MONITORING THE CONDITION OF A VIBRONIC SENSOR

Abstract

A method for monitoring the condition of a coil, wherein the coil is part of a device for determining at least one process variable of a medium in a container, includes applying an electrical excitation signal to the coil and receiving an electrical reception signal from the coil, determining a first value for the reception signal at a first predefinable measurement time, comparing the first value for the reception signal at the first measurement time with a reference value, and determining a condition indicator for the coil on the basis of the comparison. Disclosed also is a device that is designed for carrying out the disclosed method.

Claims

1-14. (canceled)

15. A method for monitoring a condition of a coil, wherein the coil is part of a device for determining at least one process variable of a medium in a container, the method comprising: applying an electrical excitation signal to the coil and receiving an electrical reception signal from the coil; determining a first value for the reception signal at a first predefinable measurement time; comparing the first value for the reception signal at the first measurement time with a reference value; and determining a condition indicator for the coil on the basis of the comparison.

16. The method according to claim 15, wherein the first predefinable measurement time is selected so that it is within a predefinable first time interval in which the reception signal reacts, in the form of a step response, to a sudden change in the excitation signal.

17. The method according to claim 16, wherein the excitation signal is a square-wave signal.

18. The method according to claim 17, wherein the sudden change of the excitation signal is a rising edge or a falling edge of the excitation signal.

19. The method according to claim 15, wherein the condition indicator is a conclusion about the presence of at least one winding short circuit in the region of the coil.

20. The method according to claim 19, further comprising: detecting a winding short circuit in the region of the coil on the basis of an underrun of the reference value at the first predefinable measurement time.

21. The method according to claim 15, wherein the condition indicator is a conclusion about a defective electrical contact or a cable break in the region of the coil or of at least two connection wires.

22. The method according to claim 21, further comprising: detecting a defective electrical contact or a cable break in the region of the coil on the basis of a deviation of the step response of the reception signal in reaction to the sudden change in the excitation signal from a reference jump response.

23. The method according to claim 15, further comprising: determining a second value for the reception signal at a second predefinable measurement time; and determining a temperature of the medium based on the second value for the reception signal.

24. The method according to claim 23, wherein the temperature of the medium is determined based on a comparison of the second value for the reception signal with at least one characteristic curve of the reception signal as a function of the temperature.

25. The method according to claim 23, wherein the second predefinable measurement time is selected so that it is outside of the first time interval.

26. The method according to claim 25, wherein the second predefinable measurement time is selected so that it is within a second time interval in which the reception signal is constant.

27. A device for determining and/or monitoring at least one process variable of a medium in a container, comprising: at least one coil, wherein the device is designed to implement a method for monitoring a condition of the at least one coil, the method including: applying an electrical excitation signal to the coil and receiving an electrical reception signal from the coil; determining a first value for the reception signal at a first predefinable measurement time; comparing the first value for the reception signal at the first measurement time with a reference value; and determining a condition indicator for the coil on the basis of the comparison.

28. The device according to claim 27, wherein the device is a vibronic sensor and further comprises: a mechanical vibration-capable unit; a driving/receiving unit with the at least one coil, wherein the driving/receiving unit is designed to excite the mechanical vibration-capable unit to mechanical vibrations via an electrical excitation signal and to receive the mechanical vibrations from the vibration-capable unit and transduce them into an electrical reception signal; and an electronic unit designed to generate the excitation signal starting from the reception signal and to determine the at least one process variable from the reception signal.

Description

[0055] The invention and its advantageous embodiments are described in more detail below with reference to Figures FIG. 1-FIG. 4. The following is shown:

[0056] FIG. 1: a representation of a vibronic sensor according to the prior art,

[0057] FIG. 2: two possible embodiments of a vibronic sensor with preferred electromagnetic driving/receiving units,

[0058] FIG. 3 a diagram of the reception signal of the coil for illustrating the condition monitoring according to the invention; and

[0059] FIG. 4 a diagram of the reception signal of the coil to illustrate the temperature determination according to the invention.

[0060] FIG. 1a shows a vibronic fill level measuring device 1. A sensor unit 2 having a mechanically vibratable unit 3 is depicted in the form of a vibrating fork that is partially immersed into a medium 4, which is located in a container 5. The vibration-capable unit 3 is excited to mechanical vibrations by means of the driving/receiving unit 6, normally an electromechanical transducer unit, and can, for example, be a piezoelectric stack or bimorph drive, but also an electromagnetic or also magnetostrictive driving/receiving unit. However, it is naturally understood that other embodiments of a vibronic sensor are also possible. Furthermore, an electronics unit 7 is depicted by means of which the signal detection, evaluation and/or supply takes place.

[0061] FIG. 1b shows a more detailed view of a vibration-capable unit 3 in the form of a vibration fork, for example as is used for the vibronic sensor sold by the applicant under the name LIQUIPHANT. A membrane 8 and a vibrating element 9 connected thereto can be seen. The vibrating element 9 has two vibrating rods 10a, 10b, to each of which a paddle 11a, 11b is integrally formed at the end. In operation, the vibration fork 3 executes vibration movements according to the vibration mode with which it is excited. Each of the two vibrating rods 10a, 10b behaves essentially like a so-called bending vibrator. In the fundamental mode, the two vibrating rods 10a, 10b oscillate in counterphase with respect to one another, for example.

[0062] Although numerous different embodiments for the driving/receiving unit 6 may be used within the scope of the present invention, the following description relates, without limitation of the generality, to electromagnetic driving/receiving units 6 with at least one coil, as they are described in the documents DE102015104533A1 or DE102016112308A1. In the context of the present application, reference is made to both patent applications in their entirety.

[0063] FIG. 2a shows a schematic view of such a drive/receiving unit 6. A housing 12 terminates with the lower wall with a membrane 8, which is to be associated with the vibratable unit 3. For the embodiment shown here, the housing 12 is cylindrical and the disk-shaped membrane 8 has a circular cross-sectional area A. However, it goes without saying that other geometries are also conceivable and fall under the present invention. Two rods 15a, 15b are fastened to the diaphragm 8 perpendicular to the base surface A of the diaphragm 8 and extend into the interior of the housing 12. This is in particular a non-positive connection. The base surface A of the diaphragm 8 is then in a plane perpendicular to the longitudinal direction of the rods 15a, 15b.

[0064] A magnet 16a, 16b, in particular a SmCo or Alnico magnet, is fastened in each case in the end region of the rods 15a, 15b facing away from the membrane 8. The magnets 16a, 16b are preferably all oriented identically. A coil 17 that comprises a wire wound around the core 18 is arranged above the magnets 16a, 16b. The core 18 of the coil 17 is part of a cup-shaped armature unit 19 with a base 20 and a circumferential wall 21. For example, the base 20, like the base surface A of the membrane 8, can have a circular cross-sectional area. From the bottom 20 of the cup-shaped anchor unit 19, the core 18 of the coil 17 extends centrally into the interior of the anchor unit 19 in the form of a connecting piece. In this instance, the circumferential wall 21 then has the function of an internal magnetic field guide. The rods 15a, 15b having the magnets 16a and 16b do not contact the coil 17 and the core 18. In continuous operation, the coil 17 is subjected to an alternating current signal in order to generate an alternating magnetic field. For this purpose, the coil has two connecting wires, not shown in FIG. 2a.

[0065] Due to the alternating field, the rods 15a and 15b are deflected horizontally, i.e. perpendicularly or transversely to their longitudinal axis, via the magnets 16a and 16b in such a way that they are set into vibration. On the one hand, the rods 15a and 15b then have a lever effect, by means of which the bending of the rods 15a and 15b generated by the horizontal deflection is transmitted to the membrane 8 in such a way that the membrane 8 is set into vibration. On the other hand, the combination of the two rods 15a and 15b and the membrane 8 is, however, a separate resonator.

[0066] FIG. 2b shows an electromechanical transducer unit 6 similar to FIG. 2a with the difference that in FIG. 2b three rods 15a-15c and three magnets 16a-16c are present, as disclosed in DE 102016112308A1. However, the electromechanical transducer unit can also have four or more rods.

[0067] In the instance of the embodiments of FIG. 2, the two swing rods 10a, 10b form the mechanical vibration-capable unit 3 and the rods 15a-15c of the transducer unit 6, respectively with the membrane 8, form a mechanical resonator. The membrane 8 is preferably, but not necessarily, embodied in one piece. In particular, it can be assigned to both the vibratable unit 3 and the transducer unit 6.

[0068] According to the invention, a condition monitoring of a vibronic sensor is performed, with which a comparison is made with a reference value on the basis of a comparison of a first value of the reception signal at a predefinable first measurement time.

[0069] An embodiment of the condition monitoring of the coil 17 according to the invention is illustrated in FIG. 3. Respectively depicted is the reception signal U of the coil 17 as a function of the sampling point AP, in principle thus as a function of time, for different temperatures T1, T2, and T3 and for a fully functional coil (1) and a partially short-circuited coil (2). For the shown embodiment, the predefinable first measurement time t1 is at AP=500, and is selected so that it is in a predefinable first time interval Δt1, in which a step response S of the reception signal U is detectable as a result of an abrupt change of the excitation signal A [not shown here]. The excitation signal A is, for example, a square wave signal, and the step response S of the reception signal U takes place in reaction to a rising or falling edge of the excitation signal.

[0070] The first measurement time t1 is selected so that it lies temporally after the jump S of the reception signal U. For the embodiment shown here, the first measurement time t1 lies in a range in which the reception signal U decays exponentially after the step response S. The shown profile thereby corresponds to a rising edge of the excitation signal A.

[0071] It can be seen from the diagram that, at the first measurement time t1, the values for the reception signal U for all selected temperatures T1, T2, T3 for the functional coils 17 (1) is respectively greater than for the partially short-circuited coils (2). In this range, i.e. in the range of the first measurement interval Δt1, a reference value U.sub.ref can be established, which is provided so that all values U>U.sub.ref for the reception signal U correspond to functional coils 17, and all values U<U.sub.ref for the reception signal U correspond to partially short-circuited coils. Thus, if a first value for the reception signal U1 at the predefinable first measurement time t1 falls below the reference value U.sub.ref, it is possible to conclude the presence of a partial short circuit in the region of the coil 17 from the underrun.

[0072] However, other conclusions regarding the condition of the coil 17 may also be generated by means of the method according to the invention. For example, using a comparison of the step response S with a reference jump response S.sub.ref, the presence of a defective electrical contact or a cable break in the region of the coil can be detected.

[0073] Moreover, in a further embodiment, the method according to the invention makes it possible to make a conclusion about the temperature T of the medium 4 in the container 5. For this purpose, a second value U2 of the reception signal U is determined at a second predefinable measurement time t2, as shown in FIG. 4. As in FIG. 3, in FIG. 4 profiles are shown for the reception signal U for three different temperatures T1, T2, T3, and respectively fora functional coil 17 (1) and a partially short-circuited coil 17 (2). In a second predefinable time interval Δt2 that is outside the first time interval Δt1, the reception signal U respectively has a substantially constant value. The values for the reception signals U thereby differ for each of the selected temperatures T1, T2, T3. By contrast, given the same temperature T, the values for the reception signals U barely differ for functional coils 17 (1) and those which are at least partially short-circuited (2). Based on a second value U2 for the reception signal U at the second predefinable measurement time T2, a conclusion about the temperature T of the medium 4 can accordingly be derived, for example by comparing the second value U2 for the reception signal U with a characteristic curve for the reception signal U as a function of the temperature T, which can be stored in the electronics unit 7 of the device 1, for example.

[0074] In summary, the present invention enables a condition monitoring for a vibronic sensor 1, and optionally additionally a determination of the temperature T of the medium 4, in an especially simple manner and especially without integration of further components into the vibronic sensor 1. The condition monitoring can take place in parallel or alternately to normal measuring operation of the sensor 1.

LIST OF REFERENCE SIGNS

[0075] 1 Vibronic sensor [0076] 2 Sensor unit [0077] 3 Vibration-capable unit [0078] 4 Medium [0079] 5 Container [0080] 6 Driving/receiving unit [0081] 7 Electronic unit [0082] 8 Membrane of the vibration-capable unit [0083] 9 Vibrating element [0084] 10a, 10b Vibrating rods [0085] 11a, 11b Paddles [0086] 12 Housing of the electromechanical transducer unit [0087] 15a, 15c Rods [0088] 16a, 16c Magnets [0089] 17 Coil [0090] 18 Core of the coil [0091] 19 Cup-shaped armature unit [0092] 20 Floor [0093] 21 Circumferential wall [0094] T, T1-T3 Temperature of the medium [0095] A Excitation signal [0096] U Reception signal [0097] U1, U2 Values for the reception signal [0098] U.sub.ref Reference signal for the reception signal [0099] Δt1, Δt2 Predefinable time interval [0100] t1,t2 Measurement time [0101] AP Sampling point [0102] f, f.sub.1-f.sub.3 Frequency of the excitation signal [0103] S Step Response