Infrared alarm can be divided into active type and passive type. As for the working principle of infrared alarm, it also needs to be divided into active type and passive type, as follows:

1, working principle of passive infrared alarm

Passive infrared alarm mainly judges whether someone is moving according to the change of external infrared energy. The infrared energy of human body is different from the environment. When people pass through the detection area, the position of different infrared energy collected by the alarm changes, and then an alarm is issued through analysis.

The human body temperature is constant, generally around 37 degrees, and it will emit infrared rays with a specific wavelength of about10 μ m. The passive infrared alarm works by detecting the infrared rays emitted by the human body.

The infrared ray emitted by human body is about 10μm, which is enhanced by Fresnel filter and concentrated on the infrared sensor. The infrared induction source usually adopts pyroelectric elements. When the temperature of infrared radiation received by human body changes, it will lose the charge balance and release the charge to the outside. The subsequent circuit can generate an alarm signal after detection and processing.

2. The working principle of active infrared alarm

Active infrared alarm consists of transmitter and receiver. The transmitter includes power supply, light source, optical system and other components. Under the action of the power supply, the infrared light emitting diode emits an infrared beam, which is converted into parallel light by the optical system and then emitted. The receiver includes an optical system, an amplifier, an optical sensor, a signal processor and other components, and is responsible for receiving the infrared rays emitted by the transmitter, converting the optical signals into electrical signals through photoelectric sensors, and transmitting them to the alarm controller after being analyzed and processed by the signal processor.