CA2235037C - Apparatus for establishing and/or monitoring a predetermined filling level in a container - Google Patents
Apparatus for establishing and/or monitoring a predetermined filling level in a container Download PDFInfo
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- CA2235037C CA2235037C CA002235037A CA2235037A CA2235037C CA 2235037 C CA2235037 C CA 2235037C CA 002235037 A CA002235037 A CA 002235037A CA 2235037 A CA2235037 A CA 2235037A CA 2235037 C CA2235037 C CA 2235037C
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- 238000012544 monitoring process Methods 0.000 title claims abstract description 9
- 230000005540 biological transmission Effects 0.000 claims abstract description 78
- 230000010355 oscillation Effects 0.000 claims abstract description 44
- 230000003534 oscillatory effect Effects 0.000 claims abstract description 39
- 230000010287 polarization Effects 0.000 claims abstract description 11
- 238000005259 measurement Methods 0.000 abstract description 15
- 230000008878 coupling Effects 0.000 description 13
- 238000010168 coupling process Methods 0.000 description 13
- 238000005859 coupling reaction Methods 0.000 description 13
- 230000006870 function Effects 0.000 description 13
- 239000000463 material Substances 0.000 description 9
- 230000009467 reduction Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 230000005284 excitation Effects 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 239000006260 foam Substances 0.000 description 3
- 230000033001 locomotion Effects 0.000 description 3
- 230000010358 mechanical oscillation Effects 0.000 description 3
- 230000001419 dependent effect Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000013016 damping Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000002446 δ-tocopherol Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/296—Acoustic waves
- G01F23/2966—Acoustic waves making use of acoustical resonance or standing waves
- G01F23/2967—Acoustic waves making use of acoustical resonance or standing waves for discrete levels
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- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
- General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
Abstract
An apparatus for establishing and/or monitoring a predetermined filling level in a container is provided, in which a reception signal (E) is equal to the measurement signal, and in which a fixed phase difference (.DELTA.~R), which is independent of the oscillation quality of the apparatus, exists between a first transmission signal (S1), and a reception signal (E) at a resonant frequency (fr). The apparatus comprises a mechanical oscillatory structure (1) and a piezoelectric element (2), which has a first region (I) having a reception electrode (21), a second region (II) having a first transmission electrode (22) and a third region (III) having a second transmission electrode (23), the two transmission electrodes (22, 23) having an identical form and being arranged symmetrically with respect to one another and to the reception electrode (21), in the first and in the second region (I, II), the piezoelectric element having a polarization which is in the opposite direction to a polarization of the third region (III), and a first transmission signal (S1) being applied to the first transmission electrode (22), which first transmission signal has the same amplitude as and is in antiphase with a second transmission signal (S2), which is applied to the second transmission electrode (23).
Description
CA 0223S037 1998-04-1~
..
E~H 309 EP
~ 05.04.1997 Apparatu~ for establ;~h;n~ and/or monitoring a predetermined f; 11 ;n~ level in a cont~in~
The invention relates to an apparatus for establi8hing and/or monitoring a predetermined filling level in a container.
Filling level limit switches of this type are employed in many branches of industry, in particular in the chemical industry and in the foodstuffs industry. They serve the purpose of limit level detection and are used, for example, as protection against overfilling or as a safeguard against pumps rnnn;ng dry.
DE-A 44 19 617 describes an apparatus for establishing and/or monitoring a predetermined filling level in a container. This apparatus comprises:
- a mechanical oscillatory structure, which is fitted at the level of the predetermined filling level, - an electromechanical transducer, -- which has at least one transmitter, --- to which an electrical transmission signal is applied and --- which excites the mechanical oscillatory structure to produce oscillations, and -- which has a receiver, --- which picks up the mechanical oscillations of the oscillatory structure and converts them into an electrical reception signal, - an evaluation unit, -- which picks up the reception signal and determines its frequency, compares this signal with a reference frequency and generates an output signal which indicates that the mechanical oscillatory structure is covered by a charge material if the frequency has a value which is less than the reference frequency, and that it is not covered if the value is greater, and CA 0223~037 1998-04-1~
..
E~H 309 EP
~ 05.04.1997 Apparatu~ for establ;~h;n~ and/or monitoring a predetermined f; 11 ;n~ level in a cont~in~
The invention relates to an apparatus for establi8hing and/or monitoring a predetermined filling level in a container.
Filling level limit switches of this type are employed in many branches of industry, in particular in the chemical industry and in the foodstuffs industry. They serve the purpose of limit level detection and are used, for example, as protection against overfilling or as a safeguard against pumps rnnn;ng dry.
DE-A 44 19 617 describes an apparatus for establishing and/or monitoring a predetermined filling level in a container. This apparatus comprises:
- a mechanical oscillatory structure, which is fitted at the level of the predetermined filling level, - an electromechanical transducer, -- which has at least one transmitter, --- to which an electrical transmission signal is applied and --- which excites the mechanical oscillatory structure to produce oscillations, and -- which has a receiver, --- which picks up the mechanical oscillations of the oscillatory structure and converts them into an electrical reception signal, - an evaluation unit, -- which picks up the reception signal and determines its frequency, compares this signal with a reference frequency and generates an output signal which indicates that the mechanical oscillatory structure is covered by a charge material if the frequency has a value which is less than the reference frequency, and that it is not covered if the value is greater, and CA 0223~037 1998-04-1~
- 2 - E+H 309 EP
05.04.1997 - a control loop, which regulates a phase difference existing between the electrical transmission signal and the electrical reception signal to a specific, constant value at which the oscillatory structure oscillates at a resonant frequency.
The control loop is formed, for example, by amplifying the reception signal and feeding it back via a phase shifter to the transmission signal.
DE-C 195 23 461 describes an apparatus for establishing and/or monitoring a predetermined filling level in a container, in which a mechanical oscillatory structure, which is fitted at the level of the predetermined filling level, is excited to produce oscillations by a single piezoelectric element. This element picks up the oscilla-tions of the mechanical oscillatory structure and con-verts them into an electrical reception signal. It therefore serves both as a transmitter and as a receiver and has a transmission electrode and a reception electrode.
These apparatuses are complex oscillatory systems which are each composed of a mechanical oscillatory structure, an electromechanical transducer and the control loop. The individual components are not completely isolated elec-trically and separated mechanically from one another.
Both electrical and mechanical coupling occurs.
Consequently, the reception signal comprises not only the desired measurement signal, which is ascribed to the oscillation of the respective mechanical oscillatory structure, but also additional signals produced by the aforementioned coupling.
To date, it has not been possible to employ apparatuses of this type additionally for measurements in highly viscous media or in hydrous or viscous foams, since CA 0223S037 1998-04-1~
.
05.04.1997 - a control loop, which regulates a phase difference existing between the electrical transmission signal and the electrical reception signal to a specific, constant value at which the oscillatory structure oscillates at a resonant frequency.
The control loop is formed, for example, by amplifying the reception signal and feeding it back via a phase shifter to the transmission signal.
DE-C 195 23 461 describes an apparatus for establishing and/or monitoring a predetermined filling level in a container, in which a mechanical oscillatory structure, which is fitted at the level of the predetermined filling level, is excited to produce oscillations by a single piezoelectric element. This element picks up the oscilla-tions of the mechanical oscillatory structure and con-verts them into an electrical reception signal. It therefore serves both as a transmitter and as a receiver and has a transmission electrode and a reception electrode.
These apparatuses are complex oscillatory systems which are each composed of a mechanical oscillatory structure, an electromechanical transducer and the control loop. The individual components are not completely isolated elec-trically and separated mechanically from one another.
Both electrical and mechanical coupling occurs.
Consequently, the reception signal comprises not only the desired measurement signal, which is ascribed to the oscillation of the respective mechanical oscillatory structure, but also additional signals produced by the aforementioned coupling.
To date, it has not been possible to employ apparatuses of this type additionally for measurements in highly viscous media or in hydrous or viscous foams, since CA 0223S037 1998-04-1~
.
- 3 - E+H 309 EP
05.04.1997 reliable excitation of the mechanical oscillatory structure to produce oscillations at the resonant frequency is not ensured in these applications.
The fixed value of the phase difference corresponds to the resonance of the system when the oscillatory struc-ture oscillates in gases or in liquids. However, if the oscillation quality of the apparatus is reduced for any reason, then the consequence of this is that the fixed value of the phase difference no longer exists. There is no frequency at which the mechanical oscillatory struc-ture executes oscillations having an amplitude other than zero and the phase difference has the fixed value. This phase difference cannot be set by the control loop.
Incorrect functioning consequently occurs.
A reduction in the oscillation quality occurs, for example, when the movement of the mechanical oscillatory structure is attenuated, for example by the latter being immersed in a viscous medium or in a liquid-cont~;n;ng or viscous foam. Furthermore, the oscillation quality is reduced by energy losses within the apparatus, for example due to instances of material fatigue or instances of asymmetry, for example on account of asymmetrical deposit formation, which lead to asymmetrical restoring forces. In principle, any type of energy 1088, be it oscillation energy released to a charge material or energy released to the container via a fastening of the apparatus, leads to a reduction in the oscillation quality.
One object of the invention is to specify an apparatus for establishing and/or monitoring a predetermined filling level in a container, in which the reception signal is as far as possible identical to the desired measurement signal and does not contain any additional signals caused by coupling.
05.04.1997 reliable excitation of the mechanical oscillatory structure to produce oscillations at the resonant frequency is not ensured in these applications.
The fixed value of the phase difference corresponds to the resonance of the system when the oscillatory struc-ture oscillates in gases or in liquids. However, if the oscillation quality of the apparatus is reduced for any reason, then the consequence of this is that the fixed value of the phase difference no longer exists. There is no frequency at which the mechanical oscillatory struc-ture executes oscillations having an amplitude other than zero and the phase difference has the fixed value. This phase difference cannot be set by the control loop.
Incorrect functioning consequently occurs.
A reduction in the oscillation quality occurs, for example, when the movement of the mechanical oscillatory structure is attenuated, for example by the latter being immersed in a viscous medium or in a liquid-cont~;n;ng or viscous foam. Furthermore, the oscillation quality is reduced by energy losses within the apparatus, for example due to instances of material fatigue or instances of asymmetry, for example on account of asymmetrical deposit formation, which lead to asymmetrical restoring forces. In principle, any type of energy 1088, be it oscillation energy released to a charge material or energy released to the container via a fastening of the apparatus, leads to a reduction in the oscillation quality.
One object of the invention is to specify an apparatus for establishing and/or monitoring a predetermined filling level in a container, in which the reception signal is as far as possible identical to the desired measurement signal and does not contain any additional signals caused by coupling.
- 4 - E+H 309 EP
05.04.1997 A further object of the invention con~ists in specifying an apparatus of this type in which a fixed phase dif-ference, which is independent of the oscillation quality of the apparatus, exists between the transmission signal and the reception signal at the resonant frequency of the mechanical oscillatory structure.
This is achieved according to the invention by means of an apparatus for establishing and/or monitoring a predetermined filling level in a container, which appara-tus comprises:
- a mechanical oscillatory structure, which is fitted at the level of the predetermined filling level, - a piezoelectric element, -- which excites the oscillatory structure to produce oscillations and pickR up its oscillations, -- which has at least three regionR, --- a first region having a reception electrode, a second region having a first transmission electrode and a third region having a second transmission electrode, - the two transmission electrodes having an identical form and being arranged symmetrically with respect to one another and to the reception electrode, - in the first and in the second region, the piezoelectric element having a polarization which i~
in the opposite direction to a polarization of the third region, and - a first transmission signal being applied to the first transmission electrode, which first transmission signal has the same amplitude as and is in antiphase with a second transmission Rignal, which is applied to the ~econd transmission electrode.
In accordance with one embodiment of the invention, a control loop i8 provided, which regulates a phase difference existing between the first tran~mission signal CA 0223~037 l998-04-l~
05.04.1997 A further object of the invention con~ists in specifying an apparatus of this type in which a fixed phase dif-ference, which is independent of the oscillation quality of the apparatus, exists between the transmission signal and the reception signal at the resonant frequency of the mechanical oscillatory structure.
This is achieved according to the invention by means of an apparatus for establishing and/or monitoring a predetermined filling level in a container, which appara-tus comprises:
- a mechanical oscillatory structure, which is fitted at the level of the predetermined filling level, - a piezoelectric element, -- which excites the oscillatory structure to produce oscillations and pickR up its oscillations, -- which has at least three regionR, --- a first region having a reception electrode, a second region having a first transmission electrode and a third region having a second transmission electrode, - the two transmission electrodes having an identical form and being arranged symmetrically with respect to one another and to the reception electrode, - in the first and in the second region, the piezoelectric element having a polarization which i~
in the opposite direction to a polarization of the third region, and - a first transmission signal being applied to the first transmission electrode, which first transmission signal has the same amplitude as and is in antiphase with a second transmission Rignal, which is applied to the ~econd transmission electrode.
In accordance with one embodiment of the invention, a control loop i8 provided, which regulates a phase difference existing between the first tran~mission signal CA 0223~037 l998-04-l~
- 5 - E+H 3 0 9 EP
05 . 04 . 1997 and the reception signal to a specific, constant value at which the oscillatory structure oscillates at a resonant frequency.
In accordance with a further embodiment, a reference electrode connected to a reference potential is arranged on the piezoelectric element.
In accordance with a further embodiment, the piezoelectric element is in the form of a disk and the reception electrode and the two transmission electrodes are arranged on a circle surface of said element.
In accordance with a further P~hodiment, the two transmission electrodes are annulus segments and are arranged on annulus segments of the circle surface which are diametrically opposite one another.
15 In accordance with a further embodiment, the first transmission signal is applied to an invertor and the second transmission signal is equal to an output signal of the invertor.
The invention and further advantages will now be explained in more detail with reference to the figures of the drawing, in which figures an exemplary embodiment is illustrated; identical elements are provided with identi-cal reference symbols in the figures.
Figure 1 shows a longit~ l section through a mechani-cal oscillatory structure having a piezoelectric element;
Figure 2 shows a diagrammatic illustration of the piezo-electric element of Figure 1 and a circuit connected thereto;
Figure 3 shows an inventive arrangement of the tran~mis-CA 0223~037 1998-04-1~
-- 6 - E+H 309 EP
05.04.1997 sion and reception electrodes;
Figure 4a shows the amplitude of the measured signal as a function of the frequency for a high and for a low oscillation quality;
Figure 4b shows the phase of the measurement signal as a function of the frequency for a high and for a low oscillation quality;
Figure 5a show6 the amplitude of an additional signal as a function of the frequency;
Figure 5b shows the phase of a first additional signal as a function of the frequency;
Figure 6a shows the amplitude of the reception signal as a function of the frequency for a high and for a low oscillation quality;
Figure 6b shows the phase of the reception signal as a function of the frequency for a high and for a low oscillation quality.
Figure 1 shows a longitll~;nAl section through an exem-plary embodiment of a mechanical oscillatory structure 1.
It has an essentially cylindrical housing 11, which is closed off flush at the front by a circular diaphragm 12.
A thread 13 is integrally formed on the housing 11, by means of which thread the apparatus can be screwed into an opening (not illustrated), which is arranged at the level of the predetermined filling level, in a container.
Other fastening methods which are known to a person skilled in the art, for example by means of flanges integrally formed on the housing 11, can likewise be employed.
Two oscillating bars 14 which point into the cont~;ner CA 0223~037 1998-04-1~
05 . 04 . 1997 and the reception signal to a specific, constant value at which the oscillatory structure oscillates at a resonant frequency.
In accordance with a further embodiment, a reference electrode connected to a reference potential is arranged on the piezoelectric element.
In accordance with a further embodiment, the piezoelectric element is in the form of a disk and the reception electrode and the two transmission electrodes are arranged on a circle surface of said element.
In accordance with a further P~hodiment, the two transmission electrodes are annulus segments and are arranged on annulus segments of the circle surface which are diametrically opposite one another.
15 In accordance with a further embodiment, the first transmission signal is applied to an invertor and the second transmission signal is equal to an output signal of the invertor.
The invention and further advantages will now be explained in more detail with reference to the figures of the drawing, in which figures an exemplary embodiment is illustrated; identical elements are provided with identi-cal reference symbols in the figures.
Figure 1 shows a longit~ l section through a mechani-cal oscillatory structure having a piezoelectric element;
Figure 2 shows a diagrammatic illustration of the piezo-electric element of Figure 1 and a circuit connected thereto;
Figure 3 shows an inventive arrangement of the tran~mis-CA 0223~037 1998-04-1~
-- 6 - E+H 309 EP
05.04.1997 sion and reception electrodes;
Figure 4a shows the amplitude of the measured signal as a function of the frequency for a high and for a low oscillation quality;
Figure 4b shows the phase of the measurement signal as a function of the frequency for a high and for a low oscillation quality;
Figure 5a show6 the amplitude of an additional signal as a function of the frequency;
Figure 5b shows the phase of a first additional signal as a function of the frequency;
Figure 6a shows the amplitude of the reception signal as a function of the frequency for a high and for a low oscillation quality;
Figure 6b shows the phase of the reception signal as a function of the frequency for a high and for a low oscillation quality.
Figure 1 shows a longitll~;nAl section through an exem-plary embodiment of a mechanical oscillatory structure 1.
It has an essentially cylindrical housing 11, which is closed off flush at the front by a circular diaphragm 12.
A thread 13 is integrally formed on the housing 11, by means of which thread the apparatus can be screwed into an opening (not illustrated), which is arranged at the level of the predetermined filling level, in a container.
Other fastening methods which are known to a person skilled in the art, for example by means of flanges integrally formed on the housing 11, can likewise be employed.
Two oscillating bars 14 which point into the cont~;ner CA 0223~037 1998-04-1~
- 7 - E+H 309 EP
05 . 04 . 1997 are integrally formed on the diaphragm 12 on the outside of the housing 11. These bars are caused to oscillate perpendicularly to their longitudinal axis by means of a piezoelectric element 2 which is in the form of a disk 5 and is arranged on the diaphragm 12 in the interior of the housing 11.
However, the invention is not restricted to mechanical oscillatory systems having two oscillating bars; it can also be employed in limit switches which have only one or no oscillating bars. In the cases mentioned last, for - example only the oscillating diaphragm comes into contact with a charge material situated in the container.
It is also possible to employ apparatuses in which the piezoelectric element 2 i8 mounted on a second diaphragm, which is arranged parallel to the diaphragm which closes off the housing. In this case, the oscillation of the second diaphragm is transmitted to the diaphragm which closes off the housing in that, for example, the second diaphragm is clamped in or retained on its outer edge and a mechanical connection exists from its center to the center of the other diaphragm. This connection is, for example, a tensioning bolt connecting both diaphragms or a plunger integrally formed on the inner diaphragm.
If the housing 11 is composed of metal, then the piezo-electric element 2 can be fitted directly on the diaphragm 12, for example by bo~;ng. The housing, which is preferably grounded, then serves as a reference electrode.
If, on the other hand, the housing 11 is composed of an insulator, then a reference electrode 20 must be arranged between the diaphragm 12 and the piezoelectric element 2, which reference electrode must be connected to a reference potential, preferably to the ground potential.
Figure 2 shows a diagrammatic illustration of the piezo-CA 0223~037 1998-04-1~
05 . 04 . 1997 are integrally formed on the diaphragm 12 on the outside of the housing 11. These bars are caused to oscillate perpendicularly to their longitudinal axis by means of a piezoelectric element 2 which is in the form of a disk 5 and is arranged on the diaphragm 12 in the interior of the housing 11.
However, the invention is not restricted to mechanical oscillatory systems having two oscillating bars; it can also be employed in limit switches which have only one or no oscillating bars. In the cases mentioned last, for - example only the oscillating diaphragm comes into contact with a charge material situated in the container.
It is also possible to employ apparatuses in which the piezoelectric element 2 i8 mounted on a second diaphragm, which is arranged parallel to the diaphragm which closes off the housing. In this case, the oscillation of the second diaphragm is transmitted to the diaphragm which closes off the housing in that, for example, the second diaphragm is clamped in or retained on its outer edge and a mechanical connection exists from its center to the center of the other diaphragm. This connection is, for example, a tensioning bolt connecting both diaphragms or a plunger integrally formed on the inner diaphragm.
If the housing 11 is composed of metal, then the piezo-electric element 2 can be fitted directly on the diaphragm 12, for example by bo~;ng. The housing, which is preferably grounded, then serves as a reference electrode.
If, on the other hand, the housing 11 is composed of an insulator, then a reference electrode 20 must be arranged between the diaphragm 12 and the piezoelectric element 2, which reference electrode must be connected to a reference potential, preferably to the ground potential.
Figure 2 shows a diagrammatic illustration of the piezo-CA 0223~037 1998-04-1~
- 8 - E+H 309 EP
05.04.1997 electric element 2.
One reception electrode 21 and two transmission electrodes 22, 23 are arranged on a circle surface of the piezoelectric element 2 which is remote from the diaphragm. This is illustrated in Figure 3. The reception electrode 21 is connected to a reception signal line 5, via which a reception signal E is available. The two transmission electrodes 22, 23 are respectively connected to a transmission signal line 221, 231. Transmission signals Sl, S2, for example AC voltages, present on these transmission signal lines 211, 231 cau8e the piezoelectric element 2 and the diaphragm 12, which is permanently connected thereto, to produce flexural vibrations. This causes the oscillating bars 14, which are integrally formed on the diaphragm 12 at their ends, to produce oscillations perpendicular to their longitudinal axis.
Conversely, an oscillation of the oscillating bars 14 effects a flexural vibration of the diaphragm 12 and of the piezoelectric element 2 which is permanently connected thereto.
The reception signal E has an amplitude A which is larger, the larger the mechanical oscillation amplitude of the oscillating bars 14 is. Exploiting this fact, the apparatus is preferably operated at its resonant ~requency fr. The mechanical oscillation amplitude has a m~Y~ ~ at the resonant frequency fr.
If a harmonic oscillator i~ considered as an example of an ideal oscillatory system, then its oscillation amplitude has a single maximum as a function of the oscillation frequency. The phase difference between the oscillation excitation and the oscillation of the oscillator experiences a sudden phase change of 180~ in the region of this maximum. At the resonant frequency, CA 0223~037 l998-04-l~
05.04.1997 electric element 2.
One reception electrode 21 and two transmission electrodes 22, 23 are arranged on a circle surface of the piezoelectric element 2 which is remote from the diaphragm. This is illustrated in Figure 3. The reception electrode 21 is connected to a reception signal line 5, via which a reception signal E is available. The two transmission electrodes 22, 23 are respectively connected to a transmission signal line 221, 231. Transmission signals Sl, S2, for example AC voltages, present on these transmission signal lines 211, 231 cau8e the piezoelectric element 2 and the diaphragm 12, which is permanently connected thereto, to produce flexural vibrations. This causes the oscillating bars 14, which are integrally formed on the diaphragm 12 at their ends, to produce oscillations perpendicular to their longitudinal axis.
Conversely, an oscillation of the oscillating bars 14 effects a flexural vibration of the diaphragm 12 and of the piezoelectric element 2 which is permanently connected thereto.
The reception signal E has an amplitude A which is larger, the larger the mechanical oscillation amplitude of the oscillating bars 14 is. Exploiting this fact, the apparatus is preferably operated at its resonant ~requency fr. The mechanical oscillation amplitude has a m~Y~ ~ at the resonant frequency fr.
If a harmonic oscillator i~ considered as an example of an ideal oscillatory system, then its oscillation amplitude has a single maximum as a function of the oscillation frequency. The phase difference between the oscillation excitation and the oscillation of the oscillator experiences a sudden phase change of 180~ in the region of this maximum. At the resonant frequency, CA 0223~037 l998-04-l~
- 9 - E+E 309 EP
05 . 04 . 1997 the oscillation amplitude is a maximum and the phase difference is 90~.
In apparatuses of this type, such as are disclosed in the prior art, just one transmission electrode and just one reception electrode are usually provided. Such an apparatus is made to oscillate at its resonant ~requency fr by providing a control loop which regulates a phase difference exi~ting between the electrical transmission signal and an electrode signal to a specific, constant value.
In a harmonic oscillator, attenuation or reduction of the oscillation guality effects a reduction in the maximum amplitude in the case of resonance. In such a case, the phase increases as a function of the frequency proceeds continuously rather than abruptly, to be precise it proceeds all the more slowly, the greater the attenuation or the reduction of the oscillation quality is. Overall, however, even with very great attenuation, a phase change of a total of 180~ ensues and a phase difference of 90~
exists at the resonant frequency. The fixed value, correspo~;ng to resonance, of the phase difference of 90~ always exists and is assumed at the resonant frequency In contrast to an ideal oscillator, coupling of an 25 electrical and mechanical nature between the piezoelectric element 2, the transmission electrode, the reception electrode and the mechanical oscillatory 8tructure exists in the abovementioned apparatuses from the prior art.
Mechanical coupling of the kind that might occur, for example, due to bracing of the piezoelectric element 2 is negligibly slight in the case of apparatuses having only a single piezoelectric element 2 and is therefore not taken into account below.
CA 0223~037 1998-04-1~
05 . 04 . 1997 the oscillation amplitude is a maximum and the phase difference is 90~.
In apparatuses of this type, such as are disclosed in the prior art, just one transmission electrode and just one reception electrode are usually provided. Such an apparatus is made to oscillate at its resonant ~requency fr by providing a control loop which regulates a phase difference exi~ting between the electrical transmission signal and an electrode signal to a specific, constant value.
In a harmonic oscillator, attenuation or reduction of the oscillation guality effects a reduction in the maximum amplitude in the case of resonance. In such a case, the phase increases as a function of the frequency proceeds continuously rather than abruptly, to be precise it proceeds all the more slowly, the greater the attenuation or the reduction of the oscillation quality is. Overall, however, even with very great attenuation, a phase change of a total of 180~ ensues and a phase difference of 90~
exists at the resonant frequency. The fixed value, correspo~;ng to resonance, of the phase difference of 90~ always exists and is assumed at the resonant frequency In contrast to an ideal oscillator, coupling of an 25 electrical and mechanical nature between the piezoelectric element 2, the transmission electrode, the reception electrode and the mechanical oscillatory 8tructure exists in the abovementioned apparatuses from the prior art.
Mechanical coupling of the kind that might occur, for example, due to bracing of the piezoelectric element 2 is negligibly slight in the case of apparatuses having only a single piezoelectric element 2 and is therefore not taken into account below.
CA 0223~037 1998-04-1~
- 10 - E+H 309 EP
05.04.1997 Electrical coupling exists between the transmission electrode and the reference electrode, between the reception electrode and the reference electrode, and between the reception electrode and the transmission electrode. This can be illustrated, in the form of an equivalent circuit diagram, by the capacitances connecting the respective electrodes.
The effect of this capacitive coupling is that a signal El which differs from zero is present at the reception electrode even when the oscillating bars 14 are permanently restrained and the diaphragm 12 and the piezoelectric element 2 do not execute any mechanical motion.
The signal E1 present at a reception electrode is composed of two components, namely a measurement signal EM1 and an additional signal Eel1 governed by the electrical coupling.
El = EM1 + Eel1 The measurement signal EM1 is based on the oscillation of the mechanical oscillatory structure and has a frequency-dependent amplitude AM1(f) and a frequency-dependent phase ~Ml(f). Here phase in each case denotes the phase offset of the re~pective component of the electrical signal E1 with reference to the electrical transmission signal.
Figure 4a ~hows the amplitude AMl(f) and Figure 4b the phase ~M1(f) of the measurement signal EM1 as a function of the frequency f. The curves can be determined computa-tionally by simulation calculations, for example by finite element calculations.
They can be measured experimentally by connecting the transmission signal line to a frequency generator and by CA 0223~037 1998-04-1~
05.04.1997 Electrical coupling exists between the transmission electrode and the reference electrode, between the reception electrode and the reference electrode, and between the reception electrode and the transmission electrode. This can be illustrated, in the form of an equivalent circuit diagram, by the capacitances connecting the respective electrodes.
The effect of this capacitive coupling is that a signal El which differs from zero is present at the reception electrode even when the oscillating bars 14 are permanently restrained and the diaphragm 12 and the piezoelectric element 2 do not execute any mechanical motion.
The signal E1 present at a reception electrode is composed of two components, namely a measurement signal EM1 and an additional signal Eel1 governed by the electrical coupling.
El = EM1 + Eel1 The measurement signal EM1 is based on the oscillation of the mechanical oscillatory structure and has a frequency-dependent amplitude AM1(f) and a frequency-dependent phase ~Ml(f). Here phase in each case denotes the phase offset of the re~pective component of the electrical signal E1 with reference to the electrical transmission signal.
Figure 4a ~hows the amplitude AMl(f) and Figure 4b the phase ~M1(f) of the measurement signal EM1 as a function of the frequency f. The curves can be determined computa-tionally by simulation calculations, for example by finite element calculations.
They can be measured experimentally by connecting the transmission signal line to a frequency generator and by CA 0223~037 1998-04-1~
- 11 - E+H 309 EP
05.04.1997 deter~;n;ng the phase and amplitude of the oscillation of the oscillating bars 14 as a function of the frequency of the frequency generator, using a laser vibrometer, for example.
In both Figures 4a, 4b, the continuous line corresponds to an apparatus having a high oscillation quality and the dashed line corresponds to an apparatus having a low oscillation quality. In both cases, both the amplitude AM1 ( f) and the phase ~M1 ( f) of the measurement signal have the profile which is typical of a harmonic oscilla-tor and has already been described above.
The additional signal Ee11 has an essentially constant amplitude Ae11 and an essentially constant phase ~ell. In this case, too, phase denotes the phase offset of the respective component of the electrical signal B1 with reference to the electrical transmission signal.
The continuous line in Figure 5a shows the amplitude Aell and the continuous line in Figure 5b the phase ~ell of the additional signal Eel1 as a function of the frequency f. These curves can also be determined by simulation calculations. They can be picked up experimentally, for example, by employing a non-polarized, piezoelectric element. In the case of the latter, no mechanical motion at all is produced by a transmission signal and the signal E1 consequently corresponds to the additional signal Eell which is based on electrical coupling. The latter signal can be measured by means of an oscillo-scope.
The amplitude Ael1 and the phases ~ell of the additional 3 0 signal Ee11 are unambiguously related to the mechanical structure of the respective apparatus and the electrical properties thereof. In the example, shown in Figures 4a, 4b, 5a, 5b, 6a and 6b, of an apparatus from the prior art as described at the beginning, the additional signal Ee11 CA 0223S037 1998-04-lS
05.04.1997 deter~;n;ng the phase and amplitude of the oscillation of the oscillating bars 14 as a function of the frequency of the frequency generator, using a laser vibrometer, for example.
In both Figures 4a, 4b, the continuous line corresponds to an apparatus having a high oscillation quality and the dashed line corresponds to an apparatus having a low oscillation quality. In both cases, both the amplitude AM1 ( f) and the phase ~M1 ( f) of the measurement signal have the profile which is typical of a harmonic oscilla-tor and has already been described above.
The additional signal Ee11 has an essentially constant amplitude Ae11 and an essentially constant phase ~ell. In this case, too, phase denotes the phase offset of the respective component of the electrical signal B1 with reference to the electrical transmission signal.
The continuous line in Figure 5a shows the amplitude Aell and the continuous line in Figure 5b the phase ~ell of the additional signal Eel1 as a function of the frequency f. These curves can also be determined by simulation calculations. They can be picked up experimentally, for example, by employing a non-polarized, piezoelectric element. In the case of the latter, no mechanical motion at all is produced by a transmission signal and the signal E1 consequently corresponds to the additional signal Eell which is based on electrical coupling. The latter signal can be measured by means of an oscillo-scope.
The amplitude Ael1 and the phases ~ell of the additional 3 0 signal Ee11 are unambiguously related to the mechanical structure of the respective apparatus and the electrical properties thereof. In the example, shown in Figures 4a, 4b, 5a, 5b, 6a and 6b, of an apparatus from the prior art as described at the beginning, the additional signal Ee11 CA 0223S037 1998-04-lS
- 12 - E+H 309 EP
05.04.1997 has a phase of 0~.
Figure 6a shows the amplitude Al(f) and Figure 6b the phase ~1(f) of the signal El. The two curves result from the phase- and amplitude-accurate superposition of the two above-described component~ of the signal El.
Elei~l = AMleia~M1 + A llei~el1 Both curves each have four regions I, II, III, IV, which are described in a greatly simplified manner below.
In the outer regions I and IV, the additional signal E
has the lar~er amplitude Ael1 and is consequently predomi-nant. Consequently, the resulting phase ~1 essentially corresponds to the phase of the additional signal ~ell.
In the regions I and II, the two signals are in phase and are added. The amplitude El rises continuously in these regions and has a m~Y;~ll~ at the resonant frequency fr.
The ~ignals are in antiphase in the regions III and IV.
The amplitude Al decreases in the region III. It is zero at the upper region boundary. At this frequency, which is referred to as the antiresonant frequency farl below, the measurement signal EM1 and the additional signal Eell have the same amplitude and opposite phases. The amplitude A
rises again in the region IV.
The phase ~1 is 0~ in the regions I, II and IV and 180~
in the region III.
Without precise knowledge of the additional signal Eell, the measurement signal EM1 cannot be determined from the signal El of the reception electrode.
If the situation now arises where the mechanical oscilla-tory structure is damped or has a reduced 06cillation quality, then the amplitude AMl(f) and phase ~M1(f) of CA 0223~037 1998-04-1~
05.04.1997 has a phase of 0~.
Figure 6a shows the amplitude Al(f) and Figure 6b the phase ~1(f) of the signal El. The two curves result from the phase- and amplitude-accurate superposition of the two above-described component~ of the signal El.
Elei~l = AMleia~M1 + A llei~el1 Both curves each have four regions I, II, III, IV, which are described in a greatly simplified manner below.
In the outer regions I and IV, the additional signal E
has the lar~er amplitude Ael1 and is consequently predomi-nant. Consequently, the resulting phase ~1 essentially corresponds to the phase of the additional signal ~ell.
In the regions I and II, the two signals are in phase and are added. The amplitude El rises continuously in these regions and has a m~Y;~ll~ at the resonant frequency fr.
The ~ignals are in antiphase in the regions III and IV.
The amplitude Al decreases in the region III. It is zero at the upper region boundary. At this frequency, which is referred to as the antiresonant frequency farl below, the measurement signal EM1 and the additional signal Eell have the same amplitude and opposite phases. The amplitude A
rises again in the region IV.
The phase ~1 is 0~ in the regions I, II and IV and 180~
in the region III.
Without precise knowledge of the additional signal Eell, the measurement signal EM1 cannot be determined from the signal El of the reception electrode.
If the situation now arises where the mechanical oscilla-tory structure is damped or has a reduced 06cillation quality, then the amplitude AMl(f) and phase ~M1(f) of CA 0223~037 1998-04-1~
- 13 - E~H 309 EP
05.04.1997 the measurement signal exhibit the profile illustrated by dashed lines in Figures 4a and 4b. The amplitude AMl(f) rises and falls considerably more slowly with the frequency and has a distinctly lower maximum value. The phase ~Ml ( f) does not exhibit a sudden pha~e change, but rather rises continuously with the frequency. The greater the reduction in the oscillation quality of the system is, the lower the maximum value of the amplitude i8 and the lower the gradient of the phase is. However, the phase ~Ml (f) always reaches the values 0~ and 180~
asymptotically and it is still 90~ at the resonant frequency. The additional signal Eell r~mA;n~ unchanged.
The amplitude Al(f) and phase ~l(f) of the reception signal El resulting from the amplitude- and phase-accurate superposition of the two components clearlydiffer from the case mentioned fir6t, in which there was no reduction in the oscillation quality. The maxima of the amplitude Al(f) are a great deal less pronounced and the pha~e ~l(f) has two continuous phase changes in opposite directions to one another instead of the two sudden phase changes each of 180~ in opposite directions to one another. The m~Y; phase difference is clearly less than 180~. Dep~n~;ng on the oscillation quality of the system, it is even less than 90~.
If, therefore, damping of the mechanical oscillatory structure, for example in foam or in a viscous medium, or a different type of reduction in the oscillation quality of the system, occurs, then the phase difference ~1 between the electrical transmission signal and the electrical signal El admittedly still has, as a function of the frequency, two continuous phase changes in oppo-site directions to one another, but the m~Y;mllm phase difference may be very ~mall. The maximum phase differ-ence is smaller, the smaller the interval between the re~onant frequency fr and the antiresonant frequency far is.
CA 0223~037 1998-04-1~
05.04.1997 the measurement signal exhibit the profile illustrated by dashed lines in Figures 4a and 4b. The amplitude AMl(f) rises and falls considerably more slowly with the frequency and has a distinctly lower maximum value. The phase ~Ml ( f) does not exhibit a sudden pha~e change, but rather rises continuously with the frequency. The greater the reduction in the oscillation quality of the system is, the lower the maximum value of the amplitude i8 and the lower the gradient of the phase is. However, the phase ~Ml (f) always reaches the values 0~ and 180~
asymptotically and it is still 90~ at the resonant frequency. The additional signal Eell r~mA;n~ unchanged.
The amplitude Al(f) and phase ~l(f) of the reception signal El resulting from the amplitude- and phase-accurate superposition of the two components clearlydiffer from the case mentioned fir6t, in which there was no reduction in the oscillation quality. The maxima of the amplitude Al(f) are a great deal less pronounced and the pha~e ~l(f) has two continuous phase changes in opposite directions to one another instead of the two sudden phase changes each of 180~ in opposite directions to one another. The m~Y; phase difference is clearly less than 180~. Dep~n~;ng on the oscillation quality of the system, it is even less than 90~.
If, therefore, damping of the mechanical oscillatory structure, for example in foam or in a viscous medium, or a different type of reduction in the oscillation quality of the system, occurs, then the phase difference ~1 between the electrical transmission signal and the electrical signal El admittedly still has, as a function of the frequency, two continuous phase changes in oppo-site directions to one another, but the m~Y;mllm phase difference may be very ~mall. The maximum phase differ-ence is smaller, the smaller the interval between the re~onant frequency fr and the antiresonant frequency far is.
CA 0223~037 1998-04-1~
- 14 - E+H 309 EP
05.04.1997 By means of the control loop, of the kind which can be found in the prior art, the mechanical oscillatory system iB excited to produce oscillations at the resonant frequency fr~ in that a fixed phase relationship, corresponding to resonance, between the transmission signal and the signal El is established. In order that the apparatus described is functional in the uncovered state in conjunction with a high oscillation quality, the fixed phase difference ~R is 90~ in the case of the exemplary embodiment shown here.
If the previously described situation where the phase (f) of the signal no longer assumes this fixed value ~R over the entire frequency range now occurs on account of the properties of the charge material or on account of a reduction in the oscillation quality of the apparatus, then reliable excitation of the mechanical oscillatory system is no longer possible. The apparatus is consequently not functional.
In contrast, an apparatus according to the invention not only generates an uncorrupted reception signal E, but is still functional even when the previously described apparatuses according to the prior art fail.
This is achieved according to the invention by virtue of the fact that the piezoelectric element 2 has at least three regions. The reception electrode 21 is arranged on a first region I, and the transmission electrodes 22, 23 are arranged on a second and a third region II, III, respectively. The piezoelectric element 2 is in the form of a di~k and the reception electrode 21 and the two transmission electrodes 22, 23 are arranged on a circle surface of said element.
The two transmission electrodes 22, 23 have an identical form and are arranged symmetrically with respect to one another and with respect to the reception electrode 21.
CA 0223~037 1998-04-1~
05.04.1997 By means of the control loop, of the kind which can be found in the prior art, the mechanical oscillatory system iB excited to produce oscillations at the resonant frequency fr~ in that a fixed phase relationship, corresponding to resonance, between the transmission signal and the signal El is established. In order that the apparatus described is functional in the uncovered state in conjunction with a high oscillation quality, the fixed phase difference ~R is 90~ in the case of the exemplary embodiment shown here.
If the previously described situation where the phase (f) of the signal no longer assumes this fixed value ~R over the entire frequency range now occurs on account of the properties of the charge material or on account of a reduction in the oscillation quality of the apparatus, then reliable excitation of the mechanical oscillatory system is no longer possible. The apparatus is consequently not functional.
In contrast, an apparatus according to the invention not only generates an uncorrupted reception signal E, but is still functional even when the previously described apparatuses according to the prior art fail.
This is achieved according to the invention by virtue of the fact that the piezoelectric element 2 has at least three regions. The reception electrode 21 is arranged on a first region I, and the transmission electrodes 22, 23 are arranged on a second and a third region II, III, respectively. The piezoelectric element 2 is in the form of a di~k and the reception electrode 21 and the two transmission electrodes 22, 23 are arranged on a circle surface of said element.
The two transmission electrodes 22, 23 have an identical form and are arranged symmetrically with respect to one another and with respect to the reception electrode 21.
CA 0223~037 1998-04-1~
- 15 - E+H 309 EP
05.04.1997 As can be discerned from Figure 3, the reception electrode 21 i6 arranged in the center of the piezoelectric element 2 and is circular. The two transmission electrodes 22, 23 are annulus segments. They are situated on mutually diametrically opposite annulus segments of the circle surface on both sides of the reception electrode 21.
In the first and in the second region I, II, the piezoelectric element 2 has a polarization which runs parallel to the axis of symmetry, that iB to say perpendicular to the circle surface, of the piezoelectric element 2. The third region III has a polarization which is in the opposite direction to that of the two regions I and II. The polarization directions are indicated by arrows in Figure 2 and by the symbols + and - in Figure 3.
A first transmiBsion Bignal sl i8 applied to the first transmission electrode 22 via the first transmission signal line 221. This signal iB additionally applied to an invertor 3. The invertor 3 is, for example, a transistor, an operational amplifier or a digital invertor. The output of the invertor 3 is connected via the second transmission signal line 231 to the second transmission electrode 23. AB a result, a second signal S2 is applied to the second transmission electrode 23, which second signal has the same amplitude as and iB in antipha~e with a first transmission signal S1 applied to the first transmission electrode 22. The two transmission electrodes 22, 23 are therefore exited in antiphase. On account of the opposite polarization in the associated regions II, III, this excitation in antiphase leads to a uniform flexural vibration of the composite element comprising the piezoelectric element 2 and the diaphragm 12.
In the apparatus according to the invention, phase or CA 0223~037 1998-04-1~
05.04.1997 As can be discerned from Figure 3, the reception electrode 21 i6 arranged in the center of the piezoelectric element 2 and is circular. The two transmission electrodes 22, 23 are annulus segments. They are situated on mutually diametrically opposite annulus segments of the circle surface on both sides of the reception electrode 21.
In the first and in the second region I, II, the piezoelectric element 2 has a polarization which runs parallel to the axis of symmetry, that iB to say perpendicular to the circle surface, of the piezoelectric element 2. The third region III has a polarization which is in the opposite direction to that of the two regions I and II. The polarization directions are indicated by arrows in Figure 2 and by the symbols + and - in Figure 3.
A first transmiBsion Bignal sl i8 applied to the first transmission electrode 22 via the first transmission signal line 221. This signal iB additionally applied to an invertor 3. The invertor 3 is, for example, a transistor, an operational amplifier or a digital invertor. The output of the invertor 3 is connected via the second transmission signal line 231 to the second transmission electrode 23. AB a result, a second signal S2 is applied to the second transmission electrode 23, which second signal has the same amplitude as and iB in antipha~e with a first transmission signal S1 applied to the first transmission electrode 22. The two transmission electrodes 22, 23 are therefore exited in antiphase. On account of the opposite polarization in the associated regions II, III, this excitation in antiphase leads to a uniform flexural vibration of the composite element comprising the piezoelectric element 2 and the diaphragm 12.
In the apparatus according to the invention, phase or CA 0223~037 1998-04-1~
- 16 - E+H 309 EP
05.04.1997 phase difference in each case denotes the phase offset between the reception signal E and one of the two transmission signals Sl or S2. Since a fixed, constant phase relationship exists between the two transmission signals S1 and S2, both signals can equally be used as reference signal.
As already explained at the beg; nn; ng in connection with the prior art, the reception signal E of the reception electrode 21 is also composed of a measurement signal EM
and additional signals which are governed by essentially capacitive coupling. The polarization direction of the individual regions I, II, III is unimportant for the additional signals, which are produced by capacitive coupling. Figure 2 illustrates an equivalent circuit diagram of the piezoelectric element 2. According to this, a capacitance Cl exists between the first transmission electrode 21 and the reference electrode 20.
Due to the symmetry, the same capacitance C1 also exists between the second transmission electrode 23 and the reference electrode 20. A capacitance C2 exists between the reception electrode 21 and the reference electrode 20. A capacitance C exists between each transmission electrode 22, 23 and the reception electrode 21. The equivalent circuit diagram is thus symmetrical with respect to the axis of symmetry of the piezoelectric element 2. Two additional signals Eell and Eel2 are consequently superposed at the reception electrode 21, of which additional signals a first Eell is attributed to capacitive coupling of the fir~t transmission electrode 22 and a second Eel2 is attributed to capacitive coupling of the second transmission electrode 23. Since the arrangement is symmetrical, the two additional signals Eell, Eel2 have the same amplitudes. On account of the amplitude identity and the in-antiphase nature of the two transmission signals Sl and S2, the two additional signals Eell~ Eel2 are, however, in antiphase. The superposition of the two additional signals Eell, Eel2 CA 0223~037 1998-04-1~
05.04.1997 phase difference in each case denotes the phase offset between the reception signal E and one of the two transmission signals Sl or S2. Since a fixed, constant phase relationship exists between the two transmission signals S1 and S2, both signals can equally be used as reference signal.
As already explained at the beg; nn; ng in connection with the prior art, the reception signal E of the reception electrode 21 is also composed of a measurement signal EM
and additional signals which are governed by essentially capacitive coupling. The polarization direction of the individual regions I, II, III is unimportant for the additional signals, which are produced by capacitive coupling. Figure 2 illustrates an equivalent circuit diagram of the piezoelectric element 2. According to this, a capacitance Cl exists between the first transmission electrode 21 and the reference electrode 20.
Due to the symmetry, the same capacitance C1 also exists between the second transmission electrode 23 and the reference electrode 20. A capacitance C2 exists between the reception electrode 21 and the reference electrode 20. A capacitance C exists between each transmission electrode 22, 23 and the reception electrode 21. The equivalent circuit diagram is thus symmetrical with respect to the axis of symmetry of the piezoelectric element 2. Two additional signals Eell and Eel2 are consequently superposed at the reception electrode 21, of which additional signals a first Eell is attributed to capacitive coupling of the fir~t transmission electrode 22 and a second Eel2 is attributed to capacitive coupling of the second transmission electrode 23. Since the arrangement is symmetrical, the two additional signals Eell, Eel2 have the same amplitudes. On account of the amplitude identity and the in-antiphase nature of the two transmission signals Sl and S2, the two additional signals Eell~ Eel2 are, however, in antiphase. The superposition of the two additional signals Eell, Eel2 CA 0223~037 1998-04-1~
- 17 - E+H 309 EP
~ 05.0~.1997 consequently means that the two signals Eell, Eel2 cancel one another out.
By this means, a reception signal E which corresponds in a completely uncorrupted manner to the desired measurement signal and in which no additional signals at all are contained is available at the reception electrode 21.
The amplitude A and phase ~ of the reception signal E
have, as a function of the frequency, exactly like the measurement signal EM~ the profile which is typical of a harmonic oscillator.
As a result, the ~ame fixed value of the phase difference ~R between the first transmission signal Sl and the reception signal E is always present at the resonant frequency fr of the mechanical oscillatory structure 1, irrespective of the oscillation quality of the system.
The reception signal E i8 thus outst~n~;n~ly suitable for the operation of a control loop which is used for setting the fixed phase relationship ~R between the first transmission signal S1 and the reception signal E.
An exemplary embodiment of a control loop of this type is illustrated in Figure 2. In that case, the reception signal E is fed back to the first transmission signal S1 via the reception signal line 6, via an amplifier 7 and a phase shifter 8, which shifts its phase by the specific, constant value ~R . The amplifier 7 should be ~;mensioned such that the self-excitation condition i8 satisfied. The mechanical oscillatory structure is concequently excited by means of the piezoelectric element 2 to produce oscillations at its resonant frequency fr.
If the oscillatory structure i8 covered by the charge material, then the resonant frequency f r has a lower CA 0223~037 1998-04-1~
~ 05.0~.1997 consequently means that the two signals Eell, Eel2 cancel one another out.
By this means, a reception signal E which corresponds in a completely uncorrupted manner to the desired measurement signal and in which no additional signals at all are contained is available at the reception electrode 21.
The amplitude A and phase ~ of the reception signal E
have, as a function of the frequency, exactly like the measurement signal EM~ the profile which is typical of a harmonic oscillator.
As a result, the ~ame fixed value of the phase difference ~R between the first transmission signal Sl and the reception signal E is always present at the resonant frequency fr of the mechanical oscillatory structure 1, irrespective of the oscillation quality of the system.
The reception signal E i8 thus outst~n~;n~ly suitable for the operation of a control loop which is used for setting the fixed phase relationship ~R between the first transmission signal S1 and the reception signal E.
An exemplary embodiment of a control loop of this type is illustrated in Figure 2. In that case, the reception signal E is fed back to the first transmission signal S1 via the reception signal line 6, via an amplifier 7 and a phase shifter 8, which shifts its phase by the specific, constant value ~R . The amplifier 7 should be ~;mensioned such that the self-excitation condition i8 satisfied. The mechanical oscillatory structure is concequently excited by means of the piezoelectric element 2 to produce oscillations at its resonant frequency fr.
If the oscillatory structure i8 covered by the charge material, then the resonant frequency f r has a lower CA 0223~037 1998-04-1~
- 18 - E+H 309 EP
05.04.1997 value than if the oscillatory structure oscillates freely. The fixed value of the phase difference is independent of whether or not the oscillatory structure is covered by the charge material.
The reception signal E is furthermore applied via the amplifier 7, the phase shifter 8 and the invertor 3 to the input of an evaluation unit 9. It is also possible to apply the unamplified, non-inverted reception signal E
directly to the input. However, the obvious choice i8 to use the amplified signal. The inversion and the phase shifting do not have an adverse effect on the frequency of this signal.
Its frequency is determined by means of a frequency-measuring circuit 91 and the result i8 fed to a comparator 92. The latter compares the measured frequency with a reference frequency fR stored in a memory. If the measured frequency iB less than the reference frequency fR, the evaluation unit 9 emits an output signal which indicates that the mechanical oscillatory structure is covered by a charge material. If the frequency has a value which is greater than the reference frequency fR, then the evaluation unit 9 emits an output signal which indicates that the mechanical oscillatory structure is not covered by the charge material.
05.04.1997 value than if the oscillatory structure oscillates freely. The fixed value of the phase difference is independent of whether or not the oscillatory structure is covered by the charge material.
The reception signal E is furthermore applied via the amplifier 7, the phase shifter 8 and the invertor 3 to the input of an evaluation unit 9. It is also possible to apply the unamplified, non-inverted reception signal E
directly to the input. However, the obvious choice i8 to use the amplified signal. The inversion and the phase shifting do not have an adverse effect on the frequency of this signal.
Its frequency is determined by means of a frequency-measuring circuit 91 and the result i8 fed to a comparator 92. The latter compares the measured frequency with a reference frequency fR stored in a memory. If the measured frequency iB less than the reference frequency fR, the evaluation unit 9 emits an output signal which indicates that the mechanical oscillatory structure is covered by a charge material. If the frequency has a value which is greater than the reference frequency fR, then the evaluation unit 9 emits an output signal which indicates that the mechanical oscillatory structure is not covered by the charge material.
Claims (6)
1. An apparatus for establishing and/or monitoring a predetermined filling level in a container, which apparatus comprises:
- a mechanical oscillatory structure (1), which is fitted at the level of the predetermined filling level, - a piezoelectric element (2), -- which excites the oscillatory structure (1) to produce oscillations and picks up its oscillations, -- which has at least three regions, --- a first region (I) having a reception electrode (21), a second region (II) having a first transmission electrode (II) and a third region (III) having a second transmission electrode (23), - the two transmission electrodes (22, 23) having an identical form and being arranged symmetrically with respect to one another and to the reception electrode (21), - in the first and in the second region (I, II), the piezoelectric element (2) having a polarization which is in the opposite direction to a polarization of the third region (III), and - a first transmission signal (S1) being applied to the first transmission electrode (22), which first transmission signal has the same amplitude as and is in antiphase with a second transmission signal (S2), which is applied to the second transmission electrode (23).
- a mechanical oscillatory structure (1), which is fitted at the level of the predetermined filling level, - a piezoelectric element (2), -- which excites the oscillatory structure (1) to produce oscillations and picks up its oscillations, -- which has at least three regions, --- a first region (I) having a reception electrode (21), a second region (II) having a first transmission electrode (II) and a third region (III) having a second transmission electrode (23), - the two transmission electrodes (22, 23) having an identical form and being arranged symmetrically with respect to one another and to the reception electrode (21), - in the first and in the second region (I, II), the piezoelectric element (2) having a polarization which is in the opposite direction to a polarization of the third region (III), and - a first transmission signal (S1) being applied to the first transmission electrode (22), which first transmission signal has the same amplitude as and is in antiphase with a second transmission signal (S2), which is applied to the second transmission electrode (23).
2. The apparatus as claimed in claim 1, in which a control loop is provided, which regulates a phase difference existing between the first transmission signal (S1) and the reception signal (E) to a specific, constant value (~R) at which the oscillatory structure (1) oscillates at a resonant frequency (fr).
3. The apparatus as claimed in claim 1, in which a reference electrode (20) connected to a reference potential is arranged on the piezoelectric element (2).
4. The apparatus as claimed in claim 1, in which the piezoelectric element (2) is in the form of a disk and the reception electrode (21) and the two transmission electrodes (22, 23) are arranged on a circle surface of said element.
5. The apparatus as claimed in claim 4, in which the two transmission electrodes (22, 23) are annulus segments and are arranged on annulus segments of the circle surface which are diametrically opposite one another.
6. Apparatus as claimed in claim 1, in which the first transmission signal (S1) is applied to an invertor (3) and the second transmission signal (S2) is equal to an output signal of the invertor (3).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP97107153.5 | 1997-04-30 | ||
| EP97107153A EP0875740B1 (en) | 1997-04-30 | 1997-04-30 | Device for determining and/or monitoring of a predefined liquid level in a container |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2235037A1 CA2235037A1 (en) | 1998-10-30 |
| CA2235037C true CA2235037C (en) | 2000-07-18 |
Family
ID=8226746
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002235037A Expired - Fee Related CA2235037C (en) | 1997-04-30 | 1998-04-15 | Apparatus for establishing and/or monitoring a predetermined filling level in a container |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0875740B1 (en) |
| JP (1) | JP2880503B2 (en) |
| CA (1) | CA2235037C (en) |
| DE (1) | DE59712748D1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10022891A1 (en) * | 2000-05-10 | 2001-11-15 | Endress Hauser Gmbh Co | Appliance for determining and/or monitoring filling level of liquids in container based on oscillating prongs induced to oscillate by piezoelectric membrane |
| DE102004010992B3 (en) | 2004-03-03 | 2005-10-13 | Endress + Hauser Gmbh + Co. Kg | Device for determining and / or monitoring a process variable |
| DE102008032887A1 (en) | 2008-07-14 | 2010-01-21 | Endress + Hauser Gmbh + Co. Kg | Device for determining and / or monitoring a process variable and method for testing a device |
| DE102010039585A1 (en) | 2010-08-20 | 2012-02-23 | Endress + Hauser Gmbh + Co. Kg | Device for determining and / or monitoring at least one predetermined fill level |
| EP2650668A1 (en) * | 2012-04-12 | 2013-10-16 | Openfield | Density and viscosity sensor and measuring method |
| DE102014118393A1 (en) | 2014-12-11 | 2016-06-16 | Endress + Hauser Gmbh + Co. Kg | Device and a method for determining and / or monitoring at least one process variable |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1581291A (en) * | 1976-12-09 | 1980-12-10 | Kkf Corp | Sensor device |
| DE3931453C1 (en) * | 1989-09-21 | 1991-02-28 | Endress U. Hauser Gmbh U. Co, 7864 Maulburg, De | |
| DE4201360C2 (en) * | 1992-01-20 | 1995-04-27 | Uwt Apparate Gmbh | Level measuring device |
| DE4402234C1 (en) * | 1994-01-26 | 1995-04-20 | Endress Hauser Gmbh Co | Process and arrangement for determining and/or monitoring a predetermined filling level in a container |
| DE4419617C2 (en) * | 1994-06-03 | 1998-07-02 | Endress Hauser Gmbh Co | Arrangement for determining and / or monitoring a predetermined fill level in a container |
| DE4429236C2 (en) * | 1994-08-18 | 1998-06-18 | Grieshaber Vega Kg | Level measurement in a container |
| DE19523461C1 (en) * | 1995-06-28 | 1996-07-11 | Endress Hauser Gmbh Co | Level detecting device for checking whether container is filled or monitoring predetermined fill level |
-
1997
- 1997-04-30 EP EP97107153A patent/EP0875740B1/en not_active Expired - Lifetime
- 1997-04-30 DE DE59712748T patent/DE59712748D1/en not_active Expired - Lifetime
-
1998
- 1998-04-15 CA CA002235037A patent/CA2235037C/en not_active Expired - Fee Related
- 1998-04-30 JP JP10120908A patent/JP2880503B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JP2880503B2 (en) | 1999-04-12 |
| CA2235037A1 (en) | 1998-10-30 |
| JPH10339657A (en) | 1998-12-22 |
| DE59712748D1 (en) | 2006-11-23 |
| EP0875740B1 (en) | 2006-10-11 |
| EP0875740A1 (en) | 1998-11-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |