Passive Infrared Motion Sensor (PIMS) (Preliminary). Operation and Maintenance Manual.
AEROSPACE RESEARCH INC BOSTON MASS
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Figures 1 and 2 are simplified block diagrams of the Passive Infrared Motion Sensor PIMS. Figure 3 shows the location of the 17 beams of coverage within the 20 ft. x 30 ft. specified area when the optics are mounted at 7 ft. 4 inches. The system is a motion detector using transient changes in the infrared background, within specified velocities, to generate alarms. A long term infrared source would eventually blend into the overall noise background and not be detected indefinitely. A filter is used to prevent visable light from generating alarms. Since infrared detection is passive any number of units can be placed in a particular location without interference. Infrared detection becomes less sensitive when the background temperature approaches that of the target human intruder. Some care must be taken upon installation that clutter such as rapidly heating pipes, windows or air ducts are not located within one or more beams. Due to the long time constants involved in processing frequencies around .1 Hz, it is necessary to allow a 5 minute warmup before alarms can be considered genuine. Author
- Infrared Detection and Detectors