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What is a motion sensor — types of security sensors and how to choose

The motion sensor is a compact device, part of the security alarm system, detecting and recording movement in the protected area. Security motion detectors are installed in public buildings, residential buildings, apartments, offices, etc. The most common is a security motion sensor, which detects changes in the heat flux emitted by the human body when crossing protected areas.

Types of security motion sensors

1. Infrared motion detectors (IR)
2. Ultrasonic motion sensors (US)
3. Microwave motion sensors
4. Combined motion sensors

Each of the above sensors has a suitable application and different functions.

Infrared (IR) motion sensors. How an infrared motion sensor works

The principle of operation of infrared motion sensors is to analyze and detect changes in the thermal radiation of surrounding objects. Each object with a temperature emits infrared heat. A system of lenses or uniquely concave segmented mirrors enters a sensitive sensor inside the security motion detector, which registers changes. During the movement of an object, detectors' IR radiation by various lenses of the system is alternately focused on the sensor (the number of lenses usually varies from twenty to sixty). This is a signal to perform the function laid down in the sensor. The sensitivity of the motion detector depends on the number of lenses in its system, the more lenses – the higher the sensitivity. Also, the larger the surface area of ​​the lens system, the wider the field of view of the motion sensor.

Ultrasonic (US) motion sensors. The principle of their action

An ultrasonic sensor examines the surrounding space with the sound waves using the ultrasound – a frequency beyond the human ear's hearing range. The ultrasonic sensor launches the function embedded in it due to detecting a change in the frequency of the reflected signal after fixing the movement of objects.

How an ultrasonic motion sensor works

A sound wave generator is located inside the ultrasonic motion sensor. The sound wave frequency is usually 20-60 kHz, depending on the manufacturer and model, which are emitted in the range of the sensor and returned to the receiver after being reflected from the surrounding objects. When a moving object appears in the sensor's field of view, the wave's frequency is reflected from the object changes (Doppler effect). The sensor receiver records the action from which a signal is received to perform the function embedded in the ultrasonic motion sensor. This can be the switching on of the lighting or the reaction of the security system. Ultrasonic security motion detectors are used in residential premises, especially in long corridors, stairs, etc. Also, ultrasonic motion detectors are widely used in the automotive industry: in automatic parking systems and monitoring systems for "blind" zones.

How a microwave motion sensor works

The operation of an ultrasonic motion sensor is based on the interaction of microwave waves with a material and the use of the Doppler effect – a change in the frequency of a wave that is reflected from moving objects. The microwave sensor operates in the microwave range, and its wavelength ranges from one millimetre to one meter. The microwave sensor registers a moving conductive object in the detection zone, after which a signal is sent to perform the function built into the sensor.

Combined motion sensors. The principle of their action

Combined motion detectors are using several motion detection technologies such as infrared and microwave. If you need the most accurate determination of movements in the sensor range, this device is suitable for use. Parallel working motion detection channels make such a sensor productive because they complement each other, replacing the disadvantages of some technologies with the advantages of others. Most commonly, there are two types of sensors: infrared and microwave.

Infrared motion detector Ajax MotionProtect

MotionProtect is a wireless indoor motion detector that detects unauthorized intrusion into a protected facility.

Features of the Ajax MotionProtect detector

• The sensor is installed without damaging the interior.
• Ajax MotionProtect wireless motion detectors use the Smart Detect software algorithm, which, when motion is detected, analyzes the waveform of the infrared sensor and compares it with the values ​​typical for the movement of people. 

The sensor does not raise the alarm because of the little animal's. They have too small heatspot.

• The "always active" mode is used in rooms requiring round-the-clock monitoring. The user will be notified of a traffic violation, regardless of whether the system is armed or not.
• The Ajax MotionProtect radio motion detector allows you to test essential parameters. For example, signal strength test, detection area test and signal fading test. This test enables the sensor to be installed in a location with the best signal strength.
• The sensor regularly transmits test signals to the central unit, and the polling period of the sensors can be adjusted at the user's discretion. If the sensor is attempted to be stolen or broken, the central security system will immediately know about it and issue an alarm. To reliably monitor the operation of the alarm, the sensor regularly transmits a signal about the discharge of its battery to the central unit. The user will be promptly notified of the need to replace the battery in the sensor.
• The information transmitted by the sensor is protected from interception and substitution attempts. The sensor case is protected against opening by a tamper.
• The maximum distance between the sensor and the central unit is 2000 m in line of a sight.
• The sensor detects movement at a distance of up to 12 m. The horizontal viewing angle is 88.5°.
• The sensor does not respond to accidental movements of inanimate objects.
• The sensitivity of the sensor is adjustable. You can choose the optimal value based on the pet's size.
• Depending on the distance to the central unit, the adaptive transmission power control allows less battery power consumption.
• Digital temperature compensation ensures high sensitivity of the sensor even in rooms where the temperature is close to the human body.
• Thanks to a special energy-saving algorithm, the sensor operates on a CR123A battery for up to 7 years.
• The sensor works with the Ajax ocBridge wireless signal receiver.

Principle of operation

Ajax MotionProtect wireless motion detector is designed to detect human movement in a protected area. The sensitivity of the room sensor is adjustable. The principle of operation of a wireless motion sensor is based on detecting infrared (IR) radiation from a living creature. As soon as the sensor detects radiation, it analyzes the mass of an object, and if it exceeds 20 kg, sends an alarm signal via a radio channel to the central security alarm unit. The algorithm for processing the incoming signal provides an additional check of the object for the presence of movement and its mass. This verification minimizes false responses to pets. Accordingly, the sensor is triggered only when a person's motion is detected. Also, the sensor does not respond to the movement of inanimate objects. The device will not work if, for example, something accidentally falls in the room or a draught opens the room door. The protection of the signalling against hacking attempts by intruders is ensured by a wireless radio communication system that uses message encryption and protection against forgery. In addition, it allows the motion sensor to work within several floors of a building or at a distance of up to 1700 m in an open area from a smart control panel. The signal range in closed rooms depends on the number of storeys, wall thickness and sources of electromagnetic interference. If the coverage area is large and the sensor signal is insufficient for stable reception, you can connect a Rex – signal range booster. The security sensor is compatible with all wired control panels provided by the Ajax ocBridge Plus radio detector receiver. This makes it possible to connect up to 45-second generation Ajax wireless devices. A wireless motion detector can be used to guard any objects: apartments, private houses, cottages, offices, shops, warehouses, industrial premises, etc. The advantage of the Ajax MotionProtect detector is a simple installation using a smart mount. The user does not need to disassemble the sensor housing to install the device. Considering that the motion sensor is one of the most common burglar alarms, this is a significant plus for the device.

Installation of an Ajax MotionProtect room detector and installation errors

The Ajax MotionProtect security detector is designed for indoor installation. The temperature range of the motion detector is from -10°C to + 40°С. The monitored area and the very effectiveness of the security system depend on the sensor's location. The location of the room sensor will depend on the distance to the Hub – smart control panel and the presence of obstacles between the devices that impede the passage of the radio signal: walls, inter–floor ceilings and large objects located in the room. The user has to make sure that furniture, houseplants or decorative objects do not obstruct the sensor's field of view.

Errors when installing IR motion detector Ajax MotionProtect

Installation of the motion detector outdoors is not recommended – the IR sensor is not intended for this. Also, do not install the sensor in the direction of the window to avoid direct sunlight on the lens and near metal objects and mirrors – they cause attenuation or screening of the radio signal. The installation height is also significant because if you do not follow the instructions, the sensor's area of ​​motion detection will be lower. The recommended height for placing the device is 2.5 m. Non-recommended mounting locations for the sensor include corners with fast air circulation (fan, windows or doors), rooms with temperatures and humidity outside the permissible limits, opposite objects with rapidly changing temperatures (electric or gas heaters) and opposite moving objects with temperatures close to human body (for example curtains over a radiator).