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Introduction & Features - Inductive Proximity Sensors

Introduction &
Features

Classification
methods &
Classification

Precautions for
prorer use

Introduction

Principles of operation

A proximity sensor detects the approach of an object without making a contact. There are three types of proximity sensors :

1)	High-frequency oscillation type using electromagnetic induction
2)	Magnetic type using magnetism
3)	Electrostatic capacity type which senses the changes in the electrostatic capacity between the sensing object and the sensor.

Proximity sensor	Using magnetic field	High-frequency oscillation type
	Using magnetic field	Magnetic type
	Using electric field	Electrostatic capacity type

Panasonic Industrial Devices SUNX proximity sensors are highfrequency oscillation type inductive proximity sensors.

Principle of high-frequency oscillation type inductive proximity sensor

The detection coil located at the front end of the sensor produces a high-frequency magnetic field as shown in the figure below. When an object (metallic) approaches this magnetic field, induced currents flow in the metal, causing thermal loss and resulting in the reduction or stopping of oscillations.
This change in state is detected by an oscillation state sensing circuit which then operates the output circuit.

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Features

Non-contact detection

Unlike a limit switch, it detects an object without any mechanical contact. Hence, there is no likelihood of the sensing object or the sensor getting damaged by contact.

Usable in severe environment

Reliable sensing is possible even in adverse conditions where it can come in contact with water, etc. Most of the sensors have IP67 protection and oil resistant construction.

High precision

It is suitable for precise object positioning because of its very high repeatability.

Short response time

Stable detection is possible even with fast traveling objects because of its high response frequency (3.3 kHz max.).

Long life

Due to its non-contact output, it has a long life and requires practically no maintenance.

*	However, it also has the following disadvantages.

Only metal detection

It cannot detect non-metals in which current cannot flow, since detection is based on thermal loss due to induced current.
(Also, metals such as ferrite, which do not allow current flow, cannot be detected.)

Short sensing range

Although there are several methods for improving the sensing range, such as increasing the detection coil size, using non-shielded sensor heads, etc., the sensing range is still smaller than that of photoelectric sensors.

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