Passive Infrared Sensor Technology
The lens of a PIR sensor divides coverage into zones. When a change in infrared energy is detected in
one of the zones, it assumes the area is occupied. PIR sensors use a dual-element pyroelectric
sensing device to detect occupancy. When one of the dual elements detects infrared energy before
the other, it generates a positive pulse – a few milliseconds later, the other element produces a negative pulse, creating an “ON” state within the sensor.
PIR sensors must be able to “see” the area they need to control. Partitions and bookshelves will
prevent detection in the blocked area. PIR sensors will also better sense motion when the movement is across the sensor’s field of coverage rather than directly towards or away from it.
• Enclosed offices where sensors can have a clear view of the entire area
• Areas with high air flow: computer rooms, laboratories, etc
• Bathrooms (sensors cannot see in the partitioned areas)
• Areas where storage areas, cabinets and shelving can block the view
Ultrasonic Sensor Technology
Ultrasonic sensors transmit a signal generated by a quartz crystal oscillator. A flat-plate, multi-directional transmitter plate broadcasts this signal into the controlled area. Receiver microphones should be electronic and tuned to the same frequency that the sensor is broadcasting on. For best results, they should also remain largely unaffected by temperature and humidity changes.
Because ultrasonic sensors broadcast in three dimensions, the ultrasound will leave the sensor and bounce off the walls, floor, and ceiling, giving them the ability to sense smaller amounts of motion. In enclosed spaces, proper sensor placement is essential, as sensors can “see” out open doorways, resulting in false triggering. Also, heavy air flow (from HVAC ducts or fans) can seriously impair ultrasonic sensor performance and result in false triggering.
• Storage areas with cabinets and shelving
• Bathrooms (ultrasonic waves will bounce off of the partitions)
• Spaces that have lots of air turbulence
• Areas that require ceiling mounting heights over 4 to 5 metres
This unique technology provides occupancy sensor coverage to building spaces which have been too troublesome for single technology sensors.
The combination of PIR and ultrasonic allows the sensor to take advantage of the best features of both technologies while eliminating the weaknesses. The result is sensors with greater sensitivity and coverage.
Dual technology sensors function by turning lighting on when both PIR and ultrasonic technologies detect occupancy. Once lighting is on, detection from only one technology is needed to keep them on. Other configurations are possible which need only one technology to trigger or both technologies to hold lighting on.
• Large conference rooms