Wiring of a three-wire fiber optic sensor

A three-wire fiber optic sensor uses two wires for power supply and one wire for output, enabling non-contact detection of objects via light modulation.

Wiring Configuration

A typical three-wire fiber optic sensor consists of: Brown wire (+VDC): Connects to the positive terminal of the DC power supply. Blue wire (0V or GND): Connects to the negative terminal of the power supply. Black wire (Output): Connects to the load, such as a PLC input, relay, or alarm system, which receives the sensor signal when an object is detected.

The sensor output is usually DC switching, capable of handling currents typically between 100 mA and 200 mA. When the sensor detects an object, the output wire switches, allowing current to flow to the connected load.

Operating Principle

Fiber optic sensors operate on the photoelectric principle: A fiber amplifier unit sends light through a flexible fiber to the sensing tip. The fiber tip detects objects by either reflecting or interrupting the light beam. The sensor converts the optical signal into an electrical output, which is transmitted via the black wire to the load.

Fiber optic sensors can be intrinsic, where the fiber itself is the sensing element, or extrinsic, where the fiber transmits light to an external sensing element. In both cases, the three-wire configuration provides power and a controlled output signal. AdvantagesNon-contact sensing: Reduces wear and damage to objects.

High-speed response: Light-based detection allows rapid switching. Flexible installation: The fiber can reach narrow or confined spaces. Environmental resistance: The sensing tip has no electrical circuits, making it resistant to vibration, temperature, and electrical noise.

Summary

In essence, the three-wire fiber optic sensor combines the standard three-wire DC sensor wiring with the optical detection principle. The brown and blue wires supply power, while the black wire delivers a switching signal when the fiber detects an object. This setup allows integration into automation systems while leveraging the advantages of fiber optic sensing for precision and reliability.