How does the PIR Motion Sensor detect the movement of a person or object? How does it work?
Publish Time: 2024-09-05
The working principle of the PIR Motion Sensor is based on infrared radiation and the temperature change of an object. When an object (usually a person) moves, it creates a temperature change in the environment, which can be detected by the PIR sensor.The specific working principle is as follows:Infrared radiation: All objects emit heat in the form of infrared radiation. This heat or energy is proportional to the temperature of the object. The higher the temperature, the stronger the infrared radiation emitted.Sensing element: The PIR sensor contains two tiny layers of semiconductor material connected in series, which are tilted in opposite directions. When infrared radiation hits the sensor from one side, the radiation is received by these two layers separately.Thermocouple effect: Each semiconductor layer is composed of thermocouples, which can convert temperature changes into voltage changes. When infrared radiation hits the thermocouple, a tiny voltage signal can be generated due to the temperature difference.Signal amplification: By placing them at both ends of the thermocouple, these voltage signals can repel each other, resulting in a voltage difference. This voltage difference can be amplified by the amplifier circuit into a signal that can drive the circuit control.Detecting Movement: In this PIR sensor, there are two such thermocouples. Due to the structural design, they are exposed to the same environment at the same time. In this way, the pressure difference between them is almost equal - in the absence of movement. However, when a hot object (such as a person) passes through the two thermocouples, it changes the infrared radiation received by each thermocouple, causing a difference in voltage change, which is how the PIR sensor senses movement.Threshold Detection: Finally, the PIR sensor is connected to a threshold setting circuit, which sets a threshold. Only when the detected voltage change exceeds this threshold will the circuit be triggered, causing the PIR sensor to output an activation signal.In practice, PIR Motion Sensors are often used to automatically start lamps, security systems, or other electronic devices to respond immediately when motion is detected. Such sensors usually have a certain angle and distance range that can specify their direction and coverage. They are often used to detect motion indoors and outdoors, such as smoke alarms and intrusion detection systems.
