DE102005011376A1 - Liquid/bulk material fill level measuring device for use in motor vehicle tank, has transmitter and receiver in the form of piezo-foils, where device is formed as dip senso, and foils have length of fill level range that is to be detected - Google Patents

Abstract

The device has a transmitter and a receiver in the form of piezo-foils (1, 2), where the device is formed as a dip sensor. The foils have a length of fill level range that is to be detected. An ultrasound signal emitted by the transmitter is controlled by a sound transmission media for the receiver. A connection is made between the transmitter and receiver piezo-foils that are provided in a pile, by a double-sided adhesive strip.

Description

The The invention relates to a device for level measurement, in particular a sensor to detect the level noise-transferring liquids and / or sound transmitting Bulk material.

Known are stepless level indicators e.g. in vehicle tanks, the float-operated potentiometer as a transmitter use. But also level gauge, the piezo oscillating heads and ultrasound technology are known. It will either a distance calculated from the running time of the signal (sonar principle) or a threshold value from the damping behavior of the ultrasound (liquid present / absent) (e.g., ultrasonic sensor the company Waycon).

adversely in particular, the known technologies is that they only with a high effort can be integrated into the products whose susceptibility, and the relatively inaccurate measurement.

task The present invention is therefore the realization of a device for stepless and linear detection of the level of liquids and / or bulk material, which can be easily integrated into a product and a reliable level indicator allows.

object The invention is a level measuring device for sound transmitting Media, at least one acoustic transmitter and at least one acoustic receiver in the form of piezo films, wherein a radiated from the transmitter Ultrasound signal passed through the sound-transmitting medium to the receiver becomes.

To an embodiment According to the invention, at least one of the piezo films is strip-shaped.

To an advantageous embodiment In the invention, the transmission piezo film and the receiver piezo film have the same geometric shape, and are parallel to each other at a small distance arranged so that in both film strips the same length section surrounded by the sound-conducting medium. This embodiment provides a particularly linear relationship between the receiver signal and level. The total length the film strip, and thus the sensor, corresponds to the one to be measured Level height. Of the Sensor is in the container (Immersion sensor), or on the container wall (external sensor) positioned so that the medium between transmitter and receiver creates a sound conductive connection.

Of the Transmitter is connected to an oscillator and is supplied with an exciter signal, preferably sinusoidal in the ultrasonic range, fed. The transmitter then acts as an ultrasonic transmitter. Preferably, the excitation signal has a constant amplitude. There may be frequencies in the range of a low audible Sound (some 10Hz, for example 30 to 40 Hz) to well over 1MHz be used.

Of the receiver captures the signal that passes to him the sound-transmitting Medium is supplied. If there is no medium, there is no transmission instead of and at the receiver No signal or only the basic signal (see below) can be detected become. However, a part of the receiver with sound transmitting Medium covered, so a more intense signal can be detected at the receiver be, with the increase of the received signal amplitude linearly proportional to the medium-covered sensor surface is.

Over a Calibration measurement can give the sensor signal (water level) the volume the sound transmitting Medium, for example liquid, in the container be assigned. This is the determination of the container contents, for example, the tank contents of a vehicle, even with more complex vessel form z. B. in liters possible.

thermal, mechanical or other interference may occur e.g. be compensated by adjusting the exciter parameters. Ty pical noise (Eg from the car ignition system) can easier to filter when the useful signal frequency (exciter frequency) in a noise-free Range of the frequency spectrum of about 1 MHz is placed.

In order to shield electromagnetic interference fields, either the respective outer piezoelectric electrode layer can be grounded, or an additional outer shielding layer with ground connection be used.

in the The invention will be described below on the basis of exemplary embodiments explained in more detail:

1 shows a submersible sensor with two parallel Piezo films, which are immersed in a liquid container.

2 shows a graph showing the linearity of the voltage rise of the sensor signal with the rise of the sound-transmitting medium to be measured,

3 shows a container with two level measuring devices, one attached to the container wall and a submersible sensor,

4 Finally, two alternative ways of designing a level measuring device according to the invention on a container wall.

1 shows in the region of the fill level range of a container to be detected two mutually parallel piezo foil strips 1 and 2 at a constant distance.

in the container These piezo film strips are arranged so that they from the zu washing medium flows around become. For aggressive media, for example, is an acoustic conductive protective sheath provided.

After the in 1 In the embodiment shown, the sensor comprises a piezo foil strip 1 as an ultrasonic transmitter and an equally long further Piezo film strip 2 as an ultrasonic receiver. Both foils are mechanically connected to one another with a constant distance over the entire length parallel and non-porous, for example glued, and thus acoustically coupled over the entire surface, so that when the transmitter is energized, even when the container is empty, a basic signal (idling signal) is forwarded by the receiver. This constant basic signal is compensated in the subsequent signal evaluation to zero value (empty container). This design ensures that all acoustically relevant parameters are kept constant, and the sensor signal varies only with the level. The piezofilm bond that is formed by this must be at least as long as the liquid height to be detected. Each subarea of the receiver foil 2 thus captures the associated subarea of the transmitter film 1 ,

At the upper end are the piezo film strips with cables 3 and 4 Mistake.

The piezo strip 1 is supplied with an AC voltage, for example via a constant amplitude oscillator and frequency over the line 3 energized and serves as an acoustic transmitter. The frequency range that can be practically used ranges from a few 10 Hz to over 1 MHz. The second piezo film 2 serves as an acoustic receiver and detects the acoustic signal already by the weak coupling on the bond or the spacer layer 9 and converts it into an AC signal that goes through the line 4 is forwarded. This signal amplitude corresponds to the level "zero" and is referred to as a basic signal.When the piezo strips are partially or completely immersed in a sound-transmitting medium such as liquid and / or bulk material, the acoustic coupling intensity increases in this range, and the signal amplitude increases linearly proportional to the water level ( please refer 2 ).

In 2 a graph is shown in which the sensor signal 5 of an external sensor in mV (millivolts) against the tank volume 6 in ml (milliliters), measured through a container wall of 2 mm. The sensitivity of a dip sensor with a 200 μm thick protective coating is more than two orders of magnitude better, ie sensor signal as a function of level level is about 7mv / mm. These values are valid under the following conditions:
U (exciter) = 10 Vpp
f (exciter) = 20 kHz
Width of the piezo strip = 12 mm
Medium: water

3 shows in a container a submersible sensor 7 , as in 1 shown and a sensor 8th , which is attached to the container wall or poured into the container wall. The sensor 8th can be both outside as also be mounted on the inside of the container wall, because laboratory tests have shown that the sensor, even if it is attached to the outside of the vessel wall (eg plastic container), still provides a sufficiently high measurement signal. The transmission intensity can be increased if necessary by using several transmission foils in the stack.

Of the Sensor is, as already mentioned, in certain circumstances on the outside wall attached by plastic containers. With wall thicknesses up to approx. 2 mm still very well evaluable signals could be recognized.

As well The sensor can be embedded in the wall of plastic containers.

The at least two piezo films 1 and 2 are with each other, with a common substrate and / or with the container wall via an adhesive 9 connected. For example, in the embodiment of the sensor 8th out 3 , at the transmitter 1 and receiver 2 Without surrounding sound-transmitting medium may have no acoustically conductive connection, no basic signal is present.

In 4 Further embodiments of the invention are shown schematically.

The sensor 10 is on or in the container wall (inside or outside) designed so that Sendepiezofolie 11 and receiver piezo foil 12 side by side on a common substrate 13 are arranged. To increase the transmission signal intensity and / or to optimize the symmetry are here, for example, two Sendepiezofolien 11 on both sides of the receiver film 12 appropriate.

According to 4b are the two piezo films 11 and 12 on a common substrate 13 on the container wall, inside or outside, layered on each other, for example, such that on the substrate 13 as a lower layer the Sendepiezofolie 11 is applied, which in turn laterally the receiver film 12 , which forms the upper layer, far surmounted. The protruding surface 12 acts as a transmission area. When layering on a substrate 13 manufacturing advantages could play a role.

Instead of the planar arrangement can Transmitter and receiver foil also be arranged coaxially.

at Vessels with Metal wall is preferable to a diving sensor, since here the acoustic Measuring signal would already be shorted in the wall.

The Transmit signal parameters (amplitude and / or frequency), receive signal processing as well as the geometric design of the sensor or the level measuring device Be appropriate to adapted the respective application. The flexibility of the films allows also an arrangement of the films on curved container surfaces.

Provided the length the piezo strip is limited due to production, can for the detection high water levels several individual sensors are strung together, and by the subsequent evaluation electronics are linked to a total level.

At the Use in moving systems (vehicle) can be a wrong measurement, the caused by acceleration or strong inclination, with two or more sensors that work differentially, be compensated. If the surface of the liquid vibrates or spills too much, the measuring signal can be smoothed with a capacitor.

At the Use in chemically aggressive environment is the sensor with a good sound transmitting but chemically resistant sheath provided.

When Piezo-active material, for example, a polymer film with piezo effect (especially PVDF), piezoceramic fiber laminates and PZT layers on metal foils used.

to Connection of transmitter and receiver foil / film are suitable e.g. double-sided adhesive tapes or thin transfer adhesive films, the commercial example of 3M, especially the product 468MP, available are.

In Table summarizes properties of piezo materials.

The invention relates to a device for level measurement, in particular a sensor for Erfas tion of the level of sound-transmitting liquids and / or sound-transmitting bulk material. In this case, at least two piezo films are used, one of which acts as a transmitter which sends a signal about the liquid to be measured to the second film, the receiver.

Claims (6)

Level measuring device or sensor for sound transmitting Media, at least one transmitter and at least one receiver in Form comprising at least one piezofilms, one of the transmitter emitted ultrasonic signal through the sound-transmitting Medium to the receiver is directed. Level measuring device according to claim 1, in which the piezo films are strip-shaped, and at least the length of the fill level range to be detected to have. Level measuring device according to one of the claims 1 or 2, on the container wall attached or designed as a dip sensor. Level measuring device according to one of the preceding claims, comprising at least one piezo film selected from the group of the following materials for polymer films with piezo effect: PVDF, piezoceramic fiber laminate and PZT layers on metal foils, as well as any combinations of said materials. Level measuring device according to any one of the preceding claims, wherein the compound of Transmitter and receiver foil / film produced by a double-sided adhesive tape and / or a thin transfer adhesive film becomes. Level measuring device according to one of the preceding claims, wherein a plurality of transmitting and / or receiver films in the stack and / or enlarged transmission and / or receiver sheets to increase the transmission intensity are provided.