To adapt to the background change characteristics of the rotating object, the active infrared sensor is set to the background suppression operation mode. The background will be detected, but will not be responded. During the detection process, only the reflection from objects in the scanning area can generate action signals to the system. Changes from the suppressed background (such as ground material, humidity, small debris, light exposure) do not trigger the signal. Background suppression technology provides reliable and effective protection measures for rotating objects, unaffected by background reflection which makes it widely used in automatic revolving door, automatic swing door. Following will give more attention to the active infrared background analysis and background suppression technology.

Active Infrared ：Background Analysis

PF21B background suppressed diffuse reflection photoelectric sensor

Active infrared sensors emit infrared light within a clearly defined area and analyze the returned reflected light. Before conducting background analysis, a reference background must be set. The sensor illuminates one or more areas on the floor with infrared light, and then analyzes the returned energy. If there is a significant difference compared to the original background image, detection will be triggered.

Active infrared background analysis technology has high sensitivity and can effectively detect static targets near doors. It is usually used in conjunction with microwave sensors and can provide both opening (microwave) and safety protection (infrared) options through a single device, usually used for automatic sliding doors.

Active Infrared ：Background Suppression

The principle of background suppression is "triangulation", where the sensor calculates the distance to the target object based on the distance between the transmitter and receiver. The emission angle is known, and the distance to the object can be calculated based on the position of the reflection point on the receiving side, so the reflection angle is also known. (When a distance and two angles are known, a triangle can be drawn)

Active Infrared Background Suppression technology requires setting a small and unobstructed blind spot above the floor to detect static objects without being affected by background reflectance. Therefore, it is mainly used in situations where the background may change (such as sensors fixed to moving door panels), and is usually used for automatic swing doors.