Sometimes two different liquids having different density have to fill in a tank for mixing. Therefore it will be two levels that have to be measured one above another. Which is important the ratio of the liquids in the vessel.
The Magnetostrictive level instrument12 is used to measure the liquid-liquid interface. Instead of one float in the magnetostrictive instrument, here we use two magnetic floats with two densities.
If the waveguide (probe) is equipped with two floats, such that one float with a density that can float above the interface and other one floats on the light liquid.
An electric pulse is sent through the waveguide and interacts with magnets fixed in both floats. On interaction, both floats produce torsional wave pulses. Both pulses are sensed at the sensing end at different times.
With such an instrument, each electrical “interrogation” pulse returns to the sensor head: the first pulse representing the total liquid level (upper, light float) and the second pulse representing the interface level (lower, heavy float).
If the instrument has digital communication capability (e.g. HART, FOUNDATION Fieldbus, Profibus, etc.), both levels may be reported to the control system over the same wire pair, making it a “multivariable” instrument.