DE102005022980A1 - Measurement and evaluation of signals from capacitative rain sensor on vehicle windscreen, determines both frequency shift and change in amplitude caused by rain - Google Patents

Abstract

The evaluation circuit (3) determines the resonant frequency and amplitude of the oscillatory circuit (5, 6) in the tuned and/or de-tuned states. It compares the de-tuned and resonant frequencies of this circuit. To evaluate the degree of de-tuning, the tuned and de-tuned amplitudes of the circuit are compared at a given frequency. The given frequency is the resonant frequency of the circuit. Excitation is provided by a step- or Dirac pulse function. The evaluation circuit employs e.g. frequency analysis to evaluate the response. A component (7) in series with the oscillator, series-modulates information concerning resonance frequency and amplitude of the oscillatory circuit, in the tuned and de-tuned states.

Description

The The invention relates to a device for humidification detection, in particular for detecting moistening on a motor vehicle windscreen, with a resonant circuit, comprising at least one inductor, and with an evaluation circuit which is coupled to the resonant circuit and with the detuning of a resonant circuit can be determined.

Such a device is known from the publication with the publication number DE 101 27 990 C2 known. This device comprises an oscillator for exciting the resonant circuit, wherein the oscillator can be tuned in terms of frequency. With a measurement and evaluation circuit for detecting the damping of the oscillator or for detecting the detuning of the resonant circuit, a signal can be provided which is proportional to the degree of moistening of the sensor. It is thereby exploited the effect that changes the capacity in the resonant circuit by moistening the vehicle window. The detuning of the resonant circuit results in a change of the resonant frequency and the amplitude. In the known devices and also in the device described in the cited document either the change in the amplitude or the resonant frequency is evaluated in order to obtain a measure of the detuning or for moistening the vehicle window.

Of the Disadvantage of on the capacity change based devices of the type mentioned is that these not always reliable signals about the Provide moistening of the disc. Thus, the signal can be falsified by external influences. About the Windshield flying leaves can For example, lead to a detuning of the resonant circuit, the then falsely Way is recognized as humidification of the disc. Also can from Outside high-frequency signals are coupled into the resonant circuit, which the signal coupled by the resonant circuit in the evaluation circuit change.

Here uses the present invention.

Of the Invention is the object of a device of the initially mentioned type to improve that more reliable signals on the humidification the disc available can be made.

ADVANTAGES OF INVENTION

These Task is inventively characterized solved, that the evaluation circuit is suitable, the resonance frequency and an amplitude of the detuned resonant circuit and / or the unvoiced To determine the resonant circuit. Unlike the known method Thus, not only the resonance frequency or an amplitude of the Resonant circuit determined, but both information is evaluated, for information about to gain the humidification of the vehicle window. Through this Redundancy can be more reliable an information about the wetting state of the disc can be obtained. Such is for example in principle conceivable that between a moistening by rain on the one Side and by a detuning by other dielectrics on the Windscreen on the other side is distinguished. By Rain or water will happen caused a certain frequency shift. To this frequency shift is then always expected a certain attenuation of the amplitude. differs actually measured amplitude at the typically present frequency detuning, however from the typically present amplitude value, so may other materials than rain are assumed.

Further For example, the evaluation circuit can also be set up in such a way that that between rainwater and salt water, which in winter stirred up from the road and is reflected on the windshield, distinguished become. Because saltwater is a conductive Material is, in the salt water by the through the inductance of the resonant circuit generated electric field induced eddy currents in salt water. These eddy currents have a retroactive effect on the inductance and diminish these. This increases the resonance frequency. simultaneously salt water has a higher permittivity as water, which leads to a proportional damping of the system.

Finally, can with a device according to the invention the coupling of high-frequency signals are detected. By the Coupling a high frequency signal changes namely the amplitude the feedback Oscillation without, however, shifting the resonance frequency. Become both the amplitude and the resonance frequency or the respective changes considered in both sizes, the coupling of high-frequency signals can be detected more reliably as in the known devices for humidification detection.

The evaluation circuit of a humidification detection device according to the invention may be suitable for the resonance frequency of the Uncompared with the resonant frequency of the detuned resonant circuit to compare. Likewise, the evaluation circuit may be adapted to compare the amplitude of the unsocial with the amplitude of the detuned resonant circuit at a predetermined frequency, for example, the resonant frequency of the non-tuned resonant circuit.

According to the invention For example, the device may include a means (stimulant) for stimulating a Include vibration in the resonant circuit. This stimulant can have an oscillator, which can be tuned in frequency. Likewise, it is also possible that the exciting means for exciting the resonant circuit by means of a Jump function or a Dirac pulse is suitable. The evaluation circuit can then to determine the detuning of the resonant circuit the Step response or the impulse response for example by a frequency analysis examine and evaluate.

In Row to the components of the resonant circuit, d. H. in series to inductance and to the capacity may be a device for modulating the oscillation in the resonant circuit be switched. This modulating device may be suitable for an information about the resonant frequency and the amplitude of the detuned resonant circuit or to modulate the non-tuned resonant circuit.

DRAWINGS

One embodiment for one inventive device for moistening detection is shown in detail in the drawing. It shows

1 a circuit diagram of the device according to the invention.

DESCRIPTION THE EMBODIMENTS

The device according to the invention has a resonant circuit 5 . 6 from a coil 5 and a capacitor 6 on. Instead of the capacitor 6 as a separate component can also the parasitic capacitance of the coil 5 be used. In series with the components 5 . 6 of the resonant circuit 5 . 6 is an integrated circuit 7 connected, with which the oscillation of the resonant circuit can be modulated in a suitable manner, in particular information about the amplitude or attenuation and the resonant frequency of the resonant circuit modulated as signals present. About the inductance 5 is the resonant circuit 5 . 6 loose with a coil 4 coupled. About the coil 4 be signals or vibrations in the resonant circuit 5 . 6 coupled, previously from the exciter 2 have been generated. In addition, vibrations or modulated signals by means of the coil 5 of the resonant circuit 5 . 6 to the coil 4 be transferred, which then an evaluation circuit 3 be supplied.

The evaluation circuit 3 is set up so that both the amplitude and the resonant frequency of the resonant circuit are evaluated in order to obtain information about the wetting of the vehicle window.

Of the Resonant circuit is embedded in a vehicle window, the Humidification should be determined.

Claims (8)

Device for detection of dampening, in particular for detecting the moistening on a motor vehicle window, with a resonant circuit ( 5 . 6 ) comprising at least one inductance ( 5 ) and with an evaluation circuit ( 3 ) connected to the resonant circuit ( 5 . 6 ) and with the detuning of the resonant circuit ( 5 . 6 ) can be determined, characterized in that the evaluation circuit ( 3 ), the resonance frequency and an amplitude of the detuned oscillating circuit ( 5 . 6 ) and / or the non-tuned resonant circuit ( 5 . 6 ) to investigate. Apparatus according to claim 1, characterized in that the evaluation circuit ( 3 ) for determining the detuning of the resonant circuit ( 5 . 6 ) is suitable, the resonant frequency of the unsocial with the resonant frequency of the detuned resonant circuit ( 5 . 6 ) to compare. Apparatus according to claim 1 or 2, characterized in that the evaluation circuit ( 3 ) for determining the detuning of the resonant circuit ( 5 . 6 ) is adapted to the amplitude of the unsocial with the amplitude of the detuned resonant circuit ( 5 . 6 ) at a given frequency. Apparatus according to claim 3, characterized in that the predetermined frequency, the resonant frequency of the non-tuned resonant circuit ( 5 . 6 ). Device according to one of claims 1 to 4, characterized in that the device comprises a means ( 2 , Stimulation means) suitable for exciting a vibration in the resonant circuit ( 5 . 6 ). Device according to claim 5, characterized in that the starting means ( 2 ) to an excitation with the form of a jump function or a Dirac-impulse function Apparatus according to claim 6, characterized in that the evaluation circuit ( 3 ) for determining the detuning of the resonant circuit ( 5 . 6 ) is adapted to analyze the step response or impulse response, for example, by a frequency analysis. Device according to one of claims 1 to 7, characterized in that in series with the components ( 5 . 6 ) of the resonant circuit ( 5 . 6 ) a component ( 7 ) which is adapted to modulate information about the resonance frequency and the amplitude of the detuned oscillating circuit ( 5 . 6 ) or the non-tuned resonant circuit ( 5 . 6 ) to modulate.