Industrial Sensors: Types, Uses, and Connectivity

Posted on Dec 15, 2024 in Electronics

Industrial Sensors

There are different types of detectors, all of which have a functioning electronic circuit. Their functions include:

  • Detecting items
  • Determining position
  • Discriminating by size, color, and type of material
  • Detecting levels of liquids and solids

Types of Detectors

  • Inductive
  • Capacitive
  • Photoelectric
  • Fiber-Optic

Inductive Sensors

  • Inductive detectors can detect a target at a close distance (from 0 to 60 mm) without the need for physical contact.
  • The target to be detected must be metallic.
  • They can replace limit switches and significantly improve switching frequency.

Advantages of Inductive Sensors

  • No physical contact with the object means no deterioration.
  • It is possible to detect fragile or newly painted objects.
  • High operating frequencies.
  • Lifespan is independent of the number of maneuvers.

Capacitive Sensors

  • Capacitive detectors can detect a target at a close distance without the need for physical contact.
  • Objects can be of different materials, both metallic and non-metallic.

Advantages of Capacitive Sensors

  • No physical contact with the object means no deterioration.
  • It is possible to detect fragile or newly painted objects.
  • High operating frequencies.
  • Lifespan is independent of the number of maneuvers.
  • Detection of objects of any type (metals, minerals, wood, plastic, glass, cardboard, ceramics, fluids, etc.).

Adjusting Detection Sensitivity

  • Capacitive sensors have a potentiometer to adjust the sensitivity and discriminate between different metals.
  • It may be necessary to:
    • Increase sensitivity to detect objects with weak influence (paper, cardboard, glass, plastic).
    • Reduce sensitivity to detect objects with strong influence (metal, liquids).

Connection Types

  • Wired
  • Connector
  • Screw clamp

Classification by Number of Wires

  • 2-wire
  • 3-wire
  • 4-wire

2-Wire Sensors

There are 4 types:

  • DC polarized: Maintain the same poles (+ brown / – blue).
  • DC non-polarized: It is not necessary to maintain the same poles.
  • Alternating current
  • Mixed DC and AC

They are connected in series with the coil of a relay or a PLC’s programmable input.

3-Wire Sensors

There are 2 types:

  • DC PNP: The output will be P (+).
  • DC NPN: The output is N (-).

If they are polarized:

  • (+) Positive: Brown
  • (-) Negative: Blue
  • (Output): Black

Photoelectric Sensors

Operation

A photoelectric sensor consists of two parts:

  • A light emitter
  • A light receptor

Detection occurs when an object interferes with the light beam. It is not very directional; it is more like a lantern than a focused beam.

Light Spectrum

  • Non-visible light (infrared): This is the most common.
  • Non-visible light (UV): Used to detect luminescent materials.
  • Visible red or green light: Used in barcode readers.
  • Red laser: Also used in some applications.

Detection Systems

  • Barrier system
  • Reflex system
  • Polarized reflex system
  • Proximity system
  • Fiber optic system

Barrier System

Advantages:

  • Separate emitter and receiver.
  • Long detection range of up to 60 meters.
  • Accurate detection.

Disadvantages:

  • Objects must be opaque.
  • Alignment of the emitter and receiver can be difficult.

Reflex System

Advantages:

  • Emitter and receiver are in the same element.
  • Medium detection range (up to 15 meters).
  • Detects transparent objects with a special reflector.

Disadvantages:

  • Does not detect shiny objects.
  • Objects must be opaque and larger than the reflector.

Polarized Reflex System

  • Has the same characteristics as the normal reflex system.
  • Detects shiny objects.

Proximity System

  • Detects reflections from the object.
  • Short detection range, up to 2 meters.
  • Susceptible to the different colors of objects.
  • Detects all types of opaque, transparent, and shiny objects.

Fiber Optic System

  • Used as a light guide.
  • Very small dimensions.
  • Allows detection of very small objects (mm).
  • Separate amplifier.
  • Two types of materials:
    • Plastic
    • Glass
  • Has a minimum radius of curvature.
Optical Heads

There are different types of optical heads adaptable to different objects to be detected.

Output Types

Two-Wire

  • No protection.
  • Connected in series with relays and PLC inputs.

Three-Wire

  • Two wires for power and one for signal output.
  • Types: PNP and NPN.

Five-Wire Relay Output

  • Relay output.
  • Power supply in DC and AC.
  • Has a split contact: NO (Normally Open) and NC (Normally Closed).
  • Limited contact lifespan.

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