Active Infrared Vs. Passive Infrared

Infrared detector is the most critical part of the anti-theft alarm system, which is the guarantee of the quality of whole system and can directly determine the sensitivity and stability of the system. It is a component that converts the radiation signal into an electrical signal. From the perspective of working methods, infrared detectors can be divided into active infrared and passive infrared detectors. So what is the difference between the two?

1. Composition Structure

The active infrared detector is composed of transmitter and receiver. The transmitter includes power supply, light source and optical system. The receiver is composed of optical system, photoelectric sensor, amplifier, signal processor etc. While passive infrared detector is composed of optical system, thermal sensor (or called infrared sensor) and alarm controller.

2. Working Principle

Active infrared detector is an infrared beam blocking alarm. The infrared light-emitting diode in the transmitter emits a modulated infrared beam (the wavelength of this beam is about 0.8 to 0.95 microns) under the excitation of the power supply. After the action of the optical system, it becomes parallel light and emits out. The light beam is received by the receiver, and the infrared photoelectric sensor in the receiver converts the light signal into a signal, which is sent to the alarm controller after being processed by the circuit.

The infrared rays emitted by the transmitter pass through the guard zone and reach 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. The change is extracted, amplified and properly processed. Alarm signal from the controller. At present, such detectors have two-beam, three-beam and multi-beam infrared barriers. It is generally used in perimeter defense, the biggest advantage is the long defense distance, which can reach more than ten times the detection distance of passive infrared.

Passive infrared detector mainly judges whether someone is moving according to the change of 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 the external environment is not only the human body emits infrared energy, but many objects emit infrared energy under certain conditions, and this energy is especially prominent in visible light, so the anti-white light interference of any passive infrared intrusion detector becomes an important index.

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