Method for leakage measurement

Abstract

A method of high sensitivity for measuring leakage of liquid from a storage tank which comprises introducing a sensor into the liquid in the tank, the sensor being coupled to means for sensing displacement of mass, measuring the displacement over a known period of time and calculating the leakage rate. The sensor is designed to compensate for evaporative losses and temperature changes.

The invention claimed is: 
     
       1. A method of high sensitivity for measuring leakage of liquid into or out of a storage tank .Iadd.normally at atmospheric pressure .Iaddend.which comprises introducing a freely suspended sensor into the liquid in the tank .Iadd.through the fill-pipe or other access hole of said tank.Iaddend., said sensor being coupled to means for sensing mass displacement, .[.and.]. observing the change of displacement of said sensor over a period of time to determine a change of liquid mass in said tank.Iadd., and subsequently removing said sensor from said tank.Iaddend.. 
     
     
       2. A method of high sensitivity for measuring leakage of liquid into or out of a storage tank, which comprises introducing a freely suspended sensor into the liquid in the tank, said sensor being coupled to means for sensing mass displacement, calibrating said mass sensing displacement means to determine the amount of liquid per unit change, measuring the units of change of displacement of said sensor over a period of time and calculating the rate of change of liquid in said tank. 
     
     
       3. A method of high sensitivity for measuring leakage of liquid into or out of a storage tank whereby effects of evaporation of said liquid in said tank are compensated, which comprises introducing a sensor into the liquid in the tank, said sensor having liquid from said storage tank in liquid holding means at its top .[.and extending above the level of liquid in said tank.]..Iadd., said sensor being disposed in the tank liquid such that said liquid holding means extends above the tank liquid level, .Iaddend.the cross-sectional area of said liquid surface in said liquid holding means being essentially equal to the cross-sectional area of the .[.outside dimension of.]. said sensor .Iadd.in contact with the tank liquid.Iaddend., said sensor being coupled to means for sensing mass displacement, calibrating said mass sensing displacement means to determine the amount of liquid per unit change, measuring the units of change of displacement of said sensor over a period of time and calculating the rate of change of liquid in said tank. 
     
     
       4. The method of claim 3 where the storage tank is underground. 
     
     
       5. The method of claim 3 wherein the tank is filled with liquid and the sensor extends to near the bottom of said tank whereby the effects of temperature are minimized. 
     
     
       6. A method of high sensitivity for measuring leakage of liquid into or out of a storage tank whereby effects of evaporation of said liquid in said tank are compensated, which comprises introducing a sensor into the liquid in the tank, said sensor having liquid from said storage tank in liquid holding means at its top .[.and extending above the level of liquid in said tank,.]..Iadd., said sensor being disposed in the tank liquids such that said liquid holding means extends above the tank liquid level, .Iaddend.the cross-sectional area of said liquid surface in said liquid holding means being essentially equal to the cross-sectional area of .[.the outside dimension of.]. said sensor .Iadd.in contact with the tank liquid.Iaddend., said sensor being coupled to the arm of a balance for sensing mass displacement and movement of said balance arm being detected by a differential transformer, calibrating the output of said differential transformer to determine the amount of liquid per unit change of displacement, measuring the units of change of displacement of said sensor over a period of time and calculating the rate of change of liquid in said tank. 
     
     
       7. The method of claim 6 where the storage tank is underground. 
     
     
       8. The method of claim 6 wherein the output of said differential transformer is coupled to a recording device. .Iadd. 
     
     
       9.  A method of improved sensitivity for measuring leakage of liquid into or out of a storage tank having a tank atmosphere whereby effects of evaporation of the tank liquid are compensated, said method comprising the steps of: introducing into the tank liquid a sensor containing liquid segregated from the tank liquid and exposed to the tank atmosphere,   sensing at least one buoyancy-dependent sensor condition which is responsive to the level of the tank liquid in the tank;   observing the change in the at least one sensor condition to determine a change of liquid mass in the tank. .Iaddend. .Iadd.10. The method of claim 9 wherein said at least one sensor condition comprises displacement of   
     
     
        said sensor from a predetermined initial position. .Iaddend. .Iadd.11. The method of claim 9 wherein the cross-sectional area of the surface of said sensor liquid is substantially equal to the cross-sectional displacement area of said sensor. .Iaddend. .Iadd.12. The method of claim 11 wherein said sensor liquid is liquid taken from said tank liquid. .Iaddend. .Iadd.13. The method of claim 12 wherein said sensor has liquid holding means at its top for holding at least some of said sensor liquid. .Iaddend. .Iadd.14. The method of claim 13 wherein said sensor is introduced into the tank such that said liquid holding means is disposed above the level of the tank liquid. .Iaddend.