Vedard Security Alarm Technical Support

According to the different vibration sensors used, vibration detectors can be divided into: mechanical vibration detector, inertial bar electronic vibration detector, electric vibration detector, piezoelectric crystal vibration detector, electronic comprehensive vibration detector and other types.Recently, the most common vibration detector is piezoelectric crystal, whose principle is to use piezoelectric effect of piezoelectric crystal.Piezoelectric crystal is a special crystal, it can be applied on the mechanical force into the corresponding size of the electrical signal, the frequency and amplitude of the electrical signal is proportional to the frequency and amplitude of mechanical vibration, when the signal value reaches the set value will send an alarm signal.

When the glass is struck and the glass is not broken, an ultra-low frequency elastic vibration wave will be generated. This mechanical vibration wave is less than 20Hz, which belongs to infrasonic wave.The loud, harsh sound of broken glass is in the range of about 10 ~ 15 kHz, which is a high-frequency sound.An alarm signal is generated when the detector detects both low and high frequency sound frequencies.

The microwave detector uses the principle of Doppler effect.In the microwave section, when transmitting at one frequency, when the emitted microwave encounters a fixed object, the reflected microwave frequency remains unchanged, that is, f =f, and the detector will not send out an alarm signal.When the emitted microwave encounters a moving object, the reflected microwave frequency will change, that is, f send ≠f receive, and the microwave detector will send out an alarm signal.

Digital pulse count: through digital count, the detector measures the number of trigger edges in the sector triggered by intruders from the beginning, and triggers the alarm signal according to the pre-set number of digital pulse count.

In general, the human body temperature is always much higher than the ambient temperature.When the intruder moves, the sensor receives the infrared change signal amplitude is large and triggers the alarm.When the ambient temperature rises to close to the temperature of the human body, the infrared change signal amplitude received by the sensor during the intruder's movement is very small, so it may not alarm because the signal is less than the trigger threshold.
Temperature compensation can automatically increase the gain of the intruder signal amplifier when the ambient temperature is close to that of the human body, thus keeping the signal of the alien intruder can be picked up without compromising sensitivity due to ambient temperature.

A detector that combines two pyroelectric sensors with the same performance but opposite polarity is a dual detector.

Passive infrared detector has two key components, one is the Fresnel lens, the other is the pyroelectric sensor.In nature, any object above the absolute temperature (-273°) will produce infrared radiation, and objects at different temperatures emit infrared energy at different wavelengths.The body has a constant temperature, which is different from the ambient temperature.As the body moves, the difference is detected by a pyroelectric sensor through a Fresnel lens, which outputs an alarm signal.

The active infrared detector consists of an infrared transmitter and an infrared receiver.An infrared transmitter sends one or more modulated infrared rays to an infrared receiver.When there is no shield between the transmitter and receiver, the detector will not alarm.When there is an object blocking, the receiver output signal changes, the detector alarm.