Abstract: A method and apparatus for measuring a liquid level by a float carrying one or more magnets and movably positioned adjacent spaced analog output voltage Hall-effect sensors. The apparatus is calibrated by moving the float relative to the sensors and measuring the voltage outputs of the sensors relative to the position of the float, and storing the measured values. After calibrating, the voltage outputs of any sensors activated by the presence of the float are measured and compared to the stored values to determine the liquid level. Preferably, the voltage output of at least two sensors are measured while the float is at one position for greater accuracy.

Abstract: A method for inventory maintenance and leak detection in liquid storage tanks and dispensing lines, that combines tank level measurements, tank product temperature measurements, output flow measurements, liquid product characteristics data, initial product delivery volume data, and redundantly calculates changes in the quantity of liquid product within the tank and compares these calculations to determine abnormalities in the changes in the quantities of product within the tank. Changes in the quantity of product within the tank are verified as either the delivery of additional product into the tank or the dispensing of product from the tank as with a customer sale. Changes that cannot be verified as either delivery into or dispensing from the tank are appropriately characterized as possible leak conditions in the tank or lines.