Magnetostriction is a property of ferromagnetic (iron-based, magnetizeable) materials that causes them to change their shape or dimensions in the presence of a magnetic field. In addition to numerous other practical uses, this magnetostrictive effect is ideally suited for use in industrial linear position measurement sensors. Magnetostrictive linear position sensors use an iron-alloy sensing element, typically called a waveguide. Referring to the diagram at right, the waveguide (1) is housed inside a pressure-rated stainless steel tube or in an aluminum extrusion. The position magnet (2) is attached to the moving part of the machine, or the piston of a hydraulic or pneumatic cylinder. Measurements are initiated by applying a short-duration electrical pulse to a conductor (3) attached to the waveguide. The current creates a magnetic field (4) along the waveguide.
The magnetic field from the position magnet interacts with the generated magnetic field, inducing a torsional mechanical strain on the waveguide. When the current pulse stops, the strain is released, causing a mechanical pulse to propagate along the waveguide. This mechanical pulse travels at a constant speed, and is detected at the signal converter (5).
The time between the initial electrical pulse and the received mechanical pulse accurately represents the absolute position of the position magnet and, ultimately position of the machine or hydraulic cylinder. The position of the magnet along the waveguide is calculated by very accurately timing the interval between the initial current pulse, also known as the Interrogation Pulse, and the detection of the mechanical return pulse.