What are the Types of Motion Sensors?

Motion sensors are divided into active motion sensors (active sensors) and passive motion sensors (passive sensors).

Active motion sensors have both a transmitter and a receiver and detect motion by measuring changes in the sound or radiation reflected back to the receiver.

In contrast to active sensors, passive motion sensors do not have a transmitter and do not emit anything. Instead, they detect motion by detecting energy.

Active motion sensors:

1. Vibration sensors

Vibration sensor detects the motion of a vibrating object or surface by sensing its frequency and converts it into an electrical signal for analysis.

Figure: How Vibration sensors works?

Applications:

Vibration switches are used to detect imbalances or other issues in assets and predict future breakdowns.

They are used in industries like wind power and mining for slow rotation of turbines and can be used as slow/medium/fast vibration switches.

2. Tilt Sensors

Tilt sensors are instruments used for measuring the change in tilt and monitoring inclination and vertical rotation in vertical structures.

They produce an electrical signal that is proportional to the degree of tilt in multiple axes (Uniaxial & Biaxial). Tilt sensors measure the tilting position with its original reference.

Figure: the principle of tilt sensor

Application:

Tilt sensors are used for machine arm angle sensing in robotics, boom angle sensing, and to monitor tip-over protection.

3. Gesture sensors

Gesture sensors can detect the movement of a user's hand or body and translate it into commands or actions. Gesture sensors use various technologies such as infrared, ultrasound, or electric field sensing to detect motion and gestures.

Application:

Gesture sensors can control various electronic devices through gesture operations, such as various functions inside cars, augmented and virtual reality environments

Figure: Google sensor lets you control your phone with the wave of a hand

4. Accelerometer

An accelerometer measures dynamic acceleration by sensing the vibrations caused by motion and converts it into an electrical charge indicating how much force was exerted.

Figure: How does an accelerometer work?

Applications:

Accelerometers and gyros are used in industrial and automotive applications.

Such as safety systems, gaming, infotainment, mobile handsets, equipment vibration monitoring, navigation integrated with GNSS, personal navigation devices (mobile phones), and more.

5. Ultrasonic Sensors:

Ultrasonic sensors emit ultrasonic pulses that travel in a cone-shaped beam by using a vibrating device known as a transducer, generating the ultrasonic wave. The frequency of vibration of the transducer determines the range of an ultrasonic sensor.

Figure: How Ultrasonic Sensors Works

Application:

Ultrasonic sensors are used for object detection, obstacle detection, distance measurement, level sensing, and more in various applications such as conveyor belts, automated robot vacuum cleaners, web guiding systems, and factories.

6. Microwave Sensors:

A microwave motion sensor detects movement by emitting high-frequency radio waves and then receiving the waves that bounce back. The sensor examines the reflected waves to determine if there is any motion in its detection range.

Figure: How Microwave Sensors Works

Application:

Microwave sensors are used in security devices to protect wide open spaces, for non-invasive monitoring in industrial and healthcare industries, and in geomorphological applications. 

Figure: Microwave Sensors in Smart Homes

7. Photoelectric sensor

A photoelectric sensor primarily consists of an emitter for emitting light and a receiver for receiving light.

When emitted light is interrupted or reflected by the sensing object, it changes the amount of light that arrives at the receiver. The receiver detects this change and converts it into an electrical output.

It can be used as motion sensors to detect the presence or absence of an object.

Figure: Reflective model of Photoelectric sensor

Passive motion sensors:

1. Passive Infrared Sensors (PIR):

Passive Infrared (PIR) sensors are sensitive to a person's skin temperature through emitted black-body radiation at mid-infrared wavelengths, in contrast to background objects at room temperature.

No energy is emitted from the sensor, thus the name passive infrared. This distinguishes it from the electric eye for instance (not usually considered a motion detector), in which the crossing of a person or vehicle interrupts a visible or infrared beam.

PIR Sensors are used in security alarms, automatic lighting applications, and for detecting the open/close status of doors and cabinets.

Figure: How PIR Sensor Works and How to use PIR motion sensor with Arduino

Conclusion

Motion sensors play an important role in a variety of industries and applications.

Active motion sensors, such as vibration sensors, tilt sensors, gesture sensors, accelerometers, ultrasonic sensors, microwave sensors and optoelectronic sensors, detect and analyse motion through different mechanisms.

Passive motion sensors, such as passive infrared sensors (PIR), detect motion by sensing energy changes.

Motion sensors enable precise motion detection and improve safety, efficiency, and automation in different areas.

Figure: Comparsion table of motion sensors