Basic introduction of intrusion controller
An intrusion detector is a device composed of electronic and mechanical components used to detect the movement or other actions of an intruder. Including active infrared intrusion detector, passive infrared intrusion detector, microwave intrusion detector, microwave and passive infrared composite intrusion detector, ultrasonic intrusion detector, vibration intrusion detector, acoustic intrusion detector, magnetic switch intrusion detector, ultrasonic Passive infrared composite intrusion detector, etc.
1. Functional principle of intrusion detector
Each type of intrusion detector has a certain means of detecting the presence of occupants in the security area. The part of the device that performs this task is called a detector or a sensor.
The ideal intrusion detector responds only to the presence of people, not to the activities of animals such as dogs, cats and mice, nor to changes in the indoor environment, such as changes in temperature and humidity and wind, rain sounds and vibrations. It is not easy to do this. Most devices not only respond to the existence of people, but also. It also responds to the influence of some unrelated factors. The selection and installation of the alarm should also be considered so that it does not respond to irrelevant factors, and the signal repeatability is better.
When designing the alarm device, we must first grasp and analyze the characteristics of various intrusion operations. When the intruder enters the room, he must first remove the obstacle. He must open the doors and windows, or open holes in the wall, floor, and ceiling. Therefore, some switch alarms can be installed to enable the intruder to trigger the switch as soon as it starts to act. Another characteristic that should be considered is that light and infrared rays cannot pass through the human body, so the method of installing photoelectric devices can be used to detect intrusion activities.
Another very important feature is that the human body's normal body temperature can emit infrared light, and the infrared sensor can detect the heat radiated by the human body. In addition, intruders inevitably make a sound when they steal, and the use of voice control sensors can detect abnormal sounds made in the room. The use of ultrasonic and microwave intrusion detectors is based on the principle that the movement of the human body interferes with ultrasonic waves or electromagnetic fields.
Various detectors have different working principles, and each has advantages and disadvantages. In order to make the detector function effectively in any occasion, it should be carefully selected and installed carefully, and the protection measures for the detector should be considered as much as possible during installation.
Due to the different circumstances of households, shops, groups and enterprises, the intrusion detectors used are also different. In order to obtain the best security effect, it is usually necessary to tailor the alarm system according to the actual situation of the user, so that the detector can function better.
The alarm issued when there is no intrusion is called a false alarm. False alarms may be caused by component failures or some external influences. The bad consequences it produces are unimaginable. The lightest consequence is that it adds a lot of unnecessary troubles that annoys people, which greatly reduces the possibility of the alarm. Reliability. It is conceivable that if store and warehouse managers are often called up from the bed due to false alarms, they will not be willing to use this kind of alarm device. The worst consequence is that it makes the police or security personnel rush to the scene unnecessarily, so that their own safety and the safety of the people around them will be jeopardized. Therefore, false alarms are the fatal weakness of the alarm.
2. Various types of detectors
1) Microwave Doppler intrusion detector
It is often referred to as a radar alarm because it is actually a Doppler radar. It is a device that uses the Doppler principle, radiates electromagnetic waves of a certain frequency, covers a certain range, and can detect a human body moving within this range to generate an alarm signal.
Technically speaking, it is generally required that the detector should be composed of one or more sensors and a signal processor, and the detector should have a method that can change the detection range.
Microwave Doppler intrusion detectors are difficult to destroy if properly installed. A microwave detector can also be used to protect more than two rooms with one facility. Microwave intrusion detectors are very effective for capturing hidden thieves, as long as the hiding person enters the security area, the alarm will be triggered.
The main disadvantage of microwave intrusion detectors is the high installation requirements. If improperly installed, the microwave signal will penetrate the wall with many windows and lead to frequent false alarms. Another disadvantage is that it emits trace amounts of harmful energy to the human body, so the energy must be controlled at a level that is not harmful to the human body. In addition, microwave warning devices can be interfered by high-energy radars used by air traffic and defense agencies.
2) Ultrasonic intrusion detector
The principle of ultrasonic intrusion detector is the same as that of microwave intrusion detector. It also uses the Doppler principle to generate an alarm by responding to the ultrasonic waves reflected by the moving human body. The same is one of the most effective security facilities. Ultrasonic alarms must be very sensitive to small movements in the security area without being affected by airflow.
The effectiveness of the ultrasonic alarm device depends on the multiple reflections of energy in the security area. Hard surfaces such as walls, tables, and file cabinets have a good reflection of sound waves, while soft materials such as carpets, curtains, and cloth are bad reflectors of sound waves. Therefore, a small area with a reflective surface such as a hard wall requires fewer sensors than an office equipped with tapestries and many curtains. It is best to use other security methods in areas filled with soft materials.
In addition, if the room is well ventilated, or if a certain part of the room is being heated to make the air flow larger, it will cause a false alarm for the relatively installed ultrasonic alarm. Because in the case of large air flow, if the transmitted signal is downwind, the emitted ultrasonic wave will reach the receiver faster than when it is stationary. In this way, the standing wave waveform will be destroyed, thereby triggering the alarm.
3) Active infrared intrusion detector
The infrared radiation beam between the transmitter and the receiver is completely or more than a given percentage partially blocked by a detection device that can generate an alarm state.
Active infrared intrusion detectors are generally composed of separate transmitters and receivers. The receiver and transmitter are installed separately. The performance requires that the infrared radiation spectrum of the transmitter should be outside the visible light spectrum. In order to prevent external interference, the infrared radiation emitted by the transmitter must be modulated, so that when the receiver receives signals of different modulation frequencies close to the radiation wavelength, or unmodulated signals, it will not affect the generation and interference of the alarm state. The generated alarm status.
4) Passive infrared intrusion detector
A detection device capable of generating an alarm state when the human body moves within the detection range, causing the received infrared radiation level to change.
The requirement for sensitivity is that when the human body is normally dressed, it can move arbitrarily laterally within the detection range at a speed of one step per second, and if it walks continuously for less than 3 meters, the detector can generate an alarm state.
Passive infrared intrusion detectors use pyroelectric infrared detection elements to detect moving targets. As long as the temperature of the object is higher than absolute zero, it will continuously radiate infrared rays to the surroundings, and use the infrared rays radiated by the moving target (such as people, animals, and vehicles) to detect it.
Compared with other types of security equipment, passive infrared intrusion detectors have the following characteristics:
1. No need to install any equipment in the security area, it can achieve remote control;
2. Because it is a passive work, it does not produce any type of radiation, and it has strong confidentiality and can effectively perform security tasks;
3. There is no need to consider the illuminance conditions, it is available day and night, especially suitable for working at night or in dark conditions;
4. Since there is no energy emission, there are no moving parts that are easy to wear, so the power consumption is low, the structure is firm, the life is long, the maintenance is simple, and the reliability is high.
5) Combined microwave and passive infrared intrusion detector
A device that combines the two units of microwave and passive infrared into one, and only issues an alarm when both are in the alarm state. This composite detector consists of a microwave unit, a passive infrared unit and a signal processor, and is installed in the same casing. The microwave and infrared detection ranges are of equal size and overlap, and there are devices to adjust the overlap of the two in the cabinet.
6) Electromechanical detector
The simplest intrusion detector consists of a closed circuit around the protected area. Once an intruder enters the area, it will destroy the circuit and trigger an alarm.
Electromechanical detectors include:
1. Metal foil detector. The most commonly used electromechanical detector is to install metal foil or metal tape on the door and window to form a part of the detection circuit. When the metal foil is damaged due to intrusion, an alarm will be triggered;
2. Door and window switch. Door and window switches can be used for electromechanical intrusion alarms;
3. Glass break detector. In all kinds of theft cases, the criminals break the glass doors and windows by violent means and invade the room to take a large proportion. Therefore, the glass break detector has a great use value in the anti-theft alarm;
4. Tilt and vibration switch. As the name implies, the so-called tilt switch or vibration switch is a device that can be turned on and off in response to tilt or vibration.
The most basic advantage of the electromechanical detector is that it has a simple working principle and few circuit components, so its reliability is relatively high. As long as it is properly installed and maintained, and a back-up hidden switch is added, the alarm can have better security performance, and it can be used as an excellent backup system for higher-level alarm systems; in addition, because the electromechanical detector can be seen and easily identified Therefore, it has a certain deterrent effect on most "amateur" thieves and saboteurs, as well as a deceptive effect on repetitive offenders. For example, when he finds an electromechanical alarm, he will first try to damage the alarm with confidence, and then start the crime with confidence, then he may trigger a more advanced alarm system.
However, electromechanical detectors cannot protect all possible access to the protected area. Even if all doors and windows are equipped with such detectors, intruders can still penetrate the wall, ceiling or floor and enter the room. Another disadvantage of the electromechanical detector is its installation problem. If it lacks imagination and installation experience, it is not easy to achieve good results. Its sensitive components are very exposed and can easily be invalidated by criminals.
7) Photoelectric detector
Photoelectric detectors use light to spread in a straight line, so it is suitable for detecting entrances or areas that are open without objects blocking the beam. If the area is large, you can use a mirror to reflect the light. The main disadvantage of the photodetector is that it is not suitable for short and not straight channels. If it is used for short and not straight channels, multiple mirrors are required, and the installation position of each mirror is incorrect or contaminated with dirt will cause false alarms. In addition, intruders may also use the mirror to reflect the light beam, so that the light beam can be sneaked into the security area without being blocked.
8) Light detector
The photodetector is a photodetector driven without a light source. This device can automatically measure the light intensity in the security zone and can respond to sudden changes.
9) Infrared body temperature detector
Infrared body temperature detector is another form of light detector, which can be triggered by the thermal energy emitted by the intruder's body. This detector will not respond to changes in room temperature rise or fall. However, when a target whose temperature is approximately equal to the human body temperature (such as an intruder) enters a non-sensitive area from a sensitive area, the alarm can detect the difference in radiation and trigger an alarm. Infrared body temperature detectors have high sensitivity and are not easily destroyed. But if the body temperature of the intruder is the same as the temperature of the indoor environment, the alarm will fail, which is actually difficult to achieve.
10) Proximity detector
A proximity detector is a detection device that can trigger an alarm when an intruder approaches it (but has not yet touched it). False alarms are prone to occur when the proximity detector is used outdoors, and special measures must be taken during application. The most common impacts are changes in temperature and humidity. When it rains, the impacts are even greater. Advanced insulation materials are used to support the discharge conductors in order to reduce the impact of rain to a minimum.
Proximity detectors are more suitable for indoor use, such as providing protection for writing desks, file cabinets and other special objects. The objects to be protected are usually metal, and can actually form part of the protection circuit. The sensitive wire is connected to the frame of the cabinet and serves as a plate of the capacitor in the sensitive circuit.
Proximity detectors are very suitable for the protection of specific objects. Its most prominent advantage is that it is easy to treat the protected object as part of the circuit, so whenever someone tries to damage the system, it will immediately trigger an alarm.
The main advantages of the proximity detection system are its versatility and versatility. It can be used to protect almost any object and will not be excited by interference a few meters away. When someone steals near a jewelry box or file cabinet, an alarm will be triggered, but normal business work in the vicinity can proceed as usual.
The main disadvantage of the proximity detection system is that it is too sensitive. If the sensitivity is adjusted too high to suit a certain application, it will easily cause frequent false alarms. Unlike other systems, it is impossible to plug the power plug to make the system work normally, but must be adjusted to reduce the probability of false alarms to a minimum.
11) Sound intrusion detector
In addition to being used for the entrance control of the portal, it can also be used to monitor the area where the intruder appears, but at this time, the guard must be listening for the sound of the intrusion. On the other hand, intruders are generally silent as much as possible, especially when a guard has to monitor several different areas. Adding a trigger circuit can overcome the above shortcomings.
Acoustic intrusion detectors have many limitations. Under normal conditions, when the background noise varies over a wide range, such a detector can easily cause false alarms. It is also not suitable for occasions where thick curtains are hung on doors and windows and thick carpets are laid on the ground. In addition, the mechanical equipment of some departments will automatically turn on and off day and night to produce non-stop sound, so it is not suitable to use the above detector. The outstanding advantage of the sound intrusion detector is that it can be used to identify the cause of the alarm.
12) Vibration intrusion detector
Vibration detectors and acoustic intrusion detectors are essentially the same. The sensor of the vibration system is a vibration detector. This type of detector must have mechanical displacement to generate a signal; the vibration detector material is most suitable for the protection of valuable and confidential special objects such as file cabinets, safes, etc. Used in combination to prevent thieves from breaking into the wall. The effectiveness of the vibration detector has a great relationship with the correctness of the application. It is often used to provide protection for special objects with people in the protected area under normal circumstances.
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