DE102022134038A1 - Method for detecting a limit level of a medium using a vibronic sensor - Google Patents

Abstract

The invention relates to a method (100) for operating a vibronic sensor (10) comprising:
a mechanically oscillatable unit (11) such as a tuning fork (11.1),
an electronic measuring/operating circuit (12) for operating the mechanically oscillatable unit and for detecting vibrations of the oscillatable unit,
wherein the electronic measuring/operating circuit excites the mechanically oscillatable unit to oscillate and derives measured values of at least one measured variable from measured values of at least one oscillation variable of the mechanically oscillatable unit,
wherein the mechanically oscillatable unit is operated intermittently at least in sections,
- wherein in a first time interval the mechanically oscillating unit is excited by the electronic measuring/operating circuit,
- wherein in a second time interval the mechanically oscillatable unit is not excited by the electronic measuring/operating circuit, wherein the electronic measuring/operating circuit measures a decay behavior of vibrations of the mechanically oscillatable unit and decides from the decay behavior whether the mechanically oscillatable unit is in contact with a medium.

Description

Mechanically vibrating units, e.g. vibrating forks of a vibronic sensor as in the DE102012101667A1 shown, are used, among other things, to determine a limit level of a medium in a tank. Usually, a measured resonance frequency is used to determine whether the vibrating unit is touched by a medium or not. When there is contact, vibronic boundary conditions change, which leads, for example, to a change in the measured resonance frequency.

However, it has been shown that the change in the resonance frequency is too small for some applications to be able to detect the reaching of a limit level at an early stage.

The object of the invention is therefore to provide a robust and sensitive method for detecting a limit level of a medium.

• eine mechanisch schwingfähige Einheit wie beispielsweise eine Schwinggabel,
• eine elektronische Mess-/Betriebsschaltung zum Betreiben der mechanisch schwingfähigen Einheit und zum Erfassen von Schwingungen der schwingfähigen Einheit,
• wobei die elektronische Mess-/Betriebsschaltung die mechanisch schwingfähige Einheit zum Schwingen anregt, und aus Messwerten von mindestens einer Schwingungsgröße der mechanisch schwingfähigen Einheit Messwerte zumindest einer Messgröße ableitet,
• wobei die mechanisch schwingfähige Einheit zumindest abschnittsweise intermittierend betrieben wird,
  • - wobei in einem ersten Zeitintervall die mechanisch schwingfähige Einheit durch die elektronische Mess-/Betriebsschaltung angeregt wird,
  • - wobei in einem zweiten Zeitintervall die mechanisch schwingfähige Einheit nicht durch die elektronische Mess-/Betriebsschaltung angeregt wird, wobei die elektronische Mess-/Betriebsschaltung ein Abklingverhalten von Schwingungen der mechanisch schwingfähigen Einheit misst und aus dem Abklingverhalten entscheidet, ob die mechanisch schwingfähige Einheit mit einem Medium kontaktiert ist.

The object is achieved by a method for operating a vibronic sensor comprising:

• a mechanically oscillating unit such as a tuning fork,
• an electronic measuring/operating circuit for operating the mechanically oscillatable unit and for detecting vibrations of the oscillatable unit,
• wherein the electronic measuring/operating circuit excites the mechanically oscillatable unit to oscillate and derives measured values of at least one measured variable from measured values of at least one oscillation variable of the mechanically oscillatable unit,
• wherein the mechanically oscillatable unit is operated intermittently at least in sections,
  • - wherein in a first time interval the mechanically oscillating unit is excited by the electronic measuring/operating circuit,
  • - wherein in a second time interval the mechanically oscillatable unit is not excited by the electronic measuring/operating circuit, wherein the electronic measuring/operating circuit measures a decay behavior of vibrations of the mechanically oscillatable unit and decides from the decay behavior whether the mechanically oscillatable unit is in contact with a medium.

It has been shown that the decay behavior of the oscillating unit is much more sensitive to media wetting than a resonance frequency of the oscillating unit.

In one embodiment, at least one time constant of the decay behavior is determined when measuring the decay behavior, wherein the at least one time constant is compared with at least one corresponding reference constant of a decay behavior of the mechanically oscillatable unit without media contact,
If the relative deviation of the determined time constant from the reference constant is greater than a limit value, it is concluded that there has been contact with a medium.

The limit value depends on various influences such as the geometry of the oscillating unit or the medium. A specialist will therefore choose a reasonable limit value.

In one embodiment, the mechanically oscillatable unit has a natural frequency, wherein the decay behavior is measured from at least 5 oscillations.

In one embodiment, the at least one time constant is determined by a non-linear fit of an oscillation amplitude during decay,
where the fitting function comprises, for example, an exponential function and/or a trigonometric function.

• 1 beschreibt einen beispielhaften vibronischen Sensor;
• 2 skizziert beispielhafte Abklingvorgänge einer mechanisch schwingfähigen Einheit;
• 3 skizziert den Ablauf eines beispielhaften erfindungsgemäßen Verfahrens.

In the following, the invention is described using embodiments.

• 1 describes an example vibronic sensor;
• 2 outlines exemplary decay processes of a mechanically oscillating unit;
• 3 outlines the sequence of an exemplary method according to the invention.

1 describes an exemplary vibronic sensor 10, which has a mechanically oscillatable unit 11 and an electronic measuring/operating circuit 12. The mechanically oscillatable unit, which as shown here can be designed as a tuning fork 11.1, is located in an inner volume of a container 20 and acts there, for example, as a limit switch. A medium 21 influences vibration properties of the oscillatable unit as soon as it touches the oscillatable unit. The mechanically oscillatable unit is excited to oscillate by the electronic measuring/operating circuit. As soon as, for example, a resonance frequency of the oscillatable unit changes, in particular becomes lower, or falls below a limit value, It can be detected that the medium in the tank has reached a limit level.

According to the invention, however, the sensor is excited intermittently at least at times, whereby it is deduced from a decay behavior whether there is media contact or not.

2 outlines example amplitude curves of an oscillation, a first curve V1 without media contact and a second V2 with media contact. In a first time interval with continuous excitation, the oscillation amplitudes of the curves are almost the same. When the excitation ends, oscillation energy is dissipated through losses. Without media contact, dissipation takes place more slowly, which is associated with better, higher oscillation quality. With media contact, on the other hand, the dissipation of oscillation energy increases and the curve in the second time interval becomes steeper. A time constant can be calculated from the curves in the second time interval, for example by fitting a curve. The time constant for the curve without media contact can be used as a reference constant for the time constant of a curve with media contact. For example, if the time constant deviates from the reference constant by a certain value, such as 2%, it can be concluded that there is media contact.

3 outlines the sequence of an exemplary method 100 according to the invention. In a method according to the invention, a mechanically oscillatable unit 11 is operated intermittently. In a first method step 101, the oscillatable unit 11 is excited to oscillate by the electronic measuring/operating circuit. In a second method step 102, the excitation is stopped so that an oscillation amplitude of the oscillatable unit decreases. By determining a time constant of the decay of the oscillation amplitude, a decision can be made in a third method step 103 as to whether there is media contact, i.e., for example, whether a limit level of a medium in a container has been reached or not.

List of reference symbols

10

vibronic sensor

11

oscillating unit

11.1

Tuning fork

12

electronic measuring/operating circuit

20

container

21

medium

100

Proceedings

101

first procedural step

102

second process step

V1

Course without media contact

V2

History with media contact

Z1

first time interval

Z2

second time interval

QUOTES INCLUDED IN THE DESCRIPTION

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

Cited patent literature

• DE 102012101667 A1 [0001]

Claims (4)

Method (100) for operating a vibronic sensor (10) comprising: a mechanically oscillatable unit (11) such as a tuning fork (11.1), an electronic measuring/operating circuit (12) for operating the mechanically oscillatable unit and for detecting vibrations of the oscillatable unit, wherein the electronic measuring/operating circuit excites the mechanically oscillatable unit to oscillate and derives measured values of at least one measured variable from measured values of at least one vibration variable of the mechanically oscillatable unit, wherein the mechanically oscillatable unit is operated intermittently at least in sections, - where in a first method step (101) in a first time interval (Z1) the mechanically oscillatable unit is excited by the electronic measuring/operating circuit, - where in a second method step (102) in a second time interval (Z2) the mechanically oscillatable unit is not excited by the electronic measuring/operating circuit, wherein the electronic measuring/operating circuit in a third Method step (103) measures a decay behavior of vibrations of the mechanically oscillatable unit and decides from the decay behavior whether the mechanically oscillatable unit is in contact with a medium. Procedure according to Claim 1 , wherein during the measurement of the decay behavior at least one time constant of the decay behavior is determined, wherein the at least one time constant is compared with at least one corresponding reference constant of a decay behavior of the mechanically oscillatable unit without media contact, wherein if the relative deviation of the determined time constant from the reference constant is greater than a limit value, it is concluded that there is contact with a medium. Procedure according to Claim 1 or 2 , wherein the mechanically oscillatable unit has a natural frequency, wherein the decay behavior is measured from at least 5 oscillations. Method according to one of the Claims 2 or 3 , wherein the at least one time constant is determined by a non-linear fit of an oscillation amplitude during the decay, wherein the fit function comprises, for example, an exponential function and/or a trigonometric function.

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