	Photoelectric Sensors

Fiber Photoelectric Sensors

The photoelectric sensor incorporates optical fibers and can be installed in areas of limited space.

Operating principle and types

Operating principle

The optical fiber consists of the core and the cladding, which have different refractive indexes. The light beam travels through the core by repeatedly bouncing off the wall of the cladding. The light beam, having passed through the fiber without any loss in light quantity, is dispersed within an angle of approximately 60º and emitted to the target.

Optical fiber

Optical fiber types

Plastic-fiber

The core of the plastic-fiber consists of one or more acrylic-resin fibers 0.25 to 1 mm 0.01" to 0.04" in diameter, encased in a polyethylene sheath. Plastic fibers are light, cost-effective, and flexible and are used for the majority of optical fiber photoelectric sensors.

Glass-fiber

The glass-fiber consists of 10 to 100 µm 0.39 to 3.90 Mil diameter glass fibers encased in stainless steel tubing, allowing it to be used at high operating temperatures (350ºC (662ºF) max.).

Features

Versatile installation

A flexible optical fiber is very useful for implementation in areas such as the small spaces between machines.

Detection of small objects

The light-emitting surface of the sensor head is extremely compact for stable detection of small objects.

Stable operation in harsh environment

The optical fibers are unaffected by electrical noise as no electric current flows through it.

Shape

The optical fiber sensors are broadly divided into two categories: thrubeam and reflective. The thrubeam type comprises a transmitter and a receiver. The reflective type, which is a single unit, is available in 3 types: parallel, coaxial, and separate, according to the shape of the cross-section of the optical fiber.

Type	Description
Parallel	Generally used for plastic fibers.
Coaxial	High-precision type, consisting of a core (transmitter) and surrounding area (receiver). The operating position can remain the same regardless of the direction from which the target enters the detecting area.
Separate	This type, containing several 10 µm 0.39 Mil glass fibers in diameter, has separate areas for the transmitter and receiver.

Bend radius

Using an excessively bent optical fiber will result in leakage of light, causing reduced detection accuracy.

Retention of light quantity vs. bend radius(typ.)

FU-6F plastic fiber (standard type):KEYENCE products		FU-49 plastic fiber (high-flex type):KEYENCE products

Fiber length and detecting distance

The detecting distance of a fiber photoelectric sensor varies depending on the fiber length.

Fiber length vs. detecting distance (typ.)

FU-6F reflective type:KEYENCE products		FU-7F thrubeam type:KEYENCE products

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