Vibration sensor with self-testing function

Abstract

The invention relates to a method for operating a vibration sensor (10), wherein the vibration sensor (10) has a mechanical oscillator (18) and a drive unit (16), and the drive unit (16) causes the mechanical oscillator (18) to oscillate, wherein the vibration sensor (10) has a control and evaluation unit (14), and the control and evaluation unit (14) controls the drive unit (16) such that the mechanical oscillator (18) is driven to resonate, wherein a main signal path (I) is formed which extends from the control and drive unit (14) via a transmission chain (24) to the drive unit (16) and from the drive unit (16) via a receiving chain (26) to the control and evaluation unit (14), wherein the transmission chain (24) and / or the receiving chain (26) is tested. The invention also relates to a vibration sensor (10).

Description

[0001] Vibration sensor with self-test function

[0002] The invention relates to a method for operating a vibration sensor according to claim 1 and a vibration sensor according to claim 6.

[0003] Vibration sensors are well known in the art. Typically, such a vibration sensor has a membrane that can be excited to oscillate via a drive, which can be used to excite a mechanical oscillator mounted on the membrane. A piezoelectric drive or an electromagnetic drive can be used as the drive. Depending on the degree of coverage of the mechanical oscillator with a filling material and the viscosity of the filling material, the mechanical oscillator oscillates at a characteristic resonant frequency, which can be detected by the vibration sensor and converted into a measurement signal.

[0004] A typical application for a vibration sensor is the detection of a limit level, i.e. a predefined fill level in a process vessel, such as a process tank, a storage tank, a silo or a pipeline in the process industry. Point level sensors are often used as so-called limit switches, i.e. to determine whether a filling medium exceeds or falls below a certain fill level, the so-called limit level. Typically, a switching command is generated when a defined limit level is reached. A switching command from the point level sensor can, for example, start or stop filling or emptying devices in order to prevent the respective process vessel from overflowing or running empty. Point level sensors can be used for various liquids, as well as granulated and powdered bulk materials.

[0005] Proper functioning of a vibration sensor, and especially a point level sensor, is particularly important with regard to these switching commands. If the vibration sensor malfunctions or emits an incorrect signal, it can cause a process vessel to run dry or overflow, resulting in significant damage, including to other equipment. Therefore, vibration sensors used as point level sensors are often subject to strict safety requirements.

[0006] The underlying object of the invention is to provide a method for operating a vibration sensor and a vibration sensor by means of which the operational reliability of a vibration sensor is increased.

[0007] The invention relates to a method for operating a vibration sensor. The vibration sensor comprises a mechanical oscillator and a drive unit, wherein the drive unit causes the mechanical oscillator to oscillate. The mechanical oscillator is, in particular, a single-rod oscillator connected to a membrane or a tuning fork connected to a membrane, in particular with two prongs. A piezoelectric drive or an electromagnetic drive can be provided as the drive unit in a known manner.

[0008] The vibration sensor has a control and evaluation unit, which controls the drive unit so that the mechanical oscillator is driven at resonance. The vibration sensor has a control loop such that the mechanical oscillator is driven at a resonant frequency, and the resulting vibration characteristics are detected.

[0009] The vibration sensor has a main signal path which extends from the control and drive unit via a transmission chain to the drive unit and from the drive unit via a reception chain to the control and evaluation unit.

[0010] The transmission chain serves to process and, if necessary, amplify the excitation signal generated by the control and evaluation unit for the drive unit. The transmission chain can, in particular, comprise one or more of the following electronic components: a signal generator, a comparator, an integrator, a driver stage (particularly for electromagnetic drives), a microcontroller, and / or an analog oscillating circuit. The signal generator can, for example, generate a square-wave signal, which can then be converted into a sinusoidal signal by the integrator. The reception chain serves to process and amplify the vibration signal of the mechanical oscillator detected by the drive unit.The reception chain comprises in particular at least one of the following electronic components: a filter stage for filtering any harmonics of the measurement signal, an amplifier stage, a comparator for converting a received sine signal into a square wave signal, a DDS module, a VC oscillator and / or digital potentiometer which is set to the parameters of the corresponding mechanical oscillator.

[0011] The transmission chain and / or reception chain are tested, i.e. it is checked whether the transmission chain and / or the reception chain are functioning correctly. According to the method, a functional test of the electronics alone is carried out. In particular, the electronics are tested independently of the mechanical components, since only the electronic part of the oscillating circuit or control circuit is tested with the transmission chain and the reception chain. In particular, the transmission chain can be tested individually and / or the reception chain can be tested individually. Alternatively or additionally, there is the option of testing the transmission and reception chains together. In particular, the test is intended to rule out the possibility of a short circuit or a wire break. Furthermore, there may be integrated circuits in the transmission chain and / or the reception chain, which can thus be checked for correct function.Possible error scenarios here include, for example, that the output of a component of an integrated circuit remains in saturation, both in the upper and lower range, that the output starts to oscillate, that the gain of amplifiers changes, or that the input resistances change.

[0012] The ability to test the transmission and / or reception chain, i.e. in particular the electronic components, provides a self-test for the vibration sensor so that the functionality of the vibration sensor can be checked regularly and, in particular, without taking the vibration sensor out of operation or removing and disassembling it. To check the transmission chain and the reception chain, a transmission and reception signal path is designed in such a way that the drive unit is located outside the transmission / reception signal path. In other words, the drive unit is bypassed. The signal generated by the control and evaluation unit is routed via the transmission / reception signal path without passing through the drive unit. This offers the advantage that the influence of the drive unit on the excitation or measurement signal is excluded.

[0013] In a practical embodiment, a transmission chain signal path is formed for testing the transmission chain, with the drive unit and the reception chain located outside the transmission chain signal path. The transmission chain signal path extends, in particular, from the control and evaluation unit via the transmission chain directly back to the control and evaluation unit. This makes it possible to test only the transmission chain. This is particularly relevant for further narrowing down a detected error.

[0014] In another practical embodiment, a receive chain signal path is formed to test only the receive chain, with the drive unit and the transmit chain being located outside the receive chain signal path. The receive chain signal path extends, in particular, directly from the control and evaluation unit via the receive chain to the control and evaluation unit. Similar to the separate testing of the transmit chain, the separate testing of the receive chain allows for a potential error to be more precisely localized.

[0015] In particular, to check the transmission chain and / or the reception chain, a test signal can be transmitted via the main signal path, whereby the test signal is received and analyzed by the control and evaluation unit. For this purpose, the evaluation electronics are in a test state during the self-test, in particular. The test signal is only used as a signal for the self-test. The test signal is in particular parameterizable and its frequency and / or amplitude can be adjusted, for example, to signal a covered or uncovered state. In particular, the test signal passes through the main signal path, and the control and evaluation unit checks whether the corresponding test signal exhibits the corresponding, predicted behavior. For example, the test signal changes as it passes through the reception chain if filter and amplifier circuits are installed there. The transfer function of the reception chain is known and can also be calibrated.This allows the transmitted signal to be calculated from the received signal. The specified amplitude and frequency of the transmitted test signal and the known transfer function of the receiving chain result in a predictable signal, which is then generated after passing through the receiving chain. If this predictable signal and the actually measured signal match, it can be concluded that the circuit is functioning. If they do not match, a fault can be assumed.

[0016] The test signal is modulated onto the excitation signal, particularly by the control and evaluation unit. The modulated signal differs from the excitation signal in frequency and amplitude. In particular, the amplitude of the test signal is small compared to the excitation signal to minimize its impact on the measurement. The frequency of the test signal is typically two to three times higher than the frequency of the excitation signal. One advantage of a modulated test signal, which runs through the main signal path, is that the electronic components can be tested while the vibration sensor is in operation.

[0017] Alternatively, the test signal could be an invalid signal, i.e., a signal that lies outside the specified parameters. Such a test signal could, for example, have a frequency outside the permitted measurement range. Likewise, the test signal could exhibit significant frequency jumps, which would then be detected as invalid. An invalid test signal would be processed, particularly by the receiving chain, allowing a malfunction in the receiving chain to be detected.

[0018] Testing of the electronic components, and in particular of the transmission and / or reception chain, is carried out regularly at specified intervals to ensure proper operation of the vibration sensor. Provision can be made to perform a test on an ad hoc basis in the event of certain irregularities, such as measurement deviations. The invention also relates to a vibration sensor with a mechanical oscillator and a drive unit for causing the mechanical oscillator to vibrate. The vibration sensor further comprises a control and evaluation unit, wherein the control and evaluation unit regulates the drive unit such that the mechanical oscillator is driven into resonance. For further details on the vibration sensor, reference is made to the above description.

[0019] The vibration sensor has a main signal path which extends from the control and evaluation unit via a transmission chain to the drive unit and from the drive unit via a reception chain to the control and evaluation unit, wherein the vibration sensor has means for checking the transmission chain and / or reception chain.

[0020] As already described above, these means for checking the transmission chain and / or the reception chain enable a simple self-test of the vibration sensor, which thus increases the operational reliability of the vibration sensor.

[0021] In a practical embodiment, the vibration sensor has at least one switch, which can be switched back and forth between a first position and at least one second position. The switch is, in particular, an electrical switch. The at least one switch and the associated signal paths enabled thereby can be considered a means for testing the transmission chain and / or reception chain.

[0022] The at least one switch, in particular in a first position, connects the transmission chain to the drive unit in the main signal path. In a second position, the switch connects the transmission chain to a transmission chain signal path, with the drive unit and the reception chain being arranged outside the transmission chain signal path. In other words, the transmission chain signal path leads from the control and evaluation unit to the transmission chain and directly back to the transmission and evaluation unit. Using a simple switch, the transmission chain can be checked independently of the drive unit and the reception chain.

[0023] At least one switch connects the receive chain to the drive unit, particularly in a first position. In a second position, the switch connects the receive chain to a receive chain signal path, with the transmit chain and the drive unit located outside the receive chain signal path. The receive chain signal path leads, in particular, from the control and evaluation unit to the receive chain and directly back to the transmit and evaluation unit. Using a simple switch, the receive chain can be checked independently of the drive unit and the receive chain.

[0024] Preferably, two switches are provided, one for the transmission chain and one for the reception chain, wherein the two switches can be switched independently of each other.

[0025] In a practical embodiment, two switches are provided. In a first position, the transmit chain is connected to the drive unit, and the receive chain is connected to the drive unit via the main path (= configuration in standard operation of the vibration sensor). In a second position of the switch, the transmit chain and the receive chain are connected to each other via a transmit-receive signal path, with the drive unit located outside the transmit-receive signal path. The drive unit is then bridged to enable separate testing of the transmit and receive chains.

[0026] The two switches described each have at least three positions, with the first switch in its third position locating the transmit chain in the transmit chain signal path, and the second switch in its third position locating the receive chain in the receive chain signal path. This third position allows the transmit chain to be integrated either into the main signal path, the transmit-receive signal path, or the transmit chain signal path. The same applies to the receive chain. Depending on the position of the respective switch, different units can be tested.

[0027] In another practical embodiment of the vibration sensor, a replacement component for simulating the drive unit is arranged in the transmit / receive signal path. This is particularly advantageous when the drive unit is bypassed, but the optimal behavior of the drive unit is to be simulated in the transmit / receive signal path. A capacitor is particularly suitable as a replacement component. To also be able to represent additional parasitic effects, additional resistors and capacitors can be used. To vary the capacitance and achieve a greater test depth, a capacitance diode can also be used.

[0028] Further practical embodiments and advantages are described in conjunction with the figures. They show:

[0029] Fig. 1 shows a vibration sensor in a schematic representation,

[0030] Fig. 2 shows a vibration sensor according to a first embodiment with a transmission chain and a reception chain in a schematic representation and

[0031] Fig. 3 shows a vibration sensor according to a second embodiment with a transmission chain and a reception chain in a schematic representation.

[0032] Fig. 1 shows a vibration sensor 10. The vibration sensor 10 has a housing 12 with a control and evaluation unit 14 and a drive unit 16 arranged therein (not visible in Fig. 1, see Fig. 2).

[0033] The vibration sensor 10 further comprises a mechanical oscillator 18, which is designed here as a tuning fork with a first prong 20 and a second prong 22. The mechanical oscillator 18 is excited to oscillate by the drive unit 16, causing it to oscillate at a resonant frequency.

[0034] If the degree of coverage of the mechanical oscillator 18 changes, the resonance frequency at which it oscillates changes, whereby the change in coverage can be detected.

[0035] Such a vibration sensor 10 is often used as a limit switch, which is subject to particularly high safety requirements.

[0036] Fig. 2 shows a first embodiment of a vibration sensor 10 with a control and evaluation unit 14 and a drive unit 16. The control and evaluation unit 14 generates an excitation signal, which is transmitted to the drive unit 16 via a transmission chain 24. The transmission chain 24 comprises several electronic components, which are represented here in a simplified manner by a box.

[0037] The measurement signal generated by the drive unit 16 is passed via a receiving chain 26 (also shown in simplified form as a box) to the control and evaluation unit 14 and analyzed there.

[0038] The signal path from the control and evaluation unit 14 via the transmission chain 24, the drive unit 16, and the reception chain 26 back to the control and evaluation unit 14 is referred to here as the main signal path I. The excitation signal and measurement signal relevant for the measurement are transmitted via the main signal path I.

[0039] The vibration sensor 10 also has a first switch 28, which is arranged downstream of the transmission chain 24 in the signal direction. The switch 28 is arranged between the transmission chain 24 and the drive unit 16. The switch 28 has two switching positions. In the first switching position, which is not shown in Fig. 2, the switch 28 connects the transmission chain 24 to the excitation unit 16 according to the main path I.

[0040] In the second switching position shown, switch 28 connects the transmission chain 24 to a transmission chain signal path II. The transmission chain signal path II extends from the control and evaluation unit 14 to the transmission chain 24 and back to the control and evaluation unit 14. The drive unit 16 and the reception chain 26 are located outside of the transmission chain signal path II. In this second switching position of switch 28, it is possible to test the transmission chain 28 separately from the drive unit 16 and the reception chain 26.

[0041] The vibration sensor 10 also has a second switch 30, which here is arranged upstream of the reception chain 26 in the signal direction of the main signal path. The switch 30 is arranged between the drive unit 16 and the reception chain 26. The switch 30 has two switching positions. In the first switching position, which is not shown in Fig. 2, the switch 30 connects the reception chain 26 to the excitation unit 16 according to the main path I. In the second switching position shown, the switch 30 connects the reception chain 26 to a reception chain signal path III. The reception chain signal path III extends from the control and evaluation unit 14 to the reception chain 26 and back again to the control and evaluation unit 14. The drive unit 16 and the transmission chain 24 are arranged outside the reception chain signal path III.In this second switching position of the switch 30, it is possible to test the receiving chain 26 separately from the drive unit 16 and the transmitting chain 24.

[0042] Fig. 3 shows a second embodiment of a vibration sensor 10. In the following, the same reference numerals are used for identical or at least functionally equivalent components as for the description of the first embodiment in Fig. 2.

[0043] Essentially, the second embodiment differs from the first embodiment in that the vibration sensor has a transmit-receive signal path IV in addition to the main signal path I, the transmit chain signal path II and the receive chain signal path II.

[0044] The vibration sensor 10 has a first switch 28 and a second switch 30, wherein the two switches 28 and 30 each have three switching positions.

[0045] In a first switching position (not shown here) of the switches 28 and 30, the transmission chain 24 and the reception chain 26 are connected to the drive unit 16 according to the main signal path I

[0046] In a second switching position (also not shown) of switches 28 and 30, the transmit chain 24 (analogous to Fig. 2) is integrated into the transmit chain signal path II and is not connected to the drive unit 16 and the receive chain 26. The receive chain 26 is integrated into the receive chain signal path III (analogous to Fig. 2) and is not connected to the drive unit 16 and the transmit chain 24.

[0047] Fig. 3 shows the third switching position, where the transmit chain 24 is connected to the receive chain 16 via the transmit / receive signal path IV. The transmit / receive signal path IV leads from the control and evaluation unit 14 via the transmit chain 24, via the receive chain 16 to the control and evaluation unit 14. The drive unit 16 is not located in the transmit / receive signal path IV, but is bridged. In this third switching position of the first switch 28 and the second switch 30, the transmit chain 24 and the receive chain 26 can be tested separately without the drive unit 16.

[0048] List of reference symbols

[0049] 10 Vibration sensor

[0050] 12 housings

[0051] 14 Control and evaluation unit

[0052] 16 Drive unit

[0053] 18 mechanical oscillator / tuning fork

[0054] 20 first prongs

[0055] 22 second prongs

[0056] 24 transmission chain

[0057] 26 Reception chain

[0058] 28 first switch

[0059] 30 second switch

[0060] I Main signal path

[0061] II Transmission chain signal path

[0062] III Receive chain signal path

[0063] IV Transmit-receive signal path

Claims

Patent claims 1. A method for operating a vibration sensor (10), wherein the vibration sensor (10) has a mechanical oscillator (18) and a drive unit (16), and the drive unit (16) causes the mechanical oscillator (18) to oscillate, wherein the vibration sensor (10) has a control and evaluation unit (14), and the control and evaluation unit (14) controls the drive unit (16) such that the mechanical oscillator (18) is driven in resonance, wherein a main signal path (I) is formed which extends from the control and drive unit (14) via a transmission chain (24) to the drive unit (16) and from the drive unit (16) via a reception chain (26) to the control and evaluation unit (14), characterized in that the transmission chain (24) and / or reception chain (26) is tested.

2. Method according to the preceding claim, characterized in that for testing the transmission chain (24) and the reception chain (26) a transmission-reception signal path (IV) is formed such that the drive unit (16) is located outside the transmission-reception signal path (IV).

3. Method according to one of the preceding claims, characterized in that a transmission chain signal path (II) is formed for testing the transmission chain (24), wherein the drive unit (16) and the reception chain (26) are arranged outside the transmission chain signal path (II).

4. Method according to one of the preceding claims, characterized in that a reception chain signal path (III) is formed for testing the reception chain (26), wherein the drive unit (16) and the transmission chain (24) are arranged outside the reception chain signal path (III).

5. Method according to one of the preceding claims, characterized in that for testing the transmission chain (24) and / or the reception chain (26) a Test signal is transmitted via the main signal path (I) and the received test signal is analyzed by the control and evaluation unit (14).

6. Vibration sensor with a mechanical oscillator (18) and a drive unit (14) for causing the mechanical oscillator (18) to oscillate, with a control and evaluation unit (14), wherein the control and evaluation unit (14) regulates the drive unit (16) such that the mechanical oscillator (18) is driven in resonance, and with a main signal path (I) which extends from the control and evaluation unit (14) via a transmission chain (24) to the drive unit (16) and from the drive unit (16) via a reception chain (26) to the control and evaluation unit (14), characterized in that the vibration sensor (10) has means for testing the transmission chain (24) and / or the reception chain (26).

7. Vibration sensor according to the preceding claim, characterized in that the vibration sensor (10) has at least one switch (28, 30), wherein the switch (28, 30) can be switched back and forth between a first position and at least one second position, a. wherein the at least one switch (28) in a first position connects the transmission chain (24) to the drive unit (16) according to the main signal path (I) and wherein the switch (28) in a second position connects the transmission chain (24) to a transmission chain signal path (II), wherein the reception chain (26) and the drive unit (16) are arranged outside the transmission chain signal path (II); b.wherein the at least one switch (30) in a first position connects the reception chain (26) to the drive unit (16) according to the main signal path (I) and wherein the switch (30) in a second position connects the reception chain (26) to a reception chain signal path (III), wherein the transmission chain (24) and the. Drive unit (16) are arranged outside the reception chain signal path (III).

8. Vibration sensor according to one of the preceding claims, characterized in that two switches (28, 30) are provided, wherein in a first switching position of the switch (28, 30) the transmission chain (24) is connected to the drive unit (16) and the reception chain (26) is connected to the drive unit (16) via the main signal path (I) and wherein in a second position of the switch (28, 30) the transmission chain (24) and the reception chain (26) are connected to each other via a transmission-reception signal path (IV), wherein the drive unit (16) is arranged outside the transmission-reception signal path (IV).

9. Vibration sensor according to the preceding claim, characterized in that the two switches (28, 30) each have at least three switching positions, wherein in the third switching position of the first switch (28) the transmission chain (24) is arranged in the transmission chain signal path (II) and in the third switching position of the second switch (30) the reception chain (26) is arranged in the reception chain signal path (III).

10. Vibration sensor according to one of the two preceding claims, characterized in that a replacement component for simulating the drive unit (16) is arranged in the transmit-receive signal path (IV).

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