PIRsensorit

PIRsensorit (PIR sensors) are motion detectors that sense infrared radiation changes in their field of view. They respond mainly to warm bodies such as humans or animals entering or moving within a monitored area. Because they do not emit energy themselves, they consume little power and are commonly used in security, lighting control, and occupancy automation.

Operation relies on a pyroelectric sensing element, typically arranged as two or more adjacent sensing elements. When a warm object moves, the infrared energy received by the elements changes differentially, producing a signal. This signal is amplified and conditioned by electronics, and a processor or comparator converts it into a digital output or an analog level. A Fresnel lens or similar optical element shapes the field of view and reduces sensitivity to small temperature fluctuations or patterns behind the lens.

Construction varies by type. Common form factors include compact modules for integration on a circuit board and standalone detectors mounted in ceilings or walls. Typical interfaces provide a supply rail (often 3.3–5 V) and a single output line (digital on/off or analogue) plus adjustment controls for sensitivity and delay, and sometimes a pet-filter feature.

Applications include security alarm systems, automatic lighting, and occupancy-based control of HVAC or other equipment. Advantages include low cost, low power consumption, and simple installation; limitations include susceptibility to false triggers from heat sources, drafts, direct sunlight, pets, or rapid ambient temperature changes. Proper placement, lens selection, and environmental conditioning are important to minimize false alarms.