Fiber Optic Linear Position Sensors

Fiber optic linear position sensors use fiber optic technology to sense position and displacement. They use an adjacent pair of fiber optic elements, flexible strands of glass that transmit light along their length by maintaining the near-total internal reflection of light accepted at the input. One fiber optic element carries light from a remote source to the object or target whose displacement is to be measured. The other fiber optic element receives the light reflected from the object and carries it to a remote photosensitive detector. Output types include analog current levels, analog voltages, modulated analog outputs, and digital signals. Analog current levels such as 4 – 20 mA are suitable for sending signals over long distances. Analog voltages are simple, usually linear functions. Modulated analog outputs such as sine waves, pulse waves, amplitude modulation (AM), and frequency modulation (FM) signals are encoded, but still analog in nature. Several types of digital outputs are available. RS232, RS422, and RS485 are common serial, digital protocols. Popular parallel protocols include the general-purpose interface bus (GPIB), a standard which is also known as IEEE 488. Other digital outputs for inductive linear position sensors and switches include transistor-transistor logic (TTL) signals. 

Selecting fiber optic linear position sensors requires an analysis of device categories and operating specifications. Suppliers typically divide products into the following categories: sensors, sensor elements, instruments, gauges, and recorders. Sensors, a category that includes thermocouples, include packaging and signal conditioning. By contrast, bare sensor elements or chips do not. Instruments or meters are self-contained fiber optic linear position sensors that produce local outputs. They often include signal processing or analysis. Gauges or indicators are sensing devices with integrated dials or simple readouts. Recorders and totalizers measure values or accumulate totals. They may also provide statistical functions. Operating specifications for fiber optic linear position sensors include measurement range, maximum range, sensing frequency range, and accuracy. Measurement range and maximum range are measured in inches (in). Sensing frequency is expressed in kilohertz (kHz). Accuracy is a full-scale percentage. Additional considerations when selecting fiber optic linear position sensors include operating temperature, maximum shock, and maximum vibration.

Fiber optic linear position sensors and switches are available with many features. Shielded sensors provide protection against electromagnetic interference (EMI) and radio frequency interference (RFI). Intrinsically safe (IS) sensors are designed for use in hazardous areas and are incapable of releasing sufficient electrical or thermal energy to cause fire or explosions. Devices that include integral high-pass and low-pass filters are commonly available. Typically, these devices are used in applications such as computer disk drive runout, magnetic tape motion, or ultrasonic tool vibration.

• Position Sensors and Position-Sensing Instruments
  Position sensors include wide range of sensors, switches and technologies that are used to determine the placement, speed or movement, direction, and location of a given target. Linear position...
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