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7 kinds of sensors for object detection

Update: 2019-10-26 16:42 Source: LUFTMY

Whether it is to detect whether there is an object passing through the conveyor belt, whether the door is closed or not, whether the means of transport arrive at the stop position or not, object detection is an important task in the automation industry.Industrial control engineers and software developers need to know reliably when objects or targets arrive or are placed in specific locations.

Although sensing devices cannot measure, check or quantify objects in any way, they must reliably communicate the presence or absence of objects to the machine's control system through electronic signals.There are many different object sensing techniques.The seven most common types are discussed below, along with a brief description of their operations, benefits, and constraints.

1. Electro-Mechanical

The most basic sensor is the electromechanical limit switch. These devices contain a sensitive microswitch that changes the state of a mechanical driver when it is replaced by a detected object. Rollers, antennae, and levers are available in the actuators version from many different manufacturers. As these devices are made up of moving parts, they are liable to wear and tear. Furthermore, physical contact with the target object is not always desirable or possible.

2. pneumatic

These sensors use compressed air and sensitive diaphragm valves to detect the presence of objects.Compressed air flows out of a tiny hole until the target blocks the air flow, causing a small change in air pressure.This pressure change is detected by the downstream diaphragm switch, which generates an electrical control signal.The environment requiring "explosion-proof" sensor, or very dirty environment, is a good application of such equipment.

3. Magnetic

Magnetic sensors are driven by permanent magnets within the induction range.Two different operating principles are usually used, one is reed contact and the other is hall effect sensor.In both cases, the presence of a magnetic field changes the state of the electrical signal.Reed and hall effect sensors are commonly used to detect the presence of pistons inside cylinders.Reed switches have a high failure rate, so many engineers specify hall effect sensors where possible.


Inductive proximity sensors - these proximity switches detect metal objects that disrupt the electromagnetic field emitted by the sensor.Reliable detection range depends on the type of metal and the amount of metal in the sensor range.These sensors come in a variety of sizes and shapes.They are very reliable and cost effective; Therefore, a large proportion of sensors are used in automation and process equipment.

5. capacitance

These proximity switches can detect nonmetallic objects with different dielectric constants from air.This makes them ideal materials for various materials such as wood, paper, fabric, liquid and plastic.They work like induction sensors, but they do not detect changes in electromagnetic fields, but use electrostatic fields.

6. photoelectric

Photoelectric sensors use different technologies to solve various application configurations.What they all have in common is that they emit a beam of light and then detect changes in the amount of light coming back.The three most popular sensors are diffuse, reflective, and beam through.The use of light sources - visible, infrared, LED or laser - will affect the sensing distance.In a diffuse sensor, the presence of an object in the optical field of view causes a diffuse reflection of the beam of light.The receiver detects light reflected from the object itself. Reflecting and penetrating the beam sensor produces a beam of light and detects any opaque object that breaks the beam.Laser sensors can produce beams of light for 50 meters or more. For photoelectric sensors, transparent objects or objects with different surface finishes can be problematic.

Photoelectric sensors
Photoelectric sensors

7. The ultrasonic

These devices typically transmit short pulses of ultrasound to the target, which are then reflected back to the sensor.Sound waves can be reflected off almost any dense material (metal, wood, plastic, glass, liquid, etc.), regardless of color, transparency, or gloss.Foam-like materials that absorb sound waves would not be a reliable application for this type of sensor.Ultrasonic sensors are often used to determine the liquid level in the groove.

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