7 Types of Object Detection Sensors - Atonm Tech Share

Although sensors cannot measure, inspect or quantify objects by themselves, they must reliably convey the presence or absence of a target to a machine control system via electronic signals. There are many different object detection technologies. Below are seven common types, their operation, advantages and constraints.

1. Mechanical

The most basic sensors are electromechanical limit switches. These devices contain a sensitive micro switch whose state changes when a mechanical actuator is displaced by a detected object. Rollers, whiskers and levers are common actuator variants provided by many manufacturers. Because these devices have moving parts, they are susceptible to wear and damage. Also, physical contact with the target is not always desirable or possible.

2. Pneumatic

These sensors use compressed air and sensitive diaphragm valves to detect presence. Air flows from a small orifice until the target blocks the flow, producing a small pressure change. A downstream diaphragm switch senses the pressure change and generates an electrical control signal. These devices suit explosive environments or very dirty conditions.

3. Magnetic

Magnetic sensors are driven by a permanent magnet within sensing range. Two common operating principles are reed contacts and Hall-effect sensors. In both cases, the presence of a magnetic field changes the electrical signal state. Reed and Hall sensors are commonly used to detect pistons in cylinders; reed switches have higher failure rates, so engineers often specify Hall-effect sensors.

4. Inductive

Inductive proximity sensors detect metal objects by disturbing an electromagnetic field emitted by the sensor. Reliable detection distance depends on metal type and the amount of metal within the sensing range. These sensors come in various sizes and shapes. They are highly reliable and cost-effective, and they are widely used in automation and process equipment.

5. Capacitive

Capacitive proximity switches can detect non-metallic objects whose dielectric constant differs from air. This makes them ideal for materials such as wood, paper, fabric, liquids and plastic. They operate similarly to inductive sensors but use an electrostatic field instead of detecting changes in an electromagnetic field.

6. Photoelectric

Photoelectric sensors use different optical techniques for different application configurations. Their common feature is emitting a light beam and detecting changes in the returned light. The three popular types are diffuse-reflective, retro-reflective and through-beam. The light source—visible, infrared, LED or laser—affects sensing distance. In a diffuse sensor, the presence of an object in the optical field scatters the beam; the receiver detects the reflected light from the object itself. Retro-reflective and through-beam sensors generate a beam and detect any opaque object that interrupts it. Laser sensors can produce beams of 50 meters or more. Photoelectric sensors may have difficulty with transparent objects or surfaces with varying gloss.

7. Ultrasonic

Ultrasonic devices transmit short ultrasonic pulses toward a target and measure echoes returned to the sensor. Sound reflects from nearly all dense materials (metal, wood, plastic, glass, liquids) and is unaffected by color, transparency or surface gloss. Foam that absorbs sound is not a good application for this sensor type. Ultrasonic sensors are commonly used to determine liquid levels in tanks.