Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-08-16
2002-04-02
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227250
Reexamination Certificate
active
06365908
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a liquid indicator, particularly a precipitation indicator, such as a rain indicator.
Liquid indicators can e.g. be used for determining the precipitation situation in the form of stationary rain indicators in the domestic and garden sector, so as to control an automatic watering system. A device of this type must e.g. be in a position to emit one or more precipitation signals in the case of rain, long-lasting, dense fog or other wetting precipitations and on whose reception the watering system can be switched off, so as to prevent overwatering of the monitored area and save water. One or more dry signals are to be emitted if precipitation adequate for the desired or necessary wetting action does not fall, so that the watering system can assume responsibility for providing the necessary wetness.
The problem of the invention is to provide a liquid indicator more particularly usable as a precipitation indicator. The device must in particular be in a position to make a reliable distinction between precipitation situations and dry situations.
SUMMARY OF THE INVENTION
This problem is solved by a liquid indicator having the features of claim
1
.
The liquid indicator usable as a rain indicator and as a result of this preferred application also called a precipitation indicator has at least one light source and at least one light guidance body or light guide, which is made from a material transparent to the light of the light source. The light guide has at least one surface portion, which is intended for contact with the liquid, particularly the liquid precipitation and which is so positioned relative to the light source that the light of the latter is totally reflectable on the surface portion if total reflection conditions exist on said surface portion. There is also at least one light detector, which can be brought into light-conducting connection with the light source by means of the surface portion.
Thus, an optical liquid or precipitation sensor is created, in which in the case of liquid, particularly precipitation, modifies the light conditions between the light source and the light detector to a significant extent. For as long as the surface portion is substantially dry, because there is e.g. little or no adequate precipitation, on the surface portion the optically dense material of the e.g. glass or visible light-transparent plastic light guide with a typical refractive index of well above 1, e.g. approximately 1.5 and the gaseous ambient atmosphere with a typical refractive index of approximately 1 are adjacent to one another. If the surface portion with respect to the light falling from the light guide side coming from the light source with respect to the average incidence direction relative to the normal to the reflecting surface is at an incidence angle greater than the material-specific critical angle of the total reflection, then the light is totally reflected on the surface portion and at this point cannot leave the light guide and is instead toally reflected into its interior. With such a dry situation one or more dry signals associated with the dry state are emitted. However, if the surface portion, particularly due to precipitation, is in contact with water and is more particularly wetted by the latter, due to the higher refractive index of water compared with air of typically approximately 1.3, the reflection conditions at the surface portion change in such a way that there is no total reflection and instead light passes out of the light guide at the surface portion, i.e. is coupled out of the same. This wetting situation referred to as the precipitation situation leads to the emission of one or more liquid or precipitation signals. Following adequate drying of the surface portion, once again total reflection conditions occur and a dry signal can be emitted. Further developments are explained hereinafter using the example of a precipitation indicator and the term “precipitation” can optionally also stand for other liquids.
For the detection of the precipitation on the surface portion it is possible to use the light intensity transmitted by the latter and also the totally reflected intensity, either in alternative or combined form. In a preferred embodiment the light detector is so positioned with respect to the surface portion, that substantially only the light source light totally reflected by the surface portion is detectable. A direct light conduction between the source and the detector is appropriately prevented. The exclusive use of the reflected intensity for precipitation detection is inter alia advantageous because the light detector can then e.g. be positioned within the light guide and/or the solid side of the surface portion, which permits a compact construction and also facilitates the protection of the light detector against moisture and damage.
Particular preference is given to embodiments in which in the light path between the light source and light detector there are several and in particular two surface portions at an angle to one another, which are so positioned relative to the light source and one another, that the light of the light source can be totally reflected by them to the light detector. As a result of the thus possible at least double deflection between the light transmitter or source and light receiver or detector, there is a significant rise in the distinction reliability between the dry state and the precipitation state, because there is only an adequate light intensity at the light detector if there are total reflection conditions, due to dryness, on all the totally reflecting surface portions in the light path.
Particular preference is given to embodiments in which at least two surface portions are positioned in such a way that the light source light, in the case of total reflection is deflected by more than 90°, particularly substantially by 180°. This permits a compact construction, in which the light source and light detector can e.g. be closely juxtaposed on one side of the light guide, whereas the surface portions to be wetted are located in the area of the opposite side. The light guide can e.g. have a circular conical segmental part with an aperture angle of approximately 90° on which are arranged in diametrically facing manner curved, totally reflecting surface portions, which can exert a certain light focussing action. It is also possible for the light guide to have at least two planar surface portions at an angle of 90° to one another and e.g. constructed in the form of a roof prism.
It is possible to use any suitable light source or combination of light sources and any suitable light detector responding to the light source light. Particularly cost-effective, reliably functioning and energy consumption-favourable embodiments are characterized in that the light source has at least one and preferably precisely one light emitting diode and/or that the light detector has at least one and preferably only one photodiode. An energy saving effect can be obtained if there is a device for the continuous operation of the light source, particularly for pulsed operation and optionally the pulse spacing can be adjustable. The time interval between successive and optionally very short light emissions can be in the second or minute range, e.g. approximately 10 or 30 or 60 seconds or more. Particularly consumption-favourable embodiments can advantageously operate in mains-independent manner and can e.g. be supplied with electric power by batteries, accumulators and/or photovoltaic elements. However, a mains-dependent supply is alternatively or additionally possible.
In preferred embodiments there is at least one precipitation reservoir for collecting precipitation and then a precipitation reservoir is preferably adjacent to a surface portion. As a result the response reliability of the indicator can be increased and erroneous indications are largely avoided, because a signal change from dry to precipitation will, in the case of a corresponding design, only occur with an adequately filled pre
Haeufele Reiner
Waigel Hans
Akerman & Senterfitt
Gardena Kress + Kastner GmbH
Le Que T.
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