Electricity: motive power systems – Automatic and/or with time-delay means – Moisture content or wetness
Patent
1996-04-15
1997-09-09
Cabeca, John W.
Electricity: motive power systems
Automatic and/or with time-delay means
Moisture content or wetness
318DIG2, 15250001, 356345, 356361, 2503391, G01J 502, H02H 708, A47L 100
Patent
active
056660375
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an arrangement for detecting or measuring a change in a reflective element which is part of a medium adapted to be penetrated by a predetermined radiation.
BACKGROUND OF THE INVENTION
In many instances, it is desirable to detect changes in a reflective element. Such changes are caused for example by a particular wetting of a surface, effected in order to derive control commands for closing windows or other openings for example, or for removing an interfering wetting. For example, an inner reflection surface of a radiation-permeable plate or wall (inner or total reflection), a mirror, or any other means, which possibly also reflects only stray light, can be considered as a reflecting element, such as, for example, a hand approaching the arrangement. The term wetting of a surface is understood to mean the covering or sprinkling of the surface with individual drops of liquid or the striking of drops of liquid against the surface, until a liquid film or foam is deposited on the surface, or until a liquid layer of a particular layer thickness has accumulated on the surface.
By means of the detection of the extent of the change of reflection ratios it is possible, for example, to detect the position changes or the appearance of an object, which moves or can be moved in front of the arrangement. If the change is a wetting, then concerted control commands can be derived, for example by means measuring of the quantity of the wetting liquid per unit of surface area and/or per unit of time on the wetted surface, by means of which, for example, the wetting can be regulated, closing events can be controlled as a function of the existing or expected quantity of liquid or an operation for removing the wetting can be optimally controlled as a function of the history of the cause of the wetting.
SUMMARY OF THE INVENTION
The object of the invention is to develop an arrangement of the type mentioned at the outset in such a way that an additional external radiation, which penetrates the arrangement from the area surrounding the arrangement for measuring or detecting a change, and is superimposed on the radiation of the arrangement, does not essentially affect, interfere with or distort the measurement or detection of the change, even if the additional external radiation constitutes an essential percentage or even a predominant portion in comparison to the radiation emitted for the measurement or detection.
The above object is attained by an arrangement for indicating a change in a reflective element of a radiation-permeable medium having a detection side disposed opposite the reflective element. The arrangement includes two measured sections for generating, reflecting and receiving radiation for measurement, each having a radiation source disposed adjacent the detection side of the medium for generating radiation for transmission through the radiation-permeable medium thereby resulting in generated radiation; a sensor-active surface on the reflective element for reflecting at least a portion of the generated radiation thereby resulting in reflected radiation emerging from the detection side of the medium; and a radiation receiver disposed adjacent the detection side of the medium at a distance from the radiation source for receiving the reflected radiation, the radiation receiver having an output for producing a detection signal representing received radiation. The arrangement further includes a switch arrangement for periodically actuating respective ones of the measured sections in a successive, repeating switching sequence according to a predetermined switching sequence frequency, wherein the detection signal includes a modulation frequency corresponding to the predetermined switching sequence frequency; an adjusting device for adjusting the detection signal so that, in a rest state of the sensor-active surface of each measured section, a part of the detection signal corresponding to each measured section has an average amplitude value equal to an average amplitude val
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