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PIR Infrared Sensor – wired
A PIR (Passive Infrared) sensor is an electronic sensor that detects infrared (IR) light radiating from objects within its field of view.
It's called "passive" because it doesn't emit any energy itself; instead, it passively monitors the existing infrared radiation in its surroundings.
All objects with a temperature above absolute zero emit some level of infrared radiation, and the hotter an object, the more radiation it emits.
PIR sensors are particularly effective at detecting the infrared radiation emitted by warm bodies, such as humans and animals.
How PIR Sensors Work
At the core of a PIR sensor is a pyroelectric sensor, a material that generates an electrical charge when exposed to changes in infrared radiation. To detect motion, most PIR sensors use a dual-sensor design:
- Dual Elements: The pyroelectric sensor is typically divided into two halves or elements, wired in a way that they cancel each other out when no motion is detected. This means that if both halves receive the same amount of IR radiation (e.g., from the ambient room temperature), their signals balance, and no output is generated.
- Fresnel Lens: A Fresnel lens is often placed in front of the pyroelectric sensor. This special lens has multiple facets that help to focus infrared light from different angles onto the sensor elements, increasing its range and sensitivity, and creating distinct detection zones.
- Motion Detection: When a warm object, like a person, moves across the sensor's field of view, it first enters one detection zone (and thus one half of the pyroelectric sensor) and then the other. This causes a differential change in the amount of infrared radiation impinging on each half of the sensor. This difference in IR energy between the two halves creates an electrical signal.
- Signal Processing: The sensor's internal circuitry processes this change in voltage. If the change is significant enough (indicating a "moving heat source"), the sensor triggers an output signal.
This differential detection mechanism makes PIR sensors highly effective at detecting movement while being less prone to false alarms caused by slow, gradual temperature changes or general ambient light fluctuations.
Applications of PIR infrared sensors
PIR infrared sensors are widely used due to their effectiveness, low power consumption, cost-effectiveness, and ease of integration. Common applications include:
- Security Systems: The PIR infrared sensor are a fundamental component of burglar alarms and motion-activated security cameras, detecting intruders by their body heat.
- Automatic Lighting: PIR infrared sensors are used in homes, offices, and public spaces to automatically turn lights on when someone enters a room or area and off when it's unoccupied, leading to energy savings.
- Smart Home Automation: The PIR infrared sensor play a crucial role in smart homes, triggering various automated actions like adjusting thermostats, turning on appliances, or opening doors based on occupancy.
- Automatic Doors: Many automatic door systems, like those found in shopping malls, use PIR sensors to detect approaching individuals and open the doors.
- Industrial Monitoring: They can be used to monitor machinery movement or detect the presence of personnel in hazardous areas for safety purposes.
- Wildlife Tracking and Research: Researchers use them to monitor animal movements unobtrusively.
