DE102008032887A1 - Device for determining and / or monitoring a process variable and method for testing a device - Google Patents

Abstract

The invention relates to a device for determining and / or monitoring a process variable, comprising a mechanically oscillatable unit (1), a drive / receiving unit (4) and an electronic unit (5), wherein the drive / receiving unit (4 ) and the electronic unit (5) by a transmitting channel (6) and a receiving channel (7) are interconnected. The invention includes that a test unit (10) is provided, which during the test phase processes and / or evaluates a transmission channel test signal dependent on an impedance value of the transmission channel (6) and a reception channel test signal dependent on an impedance value of the reception channel (7). Furthermore, the invention relates to a method for testing a device for determining and / or monitoring a process variable.

Description

The The invention relates to a device for determination and / or monitoring at least one process variable, with at least a mechanically oscillatable unit, with at least one Drive / receiving unit, which starting from an excitation signal the mechanically oscillatable unit to mechanical vibrations stimulates and which of the mechanically oscillatable unit receives mechanical vibrations and a received signal converts, and with at least one electronic unit, which the Generates excitation signal and which process the received signal, wherein the drive / receiving unit and the electronics unit at least connected by a transmit channel and a receive channel are, wherein the transmission channel of the transmission of the excitation signal and the receiving channel of the transmission of the received signal serves.

Farther The invention relates to a method for testing a device for determining and / or monitoring at least one process variable, wherein the device is at least one mechanically oscillatable Unit, wherein the device at least one drive / receiving unit which, starting from an excitation signal, the mechanical oscillatory unit to stimulate mechanical vibrations and which of the mechanically oscillatable unit mechanical Receives vibrations and converts them into a received signal, and wherein the device has at least one electronic unit, which generates the excitation signal and which generates the received signal processed, wherein the drive / receiving unit and the electronic unit such are designed and coordinated that at least a transmit channel and a receive channel, the transmit channel the excitation of the mechanically oscillatable unit to mechanical vibrations and the receiving channel receiving the mechanical vibrations the mechanically oscillatable unit is used.

at the process size is for example level, density or viscosity of a medium, which, for example, a liquid, a bulk material or generally a fluid. The medium is for example in a container.

In the state of the art so-called oscillating forks (for example, for determining the fill level and other process variables of a medium) are known. EP 0 444 173 B1 ), Sticks ( WO 2004/094964 A1 ) or membrane transducer known. Exploited in the measurements with these devices in each case that the characteristics of the mechanical vibrations (oscillation amplitude, resonant frequency, phase response over frequency) of the oscillatory unit depend on the contact with the medium or even of its properties. For example, the frequency or amplitude of the vibrations decreases as the medium reaches and at least partially covers the vibratable unit. Therefore, it can be concluded from the decrease in the oscillation frequency or the amplitude that the medium has reached a level dependent on the design and the position of the attachment of the device. Furthermore, the oscillation frequency is also for example of the viscosity (see eg. EP 1 325 301 ) and the density of the medium.

to Excitation of the respective mechanically oscillatable units often piezoelectric elements are used, and vice versa also convert the mechanical vibrations into electrical signals. Furthermore, for certain applications is also an electromagnetic Excitation of the oscillatory unit possible.

For the safe operation of such meters is particular important in safety-relevant applications, the functionality to check the gauges regularly. In particular, self-testing of the devices are very popular. Failures exist, for example, in that the piezoelectric elements old or for example by a temperature shock damage or that contacts Dissolve with time and under process conditions or that condensate forms in the meter and a conductive bridge arises.

Such a function check is described for example in the prior art in the document WO 2007/1 01 461 A1 , The local level switch has two piezoelectric vibration devices, which serve to generate or receive the vibrations. For testing the limit switch, the two piezo-electric vibrators are connected in parallel and in series to a capacity measuring device. The total capacitance value of the two piezo-electric vibration devices connected in parallel and thus understood as capacitors is measured and in one embodiment compared with a reference capacitor. The disadvantage is that thus can not be addressed or only with appropriate effort, for example, on the temperature dependence of the capacitance value of the piezoelectric elements. Moreover, for example, errors or deficiencies in the two elements, which have the opposite effect on the capacity value, are not recognized. Furthermore, the setting of the reference capacitor is complicated and associated with the production of increased costs.

Of the Invention is based on the object, a measuring device or to propose a method which is a functional check allow, which do not have the disadvantages of the prior art.

The Invention solves the problem with respect to the device in that at least one test unit is provided, and that the test unit is designed such that it at least during a test phase dependent on an impedance value of the transmission channel Transmit channel test signal and one of an impedance value of the receive channel dependent receive channel test signal processed and / or evaluates.

The Device is usually able to either to determine the process variable or to react on the exceeding or falling below a corresponding Limit. In the latter case, it is the so-called. Level switch. However, this does not only refer to the level, but also on the other process variables like Density or viscosity of the medium. With the device is it possible to derive the deviation from an existing one Limit value or a measured value for the process variable to determine.

The inventive device thus has a Test unit, which at least during a test phase evaluates two test signals: a transmit channel test signal, which depends from the impedance value of the transmission channel, and a reception channel test signal, which is dependent on the impedance value of the receiving channel. Ie. in contrast to the prior art, each channel becomes unique considered. This is also a direct comparison of the two channels over their impedance values possible. For example, have the two Channels, d. H. the respective combination of transmission and Receive element with the associated lines and possibly existing components, known ratios of impedances to each other, so the two channels can mutually used for referencing. Each channel includes at least the respective lines between drive / receiving unit and Electronic unit and also the respective proportion of the drive / receiving unit, which is functionally involved in the respective channel. Ie. of the Transmitting channel consists at least of the lines through which the excitation signal is transmitted, and from the for the Exciting the vibrations or for converting the excitation signal in mechanical vibrations responsible part of the drive / receiving unit or in other words: the transmitting part of the drive / receiving unit.

Everyone Channel has its own impedance value, in which ever after embodiment of the channel or the drive / receiving unit the capacitive or the inductive component or the ohmic resistance is dominant.

A Embodiment of the device according to the invention includes that the test unit during the test phase that depends on a capacity value of the transmission channel Transmit channel test signal and that of a capacitance value the receiving channel dependent receiving channel test signal processed and / or evaluates, or that the test unit during the test phase that depends on an inductance value of the transmission channel Transmit channel test signal and that of an inductance value the receiving channel dependent receiving channel test signal processed and / or evaluates. The impedance as a complex AC resistance results from the capacity, the inductance and the ohmic resistance of the respective channel or in particular the proportion of the drive / receiving unit assigned to the respective channel and the respective lines. In this embodiment is doing emphasizes that, depending on the design of the measuring device or the two Channels the inductive or the capacitive part of the impedance is determinative.

A Embodiment of the device according to the invention provides that the test unit is designed such that the test unit at least one sum signal from the transmission channel test signal and processing and / or evaluating the receive channel test signal, and / or that the test unit has at least one difference signal between the transmit channel test signal and the receive channel test signal and / or evaluates. In this variant, therefore, the two test signals over a subtractor compared and over adds a summing circuit and the sum or the difference is evaluated. This allows an effective determination of whether deviations of the nominal state are present by both channels of the serve mutual referencing. In other words: the functional test consists in this variant in that the signals or the so connected impedances or in particular the capacitances of the transmit and receive channels compared directly become. Alternatively, the respective signals of the two Evaluate channels individually. The difference between the two signals Essentially, it shows changes that are asymmetric on both channels, whereas the sum is the case signals that both channels are essentially a similar change have experienced the impedance values.

An embodiment of the device according to the invention includes that the test unit is designed such that the test unit in case of deviation of the transmit channel test signal and / or the receive channel test signal and / or the sum signal and / or the difference signal of one or more predetermined limits on a or several predefinable tolerance ranges generates an alarm. In this embodiment, it is thus provided that either the individual signals or the sum or difference signals or a combination of these signals are compared with suitably predefinable limit values and that an alarm is generated in the event of deviations beyond respective tolerance values, this alarm being a corresponding indication represents a fault condition or a deviation from the expected setpoint. If the difference signal is evaluated, the limit value to be expected is, for example, zero given an identical configuration of the two channels with regard to their electrical properties.

A Embodiment of the device according to the invention provides that the drive / receiving unit at least one transmitting element and a receiving element, wherein the transmitting element of the excitation the mechanically oscillatable unit to mechanical vibrations serves, and wherein the receiving element to receive the mechanical Vibrations from the mechanically oscillatable unit serves. The transmitting and receiving elements are, for example, two piezoelectric elements which are stacked in a stack, d. H. are arranged at different heights. In another Embodiment is in the transmitting and the receiving element around two planar arranged in a plane piezoelectric elements. The Transmitting and the receiving element are each part of the associated transmitting or receiving channel.

A Embodiment of the device according to the invention includes that the drive / receiving unit with at least one first line, a second line and a third line is contacted. The connection between the drive / receiver unit and electronics unit thus consists of at least three lines. In one embodiment, one of the three lines is during the measuring phases connected to ground and on the other two lines the excitation and the received signal are transmitted. These two signals are in particular electrical AC signals so that across the grounded third line gives the reference potential. This is for example associated with the grounding line as both a component of the transmission, as well as the receiving channel can be understood.

A Embodiment of the device according to the invention provides that the transmitting element, the first line and the second Line at least partially form the transmission channel, and that the Receiving element, the first line and the third line at least partially form the receiving channel. The transmitting element and the receiving element are thus combined with their lines to channels. Depending on the configuration, other components or Elements are considered as part of the channels.

A Embodiment of the device according to the invention that involves the first lead during a measurement phase with a constant electrical potential, in particular with mass, connected to the second line during the measurement phase with the excitation signal is applied, and that the third line during the measurement phase with the received signal acted upon is. The first line is during the measurement phase, so during the time in which the meter its Tasks fulfilled, preferably connected to ground and thus also provides a separation between transmitting and receiving channel or between the transmitting and receiving element. The second and the In contrast, the third line serve to transmit the excitation signal or the received signal. Both signals are it is preferably electrical alternating voltages.

A Embodiment of the device according to the invention Provides that the first line during the testing phase contacted with the electronics unit is that the second line during the test phase, especially over at least a measuring resistor, with a constant electrical potential, in particular connected to ground, and that the third line during the test phase, in particular via at least one measuring resistor, with a constant electrical potential, in particular with mass, connected is. In the test phase here are the second and the third Line connected to ground and the first line is connected to the electronics unit contacted. Since the first line is a component of both the reception, as well as the broadcasting channel, it is also easy a suitable stimulus or test signal for the implementation of the functional test on the two channels. The electronics unit is here for both the measurement, as well as for uses the generation of the stimulus or test signal. This is simplified the construction. Alternatively, however, an additional Unit can be used, which generates a suitable signal. The two measuring resistors, over which the second and third line each with a constant potential, preferably Ground, each allow the tapping of the transmit channel or the receive channel test signal.

A Embodiment of the device according to the invention that includes the first lead during the testing phase is subjected to a test request signal. At the test request signal it is, for example, an electrical voltage signal, which is the measurement of the impedances or in particular the capacitances allowed.

A Embodiment of the device according to the invention provides that at least one filter unit is provided that the filter unit and the electronics unit at least during the test phase a resonant circuit with a predetermined resonant frequency form, and that the filter unit during the test phase modified an output signal of the electronic unit and the modified Output signal to the electronics unit returns. The Filter unit and the electronics unit thus form during the test phase an additional resonant circuit whose resonant frequency about the design z. B. adjust the filter unit leaves. This resonant circuit can be used accordingly the functional test of the electronic unit can be used. At the filter unit For example, it is essentially a bandpass, which is set to a certain frequency. Is it? at the excitation signal, for example, a square wave signal, so The filter unit also causes this output signal of the electronic unit for example, in a sinusoidal - other variants are also possible - signal converted. In the this embodiment provided filter unit is designed such that it generates an amplitude, frequency or phase which a statement about the electronics (in particular the Fundamental wave excitation) is possible. This modified excitation signal then returns to the input of the electronics unit and is there appropriately processed or evaluated.

A Embodiment of the device according to the invention includes that the drive / receiving unit at least one piezoelectric Has element and / or an electromagnetic element. In the state The technology is different variants for transmission between the mechanical vibrations and the associated known electrical signals. Depending on the configuration is then the capacitive or inductive component of the impedance of the respective Channel dominant.

A Embodiment of the device according to the invention provides that the mechanically oscillatable unit in the type of tuning fork is designed, or that the mechanical oscillatory unit designed in the manner of a single rod is, or that the mechanically oscillatable unit in the Type of membrane resonator is designed.

A Embodiment of the device according to the invention implies that it is the process size the level, the density or the viscosity a medium, in particular in a container, acts.

The Invention solves the problem with respect to the method in that at least during a test phase one of a transmission channel test signal dependent on an impedance value of the transmission channel and a dependent on an impedance value of the receiving channel Receive channel test signal are evaluated with each other.

The above embodiments of the invention Device and the associated explanations apply accordingly also for the invention Method.

Summarized the invention consists in that the impedances of the transmitting and the receiving element of the drive / receiving unit or the impedances of the transmitting and receiving channels using a measuring bridge evaluated and in particular directly compared.

The Invention will become apparent from the following drawings explained.

It shows:

1 : a schematic representation of a measuring device,

2 : a simplified representation of the electronic circuit, and

3 : exemplary signal waveforms of occurring signals.

The 1 shows a measuring device according to the invention. The mechanically oscillatable unit 1 consists in this embodiment of a pair of forks 2 which is attached to a membrane 3 is attached. On the inside of the membrane 3 is a - not shown here - drive / receiving unit available, which is an electromechanical transducer and which the mechanically oscillatable unit 1 stimulates mechanical vibrations or which of the mechanically oscillatable unit 1 receives mechanical vibrations. In this embodiment, the drive / receiving unit is, in particular, one or more piezoelectric elements which, on the basis of an applied alternating electrical voltage, execute mechanical oscillations or which convert a mechanical oscillation into an electrical alternating voltage.

For the measurement or monitoring of process variables such as level, density or viscosity of a medium is exploited that the amplitude, the frequency and / or the phase of the vibrations of the mechanically oscillatable unit 1 are dependent on the interaction with the medium and that thus can be deduced on the basis of the characteristics of the oscillations on these process variables. For example, the frequency decreases when the medium vibrates Ness 1 covered. Effects on the vibrations also have the density or the viscosity of the medium.

Others - here not shown - versions of the mechanical swinging units have sticks or only the membrane on, d. H. with the medium occurs in these cases only one rod or only the membrane interacts.

Behind the membrane 3 There is a section for screwing in the measuring instrument into a suitable recess (eg a thread, a flange or any connection) at the measuring location. Serves the meter, for example, as a level switch, this level limit of the level by the design of the meter and its location of attachment -. B. in the wall of a tank or other container - given. In the event that the process variable is the density or viscosity of the medium, the measuring device or the mechanically oscillatable unit is preferably designed and mounted in such a way that in each case a known degree of coverage by the medium -. B. complete coverage - is given.

In the 2 a variant of the components for the implementation of the invention is shown. The drive / receiver unit 4 is here divided into two separate units: transmitting element 8th and receiving element 9 , These two units can be, for example, two separate and independent piezoelectric elements, which are arranged, for example, in a stack, or they are the two piezoelectric elements, as described, for example, in the document EP 0 875 740 , Since these are piezoelectric elements, the capacitive component is thus the dominant one in the impedance of the two channels.

The drive / receiver unit 4 is contacted with three lines L1, L2 and L3. The first line L1 is between the transmitting element 8th and the receiving element 9 arranged. Since this first line is L1 during the here in 2 shown measuring phase is connected to the ground potential, are the transmitting element 8th and receiving element 9 quasi decoupled and can be considered separately or each serve different tasks, as will be described below.

The second line L2 is connected to the transmitting element 8th and - during the measurement phase - with the electronics unit 5 connected. The electronics unit 5 is used in particular for the generation of excitation signals and, in one embodiment, for example, is designed such that it serves for the fundamental wave excitation of the mechanically oscillatable unit.

The first line L1, the second line L2 and the transmitting element 8th thus form the transmission channel 6 , via which the excitation signal, that of the electronic unit 5 is generated to the transmitting element 8th arrives. Starting from the excitation signal leads the transmitting element 8th then mechanical vibrations, which are transmitted to the - not shown here - mechanically oscillatable unit.

The receiving element 9 is in turn via the third line L3 to the signal input of the electronic unit 5 connected. In this case, form the first line L1, the third line L3 and the receiving element 9 the receiving channel 7 , The reception channel 9 converts the dependent of the process variable or the change of the process variable mechanical vibrations of the mechanically oscillatable unit into electrical signals, which via the receiving channel 9 to the electronics unit 5 be transmitted as a received signal. In the electronics unit 5 then takes place the evaluation or further processing of the received signal.

In the measuring phase shown here, therefore, have the three switches used here 14 the corresponding position that they the first line L1 to ground and the second and third line, L2 and L3, respectively, with the output or input of the electronic unit 5 connect.

For the test phase, the three switches 14 switched over and thus make other connections. In the - not shown here - test phase are the second and the third line L2, L3 - here in each case via a measuring resistor 15 - connected to ground.

On the other hand, the first line L1 is subjected to an electrical signal during the test phase, which virtually measures the capacitance of the transmitting channel 6 and receiving channel 7 serves. Since the first line L1 between transmitting element 8th and receiving element 9 is arranged, so are both elements 8th . 9 simultaneously applied to this test request signal. The test request signal arrives here from the electronics unit 5 , which serves in the measurement phase of the fundamental excitation of the mechanically oscillatable unit, on the first line L1 and thereby to the drive / receiving unit 4 , The test interrogation signal is, for example, the excitation signal also used during the measurement phase or a test signal which is especially suitable for the test. B. in terms of frequency or shape ausgestaltetes AC signal.

During the test phase, the transmit channel test signal is tapped from the second line L2 and the receive channel test signal is tapped from the third line L3. These two test signals are each off dependent on the impedance values or in particular on the capacitance values of the respective channels 6 . 7 and thus allow a statement about the respective impedances / capacities. In particular, this makes it possible to determine whether there are any changes to the drive / receiving unit 4 have resulted.

For the evaluation of the test signals they become a test unit 10 fed. These are, for example, a microprocessor which digitizes the signals, for example, and appropriately evaluates them. In the variant shown here are in the test unit 10 provided two operational amplifiers, which once as a subtractor 11 and once as an adder 12 are wired. Thus, in this variant, the transmit channel test signal and the receive channel test signal are compared directly with each other. It thus eliminates a reference capacity, as provided for example in the prior art. Here are the send element 8th and the receiving element 9 or the associated channels 6 . 7 directly compared with each other and thus serve each other for referencing. The further components of an evaluation unit for evaluating the transmit channel test signal and the receive channel test signal or of the sum and difference signal are not shown here.

In the case that the two elements 8th . 9 are designed identically and in particular have the same capacitance value, for example, the subtractor 11 provide a zero signal in case everything is ok. Accordingly, the capacitance value of the electrical lines L1, L2, L3 must also be taken into account, ie their design or their capacitance values also play a role when considering the test signals. It should be mentioned that the functional test by the symmetrical contact between electronics and the transmitting and receiving channel z. B. is independent of age and temperature, since both channels are subject to the same environmental conditions or process conditions.

is For example, a contact no longer okay and changes the capacity value of one of the two channels, this can be recognized by the evaluation of the two test signals. The Difference gives thus in particular about whether the channels have a different evolution of their capacity values have experienced.

The sum signal of the adder 12 allows to determine whether both channels are subject to identical changes or are inferior. Would, for example, the contact between the electronics unit 5 and drive / receiver unit 4 completely demolished, the difference signal would give the value zero, but the sum signal would also indicate with a zero signal that there is an error. Ie. the additive merging of the two test signals of the two channels 6 . 7 shows symmetrical changes of the two channels 6 . 7 on. Thus, if, for example, the deviation from the value zero is a sign of the presence of an asymmetrical error in the case of the difference signal, a sum signal, for example below a limit value, means a symmetrical error, ie an error which equally affects both channels. However, symmetric errors can also cause a general increase in the sum signal. Therefore, if necessary, specify two limit values and suitable tolerance ranges.

As can be seen, the functional test of the measuring device takes place by connecting the existing elements with additional elements during the test phase. In the measuring phase, however, the circuit of the measuring device differs - except for the three switches 14 for the switching of the three lines L1, L2, L3 and the fourth switch 16 for generating the resonant circuit from electronic unit 5 and filter unit 13 - not from that of a normal measuring device without such a test function. The advantage, therefore, is that the component of the measuring device used for the measurement remains unchanged and thus behaves like a measuring device without such a functional test. The components required for the test (in particular the switches 14 ) are then, for example, through the test unit 10 or through the electronics unit 5 or controlled by the - not shown here - unit for evaluating the test signals or the sum and the difference signal.

The desk 16 causes during the test phase, that the output signal of the electronic unit 5 , which serves as an excitation signal during the measuring phase, to the input of the electronic unit 5 is fed back. The filter 13 contributes, for example, to the fact that, for example, a square wave signal emitted by the electronics unit 5 is generated, for example, converted into a sine wave signal. This sinusoidal signal is then applied to the input of the electronics unit 5 given and processed there accordingly. This feedback path thus also includes a check of the electronics unit 5 possible, with the filter 13 - This is essentially a bandpass, for example - the signal is influenced accordingly. In the test phase results for the circle of electronics unit 5 and filters 13 specific frequency of the signal applied to the input of the electronic unit 5 arrives. This is an additional test of the electronics unit 5 which, however, not necessary for the inventive review of the two channels 6 . 7 is.

In the 3 are waveforms as they can occur during the test phase. There These are schematic examples.

The top row shows the test request signal, which is essentially a rectangular signal of a given duration. This is thus the signal which is transmitted to the transmitting element 8th and the receiving element 9 is given to those of the respective capacity values of the channels 6 . 7 to receive dependent test signals. Alternatively, however, the test interrogation signal can also be a sinusoidal or triangular or arbitrarily configured alternating electrical voltage. The test query signal serves in view of the 2 to the RC-links of the two channels 6 . 7 measure.

The transmit channel test signal and the receive channel test signal are shown here in the second row, the case being that these two signals are different from each other. So there is an error here. As you can see, one turn drops faster than the other. These are respectively the charging and discharging curves of the two RC elements, which are determined by the capacitances of the two channels and by the connected resistors 15 (please refer 2 ).

The third row shows the difference signal from transmit channel test signal and receive channel test signal. Would be the capacity values of transmitting and the receiving channel identical, so would have the Difference signal to be a zero signal. This error signal shows however, a significant departure from it. Thus occurs at the difference signal a predeterminable tolerance range beyond a deviation from a predefinable Setpoint on, so a corresponding alarm or note for the operator of the meter are generated. Such deviations the difference signal are signs of asymmetric Error.

at the evaluation of the bridge voltages in the bridge over the subtractor becomes imbalances between the two paths or channels apparently. Thus, z. B. a cable break within a channel or even a fraction of the piezoelectric Elements or one of the elements detected within a stack because it increases the capacity in one of the two Channels changes. Since the transmitting and the receiving element preferably via same length cables are connected to the electronics unit, which also spatially shared by the electronics unit are led to the drive / receiving unit, are the the transmitting and the receiving element and the lines temperature influences equally exposed. Therefore, the falsified Temperature does not measure and the sensor state can be clear more accurate than in the prior art by the measurement of the difference signal be recorded. In addition, the aging of the piezo material also has an effect and piezo-elastic properties (eg, the capacitance change by one of the process on the membrane or the underneath or in the Housing interior drive / receiving unit Lastender Pressure) to the same extent on both elements.

In the fourth line, the sum signal is shown, the deviations over a tolerance range from a setpoint also for monitoring can be used. The sum signal allows additional still checking the total capacity the two channels. This is for example advantageous if an effect has a similar effect on both channels, d. H. z. B. in case of failure of both channels. For example the demolition of the two the respective for the Measurement relevant signals leading lines. To such Detecting effects can also be a single alternative to the difference signal Test signal of one of the two channels are evaluated. However, in contrast to the described prior art no parallel connection of the two understood as capacitors Transmitting and receiving unit instead. In the evaluation of the sum signal is possibly the exceeding of a limit value and below that of another limit separately. For example can be the formation of a condensate bridge or Corrosion products in the connection area to reduce the Impedance of the channels and thus to an increase lead the sum signal.

The Evaluation of difference and sum signal thus increases the information gain and it can reveal more errors.

1

Mechanically oscillatory unit

2

forks

3

membrane

4

Driver / receiver unit

5

electronics unit

6

transmission channel

7

receiving channel

8th

transmitting element

9

receiving element

10

test unit

11

subtractor

12

adder

13

filter unit

14

switch

15

measuring resistor

16

switch

L1

First management

L2

Second management

L3

third management

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• EP 0444173 B1 [0004]
• WO 2004/094964 A1 [0004]
• - EP 1325301 [0004]
• WO 2007/101461 A1 [0007]
• - EP 0875740 [0038]

Claims (15)

Device for determining and / or monitoring at least one process variable, having at least one mechanically oscillatable unit ( 1 ), with at least one drive / receiving unit ( 4 ), which starting from an excitation signal, the mechanically oscillatable unit ( 1 ) excites to mechanical vibrations and which of the mechanically oscillatable unit ( 1 ) receives mechanical vibrations and converts them into a received signal, and with at least one electronic unit ( 5 ) which generates the excitation signal and which processes the received signal, wherein the drive / receiving unit ( 4 ) and the electronics unit ( 5 ) at least by a transmission channel ( 6 ) and a receiving channel ( 7 ), wherein the transmission channel ( 6 ) of the transmission of the excitation signal and the reception channel ( 7 ) the transmission of the received signal, characterized in that at least one test unit ( 10 ) and that the test unit ( 10 ) is configured such that, at least during a test phase, one of an impedance value of the transmission channel ( 6 ) dependent transmit channel test signal and one of an impedance value of the receive channel ( 7 ) dependent receiving channel test signal is processed and / or evaluated. Device according to claim 1, characterized in that the test unit ( 10 ) during the test phase that of a capacity value of the transmission channel ( 6 ) dependent transmission channel test signal and that of a capacitance value of the receiving channel ( 7 ) dependent receive channel test signal is processed and / or evaluated, or that the test unit ( 10 ) during the test phase that of an inductance value of the transmission channel ( 6 ) dependent transmission channel test signal and that of an inductance value of the receiving channel ( 7 ) dependent receiving channel test signal is processed and / or evaluated. Device according to claim 1 or 2, characterized in that the test unit ( 10 ) is designed such that the test unit ( 10 ) processes and / or evaluates at least one sum signal from the transmit channel test signal and the receive channel test signal, and / or that the test unit ( 10 ) processes and / or evaluates at least one difference signal between the transmit channel test signal and the receive channel test signal. Device according to one of claims 1 to 3, characterized in that the test unit ( 10 ) is designed such that the test unit ( 10 ) generates an alarm in the event of a deviation of the transmission channel test signal and / or the receiving channel test signal and / or the difference signal and / or the difference signal from one or more predeterminable limit values beyond one or more predefinable tolerance ranges. Device according to one of claims 1 to 4, characterized in that the drive / receiving unit ( 4 ) at least one transmitting element ( 8th ) and a receiving element ( 9 ), wherein the transmitting element ( 8th ) the excitation of the mechanically oscillatable unit ( 1 ) to mechanical vibrations, and wherein the receiving element ( 9 ) receiving the mechanical vibrations from the mechanically oscillatable unit ( 1 ) serves. Device according to one of claims 1 to 5, characterized in that the drive / receiving unit ( 4 ) is contacted with at least a first line (L1), a second line (L2) and a third line (L3). Device according to claims 5 and 6, characterized in that the transmitting element ( 8th ), the first line (L1) and the second line (L2) at least partially the transmission channel ( 6 ), and that the receiving element ( 9 ), the first line (L1) and the third line (L3) at least partially the receiving channel (L1) 7 ) form. Device according to one of claims 6 to 7, characterized, that the first line (L1) during a measurement phase with a constant electrical Potential, in particular connected to ground, that the second line (L2) during the measurement phase with the excitation signal is charged and that the third line (L3) during the measuring phase is acted upon by the received signal. Device according to one of claims 6 to 8, characterized in that the first line (L1) during the test phase with the electronic unit ( 5 ), that the second line (L2) during the test phase, in particular via at least one measuring resistor ( 15 ), with a constant electrical potential, in particular with ground, and that the third line (L3) during the test phase, in particular via at least one measuring resistor ( 15 ), with a constant electrical potential, in particular with ground, is connected. Device according to one of claims 6 to 9, characterized in that the first line (L1) during the test phase is subjected to a test request signal. Device according to one of claims 1 to 10, characterized in that at least one filter unit ( 13 ) is provided that the filter unit ( 13 ) and the electronics unit ( 5 ) form at least during the test phase a resonant circuit with a predefinable resonance frequency, and that the filter unit ( 13 ) during the test phase, an output signal of the electronic unit ( 5 ) and modifies the modified output signal to the electronics unit ( 5 ) returns. Device according to one of claims 1 to 11, characterized in that the drive / receiving unit ( 4 ) has at least one piezoelectric element and / or an electromagnetic element. Device according to one of claims 1 to 12, characterized in that the mechanically oscillatable unit ( 1 ) is designed in the manner of a tuning fork, or that the mechanically oscillatable unit ( 1 ) is designed in the manner of a single rod, or that the mechanically oscillatable unit ( 1 ) is designed in the manner of a membrane resonator. Device according to one of claims 1 to 13, characterized in that it is in the process size the level, the density or the viscosity a medium, in particular in a container, acts. Method for testing a device for determining and / or monitoring at least one process variable, wherein the device comprises at least one mechanically oscillatable unit ( 1 ), wherein the device has at least one drive / receiving unit ( 4 ), which starting from an excitation signal, the mechanically oscillatable unit ( 1 ) excites to mechanical vibrations and which of the mechanically oscillatable unit ( 1 ) receives mechanical vibrations and converts them into a received signal, and wherein the device comprises at least one electronic unit ( 5 ), which generates the excitation signal and which processes the received signal, wherein the drive / receiving unit ( 4 ) and the electronics unit ( 5 ) are designed and matched to one another such that at least one transmission channel ( 6 ) and a receiving channel ( 7 ), the transmission channel ( 6 ) the excitation of the mechanically oscillatable unit ( 1 ) to mechanical vibrations and the receiving channel ( 7 ) receiving the mechanical vibrations of the mechanically oscillatable unit ( 1 ), characterized in that at least during a test phase one of an impedance value of the transmission channel ( 6 ) dependent transmit channel test signal and one of an impedance value of the receive channel ( 7 ) dependent receiving channel test signal are evaluated together.