Abstract: A smoke detector containing a radiation source operating in a pulsed mode and a scattered radiation receiver connected in a coincidence circuit. This circuit contains a counter which counts both the radiation pulses and the incoming scattered radiation pulses. With undisturbed operation this counter, following each radiation pulse, has an even numbered counter state. The appearance of an uneven numbered counter state is indicative of the presence of spurious pulses and leads to resetting of the counter to null, so that there is prevented attainment of a counter state adequate for tripping an alarm signal. On the other hand, with the presence of a predetermined even numbered counter state there is triggered an alarm. Such smoke detector is almost immune to spurious pulses and does not tend to trigger faulty alarm signals.

Abstract: A smoke detector, especially for a fire alarm, comprising a radiation source possessing a substantially conical ring-shaped radiation characteristic or pattern and a radiation receiver arranged along the axis of the radiation source but externally of the direct radiation. The radiation receiver receives radiation which is scattered by smoke particles within the conical ring-shaped radiation region. In order to reduce the spurious radiation impinging on the radiation receiver the radiation region is bounded by elements located externally of the direct receiving region of the radiation receiver. Web means (which comprise the bounding elements opposite the radiation source) are provided which are specially-shaped to prevent dust from collecting on their radiation receiving surfaces, thereby keeping the smoke detector from becoming increasingly susceptible with time to the triggering of false alarms as the deposition of dust at the inner surface of the fire detector housing increases.

Abstract: A smoke detector having a radiation source operating in the infrared, visible or ultraviolet wavelength region, transmitting radiation throughout an expanded or extended solid angle region of predetermined minimal extent. A radiation receiver is arranged externally of this radiation region for the reception of radiation which has been scattered at smoke particles and for signal transmission upon exceeding a predetermined smoke density. To compensate for decrease in smoke sensitivity of the smoke detector with temperature increase there is provided a bimetallic strip which, in the presence of a temperature increase, gradually moves into a small part of the radiation region and causes an additional irradiation of the radiation receiver. By suitable selection and arrangement of the bimetallic element the smoke sensitivity remains almost constant up to a predetermined critical temperature, or the smoke sensitivity gradually increases with increasing temperature.

Abstract: An optical smoke detector comprising a radiation source which transmits radiation into a predetermined spatial region and a radiation receiver to which there is delivered the radiation which is scattered by particles located along the radiation path. The radiation source possesses a substantially conical ring-shaped radiation characteristic or pattern and the radiation receiver is arranged substantially at or along the cone axis.

Abstract: An optical smoke detector comprising a radiation source transmitting radiation throughout a predetermined spatial region and at least one radiation receiver to which there is delivered the radiation scattered by particles located in the radiation region. One or a number of elements conducting radiation by reflection are provided and arranged such that they remove radiation, which has been forwardly scattered at an acute angle with respect to the radiation direction, at a substantially ring-shaped zone about the region of direct radiation and delivers such removed forwardly scattered radiation to the radiation receiver.