By: Abhishek Sharma 

Selecting an industrial sensor can be a daunting task. With so many different sensing technologies and the endless variety of products in the market, how is it possible to find that one ideal sensor for any given application? Turns out, it’s not really so much a process of selecting the right sensor…it’s really about eliminating all the wrong choices. Selecting a sensor is a process of asking a series of questions to eliminate any technology or product that doesn’t fit the application requirements

Motion Sensors

Motion sensor is basically an electronic device which detects the physical movement of any object in the present environment. It has the capability of detecting the kinetic motion in real time. A motion sensor is also known as motion detector.

Types of Motion sensor

 Motion sensor/detector depends on following two technologies, as described below,

  • PIR (Passive Infrared)
  • Microwave
PIR sensor

PIR (Passive Infrared): In this technology motion sensor detects the any movement in the present environment by using baseline analysis (used for sensing the changes in heat patterns). Any living thing emits the heat radiation from its body and thus form a specific heat pattern. As soon as person enters in the filed view of motion sensor/detector, motion sensor raises the alarm by analysing the change in heat pattern.

Microwave motion detector: –  A microwave motion sensor works on doppler effect. It consists of transceiver and somehow its working resembles with the working of RADAR. It senses the motion of object by measuring the time difference between receiving and transmitting of signal. The motion detector conducts a baseline room analysis to detect its present distance from stationary objects, then reverts to its “normal” state.

Upon a person entering the motion detector’s field of view, this causes an interruption in the emitted microwave beam, which changes the received echo time, which the motion detector perceives as a change in distance from an object. This action causes the motion detector to trigger the alarm.

Difference between PIR motion sensor and Microwave motion sensor

PIR Motion sensor

Microwave motion sensor

Sensibility of this sensor depends on temperature. (not able to work properly above 35 ֯C) Its sensibility is independent of temperature.
Cannot work if there is metallic barrier Able to work in the presence of metallic barrier
There is dead zone in the filed view of sensor. No dead zone in the filed view of sensor.

How to choose right motion sensor/detector

Selection of appropriate motion sensor/detector completely depends on the type of application.

  • PIR motion detector is suitable for the small space where a defined detection pattern is required such as,
  • Offices
  • Bathrooms
  • Living room
  • Toilets
  • Staircase

Microwave motion sensor are useful for the large space and even they can sense the movement behind the paper wall, glass and thin wall.

Ratings of Motion sensor

Most of the PIR sensors are rated with IP44 which indicates that it’s sensibility depends on environmental condition and are not able to work properly above 35 ⸰C, but ispot microwave sensor is rated to IP65 which indicates that it is able to work in the temperature range of -20 ⸰C to 45 ⸰C.


About Author: Abhishek Sharma ( is from Electronics and Robotics Background (B.Tech, M.Tech)  and has experience and expertise in both academics (UPES Dehradun) and research (DST Project). He is pursuing his doctorate degree in robotics from Ariel university, Israel.
His research interests include robotics, embedded system, control, motion planning and swarm intelligence.

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