Optics: measuring and testing – Photometers – Comparison
Patent
1998-01-30
1999-10-26
Font, Frank G.
Optics: measuring and testing
Photometers
Comparison
G01J 110
Patent
active
059737751
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE TECHNOLOGY
The invention relates to a device for detecting a wetting of a pane having a wetting sensor which is provided with a measuring circuit having a transmitter, which emits light, and a receiver, which responds to the emitted light and emits a sensor signal, as well as with an evaluation device for the sensor signal comprising a difference former.
EP 0 460 180 B1 proposes a device of this type. By means of scanning of the output signal of a light receiver, the incident total light from the light of a transmitter and from extraneous light of the environment is detected in this known device in a first interval and, in a second interval, which is closely associated with the first interval, only the extraneous light is detected. The evaluating stage in the form of a microcontroller has an analog/digital converter. A differential summation takes place in a differential amplifier so as to form a useful light signal. This device for obtaining the useful signal is relatively complex.
SUMMARY AND ADVANTAGES OF THE INVENTION
It is the object of the invention to provide a device of the type specified at the outset wherein the useful light signal is obtained through simple measures and the wetting of a pane is detected reliably.
The above object generally is achieved according to the present invention by a device for detecting a wetting of a pane having a wetting sensor which is provided with a measuring circuit having a transmitter, which emits light, and a receiver, which responds to the emitted light and emits a sensor signal, as well as with an evaluation device for the sensor signal comprising a difference former, and wherein, it is provided that the measuring circuit has an integration stage for the detection of the amount of light of the light that is incident onto the receiver and a comparator stage with which a trigger signal can be emitted if the amount of light integrated as of a specific point in time exceeds a predetermined threshold, that the total amount of light comprising the light of the transmitter and possible extraneous light and the amount of extraneous light detected when the transmitter is turned off are measured in separate time intervals, that the evaluation device is provided with a timer whose counting value is detected which is generated during the integration time until the arrival of the trigger signal, that a reciprocal value former is provided for the determination of a quantity for the total amount of light and for the amount of extraneous light for forming the reciprocal values of the respective counting values, and that the reciprocal values can be supplied to the difference former with which a signal for the amount of useful light can be derived from the difference between the total amount of light and the amount of extraneous light.
The total amount of light and the amount of extraneous light can be detected reliably in separate intervals by means of the integration stage, for example, of a capacitor, which can be discharged at the beginning of the integration time via an electronic switch, and the counting value, which is obtained until the threshold is reached, with interferences being suppressed through the integration and the common measuring device. The processing complexity for making available the useful light signal is also small since the reciprocal values are formed from the counting values and the useful light signal is obtained from the difference of the quantities thus obtained for the total amount of light and for the amount of extraneous light. A relatively straightforward microcontroller, for example, can be used for the evaluating circuit.
For the further simplification of the processing stages, it is advantageous that the total amount of light is measured recurrently, whereas initially and subsequently the extraneous amount of light is only measured and stored when the amount of extraneous light changes by a predetermined amount, and that the currently stored amount of extraneous light is used to determine the useful light signal. To detec
REFERENCES:
patent: 4960996 (1990-10-01), Hochstein
patent: 5676154 (1997-10-01), Pettersson
patent: 5708278 (1998-01-01), Lowne
Font Frank G.
Kunitz Norman N.
Robert & Bosch GmbH
Stafira Michael P.
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