WO2016041726A1 - Dispositif et procédé permettant de surveiller une grandeur de processus d'un milieu - Google Patents

Dispositif et procédé permettant de surveiller une grandeur de processus d'un milieu Download PDF

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Publication number
WO2016041726A1
WO2016041726A1 PCT/EP2015/069058 EP2015069058W WO2016041726A1 WO 2016041726 A1 WO2016041726 A1 WO 2016041726A1 EP 2015069058 W EP2015069058 W EP 2015069058W WO 2016041726 A1 WO2016041726 A1 WO 2016041726A1
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WO
WIPO (PCT)
Prior art keywords
signal
frequency
response signal
probe
measuring
Prior art date
Application number
PCT/EP2015/069058
Other languages
German (de)
English (en)
Inventor
Maik WEISHAAR
Dietmar FRÜHAUF
Armin Wernet
Kaj Uppenkamp
Gerd BECHTEL
Original Assignee
Endress+Hauser Gmbh+Co. Kg
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 Endress+Hauser Gmbh+Co. Kg filed Critical Endress+Hauser Gmbh+Co. Kg
Publication of WO2016041726A1 publication Critical patent/WO2016041726A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
    • G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
    • G01F23/266—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors measuring circuits therefor

Definitions

  • the invention relates to a method and a device for monitoring a process variable of a medium in a container with a capacitive measuring probe.
  • the process variable may be given for example by a level, the electrical conductivity and / or the permittivity of the medium, or it is possible to monitor whether the sample has formed on the measuring probe.
  • Corresponding field devices are marketed by the applicant in many different embodiments, for example under the name Liquicap or Solicap.
  • a capacitive measuring probe generally comprises a rod-shaped measuring probe and, if appropriate, a guard electrode which coaxially surrounds the measuring probe and which lies at the same electrical potential.
  • the guard electrode serves to improve the measurement when forming a deposit on the probe.
  • the capacitive measuring method is known per se from the prior art.
  • the measuring probe is acted on by a starting signal in the form of an alternating current, and the filling level is then determined from the response signal received by the measuring probe. This depends on the capacitance of the capacitor formed by a measuring probe and the wall of the container or a second electrode. Depending on the conductivity of the medium, either the medium itself or a probe insulation forms the dielectric of the capacitor.
  • the capacitance is often determined from an apparent current reading, in which the amount of the probe is charged by the probe
  • Probe voltage applied I is measured, more suitable.
  • the additional determination of the phase angle also allows statements about possible formation of a formation, such as in the
  • Transition area can not be reliably determined, so that the corresponding media of the capacitive level measurement are usually not accessible.
  • Frequency scan determines an optimal for each application measurement frequency and is determined from the belonging to this measurement frequency response signal level. Depending on the length of the measuring probe and / or the nature of the medium, in particular the conductivity value, a different measuring frequency is accordingly determined in which the filling level can be determined most accurately. To implement the procedure described in this document, among other things, therefore, a signal generator is needed, which for applying the
  • Measuring probe with a frequency sweep is suitable.
  • a dynamic signal generator is described for example in the hitherto unpublished document DE102013107120.1. This signal generator generates the frequency sweep by means of a clock, which has a constant sampling frequency for
  • the amplitude values of the corresponding periodic signals can be stored as a function of the sampling frequency.
  • the stored amplitude values are then successively read out of the memory unit by means of a control and / or arithmetic unit with the sampling frequency of the clock generator. This then generates the periodic signals.
  • the power consumption plays a particular role when the corresponding field device is to be operated in an explosive atmosphere.
  • Measuring probe can be evaluated at different frequencies.
  • a problem here is that the capacitive load of a probe can vary with frequency.
  • the invention is therefore based on the object to provide a cost-effective and universally applicable measuring circuit for a capacitive probe.
  • the object is achieved by a device for monitoring at least one physical or chemical process variable of a medium in a container with at least one operated in the capacitive measurement mode
  • Measuring probe and an electronic unit the electronic unit to do so
  • the probe with an adjustable signal to stimulate
  • an evaluation unit is provided, which is adapted to the process variable from that of the
  • Frequency of the start signal and without loss of information can for determining the respective at least one process variable in each case a response signal of a
  • the frequency of the start signal may be in a range of 1 kHz to at least 10 MHz. Due to the fact that the response signal is transformed to a certain predefinable frequency, the evaluation unit does not need to evaluate a
  • the measuring circuit is configured to
  • the evaluation unit is configured to determine from the transformed start signal and the transformed response signal, the at least one process variable. This makes it possible, the at least one process variable by means of a
  • Admittanzflop in which in addition to the apparent current of the phase angle between the apparent current and the voltage applied to the probe voltage is to be determined. This is particularly advantageous in terms of buildup.
  • the excitation signal for acting on the measuring probe is a constant signal of adjustable frequency.
  • the invention allows the frequency of the excitation signal at the beginning optimally to the
  • the excitation signal for acting on the probe is given by a frequency sweep with successive signals discrete frequencies, which within a predetermined
  • Frequency range are.
  • the evaluation can also be considerably simplified for the multiplicity of response signals generated by means of the frequency sweep. It is advantageous if the starting signal is a rectangular signal, triangular signal or a sinusoidal signal.
  • the signal generator can be, for example, a dynamic signal generator as in the introduction of the description
  • the driver circuit in turn serves to drive the measuring probe with the start signal.
  • the driver circuit should be broadband and designed to drive large capacitive loads. This has the following reason: While the capacity of the probe remains the same at a given level, the reactance changes with the frequency of the start signal and hangs, if the
  • Measuring probe is subjected to a frequency sweep, on the bandwidth of the frequency interval. This leads to a greater load on the driver circuit, which is used to drive capacitive loads over more than an order of magnitude must be suitable. In particular, the driver circuit should be designed to drive loads between 400pF and 4000pF.
  • the driver circuit has a complementary
  • Operational amplifier or voltage follower with voltage feedback operational amplifier is.
  • a shunt resistor serves to generate a voltage signal proportional to the current flowing at the measuring probe and is connected in series therewith.
  • the start signal can be selected from a wide frequency interval, or a
  • a mixer is arranged within the measuring circuit, which mixer is designed to generate from the response signal of the probe a transformed response signal of constant frequency, wherein a first signal for the mixer received by the probe
  • a second signal for the mixer is the excitation signal, which is applied to the probe, and wherein a reference signal for the mixer is a signal with a constant predeterminable frequency difference from the excitation signal.
  • a reference signal for the mixer is a signal with a constant predeterminable frequency difference from the excitation signal.
  • the mixer is an analog down mixer
  • the electronic unit is designed such that the excitation signal and the response signal by the same switching branch for
  • Evaluation unit flow for this purpose, for example, an analog switch can be used in front of the mixer.
  • this results in a lower sensitivity to interference, such as temperature and / or voltage fluctuations.
  • Evaluation unit integrated a static filter. It is advantageous if the filter is a static low-pass filter, in particular a static low-pass filter 6.
  • the filter then filters out the signal at the desired frequency and amplifies it.
  • a static filter can be used. The filter ensures a particularly störunskye circuitry.
  • the at least one process variable is a continuous or predetermined level of a medium in a container.
  • the object according to the invention is also achieved by a method for monitoring at least one physical or chemical process variable of a medium in a container with at least one measuring probe operated in the capacitive measuring mode and an electronic unit, wherein the measuring probe is acted on by an adjustable starting signal, wherein the received from the measuring probe Response signal is transformed independently of the frequency of the start signal into a response signal of a predetermined frequency, and wherein the process variable is determined from the transformed response signal obtained from the measuring probe.
  • the present invention enables a capacitive
  • Measuring probe with a start signal with a variety of different
  • the invention is also characterized by a simple inexpensive and space-saving design, large
  • Fig. 1 a schematic representation of a measuring probe in a container according to the prior art.
  • FIG. 1 shows a typical construction for a measuring probe 1, by means of which a predetermined fill level can be monitored in the capacitive measuring method.
  • the measuring probe 1 is arranged on a container 2 and protrudes partially into it.
  • the container in turn is at least partially filled with a medium 3.
  • the measuring probe 1 is composed in the present example of a measuring electrode 5 and a guard electrode 6, which serves to avoid the formation of approach.
  • the measuring probe is connected outside the container to an electronic unit 7, which is used for signal acquisition, evaluation and / or supply
  • a block diagram of an electronic unit 7 according to the invention is the subject of FIG. 2.
  • a signal generator 9 a periodic signal is generated. This can either be a constant signal of adjustable frequency or else a frequency sweep.
  • a measuring circuit 8 the
  • Probe 1 operated, and that the response signal of the probe 1 evaluated at different frequencies. For this purpose, an admittance measurement is made in the example shown here.
  • Driver circuit 10 is provided. This amplifies the start signal and impresses it to a series circuit consisting of the measuring probe 1 and a shunt resistor 12a, 12b, which can be selected via an analog switch 11 for range switching, in a resistor network 12. About the respective shunt resistor
  • the mixer 14 is a discretely constructed circuit arrangement which makes it possible to generate different mixing frequencies by multiplying the measurement signal by a second additionally generated signal U z .
  • a downward mixing is realized, in which the reference signal used second additionally generated signal U z in the form of a rectangular signal has a constant frequency difference to the actual response signal U a .
  • the difference frequency of the two capture frequencies is achieved at the output of the mixer 14.
  • a transformed response signal of constant frequency can be generated from the response signal of the measuring probe U a .
  • the mixer 14 is followed by a static filter 15, because the output signal of the mixer 14 by the simple discrete mixture contains many different frequencies.
  • the response signal transformed in this way is finally forwarded to the microcontroller 16 and processed there.
  • By downconverting to a low constant frequency it is possible to work with a simple microcontroller 16 with an integrated analog-to-digital converter.
  • the measuring circuit is characterized by a low power consumption and a low cost.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electromagnetism (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

L'invention concerne un dispositif permettant de surveiller au moins une grandeur de processus physique ou chimique d'un milieu (2) dans un contenant (3), le dispositif comportant au moins une sonde de mesure (1) fonctionnant dans un mode de mesure capacitif et une unité électronique (7), l'unité électronique (7) étant conçue pour soumettre la sonde de mesure (1) à un signal d'excitation ajustable. Dans l'unité électronique (7) se trouve un circuit de mesure (8) qui est conçu pour transformer le signal de réponse reçu de la sonde de mesure (1) indépendamment de la fréquence du signal d'excitation en un signal de réponse présentant une fréquence prescrite, et une unité d'évaluation (16) est conçue pour déterminer la grandeur de processus à partir du signal de réponse transformé reçu de la sonde de mesure (1).
PCT/EP2015/069058 2014-09-19 2015-08-19 Dispositif et procédé permettant de surveiller une grandeur de processus d'un milieu WO2016041726A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102014113545.8A DE102014113545A1 (de) 2014-09-19 2014-09-19 Vorrichtung und Verfahren zur Überwachung einer Prozessgröße eines Mediums
DE102014113545.8 2014-09-19

Publications (1)

Publication Number Publication Date
WO2016041726A1 true WO2016041726A1 (fr) 2016-03-24

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DE (1) DE102014113545A1 (fr)
WO (1) WO2016041726A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102017128420A1 (de) * 2017-11-30 2019-06-06 Endress+Hauser SE+Co. KG Verfahren zur Prozessüberwachung
DE102021120175A1 (de) 2021-08-03 2023-02-09 Vega Grieshaber Kg Füllstandmessgerät zur Grenzstandbestimmung und zum Messen einer Impedanz eines Füllgutes
CN113959523A (zh) * 2021-09-22 2022-01-21 青岛海尔生物医疗科技有限公司 用于培养设备的液位检测装置及方法、培养设备及介质

Citations (5)

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US2962641A (en) * 1956-05-21 1960-11-29 Robertshaw Fulton Controls Co Null-balance bridge servosystem
EP0351700A2 (fr) * 1988-07-16 1990-01-24 Endress u. Hauser GmbH u.Co. Dispositif pour la mesure capacitive de niveau de remplissage
WO2006123141A2 (fr) * 2005-05-16 2006-11-23 Scientific Generics Ltd. Detecteur de position
WO2008062146A1 (fr) * 2006-11-23 2008-05-29 Sagentia Limited Détecteur de position
DE102011003158A1 (de) * 2011-01-26 2012-07-26 Endress + Hauser Gmbh + Co. Kg Vorrichtung und Verfahren zur kapazitiven Füllstandsmessung

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US4181881A (en) * 1978-05-15 1980-01-01 Preikschat F K Electrical impedance measuring apparatus for providing separate measurements of the conductivity and dielectric coefficient of various materials
DE3212434C3 (de) 1982-04-02 1991-01-03 Endress Hauser Gmbh Co Fuellstandsgrenzschalter fuer elektrisch leitende fuellgueter
GB2125553A (en) * 1982-08-10 1984-03-07 Standard Telephones Cables Ltd Multi-purpose sensor/detector for fluid
JPH04168326A (ja) * 1990-11-01 1992-06-16 Furukawa Electric Co Ltd:The 液面レベル計
DE102004008125A1 (de) 2004-02-18 2005-09-01 Endress + Hauser Gmbh + Co. Kg Verfahren und Vorrichtung zur kapazitiven Füllstandsbestimmung
US20080231290A1 (en) * 2004-05-14 2008-09-25 Scientific Generics Ltd. Capacitive Position Sensor
US7451646B2 (en) * 2005-07-28 2008-11-18 The Regents Of The University Of California Device and method for resonant high-speed microscopic impedance probe
DE102013107120A1 (de) 2013-07-05 2015-01-08 Endress + Hauser Gmbh + Co. Kg Signalgenerator für eine Messvorrichtung und Messvorrichtung für die Automatisierungstechnik

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2962641A (en) * 1956-05-21 1960-11-29 Robertshaw Fulton Controls Co Null-balance bridge servosystem
EP0351700A2 (fr) * 1988-07-16 1990-01-24 Endress u. Hauser GmbH u.Co. Dispositif pour la mesure capacitive de niveau de remplissage
WO2006123141A2 (fr) * 2005-05-16 2006-11-23 Scientific Generics Ltd. Detecteur de position
WO2008062146A1 (fr) * 2006-11-23 2008-05-29 Sagentia Limited Détecteur de position
DE102011003158A1 (de) * 2011-01-26 2012-07-26 Endress + Hauser Gmbh + Co. Kg Vorrichtung und Verfahren zur kapazitiven Füllstandsmessung

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