(3) Space-controlled intrusion detector-space control means that the selected detector can effectively control a certain range of local space, and the upper, lower, left, right, sky, and earth sides of this local space can be prevented .

Voice Control Intrusion Detector

Suspicious sounds such as prying, smashing, dragging, and sawing within the range of audible sound (20-20,000 Hz) will be picked up by the pickups installed at the protection site. When a certain loudness (in decibels) is reached, an alarm can be triggered. After the alarm, the scene can be reviewed (automatically or manually into the monitoring state) to determine whether someone has invaded.

The other is that high-frequency glass breaking sound will cause alarm, other audible sounds will not alarm. It can also automatically or manually enter the sound review (monitor) state. It is characterized by a much lower false alarm rate than the previous one. However, the sound of metal impact near the broken glass and other high-frequency sounds can cause false alarms.

The advantages of the audible alarm are its low cost and large control area. (More than 200m2) The disadvantage is that the false alarm rate is high, so it is only suitable for mountainous areas, suburbs, and relatively quiet environments.

Ultrasonic intrusion detector

Ultrasonic waves are sound waves that are inaudible to human ears (above 20,000 Hz), and we transmit them to indoor spaces through ultrasonic transmitters. If there is a reflection of a moving target within the effective distance. There will be a frequency difference between the echo frequency and the original transmission frequency (Doppler frequency difference). Detecting this frequency difference will cause an alarm. (Using the principle of Doppler radar). There will be no dead ends in a certain protected space, so the prevention is relatively strict. It is installed in the living room in the home, and someone can open the door to enter and cause an alarm. This equipment is cheap and acceptable to the average family. It should be noted that in general, the sound-generating devices use piezoelectric ceramics, and changes in air humidity will cause changes in sensitivity. The sensitivity should be adjusted at any time according to seasonal changes, so as to achieve a stable control range without excessive sensitivity High, in order to reduce the false alarm rate.

Microwave intrusion detector

Using the principle of Doppler radar, the microwave transmitting antenna and the receiving antenna are installed together. Detect the frequency difference of the reflected wave generated by the moving target to alarm. The working principle is the same as that of ultrasonic wave. The difference is that one is acoustic wave and the other is electromagnetic wave. Due to the short wavelength and strong penetration of electromagnetic waves in the microwave section, non-metallic materials such as glass, wooden boards, and brick walls can penetrate. Therefore, do not face the outdoor during installation, so as to avoid false alarms caused by people passing outside. Metal objects have strong reflections against microwaves. There should be no large-area (or large-volume) objects, such as iron cabinets, in the detector protection area. Otherwise, a shadowed area will be formed in the shadow behind it, resulting in prevention loopholes. The sensitivity of the microwave intrusion detector should not be too high, it is more appropriate to adjust it to 2/3. Excessive false positives will increase. It can be used at home as well as ultrasound.

Passive infrared intrusion detector

The principle of simple passive infrared control has been introduced in our online-controlled intrusion detector. In order to effectively control the space, we changed the optical part to a Fresnel lens. This kind of lens is formed by special plastic at one time, and several small lenses are arranged on a curved surface. It is divided into several rows from top to bottom, with more lenses on the top and less on the bottom. Because the infrared radiation of the face, knees, and arms is strong, it is just against the upper lens. There are fewer lenses at the bottom, one is because the infrared radiation of the lower part of the human body is weak, and the other is to prevent the infrared radiation interference of small animals on the ground. All lenses focus on the pyroelectric devices installed inside, so the sensitivity is high, and an alarm will be given whenever someone walks in the field of view of the lens.

Infrared light penetration is poor, and there should be no tall objects in the guard zone, otherwise someone in the shadow will not be able to alarm when walking. In order to solve the problem of occlusion of objects, a ceiling passive infrared intrusion detector was invented. It is installed on the ceiling to guard within 360o. As long as it is within the protection range, no matter which direction it invades, it will trigger an alarm. It is widely used in large spaces such as bank business halls and public activity areas in shopping malls.

Microwave, passive infrared dual-intrusion detector

We know that microwave detectors are the most sensitive to moving targets, and the movement of curtains, the movement of fan pages, and the movement of small animals within their protection ranges may all trigger false alarms. Objects in the protective zone of passive infrared detectors that can produce constantly changing infrared radiation, such as heating, air conditioning, stoves, and electric stoves, may also cause false alarms. In order to overcome the false alarm factors of these two detectors, we combined the two detectors together to form a dual-detector detector. As a result, the conditions of the detector have fundamentally changed. Both the intruding target must be moving and the alarm can only be generated when it can continuously radiate infrared rays. The disadvantages of the original single detector with high false alarm rate are greatly reduced, and the reliability of the whole machine can be greatly improved. There are two aspects to everything, because microwave and passive infrared protection zones cannot overlap completely, and the sensitivity to the direction of intrusion decreases, that is, the detection range decreases accordingly. To reach the original protection scope, it is necessary to increase the number of detectors and increase the input cost.

Ultrasonic and passive infrared dual-intrusion detector

The same as microwave and passive infrared dual detectors, but the cost of ultrasonic detectors is lower, and the cost of the whole machine is reduced accordingly. Other advantages and disadvantages are the same.