Displacement Measurement: LVDTs in Focus


Displacement measurement is a crucial function of machines that need monitoring and control. In measuring different kinds of mechanical movement, various types of displacement transducers or sensors are used. By definition, a displacement transducer is an electromechanical device that functions to convert the mechanical motion of an object into an electrical signal or vice versa. Many automated systems and technologies use displacement transducers as an integral part of the assembly.

Position sensor categories

There are different parameters considered to categorise position sensors. If according to the output conversion principle used, displacement sensors are either:

  • Magnetoelectric
  • Inductive
  • Electrostatic
  • Electromagnetic

The output signal can also be AC or DC, but a large number of sensors today produce digital outputs which make them compatible with computer systems. A common type of displacement transducer used in many applications is the LVDT or linear variable differential transducer. The primary purpose of an LVDT is to measure the movement of an object along a single direction. The sensor’s output is equivalent to the distance travelled indicated in measurement units of either inches or millimetres. Depending on the movement of the object, the differential output of a transducer is either zero, positive, or negative.

For many demanding applications, manufacturers can use various materials to strengthen the components of the sensor which is essential for high-precision or quality-control applications.

Functions and characteristics of an LVDT

An LVDT is a non-contacting type of displacement transducer which was initially developed as a laboratory device. Although LVDTs have superior performance over other sensor technologies, widespread adoption was not possible due to the high cost. But advancements in manufacturing technology have made it possible for LVDTs to be an economical choice for various industrial applications.

The primary benefit of using an LVDT is its non-contact design. With no internal moving parts that get in contact with the object being measured, the sensor can withstand shock and vibration with little to no impact on the performance. LVDTs can also be hermetically sealed for application in harsh conditions such as being submerged in fluids, exposed to extreme temperature, dust, and other environmental elements.

Applications of LVDTs

The following are examples of typical applications for LVDTs.

  • Power turbine. Power plants use turbines to generate energy and LVDTs fitted with signal conditioners are suitable for this function.
  • Hydraulic machines. The improved stroke-to-length ratio of modern LVDTs has made it possible for these sensors to be applied in hydraulic machines. Hydraulic tools are consistently subject to harsh conditions which is why an LVDT is one of the best sensor technologies for similar applications.
  • Process automation. LVDTs are used in research and development laboratories, food and beverage manufacturing, as well as other industrial applications that require these sensors for automating specific processes.
  • Apart from application in aircraft as a position transducer, LVDTs are also used in satellite production, flight simulators, tactical missiles, and other military-related uses.

Manufacturers of LVDTs also continue to experiment on new materials and enhanced designs to produce more sophisticated devices so that other industries can benefit from the outstanding features of LVDTs.

Image: https://pixabay.com/photos/machine-mill-industry-steam-2881168/

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