Advanced volume gauging device

• US 6,993,966 B2
• Filed: 06/10/2002
• Issued: 02/07/2006
• Est. Priority Date: 06/08/2001
• Status: Expired due to Term

• Current Assignee: Nanospace AB (GomSpace Group AB)
• Original Assignee: Nanospace AB (GomSpace Group AB)
• Inventors: Stenmark, Lars
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): BELLAMY, TAMIKO D
• Application Number:
  US10/479,988
• Publication Number:
  US 20040231413A1
• Time in Patent Office: 1,338 Days
• Field of Search: 732/90.B, 731/49
• US Class Current: 73/290.00B
• CPC Class Codes: G01F 22/02 involving measurement of pressure
• CPC Class Codes: G01F 23/18 Indicating, recording or alarm devices actuated electrically

Abstract

A new high precision volume gauging system for measuring the volume of a propellant VL enclosed at a first pressure PU within a propellant tank (40) of a volume VT. The improved precision compared with prior art is achieved in that it comprises a high precision pressure sensor (90) which is comprised of a reference chamber (115) that is connected to the propellant tank (40) by a communication line (140), a valve (150) for controlling the gas flow through the line (140), and a high precision differential pressure sensor (95) that is arranged to record the pressure difference between the reference chamber (115) and the propellant tank (40) to which it is connected through a communication line (130).

Claims

1. 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;

$V_u=\frac{\left(P_p-\left(P_u+d<br><br>\text{\hspace{1em}<br><br>}<br><br>P_u\right)\right)<br><br>V_p}{d<br><br>\text{\hspace{1em}<br><br>}<br><br>P_u};<br><br>$

and

(g) subtracting said ullage volume V_U from said first V_T volume to determine said propellant volume V_L.

2. The method of claim 1, characterised in that it comprises the step of:

measuring the temperatures of said ullage volume T_U and said pressurization gas T_p, and that the step of calculating the ullage volume V_U of said first tank is performed in accordance with the following equation;

$V_u=\frac{\left(P_p-\left(P_u+d<br><br>\text{\hspace{1em}<br><br>}<br><br>P_u\right)\right)<br><br>V_p<br><br>T_u}{\text{\hspace{1em}<br><br>}<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>P_u<br><br>T_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>u<br><br>\text{\hspace{1em}<br><br>}}}.$

3. High precision volume gauging system for measuring the volume of a propellant V_L enclosed at a first pressure P_U within a propellant tank (40) of a volume V_T, said system comprising a pressurisation tank (20) that is connected to a high pressure source by a high pressure gas line (230) and to the propellant tank (40) by a line (50), an injection valve (60) controlling the gas flow through the line (50), a first absolute pressure transducer (65) for monitoring the pressure P_p within the tank (20), and a second absolute pressure transducer (70) monitoring the pressure P_u within the ullage volume V_u of the tank (40), wherein the system further comprises a high precision pressure sensor (90) which is comprised of a reference chamber (115) that is connected to the propellant tank (40) by a communication line (140), a valve (150) for controlling the gas flow through the line (140), and a high precision differential pressure sensor (95) that is arranged to record the pressure difference between the reference chamber (115) and the propellant tank (40) to which it is connected through a communication line (130).

4. High precision volume gauging system according to claim 3, provided as a self-contained miniaturized volume gauging device (490) that is arranged to be mounted directly on the wall of the propellant tank (40).

5. Self-contained miniaturized volume gauging device (490) according to claim 4, wherein the high precision pressure sensor (90) is provided as a micromechanical pressure sensor unit (510).

6. Self-contained miniaturized volume gauging device (490) according to claim 5, wherein the micromechanical pressure sensor unit (510) further comprises the first absolute pressure transducer (65), the second absolute pressure transducer (70).

7. High precision micromechanical pressure sensor unit (510) according to claim 5, comprised of a first wafer A (300) which is bonded to the top surface of a second wafer B (310), wherein the differential pressure sensor (95) is formed in that, a deep cavity (320) is formed in the top surface of wafer A (300) such that a flexible membrane (120) is formed by bottom of the cavity (320) and the bottom surface of wafer A (300), a reference chamber (115) is formed in the wafer B (310) beneath the flexible membrane (120), metal electrodes (330) are arranged at the bottom surface of the flexible membrane (120) and the bottom surface of the reference chamber (115) such that they act as a capacitor where the capacitance changes when the membrane bends, wherein the valve (150) is comprised of a valve seat (360) in the shape of a ring-shaped ridge formed in the bottom surface of wafer A 300, a gas entrance (370) located inside the valve seat (360), a valve cap (380) formed in the top surface of wafer B 310 as a rigid cap portion surrounded by a thin flexible membrane (390), the valve cap (380) is closed and opened by a piezoelectric actuator arrangement (400, 410, 420), and wherein the reference chamber (115) is connected to the valve through a small channel (140).