In some sensing situations, space is too restricted or the environment is too hostile for most sensors. Fiber optics, transparent strands of glass or plastic, is used to conduct light energy into and out of such areas. This article describes advantages, considerations, and common applications for fiber optic sensors.
Why Use Fiber Optic Sensing?
Fiber optics has many advantages in photoelectric sensing, including their size, flexibility, and ability to withstand challenging environments where other sensors may not be an option.
1. Compact size for tight sensing locations
The small size and flexibility of fiber optic assemblies allow positioning and mounting in tight spaces. Plastic fiber optic assemblies are usually single strands of optical fiber. They can be routed into extremely tight areas. Plastic fibers also survive well under repeated flexing. Pre-coiled plastic fiber optics is available for sensing applications on reciprocating mechanisms.
2. Reliable Performance in Harsh or Explosive Environments
Fibers can be constructed to survive in areas of corrosive material or extreme moisture and are immune to electrical noise. Fiber optics contains no electrical circuitry and has no moving parts, so they can safely “pipe” light into and out of hazardous sensing locations.
In addition, most glass fiber optic assemblies are very rugged, and perform reliably in extreme temperatures. Sheathing materials such as polypropylene, Teflon®, and nylon are used to shield both plastic and glass fiber optic assemblies in harsh environments. Furthermore, optical fibers are low in mass, enabling fiber optic assemblies to withstand high levels of vibration and mechanical shock.
3. Flexibility to meet a wide variety of application requirements
Some fiber optics have flexible probes that can be optimally “shaped” to the physical and optical requirements of a specific application.
Considerations for Choosing a Fiber Optic Sensing Technology
There are very few disadvantages to using a fiber optic sensing system, but there are a few considerations to keep in mind when choosing a sensing technology: costs, sensing range, and excess gain.
• Sensing System Cost: Fiber optics adds cost to a system, since a fiber optic assembly is always an extra part in addition to a basic photoelectric sensor. Costs must be weighed against the benefits to determine whether fiber optics is the right solution for an application.
• Sensing Range and Excess Gain: A large percentage of the sensing light energy is lost when coupling light to and from a fiber. Fibers also attenuate some light along their length. As a result, sensing ranges are shorter and excess gain levels are lower than self-contained sensors.
Typical Applications for Fiber Optics
Because of their inherent attributes, fiber optics are ideal in the following applications:
• Punch presses
• Vibratory feeders
• Pill counting
• Small object detection
• Semiconductor processing equipment
• Robotic arms and moving machines