An occupancy sensor is a device used to detect the presence of a person. Applications include automatic adjustment of lights or temperature or ventilation systems in response to the quantity of people present. The sensors typically use infrared, ultrasonic, or microwave technology. The term encompasses devices as different as PIR sensors, hotel room keycard locks and smart meters. Occupancy sensors are typically used to save energy, provide automatic control, and comply with building codes.
Vacancy sensor A vacancy sensor works like an occupancy sensor except that lights must be manually turned on and will automatically turn off when occupancy is no longer detected.
Sensor types Occupancy sensor types include:
Passive infrared sensors, which work on heat difference detection, measuring infrared radiation. Inside the device is a pyroelectric sensor which can detect the sudden presence of objects (such as humans) who radiate more or less than the background, such as a wall at room temperature. Environmental sensors, such as temperature, humidity and CO2 sensors, which detect the change in the environment due to the presence of a human. Ultrasonic sensors, similar to radar, which work on the doppler shift principle. An ultrasonic sensor will send high frequency sound waves in area and will check for their reflected patterns. If the reflected pattern is changing continuously then it assumes that there is occupancy and the lighting load connected is turned on. If the reflected pattern is the same for a preset time then the sensor assumes there is no occupancy and the load is switched off. Microwave sensors. Similar to the ultrasonic sensor, a microwave sensor also works on the doppler shift principle. A microwave sensor will send high frequency microwaves in an area and will check for their reflected patterns. If the reflected pattern is changing continuously then it assumes that there is occupancy and the lighting load connected is turned on. If the reflected pattern is the same for a preset time then the sensor assumes there is no occupancy and the load is switched off. A microwave sensor has high sensitivity as well as detection range compared to other types of sensors. Keycard light slots, used in hotel energy management systems to detect when hotel rooms are occupied by requiring guests to place their keycards in slots to activate lights and thermostats. Smart meters, which work by detecting the change in power consumption patterns that exhibit distinct characteristics for occupied and vacant states. Barometric pressure sensors can be used to monitor door openings, which are associated with foot traffic, in rooms with positive pressure, including operating rooms. Door operated switch. Audio detection. Human sensing (via people counting) became widespread in 2020 as companies installed AI cameras and occupancy sensors to enforce social distancing and capacity limits during the COVID-19 pandemic. Bluetooth Low Energy (BLE), detect occupancy by linking to nearby devices with a dedicated app, but they miss people without the app or misread presence if a device is left behind.
Occupancy sensors for lighting control Motion sensors are often used in indoor spaces to control electric lighting. If no motion is detected, it is assumed that the space is empty, and thus does not need to be lit. Turning off the lights in such circumstances can save substantial amounts of energy. In lighting practice occupancy sensors are sometimes also called "presence sensors" or "vacancy sensors". Some occupancy sensors (e.g. LSG's Pixelview, Philips Lumimotion, Ecoamicatechs Sirius etc.) also classify the number of occupants, their direction of motion, etc., through image processing. Pixelview is a camera-based occupancy sensor, using a camera that is built into each light fixture.
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