At present, the object (including a human) detecting the position of a number of general methods and techniques as follows:

    Microwave Sensor: also known as microwave radar, Doppler principle is the use of electromagnetic waves do, we know, have any wave reflection characteristics, when a certain frequency when the wave hit barrier, will be a part of the wave is reflected back, if the barrier is stationary, the wavelength of the reflected wave is constant, if the barrier is moving to the wave source, the wavelength of the reflected wave is more than the wavelength of the wave source is short, if the barrier is a direction away from the wave source, the wavelength of the reflected wave than the length of the wavelength of the wave source, the wavelength change, it means that the frequency changes. Microwave sensor is through changes in the reflected wave approaching or moving objects know away from.

    From the above analysis, we know that the microwave sensor mainly on the object (human) movement of the reaction, and thus fast response for detecting a certain speed towards or away from the microwave sensor objects, such as people with a certain speed walking through a place, it can be easily detectable by microwave.

    Infrared detectors: infrared detector probe is detected by the human body or other objects emit infrared rays which to work, the probe gathered outside the infrared radiation through infrared sensors gather source. Infrared sensors are usually used in pyroelectric element, this element receives infrared radiation temperature changes will be released outside the charge, after detecting an alarm. In the field of electronic anti-theft detectors, infrared detectors is widely used.

    The advantage of infrared detectors is itself does not send any type of radiation, power dissipation is small, hidden, and low prices. The presence of the object reaction, regardless of whether the object is moving, as long as the sensor is within the scan range, it will react. The disadvantage is susceptible to various sources of heat, light interference; passive infrared penetration is poor, the body's infrared radiation is easy to be blocked, the probe can not easily be received; susceptible to RF radiation interference; ambient temperature and body temperature close, detection and sensitivity decreased, sometimes resulting in short-term failure; another infrared detector is only apparent against the background infrared emission valid object or body, the body does not transmit infrared rays require additional infrared light.

    From the foregoing, the infrared detector is mainly used to sense whether an object enters the detection range, and for whether the object is moving or object sizes can not perceive it.

    Infrared detectors and more affected by temperature, airflow, dust and smoke effects, infrared sensor controller is used indoors, while the microwave sensing controller completely avoid the temperature, airflow, dust and smoke effects. Now microwave sensing controller is gradually replacing infrared sensor controller.

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