, which, as already explained above, corresponds to the bridge voltage in the embodiment shown , With the aid of the actuator 31, the temperature of the medium in the reference pressure chamber is thus adjusted such that the position signal x assumes the predetermined value zero, at which the membrane of the pressure sensor just does not deform.
  • the temperature T of the medium is always tracked by the controller 30 so that the position signal x, and thus the bridge voltage of the piezoresistive bridge circuit and the material stresses in the membrane, are regulated to zero. In the regulated state, a pressure equilibrium prevails between the two sides of the membrane.
  • FIG. 4 shows the basic sequence of a cycle for measuring the system pressure P.
  • a step S1 first the position signal x is adjusted, as described with reference to FIG.
  • the position signal x goes to a step S2, in which the temperature T of the medium is measured accurately.
  • the reference pressure is subsequently determined on the basis of the stored vapor pressure curve, which reflects the previously known temperature dependence of the media pressure.
  • a value of the system pressure P is then calculated in a step S4 and output, for example, to a higher-level control station.
  • the value of the system pressure P is determined and output via a physically fundamental, substance-dependent and constant relationship, namely via the vapor pressure curve of the medium.
  • the reference pressure chamber is designed to be diffusion-tight, no medium is consumed over the entire service life of the pressure sensor, and there is also no mistaking cleaning the medium instead. Even small leaks are tolerable as long as there is still a two-phase mixture in the reference pressure chamber.
  • the measuring range of the pressure transducer is essentially determined by the vapor pressure curve of the medium, which in this case can also be referred to as liquefied gas.
  • the vapor pressure range of the liquefied gas lies within the microtechnically manageable temperature range for doped silicon, which is usually chosen as the material for the membrane.
  • the lower and upper limits of the pressure transmitter should also be overlapped if possible.
  • a suitable liquid gas must therefore be selected according to the absolute size and position of the measuring range. For high-pressure sensors, for example, low-order paraffins with a steep vapor pressure curve and for low-pressure sensors higher-order paraffins with a flatter vapor pressure curve are recommended.
  • FIG. 5 shows vapor pressure values for various paraffins in a diagram.
  • the abscissa shows the temperature in 0 C, the ordinate the pressure P in megapascals. Values of the same paraffin are marked with the same symbols. The following assignment of symbols provided with reference signs applies:
  • Vapor pressure curve 60 are derived according to Figure 5 comparative values.
  • the uncertainty of the vapor pressure curve 60 is 0.02% of the absolute value. This corresponds to a pressure of 8364 mbar at 20 ° C corresponding to the vapor pressure curve 60 with a maximum deviation of +/- 1.7 mbar.
  • a temperature measurement with a maximum error of +/- 0.02 K thus means an uncertainty of the measured pressure value of a total of +/- 5 mbar.
  • the measurement error is thus significantly lower than with the conventional pressure transmitter. It follows that the pressure can be measured much more accurately if the temperature measurement is accurate.
  • the long-term stability of the new pressure transmitter is also significantly better than that of the conventional pressure transmitter SITRANS P, as the reference pressure chamber can be made diffusion-tight and the temperature measurement can be designed for a long-term stability.
  • the pressure transmitter does not require a factory calibration or recalibration of the pressure, only the temperature measuring point has to be calibrated at the factory.
  • a recalibration can thus be completely eliminated.
  • the temperature dependence of the vapor pressure is stored in the memory 21 of the evaluation device 20 according to FIG.
  • the mechanical Demands on the diaphragm 2 of the pressure sensor shown in Figure 1 are relatively low and can therefore be realized with inexpensive components.
  • the setting of the temperature is such that the position signal of the pressure sensor corresponds to a predetermined value, with standard components without much effort feasible.
  • a temperature measuring point with the required accuracy is already integrated in a conventional SITRANS P pressure transmitter because the temperature on the diaphragm of the pressure sensor is recorded and its influence on the measured value compensated. In the condition of a temperature compensation within the sensor, this corresponds to the temperature of the medium, nevertheless it is advantageous to provide a temperature sensor directly for the medium temperature.
  • the new pressure transmitter is thus a pressure gauge with a pressure sensor which has a long-term stable pressure reference due to the dependence of the vapor pressure on the temperature.
  • the pressure measurement can be traced back to a temperature measurement and by a control pressure in the pressure sensor is built up a back pressure, which corresponds to the system pressure.
  • a pressure sensor is available in which the sensor membrane is not deformed during the measurement and is therefore free from mechanical stresses.
  • the use of a vapor pressure curve as a pressure reference has the advantage that it represents a fundamental, long-term stable material property that is highly accurately referenced for many technically relevant substances and known for example for propane with an uncertainty of 0.02%. This eliminates the need for pressure calibration at the factory and no recalibration in the field.
  • Another advantage is that the mechanical requirements on the pressure sensor are rather low and thus the use of inexpensive sensors is made possible.
  • the realization of a pressure sensor with a pressure reference on the basis of the vapor pressure curve of a medium in the reference pressure chamber is also advantageously already carried out with comparatively small deviations. Conversions of the established pressure transmitter SITRANS P possible.

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

Abstract

L'invention concerne un convertisseur manométrique pour l'instrumentation des procédés et un procédé de mesure de la pression avec un convertisseur manométrique comprenant un capteur de pression (1) avec une membrane (2) dont l'un des côtés est exposé à la pression (P) à mesurer, et l'autre côté, à une pression de référence. Afin de produire la pression de référence, une chambre de pression de référence (4) est remplie d'un fluide (5, 6) dont la pression possède une dépendance connue par rapport à la température. Il est prévu des moyens (8) de réglage de la température (T) du fluide qui font qu'un signal de position représentant la flèche de la membrane (2) correspond à une valeur prédéterminée. Un dispositif d'analyse (20) détermine et produit en sortie la pression (P) à mesurer à partir de la température (T) du fluide (5, 6) ainsi réglée. Comme on utilise une propriété fondamentale et stable à long terme du fluide comme référence de pression, à savoir sa courbe de pression de vapeur dans le cas d'un gaz liquéfié, on obtient un convertisseur manométrique de grande précision, avec une stabilité à long terme particulièrement bonne, qui n'a pas besoin d'étalonnage en usine et de réétalonnage de la pression in situ.
PCT/EP2008/009621 2008-11-13 2008-11-13 Convertisseur manométrique pour l'instrumentation des procédés et procédé de mesure de la pression Ceased WO2010054676A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2008/009621 WO2010054676A1 (fr) 2008-11-13 2008-11-13 Convertisseur manométrique pour l'instrumentation des procédés et procédé de mesure de la pression

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PCT/EP2008/009621 WO2010054676A1 (fr) 2008-11-13 2008-11-13 Convertisseur manométrique pour l'instrumentation des procédés et procédé de mesure de la pression

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9176020B2 (en) 2013-10-01 2015-11-03 Freescale Semiconductor, Inc. Pressure sensor having multiple pressure cells and sensitivity estimation methodology
US20160107887A1 (en) * 2014-10-15 2016-04-21 Freescale Semiconductor, Inc. Methodology and system for wafer-level testing of mems pressure sensors
CN114518194A (zh) * 2022-02-21 2022-05-20 中国第一汽车股份有限公司 一种压力传感器检测设备及检测方法
CN119268919A (zh) * 2024-10-14 2025-01-07 胜利油田豪威科工贸有限责任公司 一种压阻式压力变送器

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1299485A (fr) * 1961-09-07 1962-07-20 Leybolds Nachfolger E Dispositif manométrique à étalonnage absolu
US4197743A (en) * 1978-02-10 1980-04-15 Canadian Patents & Development Limited Apparatus for measuring barometric pressure
GB2091426A (en) * 1981-01-19 1982-07-28 Danfoss As Pressure gauge

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1299485A (fr) * 1961-09-07 1962-07-20 Leybolds Nachfolger E Dispositif manométrique à étalonnage absolu
US4197743A (en) * 1978-02-10 1980-04-15 Canadian Patents & Development Limited Apparatus for measuring barometric pressure
GB2091426A (en) * 1981-01-19 1982-07-28 Danfoss As Pressure gauge

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PUERS R ET AL: "A novel combined redundant pressure sensor with self-test function", SENSORS AND ACTUATORS A, ELSEVIER SEQUOIA S.A., LAUSANNE, CH, vol. 60, no. 1-3, 1 May 1997 (1997-05-01), pages 68 - 71, XP004134597, ISSN: 0924-4247 *
YANG X ET AL: "A MEMS thermopneumatic silicone membrane valve", MICRO ELECTRO MECHANICAL SYSTEMS, 1997. MEMS ' 97, PROCEEDINGS, IEEE., TENTH ANNUAL INTERNATIONAL WORKSHOP ON NAGOYA, JAPAN 26-30 JAN. 1997, NEW YORK, NY, USA,IEEE, US, 26 January 1997 (1997-01-26), pages 114 - 118, XP010216889, ISBN: 978-0-7803-3744-2 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9176020B2 (en) 2013-10-01 2015-11-03 Freescale Semiconductor, Inc. Pressure sensor having multiple pressure cells and sensitivity estimation methodology
US9488542B2 (en) 2013-10-01 2016-11-08 Freescale Semiconductor, Inc. Pressure sensor having multiple pressure cells and sensitivity estimation methodology
US20160107887A1 (en) * 2014-10-15 2016-04-21 Freescale Semiconductor, Inc. Methodology and system for wafer-level testing of mems pressure sensors
US9527731B2 (en) * 2014-10-15 2016-12-27 Nxp Usa, Inc. Methodology and system for wafer-level testing of MEMS pressure sensors
CN114518194A (zh) * 2022-02-21 2022-05-20 中国第一汽车股份有限公司 一种压力传感器检测设备及检测方法
CN119268919A (zh) * 2024-10-14 2025-01-07 胜利油田豪威科工贸有限责任公司 一种压阻式压力变送器

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