Occupancy sensors are known by different names such as motion sensors or switches, movement detectors or even automatic light switches and presence detectors. There are 5 main different kinds of Occupancy sensors available in the market today based on the technology used to detect occupancy.
- PIR based sensors
- Ultrasonic based sensors
- Microwave based sensors
- CW Radar based sensors
- Thermal Imaging based image processing sensors
All the above mentioned technology sensors except for the thermal image processing sensor use the primary factor of motion or movement of an object as the key determinant to flag for occupancy. The application of these sensors has been mostly in the field of security, residential and industrial automation and electrical energy conservation.
The most widely used sensors in the market in terms of utility, energy savings and cost savings are PIR(Passive Infrared) based sensors. These sensors detect human or automobile motion or movement and switches ON any electrical/electronic device to which it is connected to. The key component of the sensor module is the pyro-electric element. There usually is a minimum of 2 elements which enable noise cancellation and enhanced detection.
Passive infrared sensors as the name suggests detect changes in IR(infrared radiation) that is triggered by any hot moving body such as human or any other warm blooded animal movement, automobile movement or even a warm breeze. All this motion represents a time varying IR shift which triggers small signal fluctuations in the pyroelectric element. These small signal fluctuations are amplified and signal conditioned in the signal conditioning circuit.
One important aspect of PIR sensors is that the front end sensor is a passive energy component which implies that it does not actively emit energy in order to detect motion. Hence, during prolonged idle operations when there is little or no movement that is
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