Abstract: Apparatus for detecting the presence of a fire includes a pair of detectors for radiation characteristic of a fire, e.g. at 4.3 microns, and a further detector for radiation characteristic of a black body, e.g. at 3.8 microns. Filters select the detector output components at flame flicker frequencies. The filtered outputs of the detector pair are cross-correlated to produce a relatively noise-free signal. This signal is divided by a factor obtained by cross-correlating the further detector filtered output with the average of the detector pair filtered outputs. The result of the division is applied to a threshold-responsive circuit. Thus the relatively noise-free signal is effectively subjected to a threshold which is proportional to the degree of similarity between the variations with time of the output signal of the further detector and the output signals of the detector pair.

Abstract: An optical electronic scale reading apparatus comprising a scale read by a read head to determine the relative displacement therebetween. The read head comprises reflective surfaces so arranged that light from a source is reflected therefrom and interacts with the scale at first, second and third positions. At the third position, a fringe field is developed which has the same pitch as the scale. A detector is provided to receive light modulations during relative movement of the scale and read head as the fringe field interacts with the scale at the third position. These modulations are counted to determine the relative displacement between the scale and read head.

Abstract: An apparatus for determining values of a periodic function by interpolation which comprises a reading device for receiving scanning signals A,B,C,D nominally in phase quadrature with each other from the periodic function. The signals are combined in a converter to produce sine and cosine derived signals SN,CS from which interpolation is performed by a computer. Each of the derived signals SN,CS is derived from at least three of the scanning signals A,B,C,D, for example, in the forms 2B-A-D and 2B-A-B.