One of the components of the security alarm system, which increases its effectiveness, is the volume sensor. It does not measure volume and does not track volume stability; it reacts to changes in the location of objects that fall into the detection zone. If this happens, the system will trigger and raise an alarm. The device is called a volume sensor because it covers the volume of the room in which it is installed, since the detection area vertically and horizontally is 90 degrees. The detectors have different designs and operating principles. These features must be taken into account when choosing equipment.
Types of motion sensors
Motion sensors, which is essentially a volume detector, differ in the way they detect the movement of objects.
Microwave
The design of the microwave sensor provides a generator and receiver of high-frequency electromagnetic waves. The generator constantly emits waves in the microwave range. The detection principle is based on the Doppler effect. Waves bounce off surfaces, and the returned signal is received and analyzed. When changes in the characteristics of electromagnetic waves are registered, an alarm is triggered. Such devices most effectively detect motion along the radiation axis.
The advantage of a microwave sensor is that it detects movement even when the signal path is obstructed. Dense and thick obstructions will significantly attenuate the signal, but if the structure is light and rather thin, motion will be detected.
Since microwaves are harmful to human health, microwave sensors are not recommended to be installed in places of permanent residence. It is preferable to use them for security systems installed in warehouses, garages and other similar premises.
Infrared
The main elements of an infrared detector are: a pyrodetector, a segmental lens and a photocell. A lens focuses the infrared light on a photocell, and a pyrodetector registers the signal. The disadvantage of an IR sensor is that false alarms can occur due to household appliances emitting intense infrared light entering the range. The detection range of an object is in most cases from 6 to 10 m along the optical axis. But at the edges of the detection area, the range is reduced.
Ultrasonic
The ultrasonic sensor emits waves in the range of 20 to 60 kHz. Its action is also based on the Doppler effect. The reflected waves are received and compared with the emitted ones using the built-in processor. If changes are registered, the circuit is closed.
Criteria for selecting a volume sensor
It is necessary to choose a device knowing the conditions of its operation, the place of installation, the type of system in which it will be used.
- One of the important selection criteria is weather resistance. This parameter is indicated by a special marking. If the likelihood of moisture ingress on the device case is high, it is necessary to choose a device with a protection level of at least IP65. If direct contact of the case with water or a significant increase in the level of humidity of the ambient air is excluded, but high dust content is possible, choose a device with an IP44 protection level - the case protects the electronic elements from dust and solid particles.
- It is necessary to prevent false triggering of sensors. Therefore, it is preferable if active detectors will have protection from electromagnetic radiation, and passive ones will provide protection from animals - the detector will not react to their movement.
- If the sensor will be installed in a residential building, it is better to choose an infrared detector, excluding ultrasonic and microwave models.
- The devices can be designed for surface or concealed installation. The former should have an aesthetic appearance, the latter should have a compact body.
- The operating temperature is important if the detector is installed in an unheated room or outdoors. Some models can operate in the range of -30 ° C - + 50 ° C.
- Current consumption in armed mode. The cost of paying for electricity directly depends on this parameter.
- The number of alarm zones. There are detectors with several alarm zones. One such device replaces several.
There are devices that use several options for motion detection. In them, the disadvantages of one method are compensated for at the expense of another.
Scope of use
The most widely used volume sensors are in burglar alarms. The volumetric burglar alarms control the volume of the room and give a signal when foreign objects are detected, form an alarm message to be sent to the security console or the owner via the radio channel. They have enough functions and adjustment possibilities. Some first give a warning signal and only then activate the alarm.
In addition to burglar alarms, they are also used:
- as elements of a fire alarm;
- in video surveillance systems;
- to turn on the lighting;
- to control air humidity;
- in technological lines and control systems;
- in logistics when warehousing products.
As a result of the triggering of the volume sensor, which is part of the video surveillance system, video recording is activated - shooting is performed only when necessary, and not all the time, the equipment resource is saved, disk space and battery power are saved.
If the volumetric sensor is used in lighting, the light is turned on only when necessary, automatically, the switches can be completely abandoned. However, volume sensors were created specifically for burglar alarms.
Special volume sensors are available for car alarms. Special two-zone devices react to the penetration into the passenger compartment, the approach of a person to the car. Moreover, the detectors recognize movement even through armored and tinted glass.
Indoor installation of volumetric sensors
Volume sensors are installed only on hard surfaces where vibration is excluded. It is preferable to fix them at a height of at least 2 meters from the floor on the bracket that comes with the kit (you can also directly on the wall). The detection area should not include windows, as well as household equipment that generates heat and affects the movement of air flows, for example:
- heaters;
- fans;
- conditioners.
Sensors should be installed so that they do not interfere with each other's work and with the smallest number of "dead zones" are minimized.
It is advisable to install infrared detectors above the doorway, because most of them have protection against sabotage - they track movement in the detection zone and directly below them. If there are two sensors, it is desirable to arrange them in the corners, directing the optical axes diagonally.
Do not install microwave detectors nearby, because false alarms will often occur. The minimum possible distances between the devices are indicated in the user manual. It is permissible to install only those devices that emit waves of different frequencies.
Wireless systems use addressable sensors that digitize the signal. To install such a system, you need to set the detector number in the settings, and adjust the parameters through the central control device.
When connecting the detector to the mains, make sure that the voltage is not exceeded.
Additional sensor functions
The main function of the sensor is security, when, when the conditions are met, the detector closes the circuit.
Additional functions:
- Protection from animals. Pets can cause false alarms, especially if they are large enough. Protected devices do not react to animals.
- Penetration report. The sensor generates a notification about an alarm event by transmitting the status over the radio channel to the GSM alarm system.
- Opening detector.
- Sensitivity adjustment.
- Disguise detection.
- Self-diagnosis.
- Anti-interference.
Options increase equipment stability and usability.
Benefits of using burglar alarm sensors
The advantages of burglar alarm sensors include:
- Resistance to adverse working conditions - the device case has a high level of protection against dust, solid particles, moisture.
- High sensitivity - if configured correctly, the burglar alarm sensor quickly reacts to movement and gives an alarm signal.
- Complexity of search and dismantling - hidden sensors are difficult for an intruder to find, and it is even more difficult to dismantle them before they are triggered.
- Some models of volumetric sensors can operate on battery power, so it is not necessary to run a power line to install it.
- Possibility of adjusting the sensitivity - changing the settings allows you to eliminate false alarms and adjust the sensitivity range depending on the operating conditions.
The sensors also have some drawbacks. This is primarily a high cost and the need for careful adjustment.
The volumetric sensor used for burglar alarms helps prevent theft, catch an intruder immediately or find him after a break-in. The device works instantly and significantly increases the effectiveness of security systems.
