Abstract: For reducing the susceptibility to false alarms and for increasing the detection probability of a passive infrared detector, the actual signals obtained from a first sensor element are continuously compared in a correlator with reference or set signals stored in a read-only memory and/or with the actual signals obtained from a second sensor element monitoring the near region. The correlator delivers an output signal which corresponds to the correlation of both signals which are compared with one another. An alarm signal is triggered when the correlation exceeds a predetermined value, for instance 0.7, and the amplitude has reached a predetermined threshold. The infrared detector affords high security against giving of false alarms and a high detection probability, even in the presence of signals possessing a great amount of noise, but also delivers an alarm signal in the event the detector is attempted to be sabotaged, for instance by covering the inlet optical system.

Abstract: The monitoring of intrusion detectors is effected by an apparatus for testing the responsiveness to environment-caused, detector-specific useful and spurious signals. This testing apparatus is arranged inside of the intrusion detector and ensures that during installation and during the operation of the intrusion detector its electrical parameters are optimally adjusted. Deviations of these parameters from their nominal values and the location of these deviations are indicated.

Abstract: An intrusion detector evaluates the infrared radiation emitted by an intruder within a closely defined zone or area by means of a virtual protective curtain. Uniform sensitivity independent of incident angle of the radiation is provided by a cylindrical Fresnel lens of small thickness, which divides the field of reception into sharply defined strips or elongate zones of substantially uniform sensitivity. The longitudinal axis of this Fresnel lens defines an arcuate sector of a circle whose radius is determined by the focal length in perpendicular direction, and an infrared sensor is arranged at the circular center point, i.e., the focal point of the curved Fresnel lens. One particularly advantageous embodiment of the intrusion detector includes a double sensor configuration, equipped with several sensor elements cooperating with one or more cylindrical Fresnel lenses, thus covering a number of separate zones for simultaneous radiation detection.

Abstract: In a light barrier, especially for outside application and long distances monitored, insensitivity to interfering light and scattering through fumes or fog and an increased range and sensitivity to objects passing through the light barrier are achieved by subdividing radiation from a source into two radiation branches which are offset relative to each other and differently polarized, e.g., by means of a polarization filter divided into two parts, with different linear or oppositely circular polarization of the filter part surfaces. By means of an analogously subdivided polarization filter, the radiation of each of the two radiation branches is focused on a different individual sensor element. The two sensor elements are connected in a differential circuit which triggers an alarm signal in response to signals arriving from both radiation branches in short succession but does not trigger an alarm signal if both sensor elements are equally irradiated.

Abstract: In an ultrasonic alarm installation, ultrasonic waves are continuously emitted into a monitored region and a frequency shift caused by a moving object, e.g. an intruder, is received by an ultrasonic receiver and evaluated by virtue of the Doppler effect for generating an alarm signal. For testing the ultrasonic alarm installation the emitted ultrasonic waves are modulated by a plurality of modulation frequencies in the range of the frequency shifts effective for triggering the alarm signal. Thus, the function test can be carried out using the same electrical evaluation circuit as for generating the alarm signal. The plurality of modulation frequencies conjointly with the switch-off of the transmitter signal has the effect that the reflected signals, which arrive at the ultrasonic receiver with different phase relationships, are not vectorially added to the ultrasonic transmitter signal to yield zero, so that a reliable function control is always ensured.

Abstract: In an ultrasonic alarm installation ultrasonic waves are continuously emitted into a monitored region and a frequency shift due to a moving object, e.g. an intruder, by virtue of the Doppler effect is evaluated for giving an alarm signal. The function control in this installation occurs during a test phase by means of brief aperiodic modulation of the emitted ultrasonic waves. The resulting brief frequency broadening generates in the same evaluating circuit a signal if the installation is functioning correctly. The time duration of the aperiodic modulation is selected to be so short that no standing waves can form, so that the function control can also work faultlessly if the installation, because of vectorial addition of the received ultrasonic waves, accidentally is in an insensitive state. Thus even coverings of the ultrasonic transmitter during a sabotage attempt can be recognized and distinguished from an insensitive state.

Abstract: In an infrared intrusion detector which evaluates the body radiation of an intruder by means of a dual radiation sensor having two sensor elements arranged in a differential circuit for emitting an alarm signal, a functional supervision and detection of an attempt at sabotage, e.g., by covering or spraying the entrance window, are achieved by asymmetric irradiation of the two sensor elements through the entrance window by a radiation source. The asymmetry can be achieved by disposing the radiation source outside the plane of symmetry of the sensor elements or by an asymmetrically disposed auxiliary reflector.

Abstract: An infrared intrusion detector having a predetermined number of rows of radiation reception zones comprises a primary reflector and a secondary reflector for each row of radiation reception zones. The primary reflectors and their associated secondary reflectors form a folded radiation path. The folded radiation path allows for compact construction and simple manufacturing of the infrared intrusion detector. One reflector of each radiation reception zone forms together with the infrared sensor a compact structural unit. The other reflectors of each radiation reception zone are combined to form a further structural unit which is arranged in a predetermined spaced relationship to the first compact structural unit. In order to achieve uniform detection sensitivity in radiation reception zones having different angles of inclination to the horizontal plane, a larger focal length is chosen for radiation reception zones with smaller angles of inclination and longer range.

Abstract: Reactive gases like, for example reducing gases, specifically carbon monoxide, are detected in a gas mixture, particularly in air, with extremely high sensitivity and with high precision using a gas detector in which the attenuation of the intensity of an infrared radiation beam by a catalyst layer is utilized. Such catalyst layer contains at least one transition metal selected from at least one of the groups I, VII, and VIII of the Periodic Table of the Chemical Elements. Preferably, chemical elements are used having an atomic weight in the range of about 100 to about 205. The detection of carbon monoxide is particularly sensitive using a catalyst layer which substantially contains a metal capable of forming a carboncarbonyl compound with carbon monoxide.

Abstract: An alignment apparatus for a photoelectric transmitter or receiver having an emitter or detector at the focal point of a focusing lens or mirror includes a plane mirror located between the emitter or detector and the focusing device. The mirror is provided with an aperture behind which the emitter or detector is located. A center line indicating sight is provided between the focusing device and the emitter or detector. By observing the plane mirror from an appropriate angle the transmitter or receiver can be aligned with its counterpart transmitter or receiver.

Abstract: In a photoelectric smoke detector, a radiation source is driven intermittently by a control circuit and the radiation influenced by smoke particles, for instance scattered radiation, is picked up by a radiation receiver. The signal of the radiation receiver is transmitted to a signal processing circuit which is transmitted to a signal processing circuit which is simultaneously regulated by the control circuit. The signal processing circuit comprises a phase sensitive circuit which reverses or inverts the received signal according to the phase of the signal of the control circuit and transmits the thus modified signal to an integrating circuit. The integrating circuit controls a display circuit by means of its integrated output signal. The display circuit can, for instance, output an alarm signal when the integrated signal, i.e. the smoke intensity, exceeds a prescribed threshold value or can display the smoke intensity.

Abstract: A compact passive infrared detector is provided with a plane mirror which reflects infrared radiation focused by a lens onto a detector arranged between the lens and the reflector.

Abstract: In a scattered radiation smoke detector (D) the energy supply from the evaluation unit (A) and the signal returned thereto take place exclusively optically by means of radiation conducting elements (L.sub.1, L.sub.2) and all electrical components are situated in the evaluation unit (A) remote from the smoke detector (D). An approximately parallel transmitting or reception zone of small diameter is generated by collimating devices (4, 6) disposed at the ends (3, 8) of the optical conductors and thereby the interference radiation level in the smoke detector is reduced and the sensitivity increased. Since the smoke detector (D) comprises no metallic components, it is insensitive to temperature and corrosion and is especially well suited for application in environments subject to the danger of explosion and electrical interference.

Abstract: Reducing gases can be detected in a gas mixture to be investigated, particularly in air, with high sensitivity and precision by means of a gas detector. The gas detector comprises a gas sensor which is arranged within a measuring chamber. The temperature of the gas sensor can be continuously increased according to a predetermined pattern from a starting value to an upper threshold value and can be subsequently decreased again to the starting value according to the same or according to a different pattern. There are provided at least two such heating cycles. Simultaneously therewith the gas mixture to be investigated, which is present in the measuring chamber, is periodically exchanged against a pure reference gas which is contained in a reference chamber. A selected property, such as the electrical conductivity of the gas sensor is thereby periodically changed.

Abstract: Measuring stations or locations are connected in cascade to signal lines and transmit measured or measuring values to a central signal station at which the measured values are linked or appropriately processed so as to obtain distinct malfunction or alarm signals. Upon activation of the monitoring system all measuring stations are disconnected by a change in voltage appearing on the signal line. Then, the measuring stations are reconnected to the signal line in a timewise staggered fashion by means of switching elements present at each measuring station in such a manner that each measuring station additionally reconnects a subsequent measuring station to the line voltage after a predetermined time-delay. Address storages are present at the measuring stations and are charged or occupied in a predetermined sequence by the central signal station with addresses associated with the individual measuring stations.

Abstract: The circuit arrangement generating at least one noise-level warning threshold monitors the noise-level of detectors in an alarm system. The noise-level warning threshold assumes a fixed relation to the operating or working point level of the signal transmitted by the detector of the alarm system while taking into account shifts in the level of the operating or working point. An alarm storage or buffer disposed in the detector is set without transmitting an alarm signal when the noise-level warning threshold has been exceeded. The noise-level is monitored during normal operation and gives sufficiently early warning of a tendency to generate false alarms.

Abstract: The device comprises a gas sensor containing a predetermined number of sensor elements which change their electric conductivity under the action of gases. Such a gas sensor is used for selectively determining the components of gas mixtures. For this purpose the individual sensor elements are arranged on a heat-resistant, thermally insulating substrate and the individual sensor elements are sensitized for the determination of different components of the gas mixture by selecting different materials and/or operating temperatures for the individual sensor elements. The sensor elements and its components are arranged such that the gas mixture to be investigated is guided past the sensor elments in a directed flow. The temperatures of the sensor elements increase in a stepwise manner in the direction of the gas flow and thereby a further increase in the selectivity of the gas sensor is achieved.

Abstract: Due to aging of the insulating materials arranged between the electrodes in ionization fire alarms or detectors the insulating efficiency of these thus formed so-called insulating paths or spans deteriorates in the course of time despite, or maybe even due to the cleaning operations performed upon such ionization fire alarms. To ensure that the insulating capacity does not fall below a critical value the insulating path or span is formed by at least two different insulating materials. The materials are arranged in such a manner that the creepage path between the electrodes extends across all the different insulating materials. This principle also may be applied to other measuring devices which require a high input resistance of an amplifier stage.

Abstract: Novel constituent materials for gas sensors detecting gaseous impurities in air contain metal oxides and catalyst additives. The materials are prepared by mixing a colloidal solution A of an oxide or a hydroxide of at least one metal selected from the groups Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIa, VIb, VIIb, VIII and the lanthanides and actinides of the periodic system with a solution B containing a salt or a complex compound of at least one metal selected from the group: lanthanum, chromium, manganese, iron, cobalt, nickel, copper, ruthenium, iridium, palladium, platinum, rhodium, osmium, silver, gold, antimony, bismuth, thorium, and irradiating the mixture thus obtained with light of the visible and ultraviolet spectral region in order to photochemically deposit the metal in finely distributed form on the metal oxide or metal hydroxide, respectively.