Pyroelectric Human Infrared Sensor is a device that converts infrared rays emitted by humans or animals into electrical signals. It can be used to detect the presence of human body, so it is widely used in electronic products, such as safety devices, burglar alarms, induction doors, automatic lamps and smart toys.
The pyroelectric infrared sensor can detect the infrared rays emitted by the human body, but the detection distance is relatively close, generally within 2m. In order to increase the detection distance, a Fresnel lens is usually installed in front of the light receiving surface of the pyroelectric motion sensor, and the lens can be detected. The distance is more than 10m.
The lens is usually made of a transparent plastic, and the lens is divided into several equal parts according to a certain manufacturing method. Plastic Fresnel lens has two functions: one is to focus on the light, and the other is to divide the detection area into several bright and dark areas. When a person enters a certain bright area of the detection area, the infrared light emitted by the human body is focused by the corresponding lens portion of the bright area, and then is irradiated onto the sensitive component through the filter of the sensor, and the sensitive component generates a voltage when the person walks to the dark. When the area is in, the infrared light of the human body cannot reach the sensitive component, and the voltage across the sensitive component changes, that is, the voltage across the sensitive component changes with the presence or absence of the light. The changed voltage is amplified by the FET and output, and the sensor output signal The frequency is related to the speed at which the person moves between the bright and dark areas within the detection range. The faster the moving speed, the higher the output signal frequency. If the person does not move within the detection range, the sensor outputs a fixed voltage.