DE102008031783B4 - Device for determining a fill level - Google Patents

Abstract

Sensor device for detecting the level in a container comprising:
- At least one client circuit (23, 80) for generating signals; and
A server circuit (12, 70) for detecting the signals generated and output by the at least one client circuit and generating an electric field;
in which
- The at least one client circuit having a first electrode (21) and a second electrode (22);
- The at least one client circuit is capacitively coupled to the server circuit based on a modulated alternating field; and
The at least one client circuit is supplied with the electric field generated by the server circuit with energy for operating the client circuit,
characterized in that
the power supply for operating the client circuit is accomplished by the voltage drop between the first electrode (21) and the second electrode (22), wherein the voltage drop between the first electrode (21) and the second electrode (22) decreases as the level in the container increases , and...

Description

The invention relates to a sensor device for detecting the fill level in a container, wherein the sensor device comprises at least one client circuit for generating signals and a server circuit for detecting the signals generated and output by the client circuit. The server circuit also serves to generate an electric field. In particular, the invention is directed to a sensor device for detecting the level in a container by means of capacitive sensors.

From the prior art devices or systems are known to detect the level of a container. For example, systems are known in which the level of a container is determined with the aid of mechanical means. For example, it is known to provide styrofoam floats in the water tank of a condenser tumble dryer which actuate an electrical switch upon reaching a predetermined level of water. However, this requires additional structural complexity of the water tank used in the condenser dryer.

Furthermore, the mechanical device located inside the container, such as a polystyrene float, takes up additional space, which has a negative effect on the amount of water that can be absorbed by the container.

Furthermore, it is necessary to provide a corresponding opening in the container in order to reach from the outside to the mechanical level measuring device arranged in the interior of the container, for instance in the case of a defect.

Alternatively, optical and electrical measuring systems for determining the water level in a container are known from the prior art. It is imperative that optical measuring systems assume that if the measuring system is arranged outside the container, at least a part of the container is made transparent. In the case of electrical measuring systems, which use the conductivity of the water to determine the level, it is necessary to arrange this at least partially in the interior of the container to make contact with the water. Measuring systems which are based on the conductivity of the water have the disadvantage that, for example, contaminated water can have a different conductivity than clean water, which can lead to considerable measurement inaccuracies or measuring errors.

In particular, such an electrical measuring system must in each case be set or adapted to the electrical conductivity of the liquid in a container in order to be able to carry out an exact level measurement.

From the DE 20 2006 018 584 U1 a sensor device has become known in which the level in a closed container can be determined with the aid of a capacitive pressure sensor. In order to measure or detect the pressure in the interior of the closed container with the aid of the capacitive sensor, it is also necessary here to arrange at least the sensor in the interior of the container.

From the DE 199 01 814 A1 is a level switch for determining the level in closed containers has become known, and here at least a part of the level switch is arranged inside the container. An arranged inside the container transponder level switch is coupled to a arranged on the outside of the container signal receiver. The state of the transponder level switch, ie a corresponding level of a liquid in the container is transmitted contactlessly to the signal receiver.

Object of the present invention is to provide a sensor device for detecting the level in a container, which at least partially avoids the disadvantages known from the prior art, wherein the sensor device is universal, space-saving and easy to use.

According to the invention, this object is achieved with a sensor device according to the features of patent claim 1.

Thereafter, the sensor device for detecting the fill level in a container comprises at least one client circuit for generating signals and a server circuit for detecting the signals generated and output by the client circuit and for generating an electric field, wherein the server circuit at least one electrode SE, wherein the at least one client circuit has a first electrode CE1 and a second electrode CE2, wherein the at least one client circuit is capacitively coupled to the server circuit based on a modulated alternating field and wherein the at least one client circuit with the power generated by the server circuit is supplied with power for operating the client circuit, wherein the sensor device is operable on the outside of the container can be arranged, wherein the distance of the first electrode to the electrode of the server circuit is smaller than the distance of the second Electrode for electro de the server circuit and wherein the first electrode and the electrode of the server circuit are designed narrow in relation to the second electrode.

The server circuit can also have at least one electrode SE (a so-called server electrode). The client circuit may in this case be coupled to the server circuit on the basis of the modulated alternating field.

Capacitive coupling of the client circuitry to the server circuitry may be used by the AC field received from the client circuitry or its electrodes to power the client circuitry, such that additional power supplies in the client circuitry can be waived.

The electrodes CE1 and CE2 of the client circuit, as well as the electrode SE of the server circuit, can be configured in the form of a ribbon and arranged substantially parallel to one another. The distance of the first electrode CE1 to the electrode SE is preferably smaller than the distance of the second electrode CE2 to the electrode SE.

In an advantageous embodiment of the invention, the electrodes CE1 and SE are narrow in relation to the electrode CE2.

Due to the placement of the first electrode CE1 (coupling-in electrode) of the client circuit in the direct vicinity of the server electrode SE and the narrow configuration of the server electrode SE and the coupling electrode CE1, a particularly good coupling of the electrodes CE1 and SE to each other is achieved while the mass coupling is small reached. The greater width of the output electrode CE2 has the advantage that a particularly good coupling of this electrode to ground is achieved.

Preferably, the at least one client circuit and the server circuit can be arranged on a foil sticker. Particularly preferably, the client circuit and the server circuit can be printed on a polymer film, which allows a particularly flexible use of the sensor device according to the invention. The sensor device can thus be easily mounted on the container to be monitored with regard to the filling level, wherein the filling level to be detected is selected by the mounting height of the sticker.

The power supply for operating the client circuit can be accomplished by the voltage drop between the first electrode CE1 and the second electrode CE2. The alternating field picked up via the first electrode CE1 is advantageously converted into a DC voltage (for instance through a diode cascade) so that the client circuit can be operated with this rectified working voltage.

According to the invention, the power supply of the at least one client circuit is interrupted as soon as the voltage drop between the first electrode CE1 and the second electrode CE2 drops below a predetermined value. This is the case as soon as the filling level in the container to be monitored with respect to the filling level is within the width of the coupling-in electrode CE1. At this time, the client circuit turns off, since the voltage drop between the coupling electrode CE1 and the Auskoppelelektrode CE2 is no longer sufficient to power the client circuit.

Advantageously, the sensor device or the film label can be arranged in operation on the outside of the container, which allows a particularly simple detection of the level in a container. The fact that not the conductivity of a liquid but its dielectric constant is used as a sensor function, the sensor device according to the invention does not have to be in contact with the liquid in the container, since the change of existing between the electrodes electric field is used, which increases with increasing Level changed. At the same time decreases with increasing level of the liquid in the container and the voltage drop between the electrodes of the client circuit, the voltage drop is finally so small with reaching the coupling electrode CE1 that the client circuit turns off.

The switching off of the client circuit can be interpreted by the sensor device or by the server circuit as exceeding a predetermined liquid level. The sensor device thus provides a clear signal, namely by switching off the client circuit ready as soon as the liquid level is exceeded.

The sensor device according to the invention also has the advantage that even water levels in containers, which receive electrically non-conductive liquids, can be determined.

By means of the electrodes of the server circuit and the client circuit, which are arranged essentially parallel to one another, the level at which the client circuit automatically switches off can be determined solely by the vertical arrangement of the sensor device on the container.

The server circuit furthermore has a power supply, an oscillator and an evaluation unit, wherein the oscillator is operated by the power supply and wherein the evaluation unit is supplied with the modulated alternating field provided by the client circuit. This can be a sensor device with two or more Client circuits are provided which are designed so that they are distinguishable by the server circuit.

The client circuits can each have a comparator which compares an identification number, modulated by the server circuit with the electrical field generated by the latter, with a comparison identification number. The client circuit may additionally be designed such that it can only be activated if the identification number corresponds to the comparison identification number, wherein each client circuit is assigned a different (or unique) comparison identification number.

The server circuit can thus selectively activate one of several client circuits. This has the advantage that several client circuits can be coupled to a server electrode at the same time, so that different levels can be detected, for example, with a sensor device of the type according to the invention.

As an alternative to the comparator, two or more client circuits may also each have a timer, wherein the timers activate the respective client circuits in a predetermined order and duration. Here, too, exactly one client circuit is in each case coupled to the server electrode, so that likewise different levels in a container can be detected.

In a further alternative embodiment, the client circuits may also each have a free-running oscillator, wherein the frequency of the respective oscillators is different. Due to the different frequency of the individual oscillators, the client circuits are distinguishable from the server circuit.

In yet another alternative embodiment, the client circuits may each comprise a frequency divider which divides the frequency of the oscillator of the server circuit, the dividing ratio of the individual frequency divisors being different. Again, the different frequency of the individual client circuits serves to allow the server circuit to distinguish the individual client circuits.

Further advantages and advantageous embodiments of the invention are the description, the drawings and the claims removed.

Embodiments of the invention are shown schematically simplified in the drawing and are explained in more detail in the following description.

It shows:

1 a sensor device according to the invention, arranged on a foil;

2 a sensor device arranged on a tank to be monitored with regard to the water level;

3 an embodiment of the sensor device according to the invention for detecting different filling levels;

4 an embodiment of the sensor device according to the invention with a server circuit and two client circuits;

5 an example of a sensor device, which allows both the determination of the level in a container and tilting movements of a partially filled with liquid container;

6a a schematic representation of the server circuit according to the invention; and

6b a schematic representation of a client circuit.

1 shows a sensor device for detecting the level in a container, wherein parts of the sensor device on a foil 30 , are preferably applied to a polymer film. The sensor device consists of a server circuit and a client circuit. The server circuit is from a server 12 and one with the server 12 coupled server electrode 11 educated. The coupling of the server electrode 11 with the server 12 can be galvanic or capacitive.

The client circuit is handled by a client 23 and two with the client 23 coupled electrodes 21 . 22 educated. The electrode 21 the client circuit, which serves as a coupling-in electrode, is in the immediate vicinity of the server electrode 11 arranged. The electrode 22 , which serves as Auskoppelelektrode, however, is further from the server electrode 11 arranged away.

How out 1 is apparent, are the server electrode 11 and the coupling-in electrode 21 narrower than the Auskoppelelektrode 22 , Due to the narrow design of the server electrode 11 and the coupling electrode 21 a particularly good coupling of these electrodes to each other is achieved with simultaneous low mass coupling. Moreover, in a narrow embodiment of the coupling-in electrode 21 the switching threshold at which the power supply of the client circuit is interrupted, also correspondingly narrow.

The much larger width of the coupling-out electrode 22 serves to provide a better coupling of the electrode 22 to achieve mass.

The client circuit, consisting of the electrodes 21 . 22 and the client 23 , Capacitive is coupled to an alternating electric field, which from the server 12 and the server electrode 11 provided. The alternating electric field of the server or the server electrode 11 is in the coupling electrode 21 the client circuit coupled while the Auskoppelelektrode 22 (capacitive) connected to ground.

That via the coupling-in electrode 21 recorded AC field can be from the client 23 be converted into a DC voltage with a voltage converter, for example, operates an oscillator, which has a certain level according to the input voltage, which is sufficient to provide power to the client circuit.

By means of physical action variables, such as the level in the container to be monitored, it is possible to change the level of the voltage so that it is proportional to the size acting on the server 12 can be evaluated and thus forms a measure of the acting size, such as the current level in the container to be monitored.

A detailed description of the client circuit or server circuit is given below with reference to FIG 6a and 6b given.

According to the construction of the sensor device according to the invention, the activation of the client circuit always takes place when via the server electrode 11 from the server 12 a sufficiently strong electric field is provided so that the oscillator of the client circuit can swing, which in turn can be evaluated by the server circuit as an "OK" signal.

The signal thus generated by the client circuit (OK signal) can be transmitted, for example, by means of load modulation to the server circuit. The transmitted signal is supplied to the server circuit of an evaluation unit, where it can be subjected to, for example, a Fourier transform.

According to the construction of the sensor device according to the invention, the signal from the client circuit is transmitted to the server circuit as long as the client circuit can take sufficient energy from the alternating field provided by the server circuit for its operation.

The operating principle of the sensor device according to the invention is the following. The distance between the coupling electrode 21 and the coupling-out electrode 22 is chosen so that the client circuit will operate stably at the selected server voltage with no liquid in the container (eg, water), ie the oscillator will stably oscillate the client circuit, which will be detected by the server circuitry as the aforementioned "sensor -OK "signal can be evaluated. In this initial state, ie when there is no liquid in the container, there is a sufficient voltage drop between the coupling electrode 21 and the coupling-out electrode 22 so that the client circuit can be supplied with enough power for operation.

By filling, for example, water, into the container (where water has a dielectric constant of about 80), the "distance" between the electrodes effectively acting on the electric field becomes effective 21 and 22 shortened by ε-fold, ie that the voltage drop between the coupling electrode 21 and the coupling-out electrode 22 decreases with increasing liquid level.

The client circuit turns off as soon as the voltage drop between the coupling electrode 21 and the coupling-out electrode 22 is no longer sufficient to power the client circuit. Preferably, the shutdown takes place when the liquid level is within the width of the coupling electrode 21 located.

As a result, the client circuit transmits a signal to the server, for example by means of load modulation, as long as the liquid in the container to be monitored has not reached a predetermined level. After reaching the level, the client circuit automatically shuts off, as the voltage drop between the coupling electrode 21 and the coupling-out electrode 22 falls below a certain value, which can be evaluated by the server circuit and clearly recognized. This signal assignment (level reached or level not reached) has significant safety advantages, since the achievement of a level in a container is clearly identified by exactly one signal. A continuous monitoring of the liquid level in the container is not required, which is particularly advantageous in the design of the evaluation in the server circuit, since complicated circuit arrangements, for example, for a pattern comparison for different levels of a liquid in a container are not necessary. The evaluation unit only has to check whether a signal is provided by the client circuit or not.

Of course, the server circuit or the evaluation unit of the server circuit can also evaluate the signal received from the client circuit with respect to the liquid level in the container, for example to provide different status or warning messages.

2 shows a container 40 with a sensor device arranged on the outside of the container, consisting of the server 12 , the server electrode 11 , the coupling electrode 21 , the decoupling electrode 22 as well as the client 23 , In addition, the server 12 with a warning device 50 , For example, an LED connected. The evaluation device of the server circuit 12 can be designed so that upon reaching the level to be monitored in the container 40 the LED starts to light up or starts flashing. The level to be monitored is located in the region of the coupling-in electrode 21 ,

If the individual elements of the sensor device are arranged on a foil, then this foil can be easily attached to the container to be monitored with respect to the filling level on the outside of the container, wherein only care must be taken that the mounting height of the foil is chosen such that the Height of the coupling electrode 21 corresponds to the level to be detected in the container.

According to the invention, the server 12 also be operated with an external, not located on the container power source. It is also not mandatory, the warning device 50 directly on the outside of the container 40 to arrange. For example, the warning device 50 be guided to a control panel, such as a clothes dryer, wherein the sensor device can be used to detect the water level in the container of Kondenswäschetrockners. Using the sensor device according to the invention, it is particularly easy to provide already existing devices with a sensor device for detecting the fill level. Thus, the container of a condenser dryer must be provided only with the sensor device according to the invention, wherein in the case that the sensor device is arranged on a self-adhesive film, the film must be glued only at a suitable location on the outer wall of the container. A possibly existing warning device only needs to be made visible or audible to the operator at a suitable point.

A further conversion or adaptation of the container of Kondenswäschetrockners is no longer necessary. In particular, no means or devices for detecting the level inside the container must be arranged.

3 shows an alternative embodiment of a sensor device according to the invention, which on a film 30 arranged. In the 3 shown sensor device is used to detect two different levels in a container, so as to trigger different actions depending on the filling level. For example, upon reaching a first fill level, a warning function can be triggered, and upon reaching a second fill level, for example, the liquid supply in the container to be monitored can be automatically stopped.

As in 3 As can be seen, the electrodes are 11 . 21 . 22 a first sensor device different from the electrodes 11a . 21a . 22a a second sensor device arranged so as to achieve the detection of different levels in a container. In the embodiment shown here, the server electrodes are 11 respectively. 11a the two sensor devices each with a server 12 respectively. 12a connected. If the filling level of the liquid in the container reaches the coupling-in electrode 21a , can be detected by the second sensor device, a first level, since the voltage drop between the coupling electrode 21a and the coupling-out electrode 22a is no longer sufficient to the client circuit of the second sensor device with that of the server electrode 11a to supply the electric field provided with energy. The client circuit of the second sensor device thus switches on reaching the filling level in the region of the coupling-in electrode 21a automatically, leaving the evaluation of the server 12a can trigger a corresponding function. For example, this feature may be a warning feature that indicates that a critical level has been reached in the tank.

The evaluation device of the server 12a For example, it is also possible to control a regulating device which controls the supply of liquid in the container when the liquid level is reached 21a throttles accordingly.

The server electrode 11 and the coupling-in electrode 21 The first sensor device are correspondingly vertically above the server electrode 11a or the coupling-in electrode 21a the second sensor device arranged. With a further increase in the fill level, this finally reaches the coupling-in electrode 21 , so that the evaluation of the server 12 can detect this level, for example, then automatically stop the supply of liquid into the container.

Of course, the servers can 12 and 12a Also have a common evaluation, said common evaluation can control both the warning function for the first level and the automatic stopping of the liquid supply at the second level.

The first sensor device operates analogously to the already described operation of the second sensor device. If the liquid level reaches the coupling-in electrode 21 , the voltage drop between the coupling electrode decreases 21 and the coupling-out electrode 22 below a certain value which is too low to power the client circuitry of the first sensor device. The client circuit of the first sensor device then switches off automatically.

In a further embodiment, the electrode 11a the second sensor device also with the server 12 get connected. The electrodes 11 and 11a are designed so that the server 12 can distinguish the signals generated by the two client circuits (OK signals). Various design options for distinguishing the signals generated by a plurality of client circuits are provided below with reference to 4 and 6b listed.

In this embodiment (a server 12 coupled with multiple electrodes 11 . 11a ) can be on the second server 12a be omitted, which allows a more compact design of the sensor device according to the invention.

In particular, it is possible to connect one or more client circuits of the type mentioned to an already existing server so that a network of client circuits can be set up. For example, a server may be provided in a tumble dryer, to which a sensor device provided for another purpose is connected. The client circuit according to the invention can also be connected to this server. The server is designed so that it can extract the signals detected by the client circuit and thus detect the level of the condensation water tank.

4 shows a further embodiment of a sensor device according to the invention. The sensor device here has a server electrode 11 and two client circuits on. The coupling-in electrodes 21 and 21a are at the same height each near the server electrode 11 arranged so that through the server electrode 11 provided by the server circuit alternating electric fields in the coupling electrodes 21 respectively. 21a can be coupled. The decoupling electrode 22 respectively. 22a The two client circuits are also here compared to the coupling electrodes 21 respectively. 21a designed broad, so that an optimal ground coupling of the coupling-out 22 respectively. 22a is reached.

The signals provided by both client circuits (which are provided as long as the level of the liquid in the container, the coupling-in electrodes 21 respectively. 21a has not reached) are evaluated by the server circuit or by the evaluation of the server circuit.

In a preferred embodiment, the server circuit or the client circuits are configured such that the server circuit can distinguish the signals of the individual client circuits. For this purpose, each of the client circuits may comprise a comparator which compares, for example, an identification number modulated by the server circuit with the electrical field generated by it for a comparison identification number, each client circuit being assigned a unique comparison identification number. Because of the comparison identification number associated with the client circuits, each client circuit may use it to generate a signal including the identifier of the client circuit. As already described at the outset, these signals are transmitted to the server circuit by means of load modulation, the signals which differ on the basis of the comparison identification number effecting a different load modulation on the server circuit. The thus transmitted signals of the individual client circuits, which form a frequency mix while transmitting simultaneously, can be used by the evaluation device of the server 12 be separated and evaluated for example by means of a Fourier transform.

Alternatively, the client circuits may also be designed such that they are activated only if the identification number modulated onto the electrical field of the server circuit matches the number of the comparison identification of the client circuit. This provides the possibility that the server circuit can specifically address individual client circuits of the sensor device.

In an alternative embodiment, a timer may be provided instead of a comparator, wherein the timers of the respective client circuits in a predetermined order and duration activate the client circuit, so that only one client circuit is active at a time.

In a further alternative embodiment, the client circuits may instead of a Comparator also each provide a free-running oscillator, wherein the frequency of the respective oscillators is different. Due to the different frequency of the individual oscillators, the client circuits are distinguishable from the server circuit.

In yet another alternative embodiment, instead of a comparator, the client circuits may each comprise a frequency divider which divides the frequency of the oscillator of the server circuit, the division ratio of the individual frequency divisors being different. Again, the different frequency of the individual client circuits serves to allow the server circuit to distinguish the individual client circuits.

Due to the arrangement of the coupling electrodes 21 respectively. 21a the two client circuits at the same height or horizontally next to each other, this sensor device, as in 5 shown schematically, also be used to detect in addition to the filling level in the container and a possible inclination of the container. Reaches the level in the container only one of the two arranged at the same level Einkoppelelektroden 21 respectively. 21a , this can be interpreted or interpreted by the sensor device as a tilting of the container, since only one of the two client circuits shuts off in the tilted state due to the low voltage drop between the two client electrodes.

In the non-tilted state, both client circuits would have to switch off almost simultaneously, wherein to avoid misinterpretation by the evaluation a certain time interval can be provided within which the shutdown of both client circuits must be detected in order to draw the conclusion that it in fact, it is a liquid level exceedance and not a tilting of the container. By providing such a time interval, for example, false evaluations can be prevented, which can be caused by moving the liquid due to the filling process, for example.

Furthermore or alternatively, the level difference at the respective client circuits can also be used to determine whether it is a tilted container or a non-tilted container.

By in the 4 proposed arrangement of the electrodes can also be determined, in which direction the container has been tilted. For example, the evaluation device of the server can determine that the container has been tilted to the left, as well as off 5 apparent - the client circuit with the electrodes 21 and 22 itself turns off and the server thus only a signal of the further client circuit with the electrodes 21a and 22a receives.

6a schematically shows a circuit arrangement according to the invention for a server circuit. A power source 71 ensures the supply of electrical energy, eg. B. as a constant current. This will be an oscillator 72 operated, which can generate an AC voltage. This alternating voltage can be fed to a mixer (not shown here), wherein this mixer additional data for sensor control, for example, the above-mentioned identification numbers, can be supplied. From the thus mixed signal, an electric field is then generated, which via the server electrode 11 is delivered. The oscillator 72 can be a limiter 73 , For example, a resistor, be downstream in order to allow any flowing currents, such as short circuit, not to grow beyond a certain level. On the other hand, the modulation (load modulation) generated by the client circuits is fed to this element to an evaluation device, which essentially consists of a filter 74 , an amplifier 75 and an evaluation unit 76 consists.

In order to emit the electric field or to receive the modulation of the client circuits, there is at least one server electrode 11 provided, which may for example consist of a film-like structure and can be printed directly on a film.

6b schematically shows a circuit arrangement according to the invention for a client circuit. Since the client circuit of the sensor device according to the invention is capacitively coupled to the server circuit, determines the size of the surface of the coupling electrode 21 and the server electrode 11 or the distance from one another the input energy from that of the coupling-in electrode 21 recorded alternating field. That via the coupling-in electrode 21 recorded alternating field is using a voltage transformer 81 converted into a DC voltage. This can be done for example by a diode cascade, in addition to the rectification in addition to generate a correspondingly high operating voltage from the input signal. This voltage becomes a modulator 82 operated. According to the input voltage, the modulator has 82 a certain level, with which the AC voltage can be modulated. With the help of a suitable conversion of physical action variables, for example the level in the container to be monitored, it is possible to change the level of this voltage so that it depends on the physical Impact variables on the server can be evaluated and thus forms a measure of the acting size. As a result, the sensor device also makes it possible to detect not only the switching off of the client circuit according to the invention but also to monitor or evaluate a steady increase in the liquid level.

According to the present invention, the activation of the client circuit thus always takes place when a sufficient field strength (which is indeed provided by the electric field of the server circuit) is present, which in the case of a sensor device for detecting the level in a container according to present invention can be evaluated simultaneously as a "sensor OK" signal. Failure of such a signal may be evaluated by the sensor device as reaching a predetermined level in a container.

According to the present invention, the sensor means may comprise a plurality of such client circuits accessible from the electric field provided by the server circuit for powering the client circuits.

In order to distinguish several such client circuits within a sensor device by the server circuit, the client circuit may provide a comparator, a timer, a free-running oscillator or a frequency divider. Comparator, timer, free-running oscillator or frequency divider are in 6b with the reference number 83 Mistake.

The comparator can compare an identification number modulated by the server with the alternating electric field with a comparison identification number stored in the client circuit, and only if the client circuit or the modulator is matched 82 of the client. In this way all client circuits located in an electric field can be individually addressed. If the identification number matches the comparison identification number, the selected client circuit would modulate its measured values, for example the filling level in a container, onto the carrier signal and transmit it to the server circuit via load modulation as long as the identification number matches the number of the comparison identification. Instead of modulating a value onto the carrier signal, the carrier signal can also be transmitted to the server solely by means of load modulation, which corresponds to the aforementioned "OK signal".

If the identification number on the alternating electric field provided by the server changes, the identification is lost and the comparator can cause the oscillator to stop oscillating, thus depriving the power for operating the client circuit. In this case, the evaluation device of the server circuit must check whether it receives a signal transmitted by the selected client circuit by means of load modulation of the server circuit in response to the transmitted with the electric field identification number. If there is no such an answer, the server circuit can interpret this to mean that the liquid level in the container is already the coupling-in electrode 21 has reached, which causes the voltage drop between the coupling electrode 21 and the Aukoppelelektrode 22 has fallen below a certain value, which is no longer sufficient for the operation of the client circuit.

As an alternative to the comparator, the client circuit can also provide a timer, which is intended to let the client circuit operate only after a certain time after receiving an electric field of the server circuit or to make the oscillator oscillate. This provides the possibility that the server circuit can receive time-matched sensor signals from different client circuits. Again, the effect occurs that, as soon as the liquid in the container to be monitored, the height of the coupling electrode 21 has reached, the oscillator no longer starts, even if due to the setting of the timer this would have to start. The server circuit may in turn interpret this as reaching the predetermined level of liquid in the container to be monitored.

Alternatively, a free-running oscillator can be provided. In this embodiment, it is advantageous to run the individual free-running oscillators with a different frequency.

Instead of a free-running oscillator and a frequency divider may be provided which shares the frequency of the oscillator of the server circuit. Preferably, the division ratio in the individual client circuits is different, so that the client circuits each operate at a different frequency.

The simultaneously transmitted to the server circuit in the case of using a free-running oscillator or a frequency divider signals of the individual client circuits can be separated so again due to the different frequencies from the server. The separation can be done using a Fourier transform, for example.

The client circuit and at least the server electrode 11 can be applied to polymer films by printing technology, so that different forms of the sensor device can be obtained.

The decoupling electrode 22 the client circuit is (capacitively) grounded to provide a closed loop AC circuit between the server circuit and the client circuit.

Claims (17)

Sensor device for detecting the filling level in a container, comprising: at least one client circuit ( 23 . 80 ) for generating signals; and a server circuit ( 12 . 70 ) for detecting the signals generated and output by the at least one client circuit and generating an electric field; wherein - the at least one client circuit comprises a first electrode ( 21 ) and a second electrode ( 22 ) having; - The at least one client circuit is capacitively coupled to the server circuit based on a modulated alternating field; and - the at least one client circuit is supplied with the electric field generated by the server circuit with energy for operating the client circuit, characterized in that the power supply for operating the client circuit by the voltage drop between the first electrode ( 21 ) and the second electrode ( 22 ) can be accomplished, wherein the voltage drop between the first electrode ( 21 ) and the second electrode ( 22 ) decreases with increasing fill level in the container, and the power supply of the client circuit is interrupted as soon as the voltage drop between the first electrode ( 21 ) and the second electrode ( 22 ) falls below a predetermined value. Sensor device according to claim 1, wherein the server circuit has at least one electrode ( 11 ) having. Sensor device according to claim 2, wherein the electrodes ( 21 and 22 ) of the client circuit and the electrode ( 11 ) of the server circuit are designed band-shaped and are arranged substantially parallel to each other. Sensor device according to claim 2 or 3, wherein the distance of the first electrode ( 21 ) (Coupling-in electrode) to the electrode ( 11 ) is smaller than the distance of the second electrode ( 22 ) (Decoupling electrode) to the electrode ( 11 ). Sensor device according to one of claims 2 to 4, wherein the first electrode ( 21 ) of the at least one client circuit and the electrode ( 11 ) of the server circuit narrow in relation to the second electrode ( 22 ) of the client circuit are configured. Sensor device according to one of the preceding claims, wherein the at least one client circuit and the server circuit on a film label, preferably printed on a polymer film, are arranged. Sensor device according to one of the preceding claims, wherein the voltage drop between the first electrode ( 21 ) and the second electrode ( 22 ) drops below the predetermined value as soon as the level in the container of the vertical arrangement of the first electrode ( 21 ), the first electrode ( 21 ) vertically above the second electrode ( 22 ) is arranged. Sensor device according to one of the preceding claims, wherein the sensor device is arranged in operation on the outside of the container. Sensor device according to one of claims 6 to 8, wherein the film label is arranged in the operation of the sensor device on the outside of the container. Sensor device according to one of the preceding claims, wherein the detection level can be determined by the vertical arrangement of the sensor device on the container. Sensor device according to one of the preceding claims, wherein the server circuit further comprises a power supply, an oscillator and an evaluation device, wherein the oscillator is operated by the power supply and wherein the evaluation device is supplied by the at least one client circuit provided modulated alternating field. Sensor device according to one of the preceding claims, wherein two or more client circuits are configured so that they are distinguishable by the server circuit. The sensor device of claim 12, wherein the two or more client circuits each comprise a comparator which compares an identification number modulated by the server circuit with the electrical field generated therefrom with a comparison identification number. Sensor device according to claim 13, wherein the client circuit can only be activated if the identification number corresponds to the comparison identification number and wherein each client circuit can be assigned a different comparison identification number. The sensor device of claim 12, wherein the two or more client circuits each comprise a timer and wherein the timers activate the respective client circuits in a predetermined order and duration. The sensor device of claim 12, wherein the two or more client circuits each comprise a frequency divider for dividing the frequency of the oscillator of the server circuit, wherein the division ratio of each client circuit is different. The sensor device of claim 12, wherein the two or more client circuits each comprise a free-running oscillator, the frequency of each oscillator being different.

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