Even the simplest sets of burglar alarms for private use today rarely do without sensors. Thanks to sensitive sensors, the speed and autonomy of security systems is provided in terms of responding to a critical situation. At the same time, alarm sensors are quite diverse, therefore, during the design of the system, it is important to correctly correlate their capabilities with the protection requirements in specific conditions.
Sensor assignment
The general principle of operation of any sensor devices in alarm systems is focused on recording changes in the situation in a particular 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.
At the same time, detectors can respond to various factors in a changing environment - this already depends on the specific principle of action. If you divide the alarm sensors according to their purpose, then the main classification will look like this:
- Perimeter guards. Sensors of this type transmit signals of attempts of unauthorized entry into the service 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 is the glass break sensor. This device belongs to the category of devices that record the facts of penetration into the protection 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 provides an acoustic response function, then any fact of noisy penetration will be recorded. But there is the problem of using such models, which consists in a high false response rate - any noise during operation can cause activation of the siren, for example. Therefore, experts recommend turning to complex models of vibration sensors with a microprocessor-based circuit for processing the sound spectrum in a room at low-frequency and high-frequency levels.
Magnetic sensor
There are times when intruders penetrate the house even without attempting to force break-in. For example, to go to the site, just open the gate. If there is no lock in the window system or if the enemy has a master key for the door, then he will easily enter the protected area and the aforementioned vibration sensor will not be able to detect the fact of the intrusion. A magnetocontact sensor (contactor) will help to insure against such situations, which is triggered when two fields open. In the normal state, the magnet and its functional element (reed switch) are closed. One part of the device, for example, is mounted on a sash, and the second on a frame box. While the window is closed, the sensor is in standby mode, but as soon as the window opens, it will work.
Infrared Passive Sensor
In case an attacker can still 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 the object. Changing the temperature background in the observed area activates the sensor, which sends the corresponding signal to the control panel. But it is important to consider that the use of such a security alarm for an apartment can also be accompanied by false alarms. This is due to the use of climatic equipment with sharp changes in temperature conditions. The minimum false response rate is observed for multi-channel infrared sensors with sensitive heads that are resistant to thermal noise. As in the case of acoustic sensors, in this case microprocessor processing of the signal is provided, but already in the spectrum of thermal energy.
Infrared Active Sensor
Another type of sensitive infrared sensors designed to detect foreign objects inside the protected area. Such sensors are also called two-beam sensors, since they consist of a receiver and a transmitter that exchange signals with each other. The distance between them can be a few decimeters, and hundreds of meters. Active infrared burglar alarm sensors respond to intrusion only if two beams intersect at the same time. This feature of registering the fact of finding a foreign object increases the accuracy of the system and minimizes the likelihood of false alarms.
Combined sensor
The imperfection of the operation of certain types of security sensors has been noted more than once. An ideal device of this type has not yet been developed, but you can use combined or dual sensors, which implements two principles of threat detection. That is, two types of sensitive elements are combined, each of which covers the shortcomings of the other. A striking example of this approach is a combined alarm sensor that works with infrared radiation and supports the function of a magnetic contactor. Moreover, the combination of the two principles of action may involve various configurations of the security system. It can also be configured to fix alarms when any of the sensitive elements, one specific sensor or two at the same time are triggered. So, in the latter case, the risk of sending false signals will be practically nullified.
Installation of burglar alarm sensors
First of all, a general plan is drawn up with a layout of the sensors. This is a rather difficult task, since it is necessary to calculate the possible penetration options and, in accordance with the identified threats, select devices with the optimal principle of operation 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 mounted must not be exposed to vibrations.
- Next to the openings, only devices that are responsive to physical influences are mounted - shock, vibration, etc. For example, you can install vibration and magnetic sensors for burglar alarms 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 climatic equipment and ventilation.
- It is important to ensure openness to the sensitive element of the area of ββits direct protection.
From the point of view of installation, the sensors are divided into mortise, laid on and structural. The first are installed in prepared niches of ceiling, floor or wall surfaces according to the type of outlet. Overheads are usually mounted to the ceiling with the help of complete screws or self-tapping screws. As for structural models, they are built into window frames, doors and even household appliances. For this, appropriate fastening equipment with miniature clamps and clips is provided.
Device connection
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. Although there are autonomous sensors that operate on batteries or accumulators. As for the loop, the burglar alarm sensors are connected via a complete relay, which may involve connecting to several types of detectors. It is imperative to provide for tamper. This is a protective device that is triggered in the event of an unauthorized attempt to open the sensor housing. The common alarm circuit should also be provided with grounding, a fuse box and a stabilizer if power surges are observed in the local power supply.
Conclusion
The effectiveness of the sensors will depend not only on the literacy of their selection and location in the served area, but also on the quality of their management. Autonomy and automation are the main criteria for the functionality of modern security systems. Management of burglar alarms for an apartment can be organized using a small panel with an LCD display and a basic set of monitoring and configuration functions. However, a private house, provided with dozens of sensors, is provided with an extensive infrastructure with several control nodes via a computer. It will also not be amiss to envisage the possibility of connecting programmable algorithms for the operation of individual devices, which will increase the reliability and quality of signaling in a single complex with sensitive sensors of various types.