The function of the door frame metal detector used for passenger inspection at airports and stations is to be able to detect all items with a certain weight of metal components. When people pass through the door frame, the metal objects they carry can be detected. Because it is widely used in security inspection, it is also called security gate. As for this door, we often get used to it through frequent contact. As for how it developed, little is known about it, so today I will take you to understand it.

The development of door frame metal detector technology is quite rapid. Since the 1970s, the development of security door technology has generally undergone three generations of product updates.
The first generation of security doors is a passive magnetic field meter. The door frame metal detector manufacturer tells you that it installs the magnetic flux probe in a stick or a thin plate, and the channel is formed by two sticks or two thin plates. Its detection principle is to measure the change of geomagnetic field. When a ferromagnetic metal object passes by, the geomagnetism is disturbed to detect the metal object. Therefore, high requirements are placed on the sensitivity of the security door and the surrounding environment. Electric lights, motors and even car start may cause interference to the security door, so its anti-interference ability is very poor. And non-ferromagnetic metals such as gold, silver, and copper cannot be detected even through the security gate. With the emergence of contraband made of various non-ferromagnetic materials, its application limitations are also limited, making it difficult to be widely used.
The second generation security door is an active detector. This generation of products is aimed at the limitations of passive detection applications. It establishes a stable alternating electromagnetic field in the detection area by the detector itself. When a metal object passes by, the strength of the self-built alternating magnetic field, Both phase and frequency will change to detect metal objects. This security gate can detect not only ferromagnetic substances, but also non-ferromagnetic substances. The self-built field can be made very strong, and the corresponding anti-interference ability has also been improved, reducing the occurrence of false alarms. Although the second-generation security gate has been greatly improved compared with the first generation, since the self-built alternating magnetic field is a continuous sine wave voltage excitation method, the alternating magnetic field of this "continuous wave method" is not used in applications. In order to overcome the influence of the surrounding environment and ensure sufficient sensitivity, it is necessary to manually adjust the zero balance at any time. Moreover, detecting weak signals in the background of continuous strong magnetic field requires strict position adjustment of the detection coil and maintaining the shape of the rigid body. These practical problems add considerable difficulty to the manufacture and use of the product.
The third-generation security door is a further improvement on the active metal security door. On the basis of the self-built alternating field "continuous wave method" metal detection principle, the self-adaptive phase-locked amplification (self-balanced phase-locked amplification) and digital processing electronic technology are used in the electronic circuit, thus overcoming the need for artificial adjustment in the work The problem of balance has improved the sensitivity, stability, environmental adaptability and operation convenience of the system.
The fourth-generation security door is to change the continuous wave working mode to the pulse wave working mode. The pulse field technology is to use the metal object to pass through the detection channel, due to the eddy current effect, the pulse rear edge changes, the receiving coil detects this change, and distinguishes whether to alarm through the processing circuit. Since this technology only opens the receiving system to pick up useful signals after the transmitting pulse ends, it does not require the minimum coupling between the receiving and sending coils. At the same time, the sampling of useful signals can be picked up, and the sampling period can be very narrow, which further improves the anti-interference ability of the security door.
Although the security door has been updated for four generations, people are still improving the performance of this door frame metal detector in an effort to reduce the false alarm rate. In the late 1980s, metal detectors entered the era of single-chip computers. Data acquisition, data processing, control display and system management can all be performed by one or several single-chip microcomputers, which improves and enhances the performance and functions of the equipment. In addition to taking stronger anti-interference measures on the overall structure and circuit hardware, the single-board computer can use different mathematical models and algorithms for different environments, and use DSP (signal processor) to classify and process the collected signals. The material and shape of metal objects have a certain ability to identify, which reduces false alarms caused by this, and also greatly improves the man-machine interface between people and door frame metal detectors. The button function has changed from one button with one function in the past to one button with multiple functions. The display not only shows the alarm level, but also shows the setting status, self-test information and error codes. Devices and devices, and devices and computing work together to form a strong system. Social needs and scientific progress have made metal detectors beautiful in appearance, easy to use, easy to maintain and stable in work.
With the advancement of technology, I believe that the door frame metal detector may be more advanced in the future, and the various limitations of inspection will be resolved, which will contribute to our social security protection work.