A form of measurement technology used in in-tank electronic monitoring systems.

A magnetostrictive probe, installed in an underground tank, works on the principle that sound, moving down a nichrome wire, maintains a constant velocity despite temperature differences that may occur along its route of travel.

When this principle is employed in an electronic tank gauging system, a vertical pipe is installed in the tank. A tightly stretched nichrome wire runs down the center of the full length of the pipe.

Around the outside of the pipe is a doughnut-shaped float. Inside the float is a strong magnet. Magnetic flux from this floating magnet impinges on the nichrome wire at the liquid level in the tank. For measurement of this level, a sound wave is injected into the top end of the nichrome wire. When the sound wave reaches the level of the magnetic doughnut-shaped float, the vibration of the wire-in the presence of the magnetic flux at that point-causes electricity to be generated in the nichrome wire. 

Through repeated calculation of the time between the start of the sound pulse and the start of the subsequent electrical pulse, the precise level of the float can be determined. Tank-gauging systems using the principle of the magnetostrictive probe have been determined to be extremely accurate.

See also Capacitance.