PIR motion sensor: features of operation, principle of operation, use in everyday life

Devices that detect the presence of movements in their area of ​​action are called motion sensors. They are most often used to create burglar alarms and systems. The most common of these devices is the IR motion sensor. It reacts to infrared waves invisible to the human eye and, comparing their level with the background, signals the appearance of their source - for example, a person.

Operating principle

Every object that emits heat produces infrared radiation. The recording of this process is the principle of operation of the motion sensor. It compares the level of radiation in a specific area with the background and when a certain difference between them is reached, it sends a signal to the equipment connected to it, whether it be a lamp switch or an alarm.

An important detail in this process is the correct sensitivity range of the device. If it is too high, then the sensor may work falsely - for example, for warm air. If the indicator is lower than necessary, then the device will not react even when a person appears in the field of its action.

Device device

The simplest infrared sensor consists of two small Fresnel lenses - complex composite structures of many prismatic facets that form a convex bowl. They collect information about heat waves from a specific area and transmit it to sensitive sensors connected to them. Usually, the data obtained with both lenses is approximately the same - this means that there is no movement. If there is a significant difference between them, then a person or other object, emitting a large amount of heat, appears in the "field of view" of the detector.

In fact, a dual lens device would be impractical due to the sensitivity being too low. In modern models of sensors, there are several dozen of them - from 20 to 60.

The exact layout of motion detectors varies from manufacturer to manufacturer, but the approximate design is similar. The device consists of the following elements:

• Optical system. Includes a variety of lenses, which, depending on the device model, can be of different shapes and sizes required to cover the desired area of ​​the space. Separated from the rest of the system by a sealed chamber to avoid exposure to the heat generated by them. It can control one or several planes of space, as well as do it in a circular way or along a beam.
• Sensor. Most often it is a pyroelectric element, but sometimes there are models with thermocouples, microbolometers and semiconductors. It registers the readings received from the optical system, and when an inhomogeneity occurs in them, sends a signal to the required device.
• Signal processing unit. Analyzes the length, amplitude and shape of infrared interference to prevent false alarms. They can be caused by factors such as sunlight, vibration, electromagnetic waves, animal movements, heat from appliances or electronics, and even movement of air currents. Simpler processing blocks only "filter out" too weak signals, while complex versions devices analyze the duration and frequency of irregularities and, on their basis, determine whether it is interference or no.

It is worth noting that all that the principle of operation of a motion sensor consists of is obtaining information about the presence of a person in its area of ​​action. Therefore, it is almost never used without being connected to other devices that use this information. They can be such devices:

• signaling that triggers the alarm;
• security systems that send a notification to the owner of the sensor and the security service;
• lamps, pool lighting and other lighting devices that turn on or off depending on the presence of people in their area;
• climatic technology that changes its parameters according to the same principle.

Most often, IR sensors are also sold not independently, but complete with security systems or other equipment.

But there are exceptions - then you have to connect and configure the devices yourself. For this, the user will be given access to a personal account on the website and in the mobile application, from where he can set the parameters for the interaction of devices.

Advantages and disadvantages

Motion detectors that respond to infrared radiation compete with ultrasonic, microwave and combination sensors. Each has its own pros and cons, allowing each type to remain in the market. Among the advantages of IR sensors their features can be distinguished:

• Absolute health safety. The device does not generate any waves, but only receives them from surrounding objects and analyzes them. This favorably distinguishes it against the background of devices that expose the room, albeit small, but constant exposure to ultrasound. (it is safe for humans, but can cause discomfort or even serious health problems in pets) or Microwave radiation.
• The ability to fine-tune the distance and angle at which a moving object must be in order to generate a signal.
• Opportunity to work outdoors. The sensor only reacts to objects that create temperature differences.

It also has significant drawbacks. These include such properties:

• High probability of false positives from harmless influences.
• Dependence on the environment. The sensor cannot work effectively at too high or low temperatures - above +50 ° C or below -35 ° C.
• The ability to trick the detector. If you move very slowly in front of it, then the device can count the oscillations arising from this in the infrared radiation as interference. In addition, the sensor does not see objects covered with materials that do not transmit infrared radiation or have excellent thermal insulation and merge with the temperature background.

With all these pros and cons, it belongs to the middle price category - cheaper than microwave detectors, but more expensive than ultrasonic ones.

Sometimes the IR sensor is combined with them in combination devices so that different types of radiation detectors can cover each other's weaknesses and weaknesses.

Areas of use

Among all these types of sensors, infrared is the most common - and judging by the analytics, their market will only grow. Devices are quite common in everyday life and are used in the following areas of activity:

• production of electronics, including touchscreen phones and tablets, game consoles and smartwatches;
• installation of automatic door opening systems in houses and public buildings;
• Automotive - sensors are included in the design of airbags, systems to facilitate maneuvering when parking and cars with automatic control systems;
• healthcare;
• defense production;
• aircraft construction.

But their largest share falls on security systems of various kinds and control over smart home systems.

Security of premises

Installing an IR motion detector is a very common way to find out about intruders entering a residential building or any other territory. To do this, it is connected to security systems that will help prevent further damage and alert violation of the boundaries of property, not only of its owner, but also of law enforcement agencies, security and services security.

Depending on the settings, the security system can send an SMS, email, notification or even call the owner when it receives a signal from the device. In addition, it can activate additional protective mechanisms: turning on the alarm or signaling device, closing car doors and blocking locks, turning off the light or completely de-energizing premises.

The effectiveness of such protection largely depends on the correct placement of the infrared sensor on the protected perimeter. In addition to covering the entire area, it should be located at a certain height and at the right angle to minimize the chances of an intruder merging with the heat background. The installation also takes into account the presence of visors, window and door frames, ornaments - all this can affect the sensor if it is incorrectly installed.

In addition, it is very important for security sensors to have an anti-tampering system that activates the signal and notifies the owner if someone has tried to break the device or affect its radius review.

Smart home systems

In addition to being used in the security field, infrared motion sensors are widely used for automation of lighting and temperature control in residential buildings, offices and other premises, where often there are people. They receive information about changes in the external environment - for example, the appearance in the area of ​​the sensor of radiation caused by human heat. body - and transfer it to other devices, which can be lamps, air conditioners, systems for opening doors and other useful in everyday life devices. They react to the signal and change their parameters accordingly.

According to the estimates of a foreign company, the market research Markets and Markets, which was conducted in 2015, automation of equipment using sensors reduces lighting costs by 60-70%, and the total energy consumption - by 40%.

Depending on the type of tracking device, its ability to record a long presence and respond to movements, it can just control the on-off light, and adjust its brightness, color, power and others options. Infrared motion sensor in such systems is often combined with other types of tracking devices, for example, with a light detector. This combination allows you to maintain the same level of illumination in a certain room at any time of the day when someone is there.

Temperature regulation works in a similar way. The IR sensor detects the presence or absence of people in the room and sends the appropriate signals to the equipment: turn on, turn off or change the settings. For example, he can give a command to the heater or warm floor to increase the power or turn on the air conditioner if someone has entered a room that is too cold or warm.

In complexes for automatic climate regulation, in addition to infrared radiation detectors, almost always there are temperature sensors and other mechanisms that complement each other to achieve better results.

Criterias of choice

To choose the right infrared motion sensor, you must first determine the purpose for which it will be used. For the home, you can choose a device with a smaller operating temperature range, but with a wider viewing angle. For outdoor use, the device must have a certain protection class - 55 or 65 - and be protected from wind, rain and other environmental factors. Also worth paying attention to for the following parameters:

• angle and range of detection of irregularities in the thermal background;
• Accuracy and convenience of setting parameters for switching on and off, for example, response time and sensitivity threshold;
• electricity consumption, the presence of an energy-saving function;
• the field of activity for which the sensor is adapted;
• effectiveness as a security device.

An important role in the choice of a motion sensor is played by its financial availability for the buyer. However, it should be noted that in the case of this device, the most expensive option is always the best: for example, a detector equipped with mirror optics with a huge range will not be needed when installing smart lighting in a small bathroom, and an ultrasensitive sensor will be superfluous on the street, where animals and cars will provoke false triggering.