Inductive Linear Position Sensors and Switches

Inductive linear position sensors and switches are non-contact devices that determine an object’s linear or angular coordinates with respect to a reference point. Displacement is measured when the object moves from one position to another at a specified distance or angle. The output signal represents the object’s distance from the reference point. 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 wave, pulse wave, 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 inductive linear position sensors and switches requires an analysis of performance specifications, display options, power requirements, and cable connections. Important performance specifications include operating distance range, allowable over-range, frequency response, repeatability, accuracy, and minimum target distance. Analog displays include a meter with a simple visual indicator, usually a needle. By contrast, digital displays present information as numeric or alphanumeric values. Video displays that use a cathode ray tube (CRT), liquid crystal display (LCD), flat panel display (FPD) or other multi-line device are also available. In terms of power requirements, suppliers indicate whether inductive linear position sensors and switches use AC or DC voltages. Devices with fixed cable connections bundle the cable with the sensor and often include bare or stripped leads. Sensors with integral connectors can be attached to existing systems. Devices with terminals that clamp down or screw into place are also available.   

Inductive linear position sensors and switches are available with many features. Shielded sensors provide protection against electromagnetic interference (EMI) and radio frequency interference (RFI). Weld field immune (WFI) devices provide filtering at both the oscillator and output levels. 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. Inductive linear position sensors and switches that provide protection against electrical spikes from short circuits are also available. Some devices are non-magnetic. Others are made from non-ferrous materials such as aluminum, copper and brass. Sensor elements are transducers whose outputs are designed for processors, controllers or data acquisition systems. Unlike instruments or sensor systems, these devices do not include an integral display or user interface.

• 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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