Fluid level gauge having magnetic sensor

Abstract From the Canadian patent

A fluid measurement gauge is principally used to measure the fluid level in large underground storage tanks, such as for storing gasoline at service stations. A housing is positioned vertically in the fluid and includes a leadscrew which is driven by a stepper motor. A nut is mounted for longitudinal movement along the leadscrew. A float encircles the housing and includes a magnet at the surface of the fluid level. A magnetic sensor, such as a Halleffect switch, is mounted on the nut and driven in selected steps downward to encounter the magnet mounted in the float. A reference position is marked at the top of the housing and the fluid level is measured downward from the reference position …