Fiber Optic Position Sensors: Principles and Applications

A fiber optic position sensor is a device that measures the position of an object by utilizing the principles of fiber optics.

It consists of an optical fiber that acts as a sensing element and detects changes in position based on the modulation of light within the fiber. This sensor helps to measure vibration, position, and displacement of objects and offers high precision in the most demanding environments.

Working Principle

Let us explore the functions of different components used in a fiber optic position sensor to understand its working principle.

• Optical Fiber: It is usually made of glass or plastic and is capable of transmitting light through its core.
• Light Source: It emits light pulses into one end of the optical fiber. LEDs or laser diodes are used as light sources. Light pulses emitted by these light sources travel along the core using the total internal reflection phenomenon.
• Reflection Point: At a certain point along the length of the fiber, there is a reflection point or reflector attached to the object whose position is to be measured. The reflector can be a small mirror or a reflecting surface.
• Position Modulation: When the object moves, the position of the reflector changes with respect to the fiber. This leads to variations in the time it takes for light to travel from the source to the reflector and back to the receiver. The movement causes a shift in the phase of the light pulses.
• Light Detection: The other end of the optical fiber is connected to a light detector. This can either be a photodiode or a photodetector. The detector measures the returning light pulses and detects any phase shift caused by the movement of the reflector.
• Signal Processing: The signal detected by the light detector device is processed to extract phase shift information. This is converted into a displacement or position value. This represents the movement of the object relative to the fiber optic sensor.
• Output: The final output can be represented in various forms as per design, such as analog voltage, a digital signal, or any other suitable format. This is precise position information of the object to be monitored or measured.

Example: ODP fiber optic position sensors from ALTHEN offer high-precision sensing. Other manufacturers include Micronor Inc., Honeywell, Hansford Sensors, Micro Optics Inc., FiberSensing, Optocon AG, FISO Technologies Inc., Opsens Solutions Inc., and so on.

Advantages of Fiber Optic Position Sensors

Following are the benefits of this fiber optic sensor type:

• High accuracy and resolution
• Immunity against EM (Electromagnetic) interference
• Can work in harsh environments such as high temperatures, corrosive conditions, etc.
• Long-distance measurement capabilities
• Compact in size and light in weight

Conclusion

Traditional position sensors such as potentiometers and magnetic sensors have limitations in certain scenarios. Fiber optic position sensors are commonly used in various industries and applications where accurate and reliable position sensing is needed, such as robotics, aerospace, automation, and scientific research.