Radiation detector for a flame alarm

Abstract

Abstract A radiation detector contains a sensor element constituted by a pyroelectrical element, for instance formed of lithium-tantalate, lead-zirconate-titanate, lead-zirconate-iron-niobate or polyvinyldifluoride. Arranged forwardly of the sensor element is a filter combination constituted by a first filter element comprising a germanium or silicon filter having vapor-deposited thereon a narrow band filter having a transmission or throughpass maxima at about 4.3-4.4 μm, and a further filter element formed of sapphire or rutile or a calcium aluminate-, germanate- or a magnesium-fluoride glass. This filter combination has a transmission maxima at the resonance radiation of carbon dioxide at 4.3-4.4 μm, while all other wavelength regions are damped by a factor of more than 1000. Furthermore, there can be provided an additional or auxiliary filter which absorbs radiation in the region of 3.5-4.0 μm transmitted by the narrow band filter in the presence of angular or oblique incidence of such radiation. A flame alarm equipped with a radiation detector of this type responds extremely selectively to flame radiation, while not responding to spurious radiation, such as solar radiation or daylight, artificial light sources and welding sparks, even if the intensity of this spurious radiation is more than thousand-fold the intensity of the flame radiation. Thus, flames of minimal intensity are detected in a reliable, sensitive and trouble-free manner, even with the presence of strong spurious radiation.

Inventors

• 👤 Domokos Tar

Bibliographic Details