In rare cases, modern alarm systems do without sensor components. It is sensitive sensors that allow you to detect alarming signs on one or another indicator. In home security systems, such tasks are performed by light detectors, window shock sensors, devices for detecting leaks, etc. But when it comes to security functions, the PIR motion sensor, which works on the principle of infrared radiation, comes first. This is a miniature device, which in itself can act as an indicator of the status of the serviced site or be part of a common security complex. As a rule, the second use of the sensor is chosen as the most effective solution.
Sensor Overview
Almost all motion sensors are designed to detect strangers in the room. The classic security system assumes that the sensor will record the fact of an invasion of the controlled area, after which the signal will go to the control point and then certain measures will be taken. Most often, a signal is sent in the form of an SMS message to the remote control directly of the security service, as well as to the owner's phone. In this case, one of the varieties of such devices is considered - a pyroelectric PIR sensor, which is characterized by high efficiency and accuracy. However, the quality of the function of such models depends on many factors - from the chosen scheme for integrating the sensor into the security complex to the external conditions for influencing the design with sensitive filling. It is also important to note that motion sensors are not always used as a tool to protect against an attacker. It can be installed for automatic control of individual sections of the lighting system. In this case, for example, the device will be activated when the user enters the room and will also turn off when he leaves.
Principle of operation
To understand the specifics of the operation of this device, it is worth looking at the characteristics of the reactions of certain crystalline substances. The sensitive elements used in the sensor provide a polarization effect at the moments when radiation is incident on them. In this case, we are talking about thermal radiation from the human body. With a sharp change in the characteristics in the observed zone, the intensity in the electric field of the crystal also changes. Actually, for this reason, the infrared PIR sensor is also called pyroelectric. Like all detectors, such devices are not ideal. Depending on the conditions, they may be triggered by false signals or not determine the target phenomena. However, in most cases, according to the totality of operational properties, they justify their use.
Main characteristics
The main performance indicators that a consumer should take into account relate to the range of the device and its ability to work autonomously. As for the parameters for the coverage ranges, the controlled zone, as a rule, is 6-7 m. This is enough if it comes to the protection of a private house and, especially, an apartment. In some models, the microphone function is also provided - in this part it is also important to determine the radius of action, which can reach 10 m. Together with this, the PIR sensor can have direct or autonomous power supply. If you plan to organize a security system, then it is better to purchase models with built-in batteries that do not require wiring. Next, the time is determined during which the device can maintain its function without recharging. Modern models do not require large energy supply, therefore, in a passive state they can work about 15-20 days.
Device design
The sensor housing is usually made of metal. Two crystals are contained inside - these are the elements sensitive to thermal radiation. An important structural feature of this type of detector is a kind of window in a metal shell. It is designed to tolerate radiation of the desired range. Such filtering is just designed to improve the accuracy of the crystals. An optical module is also located in front of the window in the housing, which forms the necessary radiation pattern. Most often, the PIR sensor is equipped with a Fresnel lens stamped on plastic. A field effect transistor is also used to process electrical signals and cut off interference. It is located near sensitive crystals and, despite the task of cutting off interference, in some models it can lower the efficiency of the crystal function.
GSM system in the sensor
This option can be called redundant, although there are many adherents of such a concept. The essence of combining the motion detection function by means of the sensor and the GSM module is due to the desire for complete autonomy of the device. As noted above, the sensor communicates with the central control panel, from which a signal is subsequently sent to the operational security complex or to the telephone of the direct owner. If a PIR motion sensor with a GSM system is used, then an alarm signal can be sent instantly at the moment of registration of the fact of penetration. That is, the stage of transferring the signal to the intermediate controller is skipped, which sometimes allows you to win a few seconds. And this is not to mention the increase in reliability by eliminating additional links in the message transmission chain. What is the disadvantage of this solution? Firstly, it relies entirely on the GSM-communication, which, on the contrary, reduces the reliability of the system, but for a different reason. Secondly, the presence of the module as such negatively affects the operation of the sensitive element - accordingly, the accuracy of fixation of penetration is reduced.
Software
In complex security complexes, where intelligent controllers with a high degree of automation are used, sensor programming tools cannot be dispensed with. Typically, manufacturers develop special ready-made programs with an extensive set of operating modes. But if possible, the user can create his own algorithm for the operation of the sensor in certain conditions. It can be integrated through official software that comes with the hardware. Usually, in this way, the device’s action pattern is configured at the time the alarm is recorded - for example, an algorithm for sending messages is prescribed if the model has the same cellular communications module. On the other hand, home non-security PIR LED sensors are common, reviews of which indicate the effectiveness of informing about the operation of individual components of the lighting system. Each device has a microcontroller that is responsible for the actions of the device in accordance with the embedded commands.
Sensor Installation
Physical installation of the sensor is carried out using the complete clips. Usually, brackets or self-tapping screws are used, fixing not the detector case itself, but the structure into which it is initially integrated. In fact, this is an additional frame with holes provided for twisting. But the main thing in this part of the work is to correctly calculate the position of the sensor. The fact is that the PIR infrared motion sensor is most sensitive in situations when an object with thermal radiation crosses the control field from the side. Conversely, if a person is sent directly to the device, then the ability to fix the signal will be minimal. Also, do not place the device in places that are constantly or periodically exposed to temperature fluctuations due to the operation of heating equipment, opening doors and windows or a working ventilation system.
Sensor Connection
The device must be connected to the main relay of the controller and the power supply system. A typical device provides a board with terminals designed for a power source. Most often, a source with a voltage of 9-14 V is used, and the current consumption can be 12-20 mA. Typically, manufacturers indicate electrical specifications by marking the terminals. The connection is carried out according to one of the standard schemes, taking into account the operating characteristics of a particular model. In some versions, it is possible to connect the PIR sensor without wiring, that is, directly to the network. This is in some way a combination of structures that are installed in open areas and control the same lighting systems. In the case of installing a security sensor, this option is unlikely to be appropriate.
Operation Nuances
Immediately after installation and connection, the device must be set to the optimum operating parameters. For example, the sensitivity can be adjusted, the range of radiation coverage, etc. In the latest programmable modifications, it is also possible to automatically correct the parameters of the sensor depending on operating conditions. So, if you connect the PIR sensor to a central controller connected to thermostats, the sensitive element will be able to vary the boundaries of the critical radiation parameters based on the obtained temperature data.
Sensor in the Arduino system
The Arduino complex is one of the most popular home automation control systems. This is a controller to which light sources, multimedia systems, heaters and other household appliances are connected. Sensors in this complex are not final functional devices - they only serve as indicators, depending on the state of which the central unit with a microprocessor makes one or another decision in accordance with the established algorithm. The Arduino PIR sensor is connected through three channels, among which there is a digital output signal, as well as power lines with different polarity - GND and VCC.
Popular PIR Sensor Models
Most sensors are mainly produced by Chinese manufacturers, so you should prepare for problems with electrical stuffing. A truly high-quality sensor can only be purchased in conjunction with controllers. Nevertheless, many praise the PIR MP Alert A9 motion sensor, which, although it represents the budget segment, is distinguished by its decent assembly and good working qualities. Models like the Sensor GH718 and HC-SR501 are also interesting in their own way. These are open sensors that can easily be masked or included in the complex of the same controller. As for the operational properties, the coverage radius of the described models is 5-7 m, and the battery life is on average 5 days.
How much does the device cost?
Compared with the price tags of modern alarm equipment, the sensor looks very attractive. In total for 1.5-2 thousand p. You can purchase a quality model and even with advanced equipment. On average, a simple PIR sensor is estimated at an amount not exceeding 1 thousand. Another thing is that there is no question of reliability and durability in this case. At the same time, you should not think that this component will cost inexpensively as part of an integrated security system. Even ensuring the security of a small private house may require the use of a dozen of these sensors, each of which will also require auxiliary equipment for installation and connection.
Conclusion
The entry of sensor components into security systems has radically changed the principles of their operation. On the one hand, the detectors made it possible to raise the safety of the serviced object to a new level, and on the other, they complicated the technical infrastructure, not to mention the control system. Suffice it to say that the Arduino PIR sensor fully reveals its capabilities only if it is programmed for automatic operation. Moreover, it interacts not only with direct intrusion signal recorders, but also with other sensitive elements that increase its effectiveness. At the same time, manufacturers seek to facilitate the tasks of the users themselves. To do this, devices that work without wires are developed, sensor control modules using smartphones are introduced, etc.