Compensation of a phase shift of at least one component of an electronic system of a vibronic sensor

Abstract

The invention relates to a compensation device for the compensation of a phase shift caused a component of an electronic system unit of a vibronic sensor. The compensation device includes a bridging unit for the electrical bridging of at least the electromechanical converter; a signal generator for generating a test excitation signal; a phase detection unit for determining the phase shift between the test excitation signal and a test receive signal that passes through the bridging unit and the component of the electronic system unit; and a computer unit which determines a phase compensation instruction from the first phase shift.

Claims

1. A compensation device for compensating for a phase shift caused by a component of an electronic system unit of a vibronic sensor, wherein the vibronic sensor includes an electromechanical converter, the compensation device comprising: a bridging unit for electrically bridging and thereby bypassing the electromechanical converter, wherein the bridging unit includes a bridging branch connected in parallel to the electromechanical converter; a signal generation unit for generating a test excitation signal in the form of an electrical alternating signal having a first selectable frequency; a phase detection unit for determining a first phase shift between the test excitation signal and a test receive signal that passes through the bridging unit and the component of the electronic system unit; and a computer unit configured to determine a phase compensation instruction from the first phase shift, wherein the compensation device is configured to transfer the phase compensation instruction to a phase adjustment unit of the electronic system unit of the vibronic sensor.

2. The compensation device according to claim 1, wherein the compensation device is detachably connectible to the electronic system unit of the vibronic sensor.

3. The compensation device according to claim 1, wherein the bridging branch includes a switch and further includes a capacitor, a coil, or a resistor.

4. The compensation device according to claim 1, wherein the signal generation unit is a controlled oscillator configured to generate a signal of variable frequency.

5. The compensation device according to claim 1, further comprising: an adaptive filter, including a bandpass filter or a resonator filter.

6. The compensation device according to claim 1, further comprising: a phase correction unit.

7. The compensation device according to claim 1, wherein the component of the electronic system unit is an analog input stage including an operational amplifier, an analog output stage including an operational amplifier, an impedance converter, a filter, an analog-to-digital converter, a digital-to-analog converter, a transistor stage, or an analog switch of the vibronic sensor.

8. A vibronic sensor for determining a process variable of a medium in a container, comprising: an electromechanical converter; and an electronic system unit including a phase adjustment unit and a compensation device, the compensation device including: a bridging unit for electrically bridging and thereby bypassing the electromechanical converter, wherein the bridging unit includes a bridging branch connected in parallel to the electromechanical converter; a signal generation unit for generating a test excitation signal in the form of an electrical alternating signal having a first selectable frequency; a phase detection unit for determining a first phase shift between the test excitation signal and a test receive signal that passes through the bridging unit and the component of the electronic system unit; and a computer unit configured to determine a phase compensation instruction from the first phase shift, wherein the compensation device is configured to transfer the phase compensation instruction to the phase adjustment unit, wherein the electronic system unit is configured to generate an excitation signal from a receive signal, to adjust a predeterminable phase shift between the excitation signal and the receive signal using the phase adjustment unit, and to determine the process variable from the receive signal.

9. The vibronic sensor according to claim 8, wherein the electromechanical converter includes a piezoelectric element or a coil.

10. The vibronic sensor according to claim 8, further comprising: a switching element for switching back and forth between a measurement operating mode in which the process variable is determined and a compensation operating mode in which the phase correction instruction is determined and transferred to the phase adjustment unit.

11. The vibronic sensor according to claim 8, wherein the process variable is a predeterminable fill-level of the medium in the container, a density of the medium, or a viscosity of the medium.

12. The vibronic sensor according to claim 8, wherein the electromechanical converter includes an oscillatable unit including a membrane, a single rod, or a tuning fork.

13. A method for operating a vibronic sensor for determining and/or monitoring a process variable, comprising: determining in a compensation operating mode a phase compensation instruction for compensating for a phase shift caused by a component of an electronic system unit of the vibronic sensor, wherein a first test excitation signal having a first frequency and a second test excitation signal having a second frequency are used in the compensation operating mode; calculating a first phase shift between the first test excitation signal and a first test receive signal and a second phase shift between the second test excitation signal and a second test receive signal; calculating from the values of the first frequency, the second frequency, the first phase shift, and the second phase shift a polynomial function of predeterminable order as the phase compensation instruction; adjusting in a measurement operating mode a predeterminable phase shift between an excitation signal and a receive signal; adjusting the predeterminable phase shift using the phase compensation instruction; and determining the process variable.

14. The method according to claim 13, wherein the compensation operating mode is executed once when the vibronic sensor is put into operation, or wherein the compensation operating mode is executed periodically at selectable time intervals.

15. The method according to claim 13, wherein a phase shift of a component of the electronic system unit caused by a change in an ambient temperature is compensated for in the compensation operating mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantageous embodiments are explained in more detail below with reference to FIG. 1-FIG. 3. These show:

(2) FIG. 1 shows a schematic drawing of a vibronic sensor with a compensation unit according to the invention,

(3) FIG. 2 shows a block diagram of an analog electronic system unit of a vibronic sensor with a compensation device according to the invention, and

(4) FIG. 3 shows a block diagram of a digital electronic system unit of a vibronic sensor with a compensation device according to the invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a vibronic sensor 1. An oscillatable unit 4 is depicted in the form of a tuning fork which is partially immersed into a medium 2, which is located in a container 3. The oscillatable unit is excited by the excitation/receiving unit 5 to mechanical oscillations and can, for example, be a piezoelectric stack drive or bimorph drive. However, it is, naturally, understood that other embodiments of a vibronic sensor also come under the invention. In addition, an electronic system unit 6 is illustrated, by means of which the signal acquisition, evaluation, and/or supply take place. The electronic system unit is also electrically-conductively and detachably connected to a compensation unit 7 according to the invention, by means of which at least one phase compensation instruction for compensating for at least one additional phase shift caused by a component of the vibronic sensor 1 (especially, a component of the electronic system unit 6) between the excitation signal and the receive signal can be compensated for.

(6) FIG. 2 shows a block diagram of a vibronic sensor 1 with an analog electronic system unit 6 of a vibronic sensor 1 with an associated suitable compensation unit 7. Those components which are to be assigned to the electronic system unit 6 of the vibronic sensor 1 are shown in dashed lines in each case. In a measurement operating mode, the oscillatable unit 4 is excited to mechanical oscillations by means of the electromechanical converter unit 5 and by means of an excitation signal U.sub.A, which first passes through an analog output stage 8a. The receive signal U.sub.E received from the oscillatable unit 4 or the electromechanical converter unit 5 first passes through an analog input stage 8b, before being provided to a phase adjustment unit 9, e.g., a phase shifter, which is representative here for all those components of the electronic system unit 6, which, among other things, serve to adjust the predeterminable phase shift Δφ between the excitation signal U.sub.A and the receive signal U.sub.E, to evaluate the receive signal U.sub.E with respect to the respective process variable, and to generate the excitation signal U.sub.A from the receive signal U.sub.E. Various additional, analog operating modes for a vibronic sensor 1 are known to the person skilled in the art from the prior art, and are described, for example, in the documents cited in the introduction to the description, which is why this aspect is not discussed in detail below.

(7) In the embodiment of the present invention shown in FIG. 2, the compensation operating mode is started by means of the four switching elements 10a-10d. The compensation unit 7 is part of the electronic system unit 6 of the vibronic sensor 1. Other embodiments may also provide a separate compensation unit 7, which can—in particular, detachably—be connected to the electronic system unit 6—for example, in the form a needle adapter.

(8) The bridging unit 11 of the compensation unit 7 comprises a bridging branch 12 connected in parallel to the electromechanical converter unit 5 and having a capacitor 13. In this way, the phase shifts caused by the analog output stage 8a and by the analog input stage 8b are together detected in the form of a first existing phase shift Δφ.sub.test1 and compensated for in the compensation operating mode. In another embodiment, however, the bridging unit 11 can also bridge at least one further component of the electronic system unit 6—for example, the analog input stage 8b or the analog output stage 8a. Then, this additionally bridged component is not taken into account in the compensation operating mode. In order to exclude individual components from the compensation operating mode, the switching element 10b can, alternatively, also be arranged at a different position. In the case that the analog output stage 8a is not to be taken into account, the switching element 10b must, for example, be arranged in the block diagram of FIG. 2 between the vibronic sensor 4, 5 and the analog output stage 8a. In the latter case, the phase shifts Δϕ.sub.test1, Δφ.sub.test2 . . . caused by individual components of the electronic system unit 6 can be individually determined by, for example, specific variation of the circuits and, where applicable, be subsequently compensated for together.

(9) During the compensation operating mode, at least one first test excitation signal U.sub.Atest1 of a first predeterminable frequency f.sub.1 is generated by means of the signal generation unit 14—here, a controlled oscillator. The frequency f.sub.1 is in this case preferably identical to the frequency f of the excitation signal U.sub.A. The test excitation signal U.sub.Atest1 passes through the analog output stage 8a, the bridging unit 11, and the analog input stage 8b, and is subsequently supplied to the phase detection unit 15. Conceivable for the phase detection unit 15 are different, analog as well as digital, embodiments which are sufficiently known to the person skilled in the art and which all come under the present invention. The phase detection unit 15 is also supplied by the signal generation unit 14 with the test excitation signal U.sub.Atest1 so that it can determine the first phase shift Δϕ.sub.test1 existing between the test excitation signal the U.sub.Atest1 and the test receive signal U.sub.Etest1. A computer unit 16 subsequently determines a phase compensation instruction a at least from the first phase shift Δϕ.sub.test1. In the case where a frequency dependency of the phase shifts caused by the components of the vibronic sensor is to be taken into consideration, the signal generation unit 14, the phase detection unit 15, and the computer unit 16 are further designed to generate at least two test excitation signals U.sub.Atest1, U.sub.Atest2 with two different frequencies f.sub.1 and f.sub.2, to receive the two test receive signals U.sub.Etest1, U.sub.Etest2, to determine the two phase shifts Δϕ.sub.test1 and Δϕ.sub.test2, and to calculate therefrom a phase compensation instruction σ.

(10) A compensation unit 7 suitable, in particular, for a digital electronic system unit 6 of a vibronic sensor 1 is, lastly, shown in FIG. 3, also in the form of a block diagram. Components which have already been explained in conjunction with FIG. 2 are not discussed again below. In contrast to the analog electronic system unit 6 according to FIG. 2, the digital electronic system unit 6 according to FIG. 3 additionally comprises an analog-to-digital converter 17b and a digital-to-analog converter 17, both components being taking into account with regard to their phase shifts in the context of the compensation operating mode.

(11) At least one filter—in particular, an adaptive filter 18a—can, optionally, furthermore be assigned to the compensation device 7; in the embodiment shown here, two filters 18a, 18b are provided. This embodiment is, in particular, suitable for a vibronic sensor as described in DE102012101667A1. In this case, the filters 18a, 18b are adapted, in particular, to the adaptive filter (not shown separately here) of the electronic system unit 6 of the vibronic sensor 1 and are, in particular, structurally identical thereto.

(12) A further optional addition consists in the integration of a reference element 19 which can be operated via a fifth switching element 10e. Depending upon the embodiment of the electromechanical converter unit 5, the reference element 19 may, for example, be provided by a capacitor or a coil. This reference element 19 serves to determine an additional phase shift caused by at least one process parameter, as described in the previously unpublished German patent application with reference number 102015112421.1.