Resistive level sensor for cryo-liquid gas tanks

Abstract

The present invention provides a probe having a resistance that varies with temperature and is operable to determine the quantity of a fluid, such as hydrogen, in a storage tank, such as a cryogenic storage tank. The probe relies upon differing heat transfer rates for the gaseous and liquid phases of the fluid and a change in resistance due to a change in temperature of the probe to ascertain the quantity of fluid within the storage tank. The probe can be configured to account for the geometry of the storage tank thereby providing a linearized signal indicative of the quantity of fluid in the storage tank.

1 . A method of determining a quantity of a fluid in a tank, the method comprising: 
 (a) inducing current flow through a resistor in contact with the fluid in the tank, said resistor having a resistance that varies with the temperature of said resistor;    (b) measuring a characteristic of said resistor in response to said current flow;    (c) ascertaining a quantity of the fluid in the tank based on said measured characteristic; and    (d) allowing a temperature of said resistor to substantially equalize with a temperature of the fluid between each performance of (a)-(c).    
     
     
         2 . The method of  claim 1 , wherein said inducing includes inducing current flow for a predetermined period of time.  
     
     
         3 . The method of  claim 2 , wherein said measuring includes measuring said characteristic of said resistor over said predetermined period of time.  
     
     
         4 . The method of  claim 1 , wherein said measuring includes measuring one of a current flow through said resistor and a voltage drop across said resistor.  
     
     
         5 . The method of  claim 1 , wherein said resistor is free of an induced current flow while allowing said temperature of said resistor to substantially equalize with said temperature of the fluid.  
     
     
         6 . The method of  claim 1 , wherein said inducing includes supplying one of a constant voltage drop across and a constant current flow to said resistor.  
     
     
         7 . The method of  claim 1 , wherein the tank is a cryogenic storage tank and the fluid is hydrogen.  
     
     
         8 . The method of  claim 1 , wherein said ascertaining includes ascertaining a quantity of a fluid having a dielectric property.  
     
     
         9 . The method of  claim 1 , wherein said ascertaining includes comparing said measured characteristic to empirical data to ascertain the quantity.  
     
     
         10 . The method of  claim 1 , wherein said ascertaining includes ascertaining a liquid level of the fluid in the tank.  
     
     
         11 . The method of  claim 1 , wherein said ascertaining includes compensating for a non-linearly varying volumetric capacity of the tank.  
     
     
         12 . A method of determining a quantity of a fluid in a storage tank, the method comprising: 
 (a) inducing current flow through a resistor in contact with the fluid in the tank, said resistor having a resistance that varies with the temperature of said resistor;    (b) measuring a characteristic of said resistor in response to said current flow; and    (c) determining the quantity of the fluid in the tank based on said measured characteristic by using an algorithm to determine a best fit to a curve of said measured characteristic.    
     
     
         13 . The method of  claim 12 , wherein said inducing includes inducing said current flow for a predetermined period of time.  
     
     
         14 . The method of  claim 13 , wherein said measuring includes measuring said characteristic of said resistor over said predetermined period of time and said determining includes determining the quantity of the fluid using an algorithm to determine a best fit to a curve of said measured characteristic during said predetermined period of time.  
     
     
         15 . The method of  claim 12 , wherein said measuring includes measuring one of a current flow through said resistor and a voltage drop across said resistor.  
     
     
         16 . The method of  claim 12 , wherein said inducing includes selectively inducing said current flow.  
     
     
         17 . The method of  claim 12 , wherein said inducing includes supplying one of a constant voltage drop across and a constant current flow to said resistor.  
     
     
         18 . The method of  claim 12 , wherein the tank is a cryogenic storage tank and the fluid is hydrogen.  
     
     
         19 . The method of  claim 12 , wherein said determining includes determining the quantity of a fluid having a dielectric property.  
     
     
         20 . The method of  claim 12 , wherein said determining includes determining a liquid level of the fluid in the tank.