Image Credits: Baumer Ltd., HBM, and Control Products, Inc.

Inductive linear position sensors are non-contact devices that measure a target object’s distance and movement. Using similar means, inductive proximity switches determine whether the object has approached within a set distance.

How Inductive Linear Position Sensors and Switches Work

These sensors measure the change in impedance (effective resistance) of a coil through which an alternating current flows generating a magnetic field. An object made of ferrous metal (or non-ferrous metal at higher frequencies) enters and disrupts the field. This video illustrates the operation of a proximity sensor.

Video Credit: Balluff Sensors

Types of Inductive Linear Position Sensors and Switches

There are a number of different types of inductive linear position sensors and switches. They include:

  • LVITs (linear-variable-inductance transducers) are simple and economic. They may be sources of and susceptible to electromagnetic intereference. Ranges up to 40 in (1 m).
  • LVDTs (linear-variable-differential transducers) have high outputs with reasonable temperature performance. Ranges between 0.01 and 10 in (0.25 to 250 mm).
  • LVRTs (linear-variable-reluctance transducers) are less expensive than LVDTs but have lower outputs and may require support electronics. Ranges under 0.4 in (10 mm).

Specifications and Features

Inductive linear position sensors and switches can be described by a number of different specifications and features.

  • Sensors measurement range varies (e.g. 0.0394 to 0.0787 inches). Some have minimum ranges.
  • Repeatability can vary (e.g. better than 2.46E-5 mils to better than 2 mils).
  • Accuracy ranges (e.g. better than 0.01 ±%FS to better than 2 ±%FS).
  • Devices can tolerate certain temperature ranges (e.g., -13 to 158°F).
  • Targets can be magnetic/nonmagnetic, ferrous/nonferrous, and may have minimum diameters.
  • Devices may be field adjustable. 
  • Output can be analog (current, voltage, or frequency), digital (serial, parallel, or other), an alarm, or a change in state of switches.
  • Display options include analog, digital, and/or video.
  • Power supply may use AC or DC voltages.
  • Connections may be fixed cable (often include bare or stripped leads), integral (attached to existing systems) or terminals (clamp down or screw into place).
  • Sensors can be shielded (protected against EMI and RFI), weld field immune, short circuit protected, intrinsically safe (cannot cause ignition of atmospheric mixtures), and/or temperature compensation (ignore fluctuating ambient temperatures).

Applications

Inductive sensors are contact-free, inherently robust, and have infinite resolution with high repeatability. They are often used where long-term reliability is important, particularly in harsh and hostile environments.

References

Finding the Right Sensor for Linear Displacement

Gill Sensors Blade Principles

Inductive Linear Position Sensors

Inductive Linear-Position Sensor/Limit-Sensor Units

Linear Position Sensor


Related Products & Services

  • Capacitive Linear Position Sensors

    Capacitive linear position sensors are devices that sense position / displacement using capacitance technology.

  • Eddy Current Linear Encoders

    Eddy current linear encoders detect the distance from a target by using magnetic fields generated by a reference and sensing coils.

  • Linear Variable Differential Transformers (LVDT)

    Linear variable differential transformer (LVDT) linear position sensors have a series of inductors in a hollow cylindrical shaft and a solid cylindrical core. These devices produce an electrical output proportional to the position of the core

  • Optical Linear Encoders

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

  • Optical Triangulation Position Sensors

    Optical triangulation position sensors use reflected waves to pinpoint position and displacement. The source of these waves may be a light emitting diode (LED), infrared (IR) light, or laser.

  • String Potentiometers

    String Potentiometers are used to measure the movement and displacement of objects. A cable or wire is attached to an object, and as the object moves, the transducer produces an electrical signal proportional to the wire's linear extension.

  • Ultrasonic Linear Position Sensors and Switches

    Ultrasonic linear position sensors and switches use ultrasonic waves in combination with light and frequency readings for position and displacement sensing.