Occupancy sensor

An indoor light switch equipped with PIR-based occupancy sensor[1]

An occupancy sensor is a lighting or heating control device that detects occupancy of a space by people and turns the lights and/or Heating, Ventilation, and Air Conditioning (HVAC) system on or off automatically, using infrared, ultrasonic, microwave, or other technology. Occupancy sensors are typically used to save energy, provide automatic control, and comply with building codes.[2]

Types of sensors

Types of occupancy sensors include:

  1. Passive infrared sensor, which works on heat movement detection. Inside of device is a pyroelectric sensor calibrated to detect infrared radiation radiated by human body movement. Based on the detection, the sensor operates and starts lighting load connected to it.
  2. Ultrasonic sensor, similar to radar. It works 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.
  3. Microwave sensor. 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.
  4. Key-card, a hotel energy management system used to detect when a hotel room is occupied, by requiring the guest to place their key in a slot to turn on the lights and HVAC.[3]
  5. Door operated switch.
  6. Audio detection.

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 sometime 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.

System design and components

Occupancy sensors for lighting control typically use infrared (IR), ultrasonic, tomographic motion detection, microwave sensors, or camera-based sensors (image processing).[4] The field of view of the sensor must be carefully selected/adjusted so that it responds only to motion in the space served by the controlled lighting. For example, an occupancy sensor controlling lights in an office should not detect motion in the corridor outside the office. Tomographic motion detection systems have the unique benefit of detecting motion through walls and obstructions, yet do not trigger as easily from motion on the outside of the detection area like traditional microwave sensors.

Sensors and their placement are never perfect, therefore most systems incorporate a delay time before switching. This delay time is often user-selectable, but a typical default value is 15 minutes. This means that the sensor must detect no motion for the entire delay time before the lights are switched. Most systems switch lights off at the end of the delay time, but more sophisticated systems with dimming technology reduce lighting slowly to a minimum level (or zero) over several minutes, to minimize the potential disruption in adjacent spaces. If lights are off and an occupant re-enters a space, most current systems switch lights back on when motion is detected. However, systems designed to switch lights off automatically with no occupancy, and that require the occupant to switch lights on when they re-enter are gaining in popularity due to their potential for increased energy savings. These savings accrue because in a spaces with access to daylight the occupant may decide on their return that they no longer require supplemental electric light.[5]

See also

References

  1. ↑ Product Specification for PR150-1L/PR180-1L. Leviton. Retrieved 6 September 2014.
  2. ↑ Pacific Gas and Electric Company, Southern California Edison (2011). "Guest Room Occupancy Controls—2013 California Building Energy Efficiency Standards" (PDF). California Energy Commission. Retrieved May 10, 2016.
  3. ↑ Catharine Hamm (February 16, 2015). "Do hotel thermostats with motion sensors have you waking up in a sweat?". Los Angeles Times. Retrieved May 10, 2016.
  4. ↑ "Technology comparison of Occupancy sensors". Retrieved 19 July 2014.
  5. ↑ Did It Move? Detecting Motion with PIR + Arduino

http://www.google.com/patents/US4225808?hl=it&dq=US+Patent+No:+4,225,808#v=onepage&q=US%20Patent%20No%3A%204%2C225%2C808&f=false US Patent No: 4,225,808

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