Comprehensive Guide to Proximity Sensors: Principles, Types, and Selection for Multi-Industry Smart Detection

Proximity sensors are known for their long service life, high reliability, precise repeatability, no mechanical wear, no sparks, no noise, and excellent vibration resistance. Widely used in industries such as machinery, metallurgy, chemical processing, textiles, and printing, they serve as critical components in limit switches, counters, positioning controls, and automated protection systems.

What Are Proximity Sensors?

Proximity sensors are non-contact devices designed to detect objects and convert their movement or presence into electrical signals. They operate based on principles such as electromagnetic induction, which generates eddy currents in metal targets, or capacitance changes caused by target proximity.

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Types of Proximity Sensors

Proximity sensors vary in principle, design, installation, and performance.

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By Principle

Inductive Sensors

Generate a high-frequency magnetic field that induces eddy currents on metallic targets. As the target approaches, increased load on the oscillator reduces its amplitude, enabling detection.

Applications: Ideal for detecting metal objects such as iron, copper, and aluminum.

Capacitive Sensors

Utilize the sensor's surface as one electrode and the target as another. Proximity changes capacitance, enabling detection of any material.

Applications: Suitable for detecting metals, wood, liquids, plastics, etc.

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By Appearance

Cylindrical, rectangular, flat, or specialized designs (e.g., through-metal or pipeline detection)

By Installation

For flush installation, the sensor face can be level with the mounting surface. For non-flush installation, the sensor face must maintain a specific distance from the mounting surface to prevent interference.

Flush Installation: Sensor face can be level with the mounting surface.

Non-Flush Installation: Sensor face must maintain a distance ≥2Sn from the mounting surface to avoid interference.

Key Technical Terms

Standard Target: Defined material, shape, and size for performance evaluation.

Sensing Distance: Distance from the sensor face to the target during detection.

Set Distance: Stable operational range considering temperature and voltage variations, typically 70-80% of the sensing distance.

Hysteresis Distance: Distance difference between detection and reset points.

Response Time: Time for sensor output to change state upon target entry/exit.

Response Frequency: Maximum detection cycles per second.

Shielded Sensors: Magnetic flux is concentrated at the sensor's front and shielded from side interference, allowing flush mounting.

Non-Shielded Sensors: Unshielded flux requires careful installation to avoid metal interference.

Selection Guide

Proper selection ensures system reliability and stability. Consider the following factors:

Material of detected object

For metallic objects, both inductive and capacitive sensors are suitable.

For non-metallic objects, use capacitive sensors.

Material Impact on Sensing Distance

Choose a sensor with the appropriate range while accounting for material factors such as attenuation coefficients for inductive sensors or dielectric constants for capacitive sensors.

Additional Factors

Shape: Round, rectangular, or grooved designs.

Target Types: Metals, liquids, plastics, etc.

Power Supply: DC, AC, or universal.

Output Type: Normally open (NO) or normally closed (NC).

Output Mode: Two-wire, three-wire (NPN/PNP).

Mounting Type: Flush or non-flush.

Connection: Cable, connector, or intermediate plug type.

Response Frequency: Ensure compatibility with detection speed requirements.

Special Requirements

For specific environments, choose models designed for high temperatures, corrosion resistance, pipeline detection, or through-metal sensing.