Abstract: An infrared detector has at least one infrared-sensitive detector element and at least one infrared source disposed in a common housing with the detector, with the infrared radiation from the source being directed onto the detector element. A pulse generator is connected to the infrared source for pulsing the infrared radiation therefrom. A recognition circuit is connected to the detector element for identifying the pulse sequence of the detector output so as to continuously check the functioning of the detector. A number of such detector elements can be arranged in the housing, with each detector element having a respective infrared source associated therewith. The infrared source may be a heated wire, a chip resistor, or a light emitting diode.

Abstract: The invention is directed to an infrared motion alarm characterized by an infrared detector and an optical arrangement before the detector in the radiation direction for focussing the infrared radiation onto the detector. The optical arrangement is formed by a mirror arrangement and by a lens arrangement with the mirrors being on different levels so the different beam paths are being detected to prevent an intruder from crawling under the infrared detection beam paths.

Abstract: A contactless conductance potentiometer is provided in which the total conductance between two electric terminals can be selectively divided, the two parts being equal to the total conductance. This can be accomplished by using a ring-shaped photoconductor on a substrate, the ring-shaped photoconductor being divided along a diametral line. One exterior electrode is located on the substrate in a position surrounding one portion of the ring-shaped photoconductor and being in contact with the marginal edge thereof. The remaining part of the ring-shaped photoconductor is in marginal contact with the second exterior electrode. A tapping electrode is mounted inside the ring-shaped photoconductor and is in marginal contact with the inner edge of the ring-shaped photoconductor.

Abstract: The present invention involves a structure of a contactless ohmic resistance potentiometer. A current path between two exterior electrodes is provided by a photoconductor, and a means is provided for causing an exposure of a portion of the length of the photoconductor between one exterior electrode and a tapping electrode. This permits a voltage division between two exterior electrodes. The usable surface of the photoconductor layer is delimited by an exterior electrode and a tapping electrode having a definite geometric course between the exterior electrodes. The distance ratio from the tapping electrode to the two exterior electrodes is varied by means of displacing the exposure of the photoconductor which causes the active partial surface of the photoconductor to be varied at will.