Motion sensor circuits : principle of operation and applications

in HeartSTEM2 years ago

When you walk or come close to it, a motion sensor is most commonly used to switch on lights. With its assistance, you can save a lot of energy and avoid having to flip a switch. This software is also used to detect unauthorised intrusions in alarm systems. They're also on production lines, where they're needed for the automated execution of any technical mission. Presence detectors are another name for motion detectors.

Different types of motion sensors

Motion sensors are classified according to their operating theory, which is based on their operation, reaction accuracy, and features of use. Each of them has advantages and disadvantages. The final cost of a sensor like this is often determined by the design and type of element used.


The motion sensor can be installed in a single housing or multiple housings (the control unit is separate from the sensor).

How to make contact with

A limit switch or reed switch is the simplest alternative for a motion sensor. A reed switch (sealed contact) is a switch that is activated by the presence of a magnetic field. The aim is to add a limit switch with usually open contacts or a reed switch on the door so that when you open it and walk into the room, the contacts close, the relay turns on, and the lighting turns on. A diagram like this is shown below.


Infrared (IR)

Thermal radiation activates them, and they respond to temperature changes. Thermal radiation from your body triggers such a sensor when you reach its field of view. False positives are a drawback of this detection process. Anything in the environment emits thermal radiation. Such instances are as follows:

  1. The infrared motion sensor is installed in a room with an electric heater that is controlled by a timer or thermostat. False alarms are likely when the heater is switched on. You may try to prevent this by adjusting the sensitivity carefully and repeatedly, as well as attempting to steer it away from the heater's line of sight.
  1. It could be caused by warm wind gusts if it's mounted outside.

In general, these sensors perform admirably and are the most cost-effective alternative. As a sensitive element, a PIR sensor is used, which generates an electric field proportional to thermal radiation.

Infrared Motion Sensor

However, the sensor does not have a large directivity by itself; a Fresnel lens is placed on top of it.
It will be more accurate to claim multi-lens or multi-segment lens. Pay attention to the sensor's window; it is divided into parts, which are the lens segments, which concentrate incoming radiation into a narrow beam and direct it to the sensor's sensitive region. As a consequence, radiation beams from various directions fall on the small receiver.

Dual or quad sensors, or multiple different ones, may be mounted to improve the performance of motion detection. As a result, the device's field of vision extends.

Based on the above, it is important to remember that the lamp's light should not fall on the sensor, and there should be no incandescent lamps in its field of view, since this is also a strong source of IR radiation; otherwise, the system's overall activity would be erratic and unpredictable. Since infrared rays have a hard time penetrating glass, it won't work if you step outside a window or a glass door.


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