The invention relates to a PIR motion detector for detecting a moving body by detecting its intrinsic radiation in the infrared range according to the preamble of claim 1. Such motion detectors are used in conjunction with corresponding evaluation devices, in particular for detecting object movements and are also referred to as passive infrared motion detectors.

Systems for detecting the intrinsic infrared radiation of bodies with a temperature near the ambient temperature and their evaluation for detecting movements have been known for some time, for example, for detecting people or also vehicles.

In these so-called passive infrared motion detectors or abbreviated PIR motion detectors, a sensor is provided as well as an optical system which, by means of segmented mirror, lenses or similar optical elements, concentrates the optical field of a number of limited zones, and thus radiating bodies which are moving in and out of such zones, thereby creating a changing irradiation of the sensor which allow the sensor to detect motion.

Such systems are, for example, described in US 4,321 ,594 and are generally known in various designs. Corresponding systems are used to detect moving people, vehicles or other objects in order to trigger, for example, the switching or activation of light, energy, alarms, or other functions, and are particularly used for activating illumination when a person is moving within the visual range of such a system.

It is well known that infrared radiation of a body of a human being with a surface temperature of approximately 25 to 30°C or 300° Kelvin is detected in front of a background of approximately 20°C within the spectral range of Planck's radiation with a maximum in the vicinity of 10 μιη wavelength; and with the main range of the radiation from approximately 8 to 14 μιη.

Such motion detectors require one or more radiation-transmissive housing covers in order to protect the sensor(s) from environmental influences or to create windows that contain lenses or Fresnel lenses. For the above mentioned wavelength range can, on the one hand, crystalline materials such as diamond, NaCl, CaF, be used, as well as semiconductor crystals or amorphous semiconductor glass as well as the synthetic material polyethylene which, due to its simple molecular structure, has a specific permeability in the main range of the radiation spectrum from 8 to 14 μιη. PIR sensors are usually accommodated in a sensor housing which has a radiation-transmissive window. In order to protect the sensors from moisture and contamination, the connection between the sensor housing and the window is preferably designed so as to be air- and water-tight. For economic and technical reasons, the little windows of the sensors are usually made of germanium or silicon, whereby interference layers which cause an optical filter effect with respect to the wavelength are simultaneously applied to such window which is aligned on the central part of the to be detected spectrum.

The housing cover of the motion detector, which is appropriately essentially bigger than the window of the sensor housing, is only rarely designed as germanium lens or silicon wafer or with similar crystalline material, but is usually made of polyethylene foils, plates, or molded parts which in many cases contain the structure of Fresnel lenses, making it possible to omit additional optics, if necessary. The thickness of these housing covers in the form of a window or a lens made of polyethylene is typically between 0.1 mm and 1.0 mm because with larger thicknesses, the transmission in the range from 8 to 14 μιη greatly decreases and, due to the opacity, high scattering occurs.

Accordingly, thicker housing covers made of polyethylene can only be used in exceptional cases for motion detectors with very short range and sensitivity.

Typical housing covers that are designed as Fresnel lens or segmented Fresnel lens have a thickness from 0.4 to 0.5 mm and are made of polyethylene. This thickness results from a minimal mechanical stability as well as the option to be able to realize the grooves or groove profiles of the Fresnel lens using injection molding or pressing methods. On the other hand, by delimiting the thickness, the attempt is made to obtain a sufficient infrared permeability which in the central wavelength range from 8 to 10 μιη at a thickness of 0.5 mm already drops below 30%.

Other previously known designs use hemispheric or curved lens systems as described, for example, in US 4,930,864. Such lens systems can contain a plurality of lenses on a curved surface, wherein the lenses are designed as common biconvex lenses or as Fresnel lenses or pails thereof.

The use of infrared-transmissive housing covers in the form of windows made of polyethylene is, for example, described in US 4,795,908 or EP-A-0440112. Polyethylene is a very soft plastic and as a result, such thin housing covers in the form of windows or lenses have a very low mechanical strength which has proven to be very disadvantageous, particularly for motion detectors which are used as light switch or comfort control and are thus frequently within arm's reach of people because they are often destroyed willfully or

unintentionally. Furthermore, such a thin plate or lens as housing cover is prone to esthetically unsatisfactory wave- or bulge-like deformations at greater surfaces of 10 or more cm ² as is required for achieving greater operating ranges of the motion detection. Therefore, due to the polyethylene windows or lenses, PIR motion detectors can always be recognized as such and only in exceptional cases and great effort it is possible to produce esthetically satisfying and inconspicuous covers.

EP-A-0440112 describes infrared filter disks made from polyethylene as cover window for passive infrared intrusion detectors and also mentioned Infrared filter discs for flame detectors from PTFE.

GB-A-2205642 describes an infrared radiation activated control circuitry with a shell-shaped thin lens of infrared radiation-transmissive Polymehylpentene. DE-Al-19535408 describes an infrared radiation thermometer comprising a protective cap made of a thin foil of polyethylene, polypropylene, or a copolymer of these two substances. The infrared radiation thermometer also comprises an infrared sensor associated filter with a dielectric coating of infrared radiation-transmissive material which transmits the wavelength range between 5 and 14 μιη, which is usually used for the temperature measurement.

DE-A 1 -102011103818 describes an infrared sensor arrangement for a thermometer comprising a diaphragm or a wavelength-dependent filter in the direction of incidence of a sensor mirror and has optionally a dirt-repellent cover made of polyethylene, Polypropylene, polytetrafiuoroethylene or poly-para-Xylene on.

EP-A1-2060889 describes a detachable probe cover made from polyethylene, polypropylene, polycarbonate, polystyrene, polyethylene terephthalate or polyvinyl chloride for an ear thermometer. WO 2006/100672 A2 describes a PIR sensor with at least three sub-detectors for detecting the infrared radiation in various areas of vision, wherein the sensor is preferably made of an infrared- transparent window comprising HDPE, silicon or germanium.

While for various applications, such as a thermometer, the to be detected intensity of infrared radiation plays a minor role, since the reaction time of the measuring device is not critical, the radiation intensity reaching the sensor in case of a PIR motion detector plays an important role, since a short reaction time and a large-scale detection range of the motion is made possible.

Therefore, a high transmission rate of the infrared radiation to be detected in the Wavelength range by a sensor cover is of vital importance. Despite an intensive search for suitable materials, no synthetic material or any other easy-to- process and cost-efficient material has been found that has a suitable transmission in the range between 8 to 14 μιη. This is due to the known reason that a great number of molecular absorption frequencies, particularly of organic compounds, are within this range, and every synthetic material which has a more complex structure than polyethylene inevitably has more of such absorption frequencies and thus has a lower transmission in the particular range.

Only with very thin foils, the thickness of which is in the order of the wavelength or below, a transmission in the range from 8 to 14 μιηΐ can also be achieved with other synthetic materials. For example, polyester foils with a thickness of 4 μιη can be produced which, if mechanically clamped, achieve a specific strength. However, this solution is also not satisfactory because the foils are very vulnerable to external forces and sharp objects.

Therefore, after 40 years or global prevalence of PIR motion detectors, the windows and lenses are, with very few exceptions which use expensive and elaborate crystalline or amorphous crystals or semiconductors, still exclusively made of polyethylene.

The problem addressed by the present invention is that of providing a PIR motion detector for detecting a moving body by detecting its intrinsic radiation in the infrared range which eliminates the aforementioned disadvantages with regard to the housing cover. In particular, the housing cover is supposed to have high mechanical strength and to be producible cost-effectively in the form of a window or lens. The problem addressed by the present invention is particularly that of providing a PIR motion detector for detecting a moving body by detecting its intrinsic radiation in the infrared range with a maximum of the inherent radiation in the wavelength range between 7 and 10 μιη, having a housing cover in the form of a window or lens that is made of a sufficiently stable and thick synthetic material and its sensitivity to the previous motion is not inferior to a housing cover made of thin polyethylene.

According to the invention, the problem is solved with a PIR motion detector according to claim 1. Preferred embodiments are described in the dependent claims. The passive-infrared (PIR) motion sensor for detecting a moving body by detecting its intrinsic radiation in the infrared range comprises a shell-shaped cover with a cover opening and a within the cover disposed infrared-sensitive sensor in a sensor housing, which is provided with a radiation-transmissive window as optical filter and which is sealed. The cover opening is covered by a housing cover in the form of a window or a lens, wherein the by the sensor to be detected infrared radiation must pass through the cover on the one hand and through the optical filter on the other hand. The housing cover as well as the sensor housing outside the sensor window are usually not transmissive to infrared radiation. The housing cover comprises a sheet, plate or a molded part of Polymethylpentene (PMP), polytetrafluoroethylene (PTFE), polypropylene (PP) or Polyester, which has a thickness between 0.5 mm and 3 mm. Housing covers made of such synthetic materials are generally opaque for infrared radiation medium wavelength range of 8 μιη to 14 μηι of Planck radiation spectmm of infrared intrinsic radiation of bodies in room temperature, but exhibit areas, so-called transmission bands in the wavelength range of 3.5 to 6 μιη and for wavelengths between 12.5 and 50 μιη, which has a more or less high radiation transmittance.

The solution to the problem according to the invention results in a housing cover in the form of a window or lens made of a synthetic material that is predominantly or exclusively transmissive outside of the central spectmm of an intrinsic infrared radiation of bodies at room temperature with a wavelength from 8 to 14 μιη.

Therefore sensors with a with a radiation transmissive window as optical filter provided sensor housing are provided, which differ from sensor housings on the market and do not have the usual, on the central spectmm tuned optical filter of for example 8 to 14 μιη, but which are radiation- transmissive in a much wider wavelength range, in particular at wavelengths of 3.5 to 6 μιη and above 12.5 μηι, wherein the radiation-transmissivity in the central range of 8 to 12 μιη is not relevant and also zero or insignificant because in this wavelength range no radiation can be received anyway.

Polymethylpentene shows, for example, at wavelengths of 5 μιη, at 15 μιη and above 25 μιη, transmission bands which, even with higher thicknesses of the housing cover of 1 to 2 millimeters as is suitable for stable synthetic materials, still result in a high transmission at these wavelengths.

It is accepted that these synthetic materials show practically no transmission in the central range of the spectrum of intrinsic infrared radiation of bodies at room temperature from 8 to 14 μιη and that such central part of the radiation energy can thus not be utilized. Planck' s radiation also has small portions far outside the maximum or central range at significantly shorter and significantly longer wavelengths. In addition, polymethylpentene in particular has a high transparency in the transmissive spectral ranges without the opacity (turbidity of the radiation) of polyethylene; as a result, thickness has significantly less influence on the transmission than is the case with polyethylene.

If the detectable energy of the signal to be detected is added up, the solution according to the invention results in the same suitable signal strength as with previous designs due to the advantageous transmission properties of different synthetic materials for the spectral components far outside the central range, even if the central spectral component is disregarded.

As a result, it is possible to produce PIR motion detectors with mechanically stable and resilient covers or lenses which can have a thickness of up to 2 mm or even more which, when compared to the previous thin and soft polyethylene lenses or windows, results in a significant improvement of robustness and esthetics.

Due to the system according to the invention, it is also possible to provide entire caps or lamp covers of motion detectors implemented as light switches with incorporated lenses or windows, allowing for structurally simple and esthetically advantageous solutions. The lenses or Fresnel lenses incorporated in the housing cover can be structures imprinted in the housing cover, wherein a housing cover usually comprises a plurality of such lenses or Fresnel lenses.

However, the housing cover can also be a simple window, particularly if a segmented mirror is inserted as additional optical element for creating specific sensitivity zones. Appropriately, a segmented mirror consists of a plurality of parabolic mirror pieces, wherein each mirror piece focuses the infrared radiation in a different direction. Such a simple window can be designed so as to be flat or curved but usually has no optically bundling effect. For motion detectors used as burglar alarm, it is advantageous that mechanically vandal-proof designs can be produced, the function of which, when compared to the use of polyethylene, cannot be sabotaged by simple means such as stabbing or cutting the lens or cover, and which are inconspicuous and not even recognized as such by a burglar.

Preferably, the housing cover comprises a foil, a plate, or a molded part made of

polymethylpentene (PMP), polytetrafluoroethylene (PTFE), polypropylene (PP) or polyester. Furthermore, the housing cover preferably comprises a foil, a plate, or a molded part made of a composite material or a laminate containing a layer made of polymethylpentene (PMP), polytetrafluoroethylene (PTFE), polypropylene (PP) or polyester with a thickness of between 0.5 mm and 3 mm.

According to embodiments of the invention, a housing cover may be provided which is constructed of or comprises a plurality of flat, cylindrical, or curved Fresnel lenses, or a single lens. The Fresnel lenses or the single lens can be designed to be elements imprinted in the housing cover. However, the Fresnel lenses or the single lens can also be designed to be elements made of polymethylpentene (PMP), polytetrafluoroethylene (PTFE), polypropylene (PP) or polyester pressed into the housing cover.

Further advantages, features and details of the invention follow from the following description of the drawings.

Figure 1 : Schematically shows Planck's radiation spectrum of the thermal radiation radiating from a body at a room temperature of approximately 20 degrees Celsius as well as an exemplary depiction of the wavelength-dependent radiation contrast as difference of Planck's radiation between an object and its ambient temperature;

Figure 2: Shows a schematic depiction of a wavelength-dependent radiation contrast as difference of Planck's radiation between an object and its ambient temperature, the passband curve of an optical bandpass filter typically used for infrared-sensitive motion detectors, and the resulting energy spectrum of the infrared radiation which permeated the filter;

Figure 3: Shows a schematic depiction of a wavelength-dependent radiation contrast as difference of Planck's radiation between an object and its ambient temperature, the permeability of an optical filter for PIR motion detector according to the invention, and the resulting energy spectrum of the infrared radiation which permeated the filter;

Figure 4: Shows a schematic structure of a PIR motion detector according to the invention.

Figure 1 shows the known Planck's radiation (curve 1) that a body radiates at an approximate room temperature of 20 degrees Celsius. The abscissa shows the wavelength in micrometers λ[μιη] and the ordinate shows the radiation intensity. PIR motion detectors detect the object due to the surface temperature of the object which deviates from the ambient temperature. The difference of Planck's radiation of the object and its surrounding due to the different temperatures is the radiation contrast Ab _x (curve 2). Curves 1 and 2 have similar shapes; however, with regard to curve 1, curve 2 is shifted toward shorter wavelengths in abscissa direction. The energy of the radiation contrast Ab _¾ . is evaluated by the PIR motion detector.

Figure 2 once again shows curve 2 of the radiation contrast b _x as well as a curve 3 in accordance with the passband curve of a typical optical bandpass filter as used in previously known designs and transmissive for wavelengths of approximately 7 to 14 μιη. Curve 4 shows the remaining energy, when the radiation (see curve 2) passes through the filter 22 (see curve 3) and is additionally weakened by a factor of 3 by a cover 40 made of polyethylene with a thickness of 0.5 mm, and therefore shows that what is still detected by the sensor of the PIR motion detector in the previously known designs.

Figure 3 shows the spectral lines of motion detectors according to the invention, in which a housing cover made of polyethylene is removed and instead a housing cover 40 made of polypropylene, polytetrafluoroethylene (PTFE), polymethylpentene, or polyester is used. Curve 5 shows the transmissivity of the optical filter 22 used which in the depicted example allows transmission of radiation from 3.5 to 6 μιη and from 12.5 to 50 μιη. The dotted curve 6 eventually shows the radiation that reaches the sensor 20. Since the synthetic materials used in the motion detector according to the invention are largely transparent, there is no additional weakening even with thicker covers with a thickness of, for example, 2 mm.

As can be seen from the in the drawings used linear scale, the impinging radiation on a motion detector according to the invention is in total of the same order of magnitude as in known motion detectors, however in other wavelength ranges, which is no problem with the sensors normally used when they are provided with the appropriate optical filters.

In a typical design, a PIR motion detector according to the invention comprises a sensor 20 arranged in a sensor housing 23, whereby the sensor housing 23 has an opening which is closed by a radiation-transmissive window 22, wherein the window 22 comprises or consists of an optical filter, an electronic amplifier with signal evaluation unit 25, and an all-encompassing protective housing 30 with housing cover 40, wherein the housing cover 40 preferably comprises a single lens or Fresnel lenses. Figure 4 shows an embodiment of a PIR motion detector according to the invention. PIR sensor stands for passive infrared sensor. The embodiment of the PIR motion detector shown in figure 4 comprises a sensor 20 arranged in a sensor housing 23 which is provided with a radiation- transmissive window as optical filter 22 tightly closing the sensor housing 23, and two sensor elements 21, which are electrically differentially connected and which are, for example, made of pyroelectric material. The motion detector further comprises a signal evaluation unit 25. In addition, the sensor 20 conventionally may comprise a high-impedance preamplifier (not depicted). Such so-called pyroelectric dual-differential sensors 20 are available on the market in high numbers.

However, sensors 20 with only one or more sensor elements 21 and differently shaped sensor elements 21, or sensors 20 which use resistance bolometers as sensor elements 21 and which, due to radiation and the resulting heating, evaluate a change of the electric resistance, or sensor elements 21 which are designed as thermal elements and emit an electric voltage when heated, are also available. For the system according to the invention, the type of infrared sensor 20 is irrelevant as along as it is able to detect radiation in a broad range of approximately 3.5 to 50 μιη wavelength.

Sensor 20 is connected to a signal evaluation unit 25 which generates an output signal in a known manner when the sensor 20 receives changing radiation.

The entire system is installed in a protective cover 30, in which a plurality of lenses 40 is incorporated at the front side, resulting in a plurality of discrete directions 41, 41 ', 41 " , 41 " ', from which the PIR motion detector receives radiation.

Due to the use of a filter 22, which is transmissive particularly in the uppermost and lowest portion of the spectral range, a mechanically stable synthetic material such as polypropylene or polymethylpentene with a thickness of up to several millimeters can be used for the lens 40.

The design of such a PIR motion detector according to the invention is not limited to the structure shown in figure 4. All known designs with flat, cylindrical, or curved Fresnel lenses, single lenses, and the like, or segmented mirrors and other mirror systems can be used.