Digital Sensors: The Perception Devices of the Automation World

Digital sensors are critical components that form the foundation of Industry 4.0 and automation systems. They collect data from the physical world and convert physical variables (such as position, level, and distance) into digital signals. This enables control systems to make informed decisions.

Let's explore the most commonly used types of digital sensors and their operating principles in the industrial field.

1. Inductive Sensors

Inductive sensors are non-contact sensors used exclusively for detecting metallic objects. Their detection principle is based on the disturbance of an electromagnetic field.

Working Principle

• The sensor head continuously emits a magnetic field.

• When a metallic object approaches the sensor, this magnetic field is disturbed, and the sensor provides an output.

Installation Criteria

• Target Object Size:If the sensor’s surface diameter is d, the metal object must have a surface area of at least d² and a thickness of at least 1 mm.

• Side-by-Side Installation:

  • Flush-mounted (Düz kafalı) sensors: Minimum distance between sensors = d

  • Non-flush (Çıkık kafalı) sensors: Minimum distance between sensors = 2d

2. Capacitive Sensors

Unlike inductive sensors, capacitive sensors can detect both metallic and non-metallic objects.

Working Principle

• These sensors establish a capacitive field by using air as a dielectric medium.

• When an object enters this capacitive field, the change in dielectric level allows the sensor to detect the object.

Features and Applications

✔ Sensing Distance

• Generally greater than inductive sensors.

✔ Sensitivity Adjustment

• The sensing distance can be adjusted via the potentiometer on the back of the sensor.

✔ Material Sensitivity

Capacitive sensors detect different materials at different efficiency levels.Detection ratios (Sn) vary by material:

Material	Sn Value
Grounded Metal, Water	1.00
Alcohol	0.75
Ceramic	0.6 / 0.5
PVC	0.45
Wood	0.40
Oil	0.30

• Material thickness significantly affects detection distance:Thicker materials → greater sensing distance.

✔ Typical Applications

• Level control of solids and liquids

• Detecting solid or liquid materials in non-metallic containers

• Level control in non-metal tanks (or metal tanks with plastic windows)

• Height control of stacked paper

• Metal wire break detection

3. Optical Sensors (Photoelectric Sensors)

Optical sensors operate based on the principle of light emission. The sensor compares the light frequency sent from the transmitter with the light frequency received by the receiver. If it receives light at the same frequency, it activates its output.

Types of Optical Sensors

a) Diffuse Reflective (Cisimden Yansımalı)

• Light from the transmitter hits an object and reflects back to be received.

• The color and brightness of the object affect sensing distance:

  • White: 100%

  • Black: 20%

b) Through-beam (Karşılıklı)

• Light emitted by the transmitter is directly received by the receiver.

• If an object interrupts the light beam, the sensor provides an output.

• Offers the longest sensing distance and highest reliability.

c) Retro-reflective (Reflektörlü)

• Light from the transmitter is reflected back to the receiver via a reflector.

• When an object breaks the beam, the sensor switches its output.

• Provides longer ranges than diffuse reflective sensors but shorter than through-beam types.

4. Piston Sensors (Cylinder Sensors)

Piston sensors are mounted on pneumatic or hydraulic cylinders and used to determine piston position.

Working Principle

• There is a magnet inside the piston.

• When this magnet comes in front of the sensor during movement, the sensor detects it and provides an output.

🎯 Conclusion

These four basic types of digital sensors—inductive, capacitive, optical, and piston sensors—play a vital role in achieving reliable, fast, and precise operation in modern automation systems.Choosing the right sensor is essential for the success and efficiency of any industrial application.