Abstract: A sensor for determining the location of the surface of liquid in a container, includes: a hollow tubular stainless steel probe inserted into said container, said probe having one portion arranged above the surface of the liquid and having another portion submerged in the liquid; a first thermocouple operatively arranged within the probe to sense the temperature above the liquid surface; a second thermocouple operatively arranged within the probe to sense the temperature of said liquid at a point beneath the liquid surface; a resistance wire operatively arranged within the probe; a current source operatively arranged to apply a constant-current to the ends of the wire; and an ohmmeter for measuring the electrical resistance of the wire according to the equation: RT=ƒ[kaTaHh+kwTwH(1−h)] where RT is the resistance of the wire, ƒ is the symbol for “a function of”, ka is a constant for the probe first portion, Ta is the temperature sensed by the first temperatur