Patent ID: 6993966

Claim:
A method of measuring the volume of a propellant V L enclosed at a first pressure P U within a first tank of a first volume V T , where the tank volume V T is equal to the volume of the propellant V L plus an ullage volume V U , said method comprising the steps of: (a) enclosing a pressurization gas of a second volume V p in a second tank at a second pressure P p , said second pressure P p being greater than said first pressure P U ; (b) opening a connection between the ullage volume in the first tank and a reference chamber such that the reference pressure P r will be essentially equal to P U ; (c) closing the connection between the ullage volume in the first tank and a reference chamber such that the reference pressure P r will be independent of P U ; (d) opening a connection between the first tank and the second tank; (e) measuring the resulting pressure difference dP U between the ullage volume and the reference chamber using a differential pressure (dP) sensor of high accuracy; (f) calculating the ullage volume V U of said first tank in accordance with the following equation: V u = ( P p - ( P u + d ⁢ ⁢ P u ) ) ⁢ V p d ⁢ ⁢ P u ; and (g) subtracting said ullage volume V U from said first V T volume to determine said propellant volume V L .