An evaluation of a passive infrared motion detector (PID) for biological applications

Many biologists use passive-infrared motion detectors (PIDs) to monitor the motion or presence of warm-blooded animals in their research. This study determined some of the capabilities of a commercially available PID. Three small-mammal proxies (4.45 em, 14.7 em, and 21.5 em containers of warm water) were passed in front of eight identical PIDs. The PID responses (at conditions of 0.5 to 10 oc above background, 0.5 m to 16m distance, and 1 to 120 crn/s velocity) confirmed that target size, distance, subject -background temperature difference (L\ T), and velocity are primary variables and helped define the detection limits of the PID. Tests using a fixed L\ T and constant angular velocity showed that PID detection of the three different proxy sizes was equal for equal angular size. The repeatability of PID detections was highly consistent, but with a small directional dependency. There was some variation in overall sensitivity between PIDs, also with a directional bias. Tests on a large dog were used to calculate a proxy size (0.476 m2 ) that could have been substituted for the dog. Best use of PIDs by biologists depends on knowledge of PID capabilities and on use of motion-trap designs that maximize reliable capture rates by the PID. The test results here, while partially specific to this PID configuration, will provide biologists with a basic understanding of PID capabilities potentially useful in their own research. Keywords infrared, monitoring, motion detector, passive infrared detector, PID, PIR, sensor, trap, wildlife