Method for determining measured variable of medium

Abstract

The invention relates to a method for ascertaining a measured variable of a medium (4). In this case, the mechanical oscillation unit (2) is brought into contact with the medium (4) such that the medium covers at least part of the mechanical oscillation unit (2). The mechanical oscillation unit (2) is then positioned such that droplet formation of the medium (4) is enabled and excited such that mechanical oscillation is performed. Measurements are ascertained at different points in time for at least one characteristic variable of the mechanical oscillation. The temporal behavior resulting from the measured values is evaluated with respect to the measured variables.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for ascertaining a measurement variable of a medium. BACKGROUND

[0002] In the prior art, vibration sensors are known which are embodied, for example, as oscillating forks or single bars. Such sensors have a mechanical oscillation unit which is excited by an excitation / reception unit such that a mechanical oscillation is performed. Oscillations which are caused by an interaction with a medium to be measured or monitored are received by the excitation / reception unit and fed to an evaluation. What is measured is, for example, a change in the oscillation frequency or amplitude when the mechanical oscillation unit is changed from an uncovered state to a state covered by a medium. This enables, for example, a filling level of a medium in a container to be monitored.

[0003] In DE 10 2021 126 826 A1, different media are to be detected with an oscillating fork on the basis of a calibration measurement. In an embodiment, the calibration is performed while a medium is attached to the sensor.

[0004] DE 10 2020 121 610 A1 relates to an oscillating fork in which it is observed via an optical distance sensor whether a medium is attached to the fork.

[0005] DE 10 2014 115 693 A1 describes an oscillating fork whose blades are optimized with respect to their drop shedding.

[0006] For intrinsic variables of a medium, for example its viscosity, very complex measurement devices are most often required. SUMMARY

[0007] It is an object of the present application to provide a method with which an intrinsic measurement variable of a medium can also be ascertained as simply as possible.

[0008] This object is achieved by a method for ascertaining a measurement variable of a medium, wherein the method comprises the following method steps:

[0009] a) bringing a mechanical oscillation unit into contact with the medium such that the medium covers at least a portion of the mechanical oscillation unit,

[0010] b) positioning the mechanical oscillation unit such that drop formation of the medium on the mechanical oscillation unit can take place,

[0011] c) exciting the mechanical oscillation unit at least during step b) such that a mechanical oscillation is performed,

[0012] d) ascertaining measurement values of at least one characteristic variable of the mechanical oscillation at different points in time, and

[0013] e) evaluating a temporal behavior of the measurement values resulting from the ascertained measurement values with respect to the measurement variable.

[0014] In the method of the application, a mechanical oscillation unit is brought into contact with a medium, the measurement variable of which is to be ascertained, such that the medium at least partially covers the mechanical oscillation unit. The mechanical oscillation unit is then positioned such that droplet formation of the medium on the mechanical oscillation unit is possible. The medium is thus in particular a flowable medium, such as for example a liquid. In this state, in which the medium is located on the mechanical oscillation unit, the mechanical oscillation unit is excited to perform oscillations. In this case, these oscillations depend on the medium located on the mechanical oscillation unit. The characteristic variable that can be ascertained from the received mechanical oscillations thus also depends on the interaction with the medium. The characteristic variable is for example the frequency, the amplitude, the phase or the mass. At least one characteristic variable is ascertained at different points in time in order to record the temporal behavior of the medium on the mechanical oscillation unit. In particular, droplet formation or the shedding of droplets of the medium is recorded in order to ascertain the measurement variable of interest of the medium therefrom. In this case, whether droplets form also depends on the properties of the medium.

[0015] In an embodiment, a further variable of the medium is ascertained. The further variable of the medium is preferably its temperature. For example, a temperature sensor is present.

[0016] Complementarily or alternatively, at least one further characteristic variable of the oscillation is ascertained and used for the evaluation.

[0017] An embodiment of the method provides that, in step a), the mechanical oscillation unit is at least partially dipped into a quantity of the medium in a container and is then preferably pulled out completely. The mechanical oscillation unit is thus at least partially coated with the medium by immersion. In order for droplets to be able to form thereafter, the mechanical oscillation unit is pulled out of the medium. In a complementary embodiment, the mechanical oscillation unit is pulled out of the medium in the container by a relative movement between the mechanical oscillation unit and the container. The mechanical oscillation unit is thus removed from the container in an embodiment. Alternatively, the container is moved away from the stationary mechanical oscillation unit. In an additional embodiment, both variants described above can also be combined.

[0018] An alternative embodiment comprises bringing the medium to the mechanical oscillation unit by a medium line or a spraying unit.

[0019] In an embodiment, the droplet formation is supported by the following property: in step b), the mechanical oscillation unit is oriented at a predetermined inclination angle relative to the gravitational field. The mechanical oscillation unit is thus preferably arranged inclined in this embodiment, such that the medium can flow, for example, to the end of the unit and form a droplet there.

[0020] The following embodiments in particular relate to the evaluation of the characteristic variable ascertained from the oscillations.

[0021] Therefore, the embodiment provides that in step e) an instability of the time behavior is identified. If a droplet forms and detaches from the mechanical oscillation unit, this results in a sudden change of the influence of the mechanical oscillation, which in turn leads to an instability of the characteristic variable of the oscillation. If one starts from the idea that the droplet formation is a function of the measurement variable of interest, the instability is then used in this embodiment to find out the measurement variable from the at least one droplet detachment time of the medium.

[0022] Another embodiment provides that in step e) a case in which the change of the measurement value exceeds a predeterminable limit value within a predeterminable time period is evaluated as a droplet detachment time of the medium, information about the droplet detachment behavior of the medium is found out from the at least one droplet detachment time of the medium, and the information about the droplet detachment behavior is compared with the supplied data in order to find out the measurement variable. In this embodiment, it is detected whether the measurement value of the characteristic variable of the oscillation changes by more than a certain measure within a certain time window. This relates in particular to whether there is a sudden change. If this is the case of a significant change of the measurement value, this is evaluated as a droplet detachment time, i.e. a drop of the medium from the mechanical oscillation unit occurs in this time window. From the at least one droplet detachment time or preferably a plurality of droplet detachment times, the droplet detachment behavior of the medium itself is inferred. Starting from the detachment behavior thus found and using the appropriately supplied data, the measurement variable of the medium is found out. In an alternative or supplementary variant, the curve of the measurement value in the time window around the detected droplet detachment time is evaluated. This relates for example to a time period before the droplet detachment time. Alternatively or in addition, the embodiment relates to the length of time between a plurality of droplet detachment times. Preferably, a plurality of variables is derived on the basis of the measurement value and the identified droplet detachment times and taken into account for the evaluation.

[0023] The method is preferably applied to find out a rheological measurement variable of the medium. In this case, the measurement variable is likewise preferably the viscosity of the medium. BRIEF DESCRIPTION OF DRAWINGS

[0024] The application will now be explained in more detail on the basis of the drawings, which are shown below:

[0025] Figure 1 is a schematic and not to scale measuring device for applying the method of the application; and

[0026] Figure 2 is the time development of the mass of the mechanical oscillation unit in the case of wetting with water (a) and silicone oil of three different viscosities (b) to (d). DETAILED DESCRIPTION

[0027] Figure 1 The oscillating tines of a device 1 for finding out a measurement variable of a medium 4 are shown. The two tines of the mechanical oscillation unit 2 are excited to perform a mechanical oscillation.

[0028] It is noted here that during the execution of this method, the device 1 is arranged relative to the gravitational field such that the mechanical oscillation unit 2 is tilted at a predetermined tilt angle. This occurs, for example, after the mechanical oscillation unit 2 is immersed in the medium 4 within the container 3 and then pulled back. The tilted position particularly facilitates the shedding of the medium 4, which at least partially covers the mechanical oscillation unit 2.

[0029] Additionally, a temperature sensor 5 is present, which enables the recording of the temperature of the medium. The measurement signal or data relative to the oscillation of the device 1, along with the measurement result from the temperature sensor 5, is fed to the evaluation unit 6, which identifies the measurement variables of the medium 4.

[0030] Figure 2 The temporal behavior of characteristic variables of mechanical oscillations based on four different viscosities of covering media is shown.

[0031] therefore, Figure 2 Each of a) through d) plots the mass (y-axis) of the mechanical oscillation unit according to time (x-axis, t / s). For this purpose, the mass is determined at different time points in each case.

[0032] Figure 2 a) shows the droplet shedding behavior of the fork after immersion in water. Figure 2 b) to d) show the immersion viscosity of approximately 1000 mm. 2 / s of silicone oil ( Figure 2 b) The viscosity is approximately 10,000 mm. 2 / s of silicone oil ( Figure 2 c) and a viscosity of approximately 20,000 mm 2 / s of silicone oil ( Figure 2 The droplet shedding behavior after d)). The mechanical oscillating unit in the form of an oscillating fork used in the measurement has a mass of approximately 3300 in air at a resonant frequency of approximately 1130 Hz.

[0033] If you immerse the fork in silicone oil ( Figure 2 b) to d) or water ( Figure 2 In a), the mass decreases to a value determined by the density of the medium. The density of the medium is derived, for example, from the mass combined with the frequency of the mechanical oscillation and the temperature of the medium. If the fork is carried out of the medium, the frequency and mass increase. However, neither value immediately returns to its initial state because a thin water film forms upon leaving the water, and an oil film forms on the fork upon leaving the silicone oil.

[0034] In the case of water ( Figure 2 a) No droplets fell off, and the water film evaporated after a period of time.

[0035] In silicone oil ( Figure 2b) to d) a single drop detaches. If there is a low in the mass and directly thereafter a high, this means that a drop has detached. This is thus the moment of drop detachment, in this case the measured value of the characteristic variable changes over a certain time period beyond a certain limit value.

[0036] After the drop detachment the mass decreases again, because the medium flows in the direction of the end of the mechanical oscillation unit along the gravitational field from the position located above.

[0037] These special time points are in Figure 2 The graph in b) is marked with arrows. This (from left to right) is: the starting value after removal from the reservoir with medium, the local maximum of the mass after detachment of a drop and the sudden rise of the mass after detachment of a drop in the local minimum of the mass.

[0038] It is clear that the drop detachment behavior of the medium is displayed against the mass over time. Based on the duration of the drop detachment and the course of the drop detachment curve, thus based on the drop detachment characteristics, a suitable algorithm allows to find out the viscosity and the density as measured variables of the medium.

[0039] List of reference signs

[0040] 1 device

[0041] 2 mechanical oscillation unit

[0042] 3 container

[0043] 4 medium

[0044] 5 temperature sensor

[0045] 6 evaluation unit

Claims

1. A method for identifying the measurement variables of a medium (4), wherein The method includes the following steps: a) Bring the mechanical oscillation unit (2) into contact with the medium (4) such that the medium (4) covers at least a portion of the mechanical oscillation unit (2). b) Position the mechanical oscillation unit (2) so that droplet formation of the medium (4) on the mechanical oscillation unit (2) is possible. c) Excite the mechanical oscillation unit (2) at least during step b) to cause mechanical oscillation to be performed. d) Determine the measured values ​​of at least one characteristic variable of the mechanical oscillation at different time points, and e) Evaluate the temporal behavior of the measurements generated by the identified measurements with respect to the measured variables.

2. The method according to claim 1, wherein In step a), the mechanical oscillation unit (2) is at least partially immersed in a certain amount of the medium (4) in the container (3), and then preferably completely pulled out.

3. The method according to claim 1 or 2, wherein, In step b), the mechanical oscillation unit (2) is oriented relative to the gravitational field at a predetermined tilt angle.

4. The method according to any one of claims 1 to 3, wherein In step e), the instability of the temporal behavior is identified.

5. The method according to any one of claims 1 to 4, wherein In step e), the situation where the change in the measured value exceeds a predetermined limit value within a predetermined time period is assessed as the moment when the droplets of the medium (4) detach. Among them, information about the droplet detachment behavior of the medium (4) is determined from at least one droplet detachment time of the medium (4), and Information about the droplet shedding behavior is compared with the supplied data to identify the rheological measurement variables.

6. The method according to any one of claims 1 to 5, in, The viscosity of the medium (4) was determined as a rheological measurement variable.

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