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Principles of security door alarm

China Modular Holdings Limited | Updated: Jan 19, 2016

Security door alarm generated by the metal object, is due to the side door panel is equipped with transmitting and receiving electromagnetic sensors. Metal conductors when subjected to alternating electromagnetic excitation, produce eddy currents in the metal conductors, and the current launch and original magnetic field with the same frequency but in the opposite direction of the magnetic field, metal detector is to detect the Eddy current signals are there to find out whether the presence of metal in the vicinity. Inspired by transmitter emits electromagnetic waves, the signal received by a receiving sensor metal receiving signal detection of Eddy current sensor taken out, and then through the circuit is a series of amplified when the signal reaches the set value in the form of sound and light alarm.

On the world market, security doors there are two more popular use of electromagnetic emission signal mode:

1 sine wave: sine wave emission method has the advantage of signal processing is relatively simple, low cost, high sensitivity disadvantage are vulnerable to interference.

2, the pulse: pulse launches with sine wave emission method instead, signal processing is complex, expensive advantage is strong anti-interference ability.

Production of multi-locational security doors in the domestic market, its technology is from the first one or two have done the research and development of intellectual property protection in time of copying out of the factory, are based on the original sine-wave emission. From theory and signal processing, the basic production techniques, technology and materials have tended toward homogenization. Overview whole domestic production security door enterprise, only very less part enterprise has real of products development capacity, some production enterprise due to they only is imitation products, and no real master launches and received coil (received sensor) of precision and fixed of firm sex, core part of process, not knows the collection what paragraph pulse, and sine launches signal, and also using original of artificial winding method, coil of winding elastic and the winding turns number are not meet industrial standard, so user in using these enterprise of products process in the omitted, and Phenomenon is particularly serious. So I want to be well balanced sensitivity and anti-jamming capability of both relationships, not superb production technology, technology and long-term experience are almost unimaginable.

About user referred to "digital technologies" are actually applied to the metal detectors on the manufacturing technology? in fact, generally speaking, digital is digital signal coding, digital equipment's signals are all the digital signal. After some arithmetic processing of signals, via media transfer to terminal equipment, terminal equipment restores the original signal demodulation, responding to the signal or signals for special functions. In view of the characteristics of a metal detector is a sine wave or pulse wave launch, and no other component signals, signal processing natural analog signal processing is just sensitivity control with single-chip digital (such as a sensitivity of 80, number by number 10, alarm 2 ... ... This so-called "digital technologies") displayed.