Shuttered Passive Infrared Sensor for Occupancy Detection: Exploring a Low Power Electro-Mechanical Driving Approach
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Copyright © 2018 ASME. Passive infrared (PIR) sensors are the most popular deployed sensors in building lighting control for individual presence detection. However, PIR sensors are motion detectors in nature, responding only to incident radiation variation, which lead to false negative detections, inaccurate occupancy estimation, and uncomfortable lighting swings, short lifetime of the equipment, and waste of energy. In this study, a shutter driven by a Lavet motor PIR (LAMPIR) sensor is developed for presence detection for both stationary and moving occupants. Building off our previous work on chopped PIR (C-PIR) and rotationally-chopped PIR (Ro-PIR) sensors, Lavet motor, a single-phase electro-mechanical vibrator, is introduced, which has many advantages over traditional servo motors and stepper motors in terms of power consumption, size, weight and noise level. Driven by pulsed signal from a microcontroller unit (MCU), the electro-mechanical vibrator drives a semitransparent long-wave infrared (LWIR) optical shutter to shutter the field of view (FOV) of a PIR sensor periodically. Output voltage generated by a LAMPIR senor for occupied and unoccupied scenarios can be monitored and analyzed to identify presence accurately. Parametric studies are conducted to find the optimal setting of driving signal frequency, shutter width and shuttering period. The LAMPIR sensor reaches an accuracy of 100% for detecting stationary occupants up to a range of 4.5 m and moving occupants up to a range of 10 m, which improves the detection range of both C-PIR and Ro-PIR sensors (4.0 m for stationary and 8.0 m for moving occupancy detection). LAMPIR has a FOV of 90 in horizontal and 100 in vertical, which is reasonable for most applications. For a 17-hour-long presence detection test, LAMPIR can reach an accuracy of 93.52% to classify unoccupied, stationary and moving occupant scenarios. More importantly, the average power consumption of LAMPIR is 0.19 W, which is 82% less than that of the C-PIR sensor and 89% less than that of the Ro-PIR sensor.
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