Method for determining and / or monitoring viscosity of medium and vibration sensor

Abstract

The invention relates to a method for determining and / or monitoring the viscosity of a medium using a vibration sensor (10). Oscillation of a unit (11) of a vibration sensor (10) that can be mechanically oscillated is used to determine whether a medium covers the unit (11) that can be mechanically oscillated. If covered, subsequent oscillations are used to determine whether the medium continues to cover the unit (11). If not covered, the development of the oscillation mass over time is used to ascertain a statement about the viscosity of the medium. The invention also relates to a vibration sensor (10).

Description

Technical Field

[0001] The present invention relates to a method for determining and / or monitoring the viscosity of a medium. The present invention also relates to a vibration sensor. Background Art

[0002] The mechanical oscillation unit of a vibration sensor - for example a tuning fork - (see for example DE 10 2012 101 667 A1) is particularly used to determine the level limit of a medium in a tank. Usually, the measured oscillation frequency is used to determine whether the oscillation unit is touched by the medium.

[0003] For example, the condition of the mechanical oscillation unit itself can also be monitored. In DE 10 2011 075 113 A1, the damping ratio is determined based on the difference between the excitation frequencies in order to detect accumulation or corrosion during oscillation in an uncovered condition.

[0004] In addition to the liquid level, there are other process variables or properties of the medium that need to be monitored during the process. This is for example the viscosity of the medium, which usually requires very complex measuring devices to measure. Summary of the Invention

[0005] The object of the present invention is to provide a method for determining or monitoring the viscosity of a medium and a vibration sensor for implementing the method.

[0006] This object is achieved by a method for determining and / or monitoring the viscosity of a medium using a vibration sensor, wherein the method at least comprises the following steps: exciting the mechanical oscillation unit of the vibration sensor to oscillate mechanically; receiving the mechanical oscillation of the mechanical oscillation unit; using at least one measured value of the oscillation quantity of the received mechanical oscillation to determine whether the medium covers the mechanical oscillation unit; in the case where the medium covers the mechanical oscillation unit, using at least one measured value of the oscillation quantity of the subsequently received mechanical oscillation to determine whether the medium continues to cover the mechanical oscillation unit; in the case where the mechanical oscillation unit is not covered by the medium, determining a measured oscillation quality value based on at least one measured value of the oscillation quantity of the subsequently received mechanical oscillation; and ascertaining a statement about the viscosity of the medium based on the development of the measured oscillation quality value over time.

[0007] In the method according to the invention, the mechanical oscillation of the mechanical oscillation unit of the vibration sensor is evaluated. For example, the mechanical oscillation is converted into an electrical signal. For example, this can be achieved using a piezoelectric element as part of a transducer device. Then, a measured value of the oscillation quantity is determined based on the signal. The oscillation quantity is, for example, the amplitude, frequency or phase of the oscillation. Additionally or alternatively, they can also be resultant quantities, such as the oscillation mass. Then, the measured value of the oscillation quantity is in turn used to determine a measured value of a process quantity of interest, such as the medium coverage or viscosity. To process the measured value of the oscillation quantity, for example, stored formulas and / or data records such as reference values are used.

[0008] The method for determining and / or monitoring viscosity proceeds in a plurality of successive steps or phases. It is assumed that the mechanical oscillation unit is initially not covered by the medium during its oscillation - for example, when it oscillates in air. If the liquid level of the medium changes and the medium covers the - previously freely oscillating - mechanical oscillation unit, this can be identified by the characteristics of the oscillation. For this purpose, at least one measured value of the oscillation quantity is particularly evaluated. In the second phase, the oscillations that occur after the unit has been covered are used to determine whether the unit continues to be covered or whether the medium no longer covers the mechanical oscillation unit, i.e., whether the oscillation unit oscillates freely again and is uncovered. If this is the case, the measured oscillation mass value is determined as the oscillation quantity based on the oscillations that follow in the third phase. The oscillation mass then enables the detection of changes in viscosity and / or the determination of the value of the viscosity of the medium. This utilizes the fact that after the oscillation unit has been covered by the medium and subsequently uncovered, the medium continues to adhere to the oscillation unit and only detaches after a certain amount of time. Therefore, for the oscillation unit, the transition to being able to oscillate completely freely is delayed. Thus, the detachment behavior can be used to draw conclusions about the viscosity based on the oscillation mass.

[0009] The sequence of these three phases will be described again in a different way:

[0010] Phase 1: The oscillation unit oscillates in the uncovered state.

[0011] Phase 2: If the oscillation unit is covered by the medium, this can be determined based on at least one oscillation quantity. Thus, the switch from "uncovered" to "covered" is detected.

[0012] Phase 3: When the medium no longer covers the unit, this can also be detected using the oscillation quantity. Statements about the viscosity are ascertained based on the subsequent behavior of the oscillation quantity from the "end of coverage" to when the mechanical oscillation unit oscillates freely again. Thus, the way the unit returns to its normal state of freely oscillating in air is evaluated.

[0013] Therefore, the medium must cover the oscillating unit and then stop covering it again. If some of the medium remains on the mechanical oscillating unit, then the unit itself is not covered by the medium. Being covered by the medium specifically means that the medium has such a liquid level that the mechanical oscillating unit is below this liquid level due to its size and arrangement. If the unit is no longer covered, the liquid level of the medium drops below the position of the oscillating unit. Then, the way the medium drips from the mechanical oscillating unit is monitored.

[0014] One embodiment of the method includes: in the case where the mechanical oscillating unit is not covered by the medium, a measured oscillation quality value is determined based on at least one measured value of the oscillation amount of the subsequently received mechanical oscillation only when the mechanical oscillating unit is covered by the medium for at least a predetermined covering time and / or during at least a predetermined number of mechanical oscillations. In this embodiment, it is necessary to note to ensure that the mechanical oscillating unit has been in the medium for a sufficient amount of time and has performed mechanical oscillations. This is ensured by specifying the period of time or the number of oscillations to be completed. The oscillation pre-adjusts the medium to a certain extent through the vibration of the oscillating unit, causing the medium - which is preferably a liquid - to experience shear stress. In this embodiment, the medium is thus moved and adjusted in the second stage so as to be able to perform reproducible measurements.

[0015] One embodiment of the method stipulates that the oscillation amount based on which it is determined whether the medium covers the mechanical oscillating unit is the frequency of the received oscillation. In this embodiment, the received oscillation frequency is used to infer whether the medium covers the oscillating unit.

[0016] In an alternative or additional embodiment, this frequency is used to determine whether the medium continues to cover the oscillating unit.

[0017] One embodiment of the method relates to ascertaining a statement about the viscosity of the medium based on the development of the measured oscillation quality value over time until the starting value. The embodiment evaluates the oscillation quality behavior of the unit after it is no longer covered and after it is covered relative to the starting value. For example, an evaluation is performed on how the quality readapts to the starting value.

[0018] In one embodiment, the above starting value is specified. In an alternative embodiment, the measured value of the starting value of the oscillation quality is determined based on the oscillation in the uncovered state. Therefore, this starting value is also applicable to each measurement situation.

[0019] According to an additional embodiment of the method, at least one measured value of another oscillation quantity is used to ascertain a statement regarding the viscosity of the medium. This other oscillation quantity is preferably the frequency of a mechanical oscillation. In this variant, the temporal curve of the frequency is evaluated by comparison with when the oscillation unit is free and uncovered. For example, the speed at which the initial oscillation frequency value is reached is determined. Alternatively or additionally, the gradient at which the frequency approaches the starting value of the free oscillation without coverage is determined. For example, it has been shown that the transition of the frequency response from the covered state to the free state allows conclusions to be drawn regarding the viscosity. A sharp transition indicates a lower viscosity, while a rounded transition indicates a higher viscosity.

[0020] One embodiment of the method provides that the ascertained statement refers to the value of the viscosity of the medium. Alternatively, or additionally, the ascertained statement refers to the value range within which the viscosity of the medium lies. Similarly, alternatively or additionally, the ascertained statement refers to whether the viscosity of the medium has changed beyond a specifiable tolerance range.

[0021] In one embodiment, a change in viscosity is thus detected, and the vibration sensor thus acts as a kind of viscosity switch: indicating a change in viscosity. Alternatively, the value or at least the value range of the viscosity of the medium is determined. Thus, the value or value range is determined and output.

[0022] One embodiment of the method includes: when the mechanical oscillation unit is not covered by the medium, the received mechanical oscillation belongs to the decay behavior of the oscillation of the mechanical oscillation unit. In this embodiment, once the mechanical oscillation unit is no longer covered by the medium, it is no longer excited to oscillate, but instead only receives and evaluates the oscillation.

[0023] This object is additionally achieved by a vibration sensor, which includes a mechanical oscillation unit (e.g., a tuning fork, a single rod, or a membrane) and a control device for operating the mechanical oscillation unit and for recording the oscillation of the oscillation unit, wherein the control device (e.g., at least includes a transducer device, which preferably includes at least one piezoelectric element, and an electronic device for processing electrical signals and for performing measurement programs) is designed to execute the method according to any one of the preceding or following embodiments. Thus, this vibration sensor is capable of implementing this method. Alternatively, the vibration sensor only performs the measurement, while the evaluation process takes place in a unit separated from the process, for example. Description of the Drawings

[0024] The present invention will be described hereinafter with reference to embodiments.

[0025] Figure 1 An example vibration sensor is shown

[0026] Figure 2Shows the curves of the frequency of oscillation and the quality of the oscillating circuit in an uncoated oscillating unit when covered with water,

[0027] Figure 3 Shows the frequency and quality curves in a coated oscillating unit when covered with water,

[0028] Figure 4 Shows the frequency and quality curves in an uncoated oscillating unit when covered with a high-viscosity liquid, and

[0029] Figure 5 Shows the frequency and quality curves in a coated oscillating unit when covered with a high-viscosity liquid. DETAILED DESCRIPTION

[0030] Figure 1 Shows an exemplary vibration sensor 10, which has a mechanical oscillating unit 11 - which is designed here as a tuning fork - and a control device 12. A medium - not shown here - affects the oscillation properties of the oscillating unit 11 once it comes into contact with the oscillating unit 11. The mechanical oscillating unit 11 is excited to oscillate by the control device 12. In this case, the control device 12 thus includes a transducer device such as a piezoelectric element, and an electronic device that executes a measurement program and also evaluates the received oscillation or the generated electrical signal.

[0031] Due to repeated wetting and drying caused by liquid level fluctuations, a coating of medium residues can form on the oscillating unit 11 over time. One manifestation of this coating is a shift of the oscillation frequency towards a lower range. However, this effect usually appears slowly, i.e., for example, in cases where the coating is more pronounced. This indicates the robustness of the measurement method.

[0032] Figures 2 to 5 Shows how the method allows the monitoring or determination of the viscosity of a preferred liquid or a flowable medium. They each show exemplary time curves of the oscillation frequency (in each case the dashed line) and the mass (in each case the solid line) of the mechanical oscillating unit 11 when affected by different media (water or a high-viscosity medium) in different conditions (with or without a coating thereon). The x-axis is time in seconds. The left y-axis is frequency in Hertz, and the right y-axis is mass without units.

[0033] Figure 2 Shows the time curves of the oscillation frequency and the oscillation mass of the uncoated mechanical oscillating unit 11.

[0034] The oscillation unit 11 oscillates in air, for example, during the first drying phase P1, is immersed in water as the medium during the immersion phase P2, and then dried during the third phase P3. When water separates from the oscillation unit 11, i.e., during the transition from the covered state to the uncovered state, the frequency almost immediately assumes an oscillation frequency slightly above 1100 Hz in the dry state of P1, while the mass takes approximately 1000 seconds to reach an initial state with an oscillation mass slightly above 120 as the initial value. The mass is sensitive to the presence of a water film, which gradually (over time) runs off in the form of water droplets.

[0035] Figure 3 Curves of the oscillation frequency and oscillation mass are shown when immersed in water and when there is a coating made of, for example, cement on the mechanical oscillation unit 11.

[0036] After immersion in the medium (immersion can include changing the position of the oscillation unit or changing the liquid level of the medium), the frequency very rapidly reaches above 1100 Hz in phase P2, while the mass remains at a value around 70. It has been found that the mass is a good measure for detecting the coating.

[0037] In both cases ( Figure 2 and Figure 3 ), similar mass curves are shown: initially there is a strong increase, followed by a part with a relatively constant value.

[0038] Figure 4 Time curves of the oscillation frequency and mass of the uncoated mechanical oscillation unit 11 when immersed in a viscous medium with a viscosity of approximately 1000 square millimeters per second are shown.

[0039] As in the case of Figure 2 where water is the medium, it is observed that the oscillation frequency rapidly returns to a value within the range in the non-wetted state. However, it should be noted that the transition is rounded, unlike when the medium is water, which is sharp. In addition, the oscillation frequency approaches the starting value more slowly than in the case of Figure 2 .

[0040] However, after separating the medium 21 from the oscillation unit 11, the oscillation mass fluctuates within the range between 50 and 80. This fluctuation is caused by the dripping and flowing out of the medium 21 from the oscillation unit 11. At the same time, it can be seen that the mass allows conclusions to be drawn about the viscosity of the medium. In the case of water, Figure 2 an almost adiabatic increase in the mass approaching the starting value is shown. In contrast, Figure 4 shows an oscillation behavior where the valleys between individual deflections become longer over time. Therefore, statements about the viscosity of the medium can be derived based on the mass or behavior over time.

[0041] Figure 5 The oscillation frequency and the oscillation mass curve are shown when immersed in the medium 21 and when the mechanical oscillation unit 11 comprises a coating, likewise using a cement coating as an example.

[0042] and Figure 4 Compared to the curve in FIG. 1 , the oscillating mass remains in the region of 40 for a long period of time, i.e. significantly lower than the oscillating mass in the absence of a cement coating. Figure 3 Compared to , a clearly different behavior is observed, which allows conclusions to be drawn regarding the viscosity.

[0043] In general, it should be noted that the shape and course of the curves may depend on the properties of the mechanical oscillation unit. This refers, for example, to the geometry, the type of coating that may be present, or the material of the mechanical oscillation unit. They may also depend on the type and design of the transducer unit and / or the type of oscillation excitation.

Claims

1. A method for determining and / or monitoring the viscosity of a medium using a vibration sensor (10), Among them, The method at least comprises the following steps: Actuating the mechanical oscillation unit (11) of the vibration sensor (10) to oscillate mechanically; Receiving the mechanical oscillation of the mechanical oscillation unit (11); Using at least one measured value of the oscillation quantity of the received mechanical oscillation to determine whether the medium covers the mechanical oscillation unit (11); In the case where the medium covers the mechanical oscillation unit (11), using at least one measured value of the oscillation quantity of the subsequently received mechanical oscillation to determine whether the medium continues to cover the mechanical oscillation unit (11); In the case where the mechanical oscillation unit (11) is not covered by the medium, determining a measured oscillation quality value based on at least one measured value of the oscillation quantity of the subsequently received mechanical oscillation, and Ascertaining a statement about the viscosity of the medium based on the development of the measured oscillation quality value over time.

2. The method according to claim 1, Among them, In the case where the mechanical oscillation unit (11) is not covered by the medium, the measured oscillation quality value is determined based on at least one measured value of the oscillation quantity of the subsequently received mechanical oscillation only when the mechanical oscillation unit (11) is covered by the medium for at least a predetermined covering time and / or during at least a predetermined number of mechanical oscillations.

3. The method according to claim 1 or claim 2, Among them, The oscillation quantity based on which it is determined whether the medium covers the mechanical oscillation unit (11) is the frequency and / or amplitude of the received oscillation.

4. The method according to any one of claims 1 to 3, Among them, Ascertaining a statement about the viscosity of the medium based at least on the development of the measured oscillation quality value until a starting value over time.

5. The method according to claim 4, Among them, Using at least one measured value for another oscillation quantity - preferably the frequency - to ascertain the statement about the viscosity of the medium.

6. The method according to any one of claims 1 to 5, Among them, The ascertained statement refers to the value of the viscosity of the medium, the value range in which the viscosity of the medium lies, or whether the viscosity of the medium has changed beyond a specifiable tolerance range.

7. The method according to any one of claims 1 to 6, Among them, If the mechanical oscillation unit (11) is not covered by the medium, the received mechanical oscillation belongs to the decay behavior of the oscillation of the mechanical oscillation unit (11).

8. A vibration sensor (10), Comprising a mechanical oscillation unit (11) and a control device (12) for operating the mechanical oscillation unit (11) and for recording the oscillation of the oscillation unit (11), Among them, The control device (12) is designed to execute the method according to any one of claims 1 to 7.

Images