1 Active infrared detector and its application

The active infrared detector consists of a transmitter and a receiver. The transmitter is composed of a power supply, a light source, and an optical system. The receiver is composed of optical systems, photoelectric sensors, amplifiers, signal processors, and other components.

An active infrared detector is an infrared beam blocking type alarm device. The infrared light-emitting diode in the transmitter emits a modulated infrared beam (with a wavelength of about 0.8-0.95 microns) under the excitation of a power supply, which is then converted into parallel light and emitted through the action of an optical system. This beam is received by the receiver, and the infrared photoelectric sensor in the receiver converts the optical signal into a signal. After circuit processing, it is transmitted to the alarm control panel. The infrared emitted by the transmitter passes through the prevention area and reaches the receiver, forming a warning line. Under normal circumstances, the receiver receives a stable optical signal. When someone invades the warning line, the infrared beam is blocked, and the infrared signal received by the receiver changes. This change is extracted, amplified, and processed appropriately to issue an alarm signal.

At present, active infrared detectors have two beams, three beams, and multi beam infrared barriers. Active infrared detectors are generally used for perimeter defense, and their biggest advantage is that they have a long defense distance, which can reach more than ten times the detection distance of passive infrared detectors.

2 Passive infrared detector and its application

Passive infrared detectors mainly determine whether someone is moving based on changes in external infrared energy. The infrared energy of the human body is different from the environment. When a person passes through the detection area, the position of the different infrared energy collected by the detector changes, and then an alarm is issued through analysis.

But in the external environment, not only does the human body emit infrared energy, but many objects also emit infrared energy under certain conditions. This energy is particularly prominent in visible light, so the resistance of any passive infrared detector to white light interference has become an important indicator. This detection method performs very well under stable indoor lighting and relatively constant infrared energy. However, outdoors, due to various factors, it is difficult to maintain the stable operation of passive infrared detectors.