Select different alarm probes according to the place and area to be protected. Here are the working principles of several different detectors.
Infrared detector : Any object will radiate infrared rays of varying intensity due to different surface heat. Due to different objects, the wavelength of infrared radiation varies. Infrared detection is mainly used to detect the human body and other invading moving objects. When the human body enters the detection area, the stable thermal radiation is destroyed, resulting in a change of thermal radiation. After receiving, the infrared sensor amplifies, processes, and sends an alarm signal.
Microwave object movement detector The Doppler shift of high-frequency radio waves is used as a detection method, which is suitable for open spaces or squares. Microwave is a kind of radio wave with very high frequency. Its wavelength is very short, and it is easy to be reflected by objects. According to the frequency drift of incident wave and reflected wave, it can detect intrusion objects.
Infrared microwave detector : It is one of the commonly used equipment in the alarm system, and its price is generally between 200 and 1600 yuan. Its working principle combines infrared and microwave. When infrared and microwave detectors have alarm signals at the same time, the probe will have alarm output, reducing the possibility of false alarm. There are many types of infrared microwave probes, corresponding to different detection distances. Some detect a sector area, some detect a long and narrow section (such as a corridor), and some detect 360 degrees. You must select the appropriate model according to the specific needs to achieve the effect. The sensitivity of the detector is generally adjustable.
Door magnetic detector : It is a widely used detector with low cost, convenient installation and no need for adjustment and maintenance. The magnetic door switch is divided into movable parts and output parts. The movable parts are installed on the movable doors and windows; The output components shall be installed on the corresponding doors and windows, and the installation distance between them shall not exceed 10mm. There are two lines on the output part. The normal state is normally closed output. When the doors and windows are opened more than 10 mm, the output changes to normally open.
Glass breaking detector : It uses piezoelectric microphones and is installed at the position facing the glass. Since it only detects the high-frequency sound of glass breaking effectively, it will not react to the vibration of the glass itself.
Ultrasonic object movement detector : The ultrasonic object movement sensor needs a transducer that can send ultrasonic waves and another one that is responsible for receiving. There are also receiving and transmitting transducers that share the same body. The transducer used for normal transmission sends a fixed frequency ultrasonic wave, which is scattered in the detection space. If an object reflects the ultrasonic wave, its frequency will shift, so as to detect whether there is object movement. The detector is susceptible to vibration and airflow.
Infrared radiation detector : When someone crosses the monitoring protection area by using the detector of beam blocking mode, the invisible infrared beam will be blocked and an alarm will be triggered. It is often used for outdoor wall alarm. It is always used in pairs: one for transmitting and one for receiving. The transmitter emits one or more infrared lights that cannot be seen by the human eye, forming a warning line. If there are objects passing through, the light is blocked, and the receiver signal changes, the alarm will be given after amplification. Appropriate response time shall be selected for infrared radiation probe: too short is likely to cause unnecessary interference, such as birds flying over, small animals passing through, etc; If it is too long, it will fail to report. The minimum shading time is usually determined at a speed of 10 m/s. If the width of the person is 20 cm, the minimum interruption time is 20 ms. Alarm is given when the time is more than 20 milliseconds, and no alarm is given when the time is less than 20 milliseconds.
Smoke alarm detector : There are two types: photoelectric type and ionic type. The former uses smoke to block the light path to give an alarm, while the latter uses its own sensor to sense the ion concentration in the air. Different sensors sense different gases (such as gas). The commonly used smoke detector is used to detect the carbon ion concentration for fire prevention.
