DE102020132286A1 - Sensor device and method for detecting at least one property of a medium - Google Patents

Abstract

A sensor device for detecting at least one property of a medium has a first resonant circuit (10) with a first resonant frequency and a second resonant circuit (20) with a second resonant frequency that is not equal to the first resonant frequency, the first and second resonant circuits (10, 20 ) are inductively coupled, the medium being arranged between coils (11, 21) of the two oscillating circuits (10, 20) so that it influences an inductive coupling of the two oscillating circuits (10, 20); a voltage source (31) for applying a voltage to at least one of the two oscillating circuits (10, 20) in order to operate it as an active oscillating circuit, the inductive coupling of the two oscillating circuits (10, 20) resulting in a system frequency which is equal to the first resonant frequency and is different from the second resonant frequency; and an evaluation unit (32) for detecting the system frequency and/or an amplitude of a current and/or a voltage in the active oscillating circuit in order to derive the at least one property of the medium therefrom.

Description

The present invention relates to a sensor device and a method for detecting at least one property of a medium, the medium being in particular a liquid.

Methods and systems are known in the prior art that carry out impedance spectroscopy to detect a property of a medium. In this case, a frequency of a voltage to be applied is varied by a voltage source. Consequently, what is needed is a voltage source that can provide a voltage with a varying frequency. Such systems are, for example, from EP 2 145 091 B1 and EP 2 480 878 B1 known.

When impedance spectroscopy is to be performed in a system powered by a DC power source, for example, an increased effort is required to provide the power source capable of supplying a voltage with a varying frequency.

It is therefore the object of the present invention to eliminate this disadvantage of the prior art.

The object is achieved by the sensor device having the features of claim 1 and by the method having the features of claim 12.

A sensor device according to the invention for detecting at least one property of a medium has a first resonant circuit with a first resonant frequency and a second resonant circuit with a second resonant frequency, which is not equal to the first resonant frequency. The at least one property of the medium can be a mixing ratio and/or a quantity ratio and/or a density and/or a concentration and/or an electrical conductivity and/or a viscosity. The at least one property can alternatively or additionally be a filling level, in particular an empty filling level. The first and the second oscillating circuit are inductively coupled and the medium is arranged between coils of the two oscillating circuits so that it influences an inductive coupling of the two oscillating circuits. The sensor device also has a voltage source for applying a voltage to at least one of the two oscillating circuits in order to operate it as an active oscillating circuit. Due to the inductive coupling of the two oscillating circuits, a system frequency is established in the overall system, which is formed from the two inductively coupled oscillating circuits, which is different from the first resonant frequency and the second resonant frequency. The system frequency is preferably between the resonant frequencies of the two oscillating circuits. However, the system frequency can also be below or above the two resonance frequencies. The sensor device has in particular an evaluation unit for detecting the system frequency and/or for detecting an amplitude of a current and/or a voltage in the active oscillating circuit in order to derive the at least one property of the medium therefrom. Consequently, the sensor device according to the invention does not require a voltage source that is able to apply a voltage with a varying frequency, so that the circuit complexity is reduced compared to the prior art.

According to one aspect, the evaluation unit can be designed to detect or determine a frequency difference between the resonant frequency of the active oscillating circuit and the system frequency in order to derive the at least one property of the medium therefrom. For example, a table assignment or a previously determined function can be used to derive the at least one property of the medium from the recorded frequency difference. As a result, the influence of the medium on the inductive coupling between the two oscillating circuits can be precisely determined.

According to a further aspect, the evaluation unit can be designed to detect or determine an amplitude change of the current and/or the voltage in the active oscillating circuit in order to derive the at least one property of the medium therefrom. The amplitude change is a change in an amplitude of the current and/or the voltage when the active oscillating circuit oscillates at the resonant frequency, to an amplitude of the current and/or the voltage when the overall system consisting of the first oscillating circuit and the second oscillating circuit due to the inductive coupling the system frequency oscillates. For example, a table assignment or a previously determined function can be used in order to derive the at least one property of the medium from the detected change in amplitude. As a result, the influence of the medium on the inductive coupling between the two oscillating circuits can be precisely determined.

According to an additional aspect, the voltage source can be designed so that it applies the voltage in such a way that free oscillation in the active resonant circuit is excited. Consequently, the entire system oscillates at a system frequency that is influenced by the inductive coupling of the two oscillating circuits and consequently by the at least one property of the medium.

According to a further aspect, the coils of the two oscillating circuits can face each other. Accordingly, the medium is arranged between the two coils and influences the inductive coupling depending on the at least one property of the medium.

According to an advantageous aspect, the coils can be designed as print coils. Consequently, the coils are preferably formed in a planar, in particular rectangular, shape and the two opposite coils are arranged, for example, plane-parallel. As a result, an area in which the medium is arranged between the two coils is increased, so that the inductive coupling of the two oscillating circuits is more strongly influenced by the medium. This advantageously improves accuracy when determining the at least one property of the medium.

According to one aspect, the medium can be a liquid and the two oscillating circuits can be designed so that they can be brought into contact with the liquid. For this purpose, the oscillating circuits are designed in such a way that no short circuit occurs and no corrosion occurs when they come into contact with the liquid. For this purpose, the oscillating circuits can each be shielded from the liquid, for example, by a corresponding protective layer or cover or an oscillating circuit housing. However, it is also conceivable that only the two coils are designed so that they can be brought into contact with the liquid. In this case, the two oscillating circuit capacitors of the first and second oscillating circuits are accommodated, for example, in a housing of the sensor device, which is also designed to be liquid-tight. Accordingly, the at least one property of the liquid can be determined by using the sensor device according to the invention.

According to an advantageous aspect, the resonant frequencies of the two oscillating circuits can be in the range from 5 MHz to 100 MHz inclusive. The resonant frequencies of the two resonant circuits can preferably be in the range from 10 MHz to 20 MHz inclusive. As a result, the capacitances of the capacitors and the inductances of the coils must be selected in such a way that the resonance frequencies mentioned above are reached. This design of the resonant frequencies of the two oscillating circuits advantageously achieves a particularly high detection accuracy of the at least one property of the medium or the liquid.

According to a further aspect, at least one resonant circuit or both resonant circuits can have a capacitor. The capacitor and the coil of an oscillating circuit can be connected in series or in parallel. The resonant frequencies of the oscillating circuits can be changed by changing the capacitance of the capacitor and/or by switching off the capacitor from one oscillating circuit or from both oscillating circuits. In this case, the capacitance can be changed and/or switched off mechanically or electrically, for example. If a capacitor is switched off, the resonant frequency of an oscillating circuit corresponds to the natural resonant frequency of the coil of the oscillating circuit. Consequently, a working range of the sensor device can be changed and another property of the medium can be determined.

According to one aspect, the voltage source can be designed to apply a voltage to both resonant circuits. The voltage source can be provided in the form of two separate voltage sources or as a common voltage source. The voltage source can be designed so that the two oscillating circuits are operated alternately as active oscillating circuits. The evaluation unit can be designed to detect a respective system frequency. Consequently, for example, the first resonant circuit can be operated as an active resonant circuit and the evaluation unit can detect the system frequency. The second oscillating circuit can then be operated as an active oscillating circuit and the evaluation unit can detect the system frequency that is set. Consequently, different frequency ranges can be examined with regard to a property of the medium.

According to a further aspect, the sensor device can be designed for use in a vehicle or for use in a household appliance. The sensor device can be designed in particular to determine the at least one property of a liquid that is used in the vehicle or the household appliance. The sensor device is designed so that it can be arranged in a liquid container of the vehicle or of the household appliance.

A method according to the invention for detecting at least one property of a medium has the following steps: applying a voltage to at least a first resonant circuit with a first resonant frequency or a second resonant circuit with a second resonant frequency that is not equal to the first resonant frequency. If the voltage is applied to one of the oscillating circuits, it is operated as an active oscillating circuit. The first and the second oscillating circuit are inductively coupled, with the medium between coils of the two oscillating circuits is arranged so that it affects an inductive coupling of the two resonant circuits. Detecting a system frequency that differs from the first resonant frequency and the second resonant frequency and/or detecting an amplitude of a current and/or a voltage in the active resonant circuit. deriving the at least one property of the medium. Consequently, the method according to the invention can be carried out by the sensor device according to the invention and no voltage source capable of applying a voltage with a varying frequency is required.

According to one aspect, the method can include a step for detecting a frequency difference between the resonant frequency of the active oscillating circuit and the system frequency in order to derive the at least one property of the medium therefrom. As a result, the influence of the medium on the inductive coupling between the two oscillating circuits can be precisely determined.

According to a further aspect, the method can have a step for detecting a change in amplitude of the current and/or the voltage in order to derive the at least one property of the medium therefrom. As a result, the influence of the medium on the inductive coupling between the two oscillating circuits can be precisely determined.

In one aspect, the method may include a step of changing the capacitance of a capacitor or disconnecting the capacitor from one or both of the tank circuits. As a result, a working range of the overall system can be changed and another frequency range can be examined with regard to the at least one property of the medium.

According to an advantageous aspect, the method can include a step for alternately operating the two resonant circuits as active resonant circuits; have a step for detecting a respective system frequency and/or a step for detecting a respective amplitude of a current and/or a voltage in the active resonant circuit. Furthermore, the method can alternatively or additionally have a step for detecting a respective frequency difference and/or a step for detecting a respective amplitude change. Consequently, both oscillating circuits can be operated as active oscillating circuits and different frequency ranges can be examined with regard to a property of the medium.

A vehicle, for example a car, an airplane, a boat, has the sensor device according to the invention. Accordingly, the method according to the invention can be used in the vehicle to determine at least one property of a medium. The sensor device is preferably arranged in a liquid container of the vehicle in order to determine at least one property of a liquid used in the vehicle. The liquid in the vehicle can be a urea solution, which is used in particular for exhaust gas aftertreatment, and/or a washing liquid and/or engine oil and/or a cooling liquid.

A household appliance, such as a washing machine or a dishwasher, has the sensor device according to the invention. This is preferably arranged in a liquid container of the household appliance and designed in such a way that it detects a hardness of the water used and/or a detergent and/or detergent concentration and/or a rinse aid concentration and/or a salt concentration.

• 1 schematisch eine Darstellung der erfindungsgemäßen Sensorvorrichtung;
• 2 schematisch einen Schaltplan der erfindungsgemäßen Sensorvorrichtung; und
• 3 ein Ablaufdiagramm des erfindungsgemäßen Verfahrens.

Embodiments of the present invention are described below with reference to the attached figures. Show it:

• 1 a schematic representation of the sensor device according to the invention;
• 2 schematically a circuit diagram of the sensor device according to the invention; and
• 3 a flowchart of the method according to the invention.

1 shows a sensor device 1 according to the invention. This has a first resonant circuit 10 and a second resonant circuit 20, with a resonant frequency of the first resonant circuit 10 and a resonant frequency of the second resonant circuit 20 being different. In addition, the sensor device 1 has a housing 30 .

The sensor device 1 is arranged in a liquid container 40 in which a liquid 41 can be stored. The liquid container 40 is preferably designed as a liquid container for storing a liquid 41 used in a vehicle 100 and is used in a vehicle 100 .

The liquid in the vehicle 100 can be, for example, a urea solution and/or a washing liquid and/or an engine oil and/or a cooling liquid. The housing 30 of the sensor device 1 is connected via a suitable connection to an electronic control unit 50 of the vehicle 100 and the electronic control unit 50 is in turn connected to another unit 60, such as a computer or a Diagnostic device can be connected, eg via USB or CAN bus.

The housing 30 is designed to be sealed or liquid-tight in such a way that the liquid 41 cannot penetrate into the housing 30 . The first oscillating circuit 10 and the second oscillating circuit 20 protrude from the housing 30 and the liquid 41 is arranged in particular between the two oscillating circuits 10 and 20 . However, the first and the second oscillating circuit 10, 20 are also surrounded by the liquid 41 on a side facing away from the other oscillating circuit 10, 20. The two resonant circuits 10 and 20 are shielded from the liquid so that no short circuit and no corrosion can occur. For this purpose, the oscillating circuits 10 and 20 can be covered with a protective layer or accommodated in a respective oscillating circuit housing. The two oscillating circuit housings protrude from the housing 30 and are arranged in a respective plane at a parallel distance from one another. Alternatively, the two oscillating circuit housings can have a predetermined angle to one another. In addition, it is also conceivable that only one coil 11 of the first oscillating circuit 10 and one coil 21 of the second oscillating circuit 21 can be brought into contact with the liquid 41 . In this case, a capacitor 12 of the first oscillating circuit 10 and a capacitor 22 of the second oscillating circuit 20 are arranged in the housing 30 . In the housing 30 are, as in 2 to see, a voltage source 31 and an evaluation unit 32 are arranged, which will be described later.

The sensor device 1 is preferably arranged in a lower region of the liquid container 40 so that the at least one property of the liquid 41 can still be reliably detected even when the fill level in the liquid container 40 is low.

2 shows a schematic circuit diagram of the sensor device 1 according to the invention. The first resonant circuit 10 is formed from a coil 11 and a capacitor 12 . The second oscillating circuit 20 is formed from a coil 21 and a capacitor 22 . in the in 2 example shown, the resonant circuits 10 and 20 are designed as series resonant circuits. Alternatively, the resonant circuits 10 and 20 can also be designed as parallel resonant circuits. The two coils 11 and 21 face each other. They are designed, for example, as print coils, so that an area in which the liquid 41 is arranged between the two coils 11 and 21 is enlarged. For example, a respective coil 11 and 21 is arranged in a respective plane. The planes can extend in a parallel distance to each other or alternatively have an angle of incidence to each other.

Since the two coils 11 and 21 face each other, the two oscillating circuits 10 and 20 are inductively coupled, with the inductive coupling being influenced by the liquid 41 present between the two coils 11 and 21 .

The first oscillating circuit 10 and the second oscillating circuit 20 are operated by a voltage source 31 . The voltage source 31 is designed so that it applies a voltage in such a way that free oscillation in the two oscillating circuits 10 and 20 can be excited. The tank circuit 10 or the tank circuit 20 to which a voltage is applied by the power source 31 is hereinafter referred to as an active tank circuit and the other tank circuit, tank circuit 20 or tank circuit 10, is referred to as a passive tank circuit.

In addition, the sensor device 1 has an evaluation unit 32 . Evaluation unit 32, which is configured, for example, from a microcontroller with CPU and memory, is designed to calculate a frequency of a voltage U1 present at first oscillating circuit 10 and a current 11 flowing in first oscillating circuit 10 and/or a frequency of a voltage at second oscillating circuit 20 applied voltage U2 and a current flowing in the second resonant circuit 20 I2 to detect. For this purpose, the evaluation unit 32 can have an analog/digital converter (not shown in the figures) or another means suitable for this purpose. The analog/digital converter or the means can be integrated into the evaluation unit 32 or be provided separately from the evaluation unit 32 . According to another embodiment, the evaluation unit 32 can also be designed as part of the electronic control unit 50 . Furthermore, the evaluation unit 32 can be designed to detect a frequency difference between the resonant frequency and a system frequency that occurs due to the inductive coupling, in order to derive the at least one property of the liquid 41 therefrom. Alternatively or additionally, evaluation unit 31 can be designed to detect an amplitude of current I1 and/or voltage U1 and/or an amplitude of current I2 and/or voltage U2 in order to derive the at least one property of liquid 41 therefrom. Furthermore, the evaluation unit 32 can alternatively or additionally also be designed to detect an amplitude change in the current I1 and/or the voltage U1 and/or an amplitude change in the current I2 and/or the voltage U2. The amplitude change is a change between an amplitude of the current I1 or I2 and/or the voltage U1 or U2 when the active oscillating circuit, ie the first oscillating circuit 10 or the second oscillating circuit 20, oscillates at the resonant frequency, and the amplitude of the current I1 or I2 and/or the voltage U1 or U2, if the entire system consisting of the first oscillating circuit 10 and the second oscillating circuit 20 oscillates at the system frequency due to the inductive coupling In addition, the evaluation unit 32 is designed to control an operation of the voltage source 31, so that a method according to the invention for determining at least one property of the liquid 41 can be carried out.

It should be noted that in the in 2 shown embodiment, a voltage source 31 and an evaluation unit 32 is used. However, it is also conceivable for two separate voltage sources and/or two separate evaluation units to be used for the two resonant circuits 10, 20. In addition, 2 the liquid 41 is only shown between the coils 11 and 21, of course the liquid 41 is present up to a level over the entire width of the liquid container 40.

A method according to the invention for detecting at least one property of the liquid 41 is described below with reference to the flowchart in 3 described. The method according to the invention is preferably carried out by the evaluation unit 32 at specific points in time. However, it is also conceivable that an execution of the method according to the invention is triggered by the electronic control unit 50 .

In step S1, a voltage is applied to the first oscillating circuit 10 by the voltage source 31 so that free oscillation in the first oscillating circuit 10 is excited. Due to the inductive coupling of the first oscillating circuit 10 and the second oscillating circuit 20, the overall system oscillates at the system frequency.

In step S2, the evaluation unit 32 detects the system frequency and stores it.

In step S3, a voltage is applied to the second oscillating circuit 20 by the voltage source 31, and free oscillation in the second oscillating circuit 20 is thereby excited. Due to the inductive coupling of the second oscillating circuit 20 and the first oscillating circuit 10, the overall system oscillates at the system frequency.

In step S4, the evaluation unit 34 detects the system frequency and stores it.

In step S5, a capacitance of the capacitor 12 of the first oscillating circuit 10 is changed or switched off. As a result, a working range of the entire system can be changed, so that another property of the liquid 41 can be determined. Additionally or alternatively, the capacitance of the capacitor 22 can be changed or switched off in step S5. Accordingly, a working range of the second oscillating circuit 20 can also be changed, so that another property of the liquid 41 can be determined.

If a capacitance of the capacitor 11 and/or the capacitor 21 has been changed or one or both of the capacitors 11, 21 has been turned off (YES in S5), steps S1 to S4 are performed again to detect the respective system frequencies.

In step S6, the at least one property or properties of the liquid 41 are derived from the previously determined system frequency(s).

It should be noted that the method according to the invention was described in which the two oscillating circuits 10 and 20 are operated alternately as active oscillating circuits, but it is also conceivable that only one of the two oscillating circuits, e.g. the first oscillating circuit 10, is operated as an active oscillating circuit and only one system frequency is detected. In this case, steps S3 and S4 of the method according to the invention are preferably not carried out. In addition, it is conceivable that a capacitance of the capacitors 11 and 22 is not changed or that none of the capacitors 11, 22 is switched off. In this case, step S5 of the method according to the invention is preferably not carried out.

Alternatively or additionally, in the method according to the invention, a frequency difference between the resonant frequency of the active oscillating circuit and the system frequency can be detected in steps S2 and S4 in order to derive the at least one property of the medium therefrom.

Additionally or alternatively, in the method according to the invention, an amplitude of a current and/or a voltage in the active oscillating circuit can be detected in steps S2 and S4 in order to derive the at least one property of the medium therefrom. Furthermore, in steps S2 and S4, alternatively or additionally, a change in the amplitude of the current and/or the voltage in the active resonant circuit can be detected.

The present invention was described for a vehicle 100, but it is possible for the sensor device 1 according to the invention and the method according to the invention to also be used for a household appliance, such as a washing machine, a dishwasher or the like will. The sensor device 1 can be designed in such a way that it detects a hardness of the water used and/or a detergent and/or detergent concentration and/or a rinse aid concentration and/or a salt concentration etc.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2145091 B1 [0002]
• EP 2480878 B1 [0002]

Claims (14)

Sensor device for detecting at least one property of a medium with: a first resonant circuit (10) having a first resonant frequency and a second resonant circuit (20) having a second resonant frequency which is unequal to the first resonant frequency, the first and second resonant circuits (10, 20) being inductively coupled, the medium between coils (11, 21) of the two oscillating circuits (10, 20) is arranged so that it influences an inductive coupling of the two oscillating circuits (10, 20), a voltage source (31) for applying a voltage to at least one of the two oscillating circuits (10, 20) in order to operate it as an active oscillating circuit, with the inductive coupling of the two oscillating circuits (10, 20) resulting in a system frequency which is equal to the first Resonance frequency and the second resonance frequency is different, and an evaluation unit (32) for detecting the system frequency and/or an amplitude of a current and/or a voltage in the active oscillating circuit in order to derive the at least one property of the medium therefrom. Sensor device according to claim 1 , wherein the evaluation unit (32) is designed to detect a frequency difference between the resonant frequency of the active resonant circuit and the system frequency in order to derive the at least one property of the medium. Sensor device according to one of the preceding claims, wherein the evaluation unit (32) is designed to detect an amplitude change of a current and/or a voltage in the active oscillating circuit in order to derive the at least one property of the medium therefrom. Sensor device according to one of the preceding claims, wherein the voltage source (31) is designed such that it applies the voltage in such a way that free oscillation in the active oscillating circuit is excited. Sensor device according to one of the preceding claims, the coils (11, 21) of the two oscillating circuits facing one another. Sensor device according to one of the preceding claims, wherein the coils (11, 21) are designed as printed coils. Sensor device according to one of the preceding claims, wherein the medium is a liquid (41) and the two oscillating circuits (10, 20) are designed such that they can be brought into contact at least partially with the liquid (41). Sensor device according to one of the preceding claims, wherein the resonant frequencies of the two oscillating circuits (10, 20) are in the range from 5 MHz to 100 MHz, preferably in the range from 10 MHz to 20 MHz. Sensor device according to one of the preceding claims, wherein at least one resonant circuit (10, 20) or both resonant circuits (10, 20) have a capacitor (12, 22), and the resonant frequencies of the oscillating circuits (10, 20) can be changed by changing the capacitance of the capacitor (12, 22) and/or by switching off the capacitor (12, 22) of one oscillating circuit (10, 20) or of both oscillating circuits (10, 20). . Sensor device according to one of the preceding claims, wherein the voltage source (31) is designed to apply a voltage to both resonant circuits (10, 20), the voltage source (31) is designed such that the two oscillating circuits are operated alternately as active oscillating circuits (10, 20), and the evaluation unit (32) is designed to detect a respective system frequency. Sensor device according to one of the preceding claims, wherein the sensor device (1) is designed for use in a vehicle (100) or for use in a household appliance. Method for detecting at least one property of a medium, comprising the following steps: Application of a voltage to at least a first oscillating circuit (10) with a first resonant frequency or a second oscillating circuit (20) with a second resonant frequency, which is not equal to the first resonant frequency, in order to operate this as an active oscillating circuit, the first and the second oscillating circuit ( 10, 20) are inductively coupled, the medium being arranged between coils (11, 21) of the two oscillating circuits (10, 20) so that it influences an inductive coupling of the two oscillating circuits (10, 20), detecting a system frequency which differs from the first resonant frequency and the second resonant frequency, and/or detecting an amplitude of a current and/or a voltage in the active oscillating circuit, and deriving the at least one property of the medium. procedure according to claim 12 with the following step: changing a capacitance of a capacitor (12, 22) and/or switching off a capacitor (12, 22) from an oscillating circuit (10, 20) or from both oscillating circuits (10, 20). Method according to one of Claims 12 or 13 with the following steps: alternately operating the two oscillating circuits (10, 20) as active oscillating circuits, and detecting a respective frequency difference between the resonant frequency of the active oscillating circuit and the system frequency that is set, and/or detecting a respective amplitude of a voltage and/or a current in the active resonant circuit.

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