	Proximity Sensors

Proximity Sensors/Operating Principle/Type

Outline

A proximity sensor can detect metal targets approaching the sensor, without physical contact with the target. Proximity sensors are roughly classified into the following three types according to the operating principle: the high-frequency oscillation type using electromagnetic induction, the magnetic type using a magnet, and the capacitance type using the change of capacitance.
KEYENCE proximity sensors are of the high-frequency oscillation type.

Features

	Non-contact detection, eliminating damage to sensor head and target.
	Non-contact output, ensuring long service life.
	Stable detection even in harsh environments exposed to water or oil splash.
	High response speed.

Operating Principle of High-frequency Oscillation Type Proximity Sensor

Operating principle of general sensor

Operational details of a high-frequency oscillation proximity sensor

A high-frequency magnetic field is generated by coil L in the oscillation circuit. When a target approaches the magnetic field, an induction current (eddy current) flows in the target due to electromagnetic induction. As the target approaches the sensor, the induction current flow increases, which causes the load on the oscillation circuit to increase. Then, oscillation attenuates or stops. The sensor detects this change in the oscillation status with the amplitude detecting circuit, and outputs a detection signal.

Aluminum Proximity Sensor

Generally, the frequency of high-frequency, oscillation type proximity sensors tend to change when a nonferrous metal is placed near it. The aluminum proximity sensor detects any changes in oscillating frequency.

Type

Classification by configuration

	Standard configuration	Features
Self-contained proximity sensor		Readily operative by adding DC power supply.
Separate/In-cable amplifier		Compact sensor head Long-detecting distance

Glossary

Shielded type	Non-shield type

The sensing coil is encased in a metal-shielding. This type is less affected by surrounding metal, and can be embedded in a metal base.	The sensing coil is not metal-shielded. This type provides a longer detecting distance, compared to a shielded type of the same size. This type is easily affected by surrounding meta, and therefore no object other than the target must be present around the tip of the sensor head.

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