Abstract: An infrared radiation-burglary detector comprising radiation-focusing means and a radiation receiver. A bunch of radiation-conducting elements is provided, the radiation inlet openings of which are arranged at the focal surface of the radiation-focusing means and the radiation outlets of which are arranged in front of the radiation receiver.

Abstract: To render an ionization-type sensing element essentially immune to changes in ambient conditions, principally temperature or operating voltage, while still using low-current draining circuits to sense response of the ionization chamber of the sensor, the threshold response level of a field effect transistor (FET) is arranged to have approximately the same temperature response characteristic, within the range of ambient temperature considered, as the ionization cell so that the overall circuit or system combination of the cell and FET amplifier will have a response which is essentially independent of ambient temperature or similar conditions. The source path of the FET is connected to a voltage divider which is so dimensioned that the voltage division ratio (R.sub.2 /R.sub.1) is related to the temperature coefficient (.alpha.) of the base-emitter voltage of the FET and the temperature coefficient (.beta.) of the measuring ionization cell chamber:R.sub.2 /R.sub.1 = (.beta./.alpha.) - 1.

Abstract: When applying light gates in burglar alarm systems and the like, in which pulsed sources provide pulsed beams of light (which may be UV, visible, or IR radiation), an evaluation circuit is provided coupled to the pulse source which detects coincidence of radiation received when it is being transmitted and also radiation received when none is transmitted, providing an output signal if: (a) no radiation is received when radiation is transmitted, or (b) radiation is received when none is being transmitted, so that phasing of transmitted radiation, as received, with respect to the transmitter becomes an additional recognition factor.

Abstract: To eliminate sources of error in fire detection apparatus regarding variation of light output from a radiation cell, and to eliminate varying ambient conditions such as dust and dirt contamination of reflectors and transducers, the radiation is directed over at least two paths by reflectors which are located such that the numbers of reflections in the paths and the reflection points are the same, whereas the lengths of the paths are different, and evaluating the difference signal to obtain a measure of the density of the medium through which the paths extend, typically the transmissivity of air which may be contaminated by smoke. In one embodiment, reflectors are located in the corners of a polygon, one of the paths extending across the polygon, and the other path extending essentially circumferentially thereof.

Abstract: To detect breakage of glass panes, panels of display cases, or movement in a room, ultrasonic waves, preferably in the order of from 120 kHz to 180 kHz, are transmitted to the sonically conductive medium (glass panes, plastic sheets, or into the air of the room), and the waves are received in a receiver. The time shift of the received waves at the receiver location, with respect to the transmitted waves is determined, and if this time shift changes beyond a predetermined limit, an alarm signal is generated. Preferably, the ultrasonic signals are frequency modulated, for example by shifting the generated waves by a predetermined frequency shift, and determining the temporal change, or delay of the frequency shift, as received, with respect to the time of frequency shift at the transmitter. To prevent the effect of drift, the rate of change of received with respect to transmitted frequency shift can be used to generate the alarm.

Abstract: At least two photoelectric sensors, sensitive to different spectral ranges of incident light, provide two sensed output signals; the relationship of the a-c components of the sensed output signals is evaluated, and it is determined if these a-c components fall within predetermined low frequency ranges, for example, 2 to 50 Hz, preferably 5 to 25 Hz; if so, a "flame present" signal is provided, for example to give a fire alarm, or to indicate that a burner is operating. Preferably, the relationship of the signals is such that a different signal is provided between one of the sensed signals and a fraction of the other, and conversely, and the sensitivity of the sensors is adjusted to have the same output signals at a predetermined color temperature, for example about 1,400.degree. K.