Vibronic sensor

Abstract

Disclosed is an apparatus for determining a process variable of a medium in a containment, comprising a first oscillatory element and a second oscillatory element, a first driving/receiving unit and a second driving/receiving unit, and an electronics, wherein the first driving/receiving unit is embodied to excite the first oscillatory element by means of a first electrical excitation signal to execute mechanical oscillations, and to receive the mechanical oscillations of the first oscillatory element and to convert such into a first electrical, received signal, wherein the second driving/receiving unit is embodied to excite the second oscillatory element by means of a second electrical excitation signal to execute mechanical oscillations, and to receive the mechanical oscillations of the second oscillatory element and to convert such into a second electrical, received signal, and wherein the electronics is embodied to determine the process variable from the first received signal and/or the second received signal.

Claims

1. An apparatus for determining and/or monitoring a process variable of a medium in a containment, comprising: a first oscillatory element and a second oscillatory element; a first driving/receiving unit and a second driving/receiving unit; and an electronics, wherein the first driving/receiving unit is embodied to excite the first oscillatory element using a first electrical excitation signal to execute mechanical oscillations, and to receive the mechanical oscillations of the first oscillatory element and to convert them into a first electrical, received signal, wherein the first oscillatory element and/or the first driving/receiving unit are/is arranged and/or embodied in such a manner that the first oscillatory element executes oscillations in a first predeterminable plane, wherein the second driving/receiving unit is embodied to excite the second oscillatory element using a second electrical excitation signal to execute mechanical oscillations, and to receive the mechanical oscillations of the second oscillatory element and to convert them into a second electrical, received signal, wherein the second oscillatory element and/or the second driving/receiving unit are/is arranged and/or embodied in such a manner that the second oscillatory element executes oscillations in a second predeterminable plane, wherein the first plane and the second plane have a first predeterminable angle relative to one another, and wherein the electronics is embodied to determine the process variable from the first received signal and/or the second received signal.

2. The apparatus as claimed in claim 1, wherein the process variable is a predeterminable fill level, a density of the medium, or a viscosity of the medium.

3. The apparatus as claimed in claim 1, wherein the electronics is further embodied to determine a first process variable from the first received signal and a second process variable from the second received signal.

4. The apparatus as claimed in claim 1, wherein the electronics is further embodied to ascertain from the first and/or the second received signal a presence of an accretion on at least one of the oscillatory elements.

5. The apparatus as claimed in claim 1, wherein at least the first oscillatory element or the second oscillatory element is rod-shaped.

6. The apparatus as claimed in claim 1, wherein a paddle is formed terminally on at least the first oscillatory element or the second oscillatory element.

7. The apparatus as claimed in claim 1, wherein the first predeterminable angle is 90°.

8. The apparatus as claimed claim 1, wherein the first oscillatory element and/or the first driving/receiving unit and the second oscillatory element and/or the second driving/receiving unit are arranged and/or embodied such that the first oscillatory element and the second oscillatory element execute oscillations in a predeterminable plane.

9. The apparatus as claimed in claim 1, wherein at least the first oscillatory element or the second oscillatory element has a hollow space, and wherein at least the first driving/receiving unit or second driving/receiving unit is arranged at least partially within the hollow space.

10. The apparatus as claimed in claim 1, wherein the first oscillatory element and the second oscillatory element are mounted on a disc shaped element.

11. The apparatus as claimed in claim 1, wherein a footprint at least of the first oscillatory element or the second oscillatory element is embodied perpendicularly to a longitudinal axis of the respective oscillatory element such that a base of the footprint is longer than a height of the footprint.

12. The apparatus as claimed in claim 11, wherein the footprint is rectangular, rectangular with rounded corners, oval, or elliptical.

13. The apparatus as claimed in claim 1, further comprising: a third oscillatory element and a fourth oscillatory element.

14. The apparatus as claimed in claim 13, wherein the first and the third oscillatory elements are embodied equally and arranged symmetrically relative to one another, and the second and the fourth oscillatory elements are embodied equally and arranged symmetrically relative to one another.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention as well as its advantageous embodiments will now be described in greater detail based on the appended drawing, the figures of which show as follows:

(2) FIG. 1 shows a schematic view of a vibronic sensor according to the state of the art,

(3) FIG. 2 shows a schematic drawing of an oscillatory fork,

(4) FIG. 3 shows an apparatus of the present disclosure having two oscillatory elements,

(5) FIG. 4 shows an apparatus of the present disclosure having three oscillatory elements, and

(6) FIG. 5 shows two different embodiments of apparatuses of the present disclosure having four oscillatory elements.

DETAILED DESCRIPTION

(7) FIG. 1 shows a vibronic sensor 1. The sensor includes a mechanically oscillatable unit 4 in the form of an oscillatory fork, which is immersed partially in a medium 2, which is located in a containment 3. The oscillatable unit 4 is excited by means of the exciter/receiving unit 5, such that mechanical oscillations are executed. The exciter/receiving unit 5 can be, for example, a piezoelectric stack- or bimorph drive. Other vibronic sensors use, for example, an electromagnetic driving/receiving unit 5. It is possible to use a single driving/receiving unit 5, which serves for exciting the mechanical oscillations as well as for receiving them. Likewise an option, however, is to provide separate driving and receiving units. Shown in FIG. 1, furthermore, is an electronics unit 6, by means of which signal registration, —evaluation and/or—feeding occurs.

(8) FIG. 2 shows an oscillatable unit 4 in the form of an oscillatory fork, such as used, for example, in the vibronic sensor 1 sold by the applicant under the mark, LIQUIPHANT. The oscillatory fork 4 includes, attached to a membrane 8, two oscillatory tines 9a,9b, on each of a terminal paddle 10a, 10b which is formed. Such are consequently also referred to as fork tines. Secured on the oscillatory tines 9a,9b far face of the membrane 8 by means of material bonding and/or force interlocked connection is the driving/receiving unit 5. For this embodiment shown by way of example, it is assumed that the driving/receiving unit 5 comprises at least one piezoelectric element. In operation, a force is applied to the membrane 8 using an excitation signal U.sub.E, for example, in the form of an alternating electrical voltage, which is generated in electronics unit 6. A change of the applied electrical voltage effects a change of the geometric shape of the driving/receiving unit 5, thus, a contraction or expansion of the piezoelectric element, in such a manner that the applying of an alternating electrical voltage as excitation signal U.sub.E brings about an oscillation of the membrane 8 connected by material bonding with the driving/receiving unit 5. Oscillation of the membrane 8 causes the mechanically oscillatable unit 4 to oscillate.

(9) The idea of the present invention is to provide a vibronic sensor 1 with at least two oscillatory elements 11a, 11b, which are excitable separately from one another to execute mechanical oscillations, and wherein the oscillations of the two oscillatory elements 11a, 11 b can likewise be received and evaluated separately from one another. This means that the first oscillatory element 11a is excited by means of a first excitation signal U.sub.E1 and the second oscillatory element 11b by means of a second excitation signal U.sub.E1, and the first oscillatory element 11a receives a first received signal U.sub.R1 and the second oscillatory element 11b a second received signal U.sub.R2. The two excitation signals U.sub.E1 and U.sub.E2 can be equal or different. In the case of more than two oscillatory elements 11a-11x, it is sufficient that at least two of the oscillatory elements are excitable separately from one another and the oscillations are received and evaluated separately from one another.

(10) The separate evaluation of the received signals U.sub.R1 and U.sub.R2 of the first 11a and second oscillatory element 11b enables a comprehensive evaluation of the oscillatory behavior of the sensor 1 as regards the at least one process variable. In the case of a conventional vibronic sensor 1, such as shown in FIGS. 1 and 2, the received signal is always a superpositioning of the oscillations of the two oscillatory tines 9a, 9b of the oscillatory fork 4. This results especially from the fact that the two oscillatory tines 9a, 9b are excited to execute oscillations together by means of the membrane 5, to which the driving/receiving unit is secured by material bonding.

(11) A first embodiment of the present invention is shown schematically in FIG. 3 by way of example. The vibronic sensor 1 includes a first oscillatory element 11a and a second oscillatory element 11b, each in the form of an oscillatory tine, as well as a first driving/receiving unit 12a and a second driving/receiving unit 12b. The two oscillatory tines 11a and 11b are secured on a disc shaped element 13. Both oscillatory tines 11a and 11b have, in each case, a hollow space 14a and 14b, in which in the region facing the disc shaped element 13, in each case, a driving/receiving unit 12a and 12b is arranged.

(12) Each of the two oscillatory elements 11a, 11 b is rod-shaped. For purposes of perspicuity, the following reference characters are applied only to the second oscillatory element 11b. The rod of the second oscillatory element 11b has a length 12 and a rectangular footprint F.sub.2 with base b.sub.2 and height h.sub.2. The base b.sub.2 is longer than the height h.sub.2. Because of the choice of a footprint F.sub.2, in the case of which a base b.sub.2 is longer than a height h.sub.2, the particular interaction with the medium 2 can be influenced with targeting. As already indicated, besides the shown rectangular embodiment of the footprint F.sub.2, numerous other options are possible, which likewise fall within the scope of the present invention.

(13) The first oscillatory element 11a and the second oscillatory element 11b are arranged, furthermore, differently relative to the disc shaped element 13. In the illustrated example, the two bases b.sub.1 and b.sub.2 of the two oscillatory elements 11a and 11b have a second predeterminable angle α.sub.2 in the form of a right angle between one another. Both oscillatory elements 11a and 11b are excited to execute oscillations in the same, third plane P.sub.3. This leads to the fact that, for the first oscillatory element, the base b.sub.1 extends in parallel with the third plane P.sub.3, and therewith in parallel with the oscillation direction, while, in the case of the second oscillatory element 11b, the base b.sub.2 extends perpendicularly to the third plane, and therewith perpendicularly to the oscillation direction. Therefore, the interaction of the first oscillatory element 11a and the medium 2 is dominated by a frictional force between the area formed by the base b.sub.1 and length l.sub.1 and the medium 2, while the interaction of the second oscillatory element 11b and the medium 2 is dominated by a compressive force between the area formed by the base b.sub.2 and length l.sub.2 and the medium 2. By means of the first oscillatory element 11a, thus, preferably the viscosity n of the medium 2 can be determined, while the second oscillatory element has an increased sensitivity relative to the density ρ of the medium 2.

(14) A second embodiment of the present invention is shown in FIG. 4 by way of example. Already explained reference characters are not explored in detail anew in the following figures. The sensor shown in FIG. 4 includes besides a first oscillatory element 11a and a second oscillatory element 11b, which are embodied and arranged as shown in FIG. 3, a third oscillatory element 11c as well as a third driving/receiving unit 12c. The third oscillatory element 11c is embodied identically to the first two oscillatory elements 11a and 11b. However, the third oscillatory element 11c is arranged so relative to the first two oscillatory elements 11a and 11b that the base b.sub.3 of the third oscillatory element has angles of 45° relative to the first oscillatory element 11a and the second oscillatory element 11b.

(15) Shown in FIG. 5, finally, are two different embodiments for sensor 1 of the invention with, in each case, four oscillatory elements 11a-11d and four driving/receiving units 12a-12d. As shown in FIG. 5a, all four oscillatory elements 11a-11d are embodied equally. The bases b.sub.1-b.sub.4 of the four oscillatory elements 11a-11d extend in parallel with one another. The oscillatory elements 11a-11d are, in each case, positioned pairwise at the same distance from the center (midpoint) M of the disc shaped element 13. A first pair is, in such case, formed here by the first oscillatory element 11a and the third oscillatory element 11c, and a second pair by the second oscillatory element 11b and the fourth oscillatory element 11d. The first pair of oscillatory elements 11a and 11c is excited to execute oscillations in a first plane P.sub.1, while the second pair of oscillatory elements 11b and 11d is excited to execute oscillations in a second plane P.sub.2. The two planes have a first predeterminable angle α.sub.1 relative to one another, which in the present example amounts to 90°. To this end, the only schematically shown drive-receiving units 12a-12d are suitably embodied for producing oscillations in the two planes P.sub.1 and P.sub.2.

(16) As shown in FIG. 5a, in the case of the first pair of oscillatory elements 11a, 11c, the bases b.sub.1, b.sub.3 of the footprints F.sub.1, F.sub.3 of the oscillatory elements 11a, 11c extend perpendicularly to the plane P.sub.1, thus, perpendicularly to the oscillation direction, while in the case of the second pair of oscillatory elements 11b, 11d, the bases b.sub.2, b.sub.4 of the footprints F.sub.2, F.sub.4 of the oscillatory elements 11b, 11d extend in parallel with the plane P.sub.2, thus, in parallel with the oscillation direction. With the first pair of oscillatory elements 11a, 11c, thus, preferably the density p of the medium 2 can be determined, and with the second pair of oscillatory elements 11b, 11d the viscosity η.

(17) As shown in FIG. 5b, likewise all four oscillatory elements 11a-11d are embodied equally. Again, a first pair of oscillatory elements is formed by the first oscillatory element 11a and third oscillatory element 11c, and a second pair by the second oscillatory element 11b and the fourth oscillatory element 11d. The two bases b.sub.1 and b.sub.3 of the first pair extend in parallel with one another, wherein the first oscillatory element 11a and the third oscillatory element 11c are arranged opposite one another at the same distance from the center M [not shown in FIG. 5b] of the disc shaped element 13. Also the two bases b.sub.2 and IN of the second pair of oscillatory elements extend in parallel with one another, wherein the second oscillatory element 11b and the fourth oscillatory element 11d are likewise arranged opposite one another at the same distance from the center M [not shown in FIG. 5b] of the disc shaped element 13. The bases b.sub.1, b.sub.3 of the first pair of 11a, 11c and the bases b.sub.2, b.sub.4 of the second pair of 11b, 11d have, thus, similarly as shown in FIG. 3, a second predeterminable angle α.sub.2 of 90° relative to one another.

(18) All oscillatory elements 11a-11d are excited to execute oscillations in the same, third plane P.sub.3. This leads to the fact that, for the first pair of oscillatory elements 11a,11c the bases b.sub.1 and b.sub.3 extend perpendicularly to the third plane P.sub.3, and therewith in parallel with the oscillation direction, while in the case of the second pair of oscillatory elements 11b the bases b.sub.2 and IN extend in parallel with the third plane P.sub.3, and therewith perpendicularly to the oscillation direction. Correspondingly, it is advantageous to determine and/or to monitor the density ρ of the medium 2 by means of the first pair of oscillatory elements 11a and 11c and the viscosity η of the medium 2 by means of the second pair of oscillatory elements 11b and 11d.

(19) It is to be noted here that the embodiments shown in the figures are only some possible examples. The invention enables a number of other embodiments, which cannot all be shown here. Also, it is to be noted that individual components of individual embodiments can be combined with one another to the extent desired.

LIST OF REFERENCE CHARACTERS

(20) 1 vibronic sensor 2 medium 3 containment 4 oscillatable unit 5 driving/receiving unit 6 electronics unit 8 membrane 9 oscillatory tines 10 paddle 11a-11d oscillatory elements 12a-12d driving/receiving units 13 disc shaped element 14a,14b hollow spaces in the oscillatory elements U.sub.E excitation signal U.sub.R received signal Δϕ predeterminable phase shift ρ density of the medium v viscosity of the medium l.sub.1-l.sub.4 length of the oscillatory elements F, F.sub.1-F.sub.4 footprints of the oscillatory elements b, b.sub.1-b.sub.4 bases of the oscillatory elements h, h.sub.1-h.sub.4 vertical dimensions of the oscillatory elements α.sub.1, α.sub.2 predeterminable angle P.sub.1-P.sub.3 oscillation planes