Image Credits: Baumer and MTI Instruments

Optical linear encoders use fiber optic technology to sense position, displacement, and vibration. 

How Optical Linear Encoders Work

Optical linear encoders are flexible strands of glass that transmit light along their length by maintaining the near-total internal reflection of light accepted at the input. Optical linear encoders contain pairs of these elements. One element carries light from a remote source/probe to the target to be measured. The other element receives light reflected from the object and carries it to a remote photosensitive detector. 

Classification

Sensors can be classified based on the properties of the fiber. Sensing with extrinsic sensors takes place in a region outside of the fiber. The fiber serves as a conduit for the to-and-fro transmission of light to the target and detector. In an intrinsic sensor, one or more of the physical properties of the fiber undergo a change.

Sensors can also be classified based on the measurement point. In point to point sensors, a single measurement point exists at the end of the fiber optic connection cable. Multiplexed sensors allow measurement at multiple points along a single fiber line. Distributed sensors are able to sense at any point along a single fiber line.

Specifications and Features

Optical linear encoders have a number of specifications and features used to describe them.

  • The extent of measurement range varies (e.g. 0.048 to 2 inches).
  • Sensing frequency can vary (e.g. at least 62 to at least 166 kHz).
  • Analog (current, voltage, or frequency) or digital (serial, parallel, or other) output is available.
  • Packaging can be a raw sensor element or a housed transducer. Self-contained instruments or meters display output at or near the device. Gauges/indicators have an analog display and no electronic output.
  • Devices can tolerate certain temperature ranges (e.g., -94 to 302°F).

Applications

Typically, these devices are used in applications such as computer disk drive runout, magnetic tape motion, or ultrasonic tool vibration. They are capable of functioning in extreme, EM, RF, microwave, cryogenic, high voltage, nuclear, and hazardous environments. Optic linear sensors are found in automotive, robotic, aeronautic, aerospace, civil engineering, and geotechnical applications.

References

Fiber Optic Sensors

A Fluorescent Long-Line Fiber-Optic Position Sensor

Target Motion


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