How A Magnetostrictive Sensor Works?

By Author: Control Products
Total Articles: 33
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Magnetostriction is the property of certain materials including iron, nickel and cobalt. Change in the magnetic field can be attributed to the alignment of the magnetic domains within the material. Before the magnetic field is developed, magnetic domains are nothing but randomly arranged tiny magnets.

A magnetostrictive sensor operates on the principle of magnetostriction. The measuring principle, based on elapsed time measurement, determines the position, distance and speed with pinpoint accuracy. Different versions are available in pressure-resistant stainless steel housing and these can be fully integrated in hydraulic cylinders.

A magnetostrictive linear position sensor measures the distance between the head end of the sensing rod and the position magnet. The position magnet does not touch the sensing rod so there is no possibility of the parts becoming worn out. The sensing rod is mounted along the motion axis that has to be measured, while the position magnet is linked to the member, which will be moving. There is an electronics module on the head, reporting the position information to a controller. The ...
... reporting is done in analog or digital format as required.

Electrical connection interface, either an integral connector or cable, is also incorporated in the electronics housing. It is supported by visual diagnostic LED’s to ensure adequate wiring, power and magnet positioning. Five basic components of a magnetostrictive position sensor are position magnet, wave-guide, damp, pickup and electronics module.

The position magnet is in the shape of a ring and travels along the sensing rod. The wave-guide is located within the sensing rod. It is a small diameter tubing or wire made from a magnetostrictive material. Magnetostriction is a property of certain materials including iron, nickel and cobalt. A magnetic field causes strain during the application resulting in a change in the size or shape of the material. This can be attributed to the alignment of the magnetic domains within the material. Magnetic domains can be envisioned as randomly arranged tiny magnets before the magnetic field is applied.

Application of the interrogation pulse to the waveguide starts an electronic timer. The electronics module receives the return pulse from the pickup and stops the timer after a time delay that is proportional to the distance between the position magnet and the pickup. Location of the position magnet is indicated by the magnitude of the time delay.

One of the advantages of the magnetostrictive sensor is its ability to read the position magnet even when there is a barrier between the sensing rod and the position magnet. Various materials such as stainless steel, ceramics, aluminum, plastics and non-ferrous metals can be used for this duty.

A magnetostrictive transducer can also measure multiple magnets while using one sensing rod. Thanks to this feature, you can make more than one measurement by incorporating additional position magnets.

Various models of magnetostrictive position sensors have their respective specs that depend on the intended use and output. Several things have to be factored in when designing a sensor and close attention has to be paid for matching the device to the application requirements.

The author of the article is associated with Control Products that deals in linear position sensors, position transducers and a range of other such products.