infra-red movement detector - for use in intruder alarms

infra-red movement detector elektor June 1985 The detector described in this article reacts to fast temperature variations caused by the movement of people or animals in an enclosed space. All mammals radiate a certain amount of heat, and it is this that causes local variations in temperature. The radiant heat energy occupies the electromagnetic spectrum between light and radio waves, i.e., 0.74...300 pm, which is usually called the infra-red region. The radiant energy is picked up by a Fresnel lens, at the focus of which is a double differential pyroelectric sensor. The detector is largely unaffected by other electrical radiation. Also, it does not react to movement outside the guarded space. infra-red movement detector for use in intruder alarms The space to be monitored is divided by the lens into a number of zones as illustrated in figure 1. The number of zones depends on the number of segments of which the lens is composed. When somebody moves from one zone into another, ther...