Sensor device for detecting the degree of wetting and/or contami

Details Sensor device for detecting the degree of wetting and/or contami Sensor device for detecting the degree of wetting and/or contami

1995-07-13

1998-09-08

Allen, Stephone

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250577, 318483, G01N 2117

Patent

active

058048170

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Prior Art
The invention relates to a sensor device for detecting the degree of wetting and/or contamination of windows, especially windshields of motor vehicles, of the type having a radiation source emitting a radiation into the window from the inside of the window, a radiation measuring device detecting the radiation reflected by total reflection in the window between an outer surface and an inner surface of the window along a measurement path, and a heating device.
DE-C 38 23 300 and DE-C 40 06 174 disclose sensor devices of this type which operate according to the principle of attenuated total reflection. For this purpose, the radiation emitted by a radiation source is reflected many times (total reflection) at the window outer and inner surface along a measurement path and is then detected by a radiation measuring device. Dirt particles or raindrops on the outside prevent the total reflection and therefore attenuate the reflection in the window interior, which results in a signal attenuation which can be detected by the radiation measuring device. Below a predeterminable limiting value, means for window cleaning, for example, are then automatically switched on.
In the case of a sensor device of this type, the problem can arise that condensation is formed on the window inside, that is to say between the sensor device and the window, as a result of large temperature differences between the inside and outside of the window. This condensation likewise leads to a falsification of the measurement result, since the total reflection is now impaired by the condensation formation on the inside of the window. The known sensor devices therefore have a reflection layer with a high-gloss surface, which is applied to the inside of the window in a sealing manner with an optical intermediate medium, in order to prevent the penetration of air and condensation. The high-gloss surface ensures total reflection. However, the production of such reflection layers coupled in a sealing manner to the inside of the window is very complicated and increases the cost of the production of the sensor device. Furthermore, this reflection layer can clearly be detected from outside and is optically disturbingly noticeable to the observer.
In addition, the known sensor devices are provided with a heating device in order to achieve heating up of the entire sensor device to, for example, 40.degree. C. This is used, for example, to thaw a snow covering on the outside of the window in the region of the sensor device and to evaporate partially formed condensation in the event of the encapsulation of the reflection layer with the high-gloss surface not being completely airtight. Despite the heating device, the high-gloss surface which is applied as tightly as possible to the inside of the window is therefore necessary. Furthermore, as a result of the heating-up of the entire sensor device, a relatively high electrical energy requirement arises and the components must be designed accordingly.


SUMMARY AND ADVANTAGES OF THE INVENTION

A sensor device for detecting the degree of wetting and/or contamination of windows, especially windshields of motor vehicles, having: a radiation source emitting a radiation into the window from the inside of the window, a radiation measuring device detecting the radiation reflected by total reflection in the window between an outer surface and an inner surface of the window along a measurement path, and a heating device; and wherein the heating device is disposed on the contact surface between the sensor device and the window or in the window adjacent the measurement path to directly and deliberately heat the measurement path.
In contrast to known arrangement, the sensor arrangement according to the invention as described above has the advantage that an additional reflection surface with a high-gloss surface on the inside of the window can be completely omitted, since the formation of condensation can be prevented by means of direct targeted heating of the inside of the window in the

REFERENCES:
patent: 4652745 (1987-03-01), Zanardelli

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