DE9321132U1 - Measuring device - Google Patents

Description

WESTPHAL- MUSSGNUG & PARTIS^. ¹ ''^l J\

PATENT ATTORNEYS · EUROPEAN PATENT ATTORNEYS veg060g

VEGA. Grieshaber: KG; 77709 Wolfach.

DIPL-ING. KLAUS WESTPHAL DR. RER. NAT. BERND MUSSGNUG DR.-ING. PETER NEUNERT DIPL-ING. ROBERT GÖHRING

Waldstrasse 33 D-78048VS-Villingen Telephone 07721 56007 Fax 07721 55164 Telex 7921573 wemu d

MUNICH

DR. RER. NAT. OTTO BUCHNER

Mozartstrasse 8 D-80336 Munich Telephone 089 54403089 Fax 089 54403080

measuring device.

The invention relates to a measuring device, in particular for measuring the fill level in containers, according to the preamble of claim 1.

Such a measuring device is known, for example, from DE: 37 21 209 AL. It has several ultrasonic transducer elements which are integrated in a housing, together and decoupled from one another. The transducer elements can be operated individually or in groups as transmitters and/or receivers via an electronic circuit. Depending on the distance to the object being measured, for example to the surface of the filling material in a container, two different operating modes are provided.

For measurements of larger distances, all converter elements are synchronized and controlled both as transmitters and receivers. The system switches between transmitting and receiving modes periodically, so that each converter element is switched in both operating states. This makes it possible to generate a strong ultrasonic pulse, which is required for measuring medium to larger distances, since depending on the medium, a higher frequency is required.

Postbank Karlsruhe 769 79-754 · German ßaaR &Agr;&&iacgr;&Ogr;&tgr;&phgr;&Bgr; {B£Z S9A70Q2S) 146332

VAT No. DE 142989261

• » ·· ■

or less attenuation" of the signal occurs.

When each ultrasonic pulse is emitted, a decay process occurs, so that the transducers are blocked for a certain time and are therefore unable to receive pulses reflected from the surface of the filling material. This time period depends on the decay behavior of the transducer elements used and is therefore device-specific. Depending on the transmission medium, i.e. the medium between the transducer elements and the measuring object, the decay time results in a measuring distance that is referred to as the blocking distance. Accordingly, distances that lie within the blocking distance can no longer be recorded with the operating mode described and an automatic switchover to the second operating mode takes place, which can be referred to as parallel operation. One of the transducer elements is permanently switched as a receiver, while the other transducer elements are operated exclusively as transmitters. An ultrasonic pulse emitted by the transducer element group operated as a transmitter can be detected immediately afterwards by the transducer element that is operated as a receiver. This means that the two groups of transducer elements must be housed in the housing in a way that is acoustically decoupled from one another, so that there is no unintentional crosstalk to the transducer element connected as a receiver and only the ultrasonic pulses reflected from the measuring object are recorded.

Such measuring devices have proven themselves in practice because they can be installed just above the maximum level to be measured. In particular, the otherwise required OL punching tube, which was used to maintain the blocking distance, is no longer necessary. However, a disadvantage of such a device is that several, or at least two,

similar transducer elements must be provided. This leads to high costs, especially when designing for small measuring distances, because a single ultrasonic transducer element is sufficient to generate a sufficient measuring signal for the maximum measuring distance to be provided. Furthermore, the construction volume is large due to the transducer elements being arranged next to each other, so that it is particularly difficult to use such a measuring device in cramped installation conditions.

DS 38 39 057 A1 discloses a so-called group radiator with a large number of ultrasonic transducers, in which two transducer elements are arranged coaxially one behind the other in the direction of radiation. For example, a transducer element with a piezoceramic is used as a transmitter. In front of it, i.e. in the direction of radiation, another transducer element in the form of a piezo film is attached, which serves as a receiver. However, transferring such an arrangement to a measuring device of the type does not lead to the desired result, since the piezo film is located directly in the main propagation direction of the ultrasonic pulse and is also excited to oscillate for the duration of the oscillation process of the piezoceramic, so that no measurement is possible during the oscillation phase and in the same way a specific blocking distance arises within which a measurement is not possible.

The invention is therefore based on the task of further developing a measuring device of the type mentioned at the beginning in such a way that ■ no longer has the disadvantages described. In particular, a measuring device is to be made available that can be manufactured inexpensively. . ·

The problem is solved with a measuring device that measures the

-A-

of claim 1". Advantageous embodiments of the invention are specified by the features of the subclaims.

The invention is based on the idea of providing a piezoceramic disk with a coaxially aligned radiation cone centrally in a housing in the manner of conventional ultrasonic transducers for level measurement and a piezo film as an additional sound receiver radially to the side of the piezo body.

(~\ sets and ■ outside its radiation cone in the housing. The piezoceramic disk and the piezo film are operated as transmitters and/or receivers by the electronic control in the manner described, depending on the distance to the measurement object. In this way, it is possible to use the well-known positive properties of a piezoceramic disk, such as high sound power, high durability and mechanical stability, and to compensate for the disadvantage of a long decay time, which leads to a large blocking distance, by the additional, but inexpensive, receiver in the form of a piezo film. The construction effort for this is extremely low, because a comparatively small film surface is sufficient.

v—is sufficient to reliably detect a reflected ultrasound pulse.

Due to their high flexibility, such piezo foils can be deformed in almost any way. This means that the reception properties, such as directional characteristics, frequency selectivity and sensitivity, can be optimized by appropriate shaping.

Both transducer elements are largely acoustically and electrically decoupled, so that crosstalk from the piezoceramic disc to the piezo film is practically completely avoided.

—5—

The block distance can thus be reduced to just a few centimeters.

Preferably, the piezo film is designed in the manner of a half-cylinder, curved towards the measuring object, in order to achieve a high directional effect. The effect can be further improved if the piezo film is curved several times and takes on the shape of several half-cylinders touching one another.

To improve signal transmission, according to a further preferred embodiment, a first matching layer for the piezoceramic disk and a second common matching layer for the piezoceramic disk and the piezo film, located immediately in front of it in the direction of radiation, are provided. The second matching layer can completely close the housing in the main direction of radiation, so that the mechanical structure is greatly simplified. The second matching layer is preferably designed in the manner of a clamping membrane, whereby it projects radially outward beyond the housing, so that a protruding ring is produced as a clamping surface for a _flange or the like.

Preferably, the first adaptation layer is made of silicone rubber and the second adaptation layer of PVDF polymer. The PVDF polymer has good mechanical stability, so that the ultrasonic transducers in the housing are optimally protected against mechanical damage. Furthermore, it is chemically resistant, so that it is also suitable for use in containers with aggressive media. -

Preferably, the first matching layer is not only directly associated with the piezoceramic disk, but is guided _radially to the vicinity of the housing wall so that the lateral

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arranged piezo film is embedded in it. In this case, a sound-absorbing layer can be integrated, which shields the piezo film axially and radially in the direction of the piezo ceramic disk, also for acoustic decoupling. For electrical shielding, a reflector layer made of metal can also be arranged directly adjacent to the sound-absorbing layer. Alternatively, however, according to a further, preferred embodiment, the ceramic disk can also be completely surrounded by a Faraday cage for electrical shielding.

According to a further preferred embodiment, the piezo film is fixed directly to a PVDF block which is directed axially inwards from the second matching layer and is made of the same material and, if necessary, in one piece as an integral part of the second matching layer. The block can thus be used for optimal impedance matching because it can be designed as a matching layer without additional boundary layers in ./L/4 matching.

For electrical shielding, a Faraday cage can be provided in such a ^ configuration, which largely completely surrounds the block including the piezo foil attached to it, with the exception of the direction that corresponds to the main radiation direction.

The invention is explained in more detail below using the embodiments shown in the figures. They show in schematic representation

Figure 1 Measuring device in a first embodiment

riant,

Figure: 2. Measuring device, in a second version

riante and

Figure 3 Measuring device in a third embodiment

riant,

Each of the above shows a view of the respective measuring device from below in half section, with the outlines of the internal components drawn in to clarify (~) the arrangement. The respective measuring device is shown in a sectional view in the middle. In Figures 1 and 2, an enlarged section of the sectional view above is also shown below to illustrate details in the area of the piezo film. For reasons of clarity, the housing in which all the components are integrated is not shown.

First, the first embodiment shown in Figure 1 is explained. A piezoceramic disk 1 is used to generate the ultrasonic pulse. An input signal TJin is fed to this via connecting lines 11, which causes the piezoceramic disk 1 to vibrate and generates the ultrasonic pulse. The pulse is coupled into the sound-transmitting medium, usually air, via a first matching layer 2 and a second matching layer 3 and spreads out essentially in the direction of the main radiation direction 4.

The piezoceramic disk 1 is completely surrounded on the back and radially on the sides by a damping layer 5, with which it is held in the housing. The damping layer 5 simultaneously serves for acoustic decoupling of the piezoceramic disk 1 from the surrounding housing. For electrical isolation.

Shielding A Faraday cage 6 is provided which completely surrounds the piezoceramic element 1. The Faraday cage 6 is earthed via a cable 9.

The first adaptation layer 2 consists of silicone rubber and is connected to the second adaptation layer 3. The second adaptation layer 3 consists of PVDF polymer, which is mechanically stable on the one hand and thus protects the components in the housing from mechanical influences, and on the other hand has excellent chemical resistance, so that it can also be used in aggressive media. The second adaptation layer 3 not only seals the housing tightly at the front, but is also extended radially beyond the housing at the sides, so that a clamping membrane is created. This means that the measuring device can be placed on a flange, for example, which is attached to a filling container. Special fastening means on the housing itself are therefore unnecessary. The two adaptation layers 2, 3 are dimensioned in such a way in terms of their thickness that they are optimally matched to the frequency of the ultrasonic pulse, so that the impedance is matched.

^- The piezoceramic disk I also serves as a receiver, provided that the filling material is outside the blocking distance. An electronic circuit (not shown here in detail) records the echo reflected from the surface of the filling material and calculates the distance between the surface of the filling material and the measuring device, i.e. the filling level in the container, from the transit time. A second transducer element 7 is mounted radially laterally to the piezoceramic disk 1. It essentially consists of a piezoceramic film 8 with a multi-fold, cylindrically curved geometry. It is implemented in the first adaptation layer 2- and brought axially close to the vicinity of the second adaptation layer 3. The

-S-

The semicircular cross-section determines the sensitivity of the piezo film 8 and is tuned to the frequency of the ultrasonic pulse emitted by the piezoceramic disk 1. This achieves a high directional effect with respect to the ultrasonic echo. The material-specific wavelength of the sound-transmitting medium as a function of the transmission frequency of the piezoceramic disk must be taken into account.

Connecting lines 12 are attached to the piezo foil 8, which are connected to the electronic circuit not shown here and transmit the reception signal Uout triggered by the echo.

The first adaptation layer 2 not only accommodates the piezoceramic film 8, but also a sound-absorbing layer 10. It is aligned axially at the back and radially in the direction of the piezoceramic disk 1 and prevents acoustic crosstalk from the piezoceramic disk L to the piezo film 8. The sound waves emitted by the piezoceramic disk 1 are completely absorbed and do not reach the piezo film 8. This makes it possible to keep the transducer element 7 ready to receive even if the decay phase of the piezoceramic disk 1 is not yet complete at the end of the pulse emission. This therefore also enables the filling level to be determined in cases in which the distance from the surface of the filling material is within the blocking distance and the reflected echo reaches the piezoceramic disk 1 at a time when the decay process is not yet complete. In this operating mode, the piezoceramic disk L serves exclusively as a transmitter and the piezo film 8 exclusively as a receiver. The electronic circuit uses the connecting lines 12 to calculate the distance.

- &iacgr;&ogr; -

transmitted output signal Uout. The connecting lines 11, which are attached to the pixel ceramic disk 1, are only used to feed in the input signal üin.

The electronic circuit automatically selects the operating mode, i.e. it is able to distinguish whether the surface of the filling material is inside or outside the blocking distance and automatically switches the operating mode accordingly.

The embodiment shown in Figure 2 differs from the one described above essentially in that the electrostatic shielding is designed differently. In the present case, a Faraday cage surrounding the piezoceramic disk 1 is completely dispensed with. Instead, an additional reflector layer 13 made of metal is positioned between the piezoceramic disk 1 and the piezo film 8. It is embedded in the matching layer 2, just like the sound-absorbing layer 10.

For manufacturing reasons, it can be planned to connect the sound-absorbing layer 10 and the reflector layer 13 to one another and to introduce them as a double layer into the first matching layer 2. The layer structure is selected so that the reflector layer 13 is first placed facing the piezo film and the sound-absorbing layer 10 is placed above it. This special type of arrangement has the advantage that the sound waves emitted by the piezoceramic disk 1 are first dampened by the sound-absorbing layer 10 and then redirected by the reflector layer 13 in the direction of the sound-absorbing layer 10, where they are completely absorbed. The echo signal reflected from the surface of the filling material is:

Piezo film 8 is detected. and then reflected when it hits the reflector layer 13 and guided back in the direction of the piezo film 8, where it is detected again. The reflector layer 13 therefore not only serves to shield the piezo film 8, but also increases the sensitivity of the converter element 7.

In the embodiment according to Figure 3, the piezo film 8 is no longer integrated in the first matching layer 2, but is fixed directly to a block 14, which is an integral part of the second matching layer 3. It is formed in one piece on the second matching layer 3, which is otherwise designed as a flat disk, and runs into the interior of the housing. The height of the block 14 corresponds to a quarter of the material-specific sound wavelength, so that the block 14 is designed as a matching layer for the piezo film 8, thus improving the transmission of the echo signal. The same material is therefore used for the impedance matching of the piezo ceramic disk 1 and the piezo film 8, so that no additional boundary layer is created and the second matching layer 3, which acts as a sound-emitting membrane, can be included in the calculation for the impedance matching of the piezo film 8. Again, a PVDF polymer is used for the second matching layer 3.

In comparison to the previous embodiments, the radius of the cylindrical curvature of the piezo film 8 is chosen to be larger, since the material-specific speed of sound within the block 14 is different than that of the elastomer used there in the form of the silicone rubber of the first adaptation layer 2.

9 0 *&Lgr;

- 12

The block 14 is guided to the side and to the front surface carrying the piezo film 8 without contact with the components surrounding it, i.e. there is no connection to the piezoceramic disk 1, the first adaptation layer 2 and the damping layer 5. This means that the piezo film 8 fixed to it is acoustically decoupled without the need for special, additional sound-insulating layers. A Faraday cage 15 is provided for electrical shielding, which completely surrounds the block 14 including the piezo film 8 attached to it and only leaves the area in the direction of arrow 4, i.e. in the receiving direction, free. The Faraday cage 15 is grounded via a line 9.

Dipl.-lng. KLAUS WESTPHAL Dr. rar. nat. BERND MUSSQNUG Dn-Ing.PETER NEUNERT V^ldftrasse 3&&idigr;&idigr;

. AHMIT; (O 7721) 56 007 , .Tefe*. * 7 921573 wemu d Fax (07721) 55164

Dr. rar. nat.OTTO BUCHNER

PATENT ATTORNEYS European Patent Attorneys Rossmannstrasse 30 a
D-81245 MUNICH

Telephone (089) 832448 Fax (089) 8340966'

List of reference symbols

veg060g

Piezoceramic disc first matching layer second matching layer Main radiation direction

Damping layer

Faraday cage

Transducer element

Piezo foil

Line-

sound-absorbing layer

Line

Line

Reflective layer

block

Faraday cage

Postbank: Karlsruhe 76979-754 Bank account: Deutsche BankAG Villingen {BLZ.69470039) 146332. V.A.T. No.DE142989261",

Claims (14)

WESTPHAL · MUSSGNUG &PARTNERI'll in
. «" «» ·· * .« PATENT ATTORNEYS · EUROPEAN PATENT ATTORNEYS DIPL-ING. KLAUS WESTPHAL DR. RER. NAT. BERND MUSSGNUG DR.-ING. PETERNEUNERT DIPL.-ING. ROBERT GÖHRING Waidstrasse 33
D-78048VS-Villingen Telephone 07721 56007 Fax 07721 55164 Telex 7921573 wemud vegOSOg MUNICH DR. RER. NAT. OTTO BUCHNER Mozartstrasse 8
D-80336 Munich Telephone 089 54403089 PROTECTION CLAIMS Fax 089 54403080 1. Measuring device, in particular for measuring the level in containers, with electroacoustic transducer elements, in particular ultrasonic transducer elements, whereby several transducer elements are integrated together and sound-decoupled from one another in a housing and can be controlled by an electronic circuit in such a way that, depending on the distance to the measuring object, in particular to the surface of the filling material, a) for measurements within a device-specific blocking distance: a first transducer element or all transducer elements of a first group synchronized exclusively as a transmitter and a second transducer element or all transducer elements of a second group synchronized exclusively as a receiver, or b) for measurements outside the blocking distance, a transducer element or a plurality of transducer elements, synchronized, can be operated both as a transmitter and as a receiver, characterized in that a piezoceramic disk (L) with coaxially aligned radiation cone. zeatral and a piezo film (8) radial Postbank Karlsruhe 789 79-754 ■ German SmR A&VMIojan (SiZ 8Q4?O£ß9J 146332 VAT. No. DE 142989261 are offset laterally and arranged outside the radiation cone in the housing, whereby a) for measurements within the blocking distance, the piezoceramic disk (1) as transmitter and the piezo foil (8) as receiver and b) for measurements outside the blocking distance, the piezoceramic disk (1) can be operated as a transmitter and receiver. 2. Measuring device according to claim 1 ₁ , characterized in that the piezo film (8) is designed in the manner of a half-cylinder and is curved towards the measuring object. 3. Measuring device according to claim 2, characterized in that the piezo film (8) is designed to be curved in several ways. 4. Measuring device according to one of the preceding claims, characterized in that a first adaptation layer (2) for the piezoceramic disk (1) and a second adaptation layer (3) are provided jointly for the piezoceramic disk (1) and the piezo film (8). 5. Measuring device according to claim 4, characterized in that the second adaptation layer (3) closes the housing axially in the direction of the main radiation direction (4). 6. Measuring device according to claim 5, characterized in that the second adaptation layer (3) projects radially beyond the housing in the manner of a clamping membrane. 7. Measuring device according to one of claims 4 to 6, characterized —3— characterized in that the first adaptation layer (2) consists of silicone rubber. 8. Measuring device according to one of claims 4 to 7, characterized in that the second adaptation layer (3) consists of PVDF polymer. 9. Measuring device according to one of the preceding claims, characterized in that the first adaptation layer (2) is guided radially into the vicinity of the housing and the piezo film (8) is embedded therein. 10. Measuring device according to claim 9, characterized in that for acoustic decoupling a sound-absorbing layer (10) is integrated in the first matching layer (2), which shields the piezo film (8) axially and radially in the direction of the piezoceramic disk (1). . . 11. Measuring device according to claim 10, characterized in that a reflector layer (13) made of metal is arranged immediately adjacent to the sound-insulating layer (10) for electrical shielding. 12. Measuring device according to claim 10, characterized in that the piezoceramic disk (1) is completely surrounded by a Faraday cage (6) for electrical shielding. 13. Measuring device according to one of claims 1 to 8, characterized in that the piezo film (8) is mounted directly on an axially inwardly directed block (14) which is an integral part of the second adaptation layer (3). - 4 14. Measuring device according to claim 13, characterized in that for electrical shielding, a Faraday cage (15) is provided, which largely completely surrounds the block (14) including the piezo film (8) attached thereto with the exception of the direction that corresponds to the main radiation direction (4).