MOTION AND TEMPERATURE SENSITIVE INFRARED DETECTOR

摘要

1489097 Motion sensitive infrared detector MINNESOTA MINING & Mfg CO 31 Dec 1974 [2 Jan 1974] 56170/74 Heading G1A [Also in Division H1] A detector 1 of the motion of a source of infrared comprises a front wall 3 with radiation transmissive apertures 8, a back wall 7 with inner, 13, and outer, 14, conductive layers with poled pyroelectric material, 15, between, said inner layer being nearest to wall 3, one of the conductive layers having one or more sets of electrically connected - sets of fingers 11, 12, parallel to the apertures, part of one conductive layer being earthed, layer 13 having areas that are simultaneously heated by and areas that are shielded from radiation through the apertures from the source, the material 15 being heated by the heated areas, so that electrostatic charges form on it and on one or more sets of fingers in contact with it, to which a circuit is connected to develop an alarm triggering signal for a predetermined sequence of voltage potentials in a predetermined period. Layer 15 is of polyvinylidene fluoride or a ceramic plate of lanthanummodified lead zirconate-titanate. The interdigitated finger sets 11, 12 are formed by etching wall 7, their width being “ of the distance between walls 3 and 7, so that a radiation source will be in line of sight with only one finger at a time. The etch width should be at least the thickness of layer 15 for correct heat distribution. Leads 16 connect the fingers to a circuit which may be on the back of detector 1 or remote. A differential amplifier (17), Fig. 5 (not shown), feeds full-wave rectifier (18), voltage amplifier (19) and Schmitt trigger (20). In a stable temperature environment one finger set, amplifier (17) and rectifier (18) may be omitted. On receiving say three pulses within a certain time counter (21) delivers an actuating pulse to alarm (22). Otherwise it resets. In an alternative embodiment the back conductive layer of wall 7 is fingered and the front layer. is the earthed conductor, which shields from electrostatic charges.