Abstract: An overheat detector comprises an optical fiber connected at one end to a light source and at the other end to a photodiode for monitoring the light level transmitted through the fiber. When the light level falls below a predetermined threshold due to melting of the fiber, an alarm signal is output. The temperature at which the alarm signal is output depends upon the material of which the light conducting part of the fibre is constructed.

Abstract: A fire or explosion detection system is disclosed for reliably discriminating between a hydrocarbon fire in an armored vehicle and other sources of radiant energy including explosion of an armor-piercing ammunition round without an accompanying hydrocarbon fire. Radiation detectors sensitive to radiation at 4.4 microns and 0.9 microns, respectively, each produce logic outputs if the viewed radiation intensity exceeds a predetermined relatively low threshold and, in the case of the 4.4 micron detector, is rising at least a predetermined rate or, in the case of the 0.9 micron detector, is not falling at more than a predetermined rate. The logic outputs are fed to a coincidence gate which produces a fire- or explosion-indicating output only if all of the outputs are received concurrently for at least a predetermined period of time. A third radiation detector, in combination with the 0.

Abstract: The invention discriminates between the explosion of an ammunition round itself and the fire or explosion (e.g. a hydrocarbon fire) which may then take place in the object (e.g. a vehicle) struck by the round and initiates suppression of the latter fire or explosion only. The vehicle carries a radiation detector which measures the ratio of the intensities of the radiation at 3.4 and 4.4 microns. When an exploding ammunition round passes through the fuel tank entraining initially unburning hydrocarbon fuel with it, the detector measures a relatively low ratio because the unburning hydrocarbon fuel vapor between the burning round and the detector has a very intense absorption band at 3.4 microns. Fire suppression is thus initiated, so as to suppress the hydrocarbon fire which would very shortly follow.

Abstract: The invention is for discriminating between the fire or explosion of an ammunition round and the fire or explosion which may then take place in the object struck by the round, and for initiating suppression of the latter fire or explosion only. Short wavelength radiation detectors feed a ratio detector which produces a logical output dependent on whether or not the color temperature of an event being monitored is above or below a fixed value. If the event is an exploding round then this will take the color temperature above this fixed value. A threshold unit and a rate of rise unit produce logical outputs dependent on whether the magnitude and rate of rise of the output of one of these two detectors are above or below fixed values. An infra-red detector detects radiation at a wavelength characteristic of a fire in the object; its output rises relatively slowly.

Abstract: Photoelectric type detector responds to radiation in a narrow wavelength band characteristic of a fire or explosion, and a slow-response detector, such as a thermopile, is sensitive to radiation in a different narrow wavelength band centered at, for example, 4.4 microns, again characteristic of the same fire or explosion. The electrical outputs of the detectors are fed into a ratio unit which causes an AND gate to produce a fire or explosion indicating output only when the ratio of the output of the thermopile detector to the output of the other detector exceeds a predetermined value.

Abstract: Methods and apparatus for optimizing the response of a radiation detecting device such as a cold cathode discharge tube are disclosed. The tube is energized at each instant of repeated sequences of successive time instants which are fixed in time relative to a time datum, and held energized for not more than a respective activation period following each said instant, consecutive activation periods being mutually separated by recuperation time periods. Response of the device during each of the activation periods is sensed for, and a warning output is produced only when the device responds during each of the activation periods of at least one sequence. The lengths and number of activation periods during each sequence are selected to increase the probability of a warning output being produced in response to radiation of a predetermined wavelength relative to the probability of a warning output being produced in response to background radiation.