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...http://www.google.com.au/patents/US4554494?utm_source=gb-gplus-sharePatent US4554494 - Fluid level gauge having magnetic sensor
