Magnetostriction is a property of magnetic materials that causes them to change size or shape during magnetization. This property is used in magnetostrictive sensors to detect a position, the technique is established and is used in all areas of the market to detect a position. Magnetostrictive sensors has very high accuracy and contact less operation which gives extremely long mechanical lifetime.
The sensors are available as linear sensors with mechanical housing and as cylinder sensors that is mounted inside of pneumatic or hydraulic cylinders. Combined with a float the sensors can also be used as a level sensor/transmitter.
How a magnetostrictive sensor work
The sensors contain electronics, sensor rod and a permanent magnet. A waveguide is mounted inside of the sensor rod, this waveguide is a magnetostrictive wire. The permanent magnet travels along the sensor rod, in a cylinder the magnet is mounted in the piston of the cylinder and in a level sensor the magnet is placed in the float.
The electronics applies a current pulse to the waveguide, the current and the permanent magnet causes the waveguide to twist, this is called the Wiedemann effect. As the current is applied as a pulse the twisting of the wire will behave as an ultrasonic wave that travels with the speed of sound in the material, hence the name waveguide. The wave is detected by the sensor electronics and the position is calculated by the sensor as the time and speed in known.
The wave will also travel in the opposite direction, away from the electronics towards the end of the sensor rod. There the wave is absorbed by damping elements, therefore magnetostrictive sensors has a non-active zone in the end of the sensor rod.
It is not necessary for the sensor electronics to be situated together with the sensor rod, it can be placed elsewhere. This is an advantage if there is limited space to mount the sensor rod, for example in a cylinder. GY-mini is a sensor model that is designed this way and the electronics can be mounted far away from the sensor rod. Magnetostrictive sensors are available with different signal outputs such as voltage, 4-20 mA, Profibus, SSI etc.