1. The basic principle: electromagnetic induction
A walk-through metal detector (WTMD) works on electromagnetic induction: transmitter and receiver coils are mounted on each side of the arch, creating an alternating magnetic field when powered. When a metal object passes through the arch, it disturbs the field and induces eddy currents; the receiver coil detects the change and triggers an alarm.
This is the same principle used by airport and railway security gates — the differences lie in engineering indicators such as sensitivity, detection zone count and anti-interference capability.
2. Sensitivity levels and detection capability
Sensitivity is the most important indicator; the industry-standard baseline is "the metal object size detectable at the center of the passage" — a coin placed at the center is detectable by mainstream products. Sensitivity is usually adjustable from 0–99 levels: higher levels detect smaller objects but also amplify environmental interference into false alarms.
Note that maximum sensitivity is not always better: high sensitivity magnifies ground metal, phone signals and electromagnetic interference. Choose the right level for the site environment and calibrate with standard test objects (coins, test plates) on site.
3. Zone locating: alarm position at a glance
Mainstream gates divide the detection area into 6–8 zones (left/center/right × top/middle/bottom). The zone containing the metal is indicated by lit LED bars, letting screening staff pinpoint the concealed position quickly and reducing pat-down scope and time.
Zone count is configured by scenario: 6 zones suffice for general passenger screening; 8 zones suit fine-positioning scenarios such as phone detection gates. The cost difference is small, but positioning accuracy directly affects handling efficiency.
4. Why do security gates sometimes false-alarm?
Common false-alarm causes: 1) environmental electromagnetic interference — substations, elevators, large motors nearby; 2) ground metal objects — metal floor tiles, drain covers; 3) carried items — keys, belt buckles, phones; 4) frequency conflicts between side-by-side gates.
Countermeasures: adjust sensitivity level, move away from EMI sources, deploy multiple gates on different frequency bands, and calibrate periodically with standard test objects. Most "false alarms" are resolved by environment review and parameter adjustment.
5. Security gate buying essentials quick reference
Check by priority: 1) compliance with GB15210 (Walk-Through Metal Detector national standard — request the test report); 2) sensitivity and detection verified on site; 3) zone count and positioning accuracy; 4) anti-interference in side-by-side deployment; 5) security features such as password protection and alarm records; 6) warranty and after-sales.
For high-traffic venues, design lanes in three segments — "guidance—screening—handling" — and connect gates to a centralized management system with unified alarm records and captured images for traceability.
6. Quick FAQ
Q: Are security gates harmful to people? A: No — passive detection is completely harmless, including for pregnant women and pacemaker wearers. Q: Can a gate detect non-metal items? A: Standard metal detection gates cannot; phone/camera detection needs a phone detection gate, and prohibited-item imaging needs an X-ray scanner.
Q: Can gates be moved? A: Mainstream products are movable — plug in and use, no civil works; fixed installation suits long-term channels. Q: Is maximum sensitivity best? A: No — false alarms increase noticeably; choose the right level for the environment.
