Even the simplest security alarm systems for private use today rarely do without sensors. Thanks to sensitive sensors, the speed and autonomy of security systems in terms of responding to a critical situation is ensured. At the same time, burglar alarm sensors are quite diverse, so during the design of the system it is important to correctly correlate their capabilities with the requirements for protection in specific conditions.
Assignment of sensors
The general principle of operation of any sensor devices in alarm systems is focused on fixing changes in the situation in a certain area. The sensor has two basic tasks - to detect this change due to the operation of the sensitive element and transmit the corresponding signal to the alarm control panel.
In this case, the detectors can respond to different factors of changesituation - it already depends on the specific principle of action. If we divide the security alarm sensors according to their purpose, then the main classification will look like this:
- Perimeter security devices. Sensors of this type transmit signals about attempts of unauthorized entry into the serviced area.
- Devices for internal security. Sensors that record the presence of an unauthorized person in a protected area.
The most common types of security sensors include vibration, magnetic, infrared and combined devices. Now it is worth considering them in more detail.
Vibration sensor
This is an extensive group of sensitive elements, the most popular of which can be called a glass break sensor. This device belongs to the category of devices that record the facts of penetration into the security zone. Moreover, vibration alarm sensors respond not only to physical vibrations of materials and structures, but also to acoustic radiation. That is, it is not necessary to mount such a detector in close proximity to the window opening. If it has an acoustic response function, then any fact of noisy penetration will be recorded. But there is also the problem of using such models, which lies in the high rate of false positives - any noise during operation can cause the siren to activate, for example. Therefore, experts recommend turning to complex models of vibration sensors withmicroprocessor circuit for processing the sound spectrum in the room at low-frequency and high-frequency levels.
Magnetic pickup
There are cases when intruders get into the house even without trying to force break-in. For example, to enter the site, it is enough to open the gate. If a lock is not provided in the window system or the enemy has a master key from the door, then he will easily enter the protected area and the aforementioned vibration sensor will not be able to record the fact of intrusion. To insure against such situations, a magnetic contact sensor (contactor) will help, which is triggered at the moments of opening of two fields. In the normal state, the magnet and its functional element (reed switch) are closed. One part of the device, for example, is installed on the sash, and the second on the frame box. While the window is closed, the sensor is in standby mode, but as soon as the window is opened, it will work.
Passive infrared sensor
In case an intruder still manages to penetrate the protected area unnoticed, internal sensors should be provided. The best option would be a passive infrared sensor that responds to movement. The principle of operation of such devices is based on the fixation of thermal radiation from an object. A change in the temperature background in the observed zone activates the sensor, which sends a corresponding signal to the control panel. But it is important to consider that the use of such a burglar alarm for an apartment can also be accompanied by false alarms.triggers. This is due to the use of climatic equipment with sharp changes in temperature. The minimum rate of false positives is noted for multi-channel IR sensors with sensitive heads that are resistant to thermal noise. As in the case of acoustic sensors, in this case microprocessor signal processing is provided, but already in the thermal energy spectrum.
Infrared active sensor
Another kind of sensitive IR sensors designed to detect foreign objects inside the protected area. Such sensors are also called dual-beam sensors, since they consist of a receiver and a transmitter that exchange signals with each other. The distance between them can be several decimeters, and hundreds of meters. Active infrared burglar alarm sensors react to intrusion only if two beams cross at the same time. This feature of registering the presence of a foreign object increases the accuracy of the system and minimizes the likelihood of false alarms.
Combined sensor
The imperfection of the work of certain types of security sensors has already been noted more than once. An ideal device of this type has not yet been developed, but combined or dual sensors can be used, in which two principles of threat detection are implemented. That is, two types of sensitive elements are combined, each of which covers the shortcomings of the other. A prime exampleThis approach is a combined intruder alarm sensor that works with infrared radiation and supports the function of a magnetic contactor. Moreover, the combination of the two principles of operation may involve different configurations of the security system. It can also be configured to record alarms when any of the sensitive elements, one specific sensor, or two at the same time is triggered. So, in the latter case, the risk of sending false signals will be practically reduced to zero.
Installation of burglar alarm sensors
First of all, a general plan is drawn up with a diagram of the location of the sensors. This is a rather difficult task, since it is necessary to calculate possible penetration options and, in accordance with the identified threats, select devices with the optimal operating principle in a particular place. In terms of choosing a place for installation, there is a set of universal rules:
- The wall to which the sensor is to be attached must not be subjected to vibrations.
- Near the openings, only devices that respond to physical influences - shocks, vibrations, etc. are mounted. For example, you can install vibration and magnetic security alarm sensors on doors and windows, but infrared, acoustic and some combined models in this area will be ineffective.
- It is not allowed to install all types of sensors near climate equipment and ventilation.
- It is important to ensure that the immediate area of the sensing element is opensecurity.
From the point of view of installation, the sensors are divided into mortise, overhead and structural. The first are installed in prepared niches of ceiling, floor or wall surfaces like a socket. Overhead are usually mounted to the ceiling using complete screws or self-tapping screws. As for structural models, they are built into window frames, doors and even household appliances. For this, appropriate mounting hardware is provided with miniature clips and latches.
Connecting devices
Regardless of its type, the sensor must be connected to two circuits - the power supply wiring and the loop of the security control panel. As a rule, a line with a voltage converter up to 12 V is used for power supply. Although there are also stand-alone sensors that operate on batteries or accumulators. As for the loop, the security alarm sensors are connected through a complete relay, which may involve connection with several types of detectors. A tamper must also be provided. This is a protective device that is triggered in cases of unauthorized attempts to open the sensor housing. The general burglar alarm circuit must also be provided with grounding, a fuse box, and a stabilizer if power surges occur on the local power grid.
Conclusion
The efficiency of the sensors will depend not only on the literacy of their selection and location in the service area, but also on the quality of their management. Autonomy and automation are the main criteria for the functionality of modern security systems. Security alarm management for an apartment can be organized using a small panel with an LCD display and a basic set of control and configuration functions. However, a private home, provided with dozens of sensors, is provided with an extensive infrastructure with several control nodes via a computer. It would also not be superfluous to provide for the possibility of connecting programmable algorithms for the operation of individual devices, which will increase the reliability and quality of the alarm in a single complex with sensitive sensors of different types.
