In rare cases, modern alarm systems do without sensor components. It is sensitive sensors that allow you to detect alarming signs according to certain indicators. In home security systems, such tasks are performed by light detectors, window impact sensors, devices for detecting leaks, etc. But when it comes to the security function, then the PIR motion sensor, which works on the principle of infrared radiation, comes first. This is a miniature device that can itself act as an indicator of the status of the serviced area or be part of a general security complex. As a rule, the second option for using the sensor is chosen as the most effective solution.
Sensor overview
Almost all motion sensors are designed to detect strangers in the room. The classical security system assumes that the sensor will record the fact of intrusion into the controlled area, after which the signal will be sent 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 control panel directly to 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 of impact on the structure with sensitive filling. It is also important to note that motion sensors are not always used as a tool to protect against an intruder. It can be installed to automatically control individual sections of the lighting system. In this case, for example, the device will be activated when the user enters the room and also turn off when he leaves it.
Working principle
To understand the specifics of the operation of this device, it is worth referring to the features of the reactions of some crystalline substances. The sensitive elements used in the sensor provide the effect of polarization at the moments when radiation falls 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 strength in the electric field of the crystal also changes. Actually, for this reason, the PIR infrared sensor is also called pyroelectric. Like all detectors, such devices are not perfect. Depending on the conditions, they may respond to false signals or not determine the target events. However, in terms of the combination of operational properties, in most cases they justify their use.
Key Features
The main performance indicators that the consumer should consider relate to the range of the deviceand ability to work independently. As for the parameters for coverage ranges, the controlled zone, as a rule, is 6-7 m. This is enough when it comes to protecting a private house, and even more so an apartment. Some models also provide a microphone function - in this part it is also important to determine the range, which can reach up to 10 m. At the same time, the PIR sensor can have a 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 will be able to maintain its function without recharging. Modern models do not require a large energy supply, therefore, in a passive state, they can work for about 15-20 days.
Device design
The body of sensors is usually made of metal. Inside there are two crystals - these are the elements sensitive to thermal radiation. An important design feature of detectors of this type is a kind of window in a metal shell. It is designed to allow radiation in 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 wave 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 reduce the efficiency of the crystal function.
GSM system in sensor
This optional can be called redundant, although there are many adherents of this concept. The essence of combining the function of detecting movement by means of a sensor and a GSM module is due to the desire to have a 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 phone 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 forwarding 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 due to the elimination of additional links in the message transmission chain. What is the disadvantage of this solution? Firstly, it completely relies on the operation of 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 fixing the penetration decreases.
Software
In complex security systems, where intelligent controllers with a high degree of automation are used, one cannot do without sensor programming tools. Usuallymanufacturers 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 the official software that comes with the hardware. Usually, in this way, the scheme of the device’s action is set up at the moments when an alarm is fixed - for example, an algorithm for sending messages is prescribed if the model has the same cellular communication module. On the other hand, home non-security LED PIR sensors are common, reviews of which note 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.
Installing the sensor
Physical installation of the sensor is carried out with the help of complete clamps. Usually, brackets or self-tapping screws are used, which fix not the detector body 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 where an object with thermal radiation crosses the control field from the side. Conversely, if a person is heading straight for the device, then the ability to capture the signal will be minimal. Also, do not place the device in places that are constantly or periodically exposed totemperature fluctuations due to the operation of heating equipment, opening doors and windows, or a functioning ventilation system.
Sensor connection
The device must be connected to the main relay of the controller and the power supply system. A typical machine has a board with terminals dedicated to the power supply. The most commonly used source with a voltage of 9-14 V, 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 features of the operation of a particular model. In some modifications, it is possible to connect a PIR sensor without wiring, that is, directly to the network. These are in some way combined structures that are installed in open areas and control the same lighting systems. If a security sensor is installed, this option is unlikely to be appropriate.
Exploitation nuances
Immediately after installation and connection, you should set the device to optimal operating parameters. For example, the sensitivity strength, radiation coverage range, etc. can be adjusted. The latest programmable modifications also allow the possibility of automatic correction of the sensor operation parameters depending on the operating conditions. So, if you connect a PIR sensor to a central controller connected to thermostats, then the sensitive element will be able to vary the limits of critical radiation indicators based on the data received.about temperature.
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. The 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 underlying algorithm. The Arduino PIR sensor is connected through three channels, including a digital output signal, as well as power lines with different polarity - GND and VCC.
Popular PIR sensors
Most of the sensors are mainly produced by Chinese manufacturers, so you should prepare for problems with electrical stuffing. You can buy a truly high-quality sensor only in combination with controllers. Nevertheless, many praise the PIR MP Alert A9 motion sensor, which, although it represents the budget segment, is distinguished by a decent assembly and good working qualities. Models such as the Sensor GH718 and HC-SR501 are also interesting in their own way. These are open-type sensors that can be easily disguised 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 an average of 5 days.
How much does the device cost?
Compared to the price tags of modernsignaling equipment, the sensor looks very attractive. In total for 1.5-2 thousand rubles. you can buy a high-quality model and even with extended equipment. On average, a simple PIR sensor is estimated at an amount not exceeding 1 thousand. Another thing is that reliability and durability are out of the question in this case. At the same time, you should not think that this component will be inexpensive as part of an integrated security system. Even securing a small private home 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 how they work. On the one hand, the detectors made it possible to raise the security of the serviced object to a new level, and on the other hand, 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 strive to facilitate the tasks of the users themselves. To do this, wireless devices are being developed, sensor control modules are being introduced using smartphones, etc.
