High accuracy mass sensor for monitoring fluid quantity in storage tanks
First Claim
1. A system for monitoring fluid quantity in a storage tank, comprising(a) a detection device for location at a bottom of the tank and in contact with the fluid, the device includinga bellows unit immersed in the fluid, anda displacement sensor for detecting displacement of the bellows and for issuing an output signal representative of the detected bellows displacement, and(b) a processor unit for monitoring said sensor output signal and for correlating such output signal with changes in the mass of the fluid, for determining fluid quantity and loss rate of the stored fluid.
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Abstract
A mass sensoring system for monitoring the amount of fluid in a storage tank with an accuracy high enough to determine both the quantity present and the potential loss of fluid at a loss rate of 0.05 gal/hr or at least 0.1 gal/hr. The system utilizes a pressure sensor positioned at the bottom of the tank and in contact with the fluid. This device includes a bellows unit whose displacement is correlated to changes in the mass of fluid in which it is immersed, and a transducer for monitoring the position of the bellows, wherein the interior of the bellows unit is in the same atmosphere as the sensor, and the sensor is in communication with the vapor pressure immediately above the fluid in the tank. The outside of the bellows is subjected to the stored fluid. A multiple-capsule bellows assembly is coupled to an LDVT transducer in a thermal-expansion-cancelling configuration of the invention.
63 Citations
16 Claims
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1. A system for monitoring fluid quantity in a storage tank, comprising
(a) a detection device for location at a bottom of the tank and in contact with the fluid, the device including a bellows unit immersed in the fluid, and a displacement sensor for detecting displacement of the bellows and for issuing an output signal representative of the detected bellows displacement, and (b) a processor unit for monitoring said sensor output signal and for correlating such output signal with changes in the mass of the fluid, for determining fluid quantity and loss rate of the stored fluid.
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13. A method for determining storage tank fluid inventory quantity in a system comprising a detection device for location at a bottom of the tank and in contact with the fluid, the device including a bellows unit immersed in the fluid, and a displacement sensor for detecting displacement of the bellows and for issuing an output signal representative of the detected bellows displacement, and a processor unit for monitoring said sensor output signal and for correlating such output signal with changes in the mass of the fluid, for determining quantity of the stored fluid, the method comprising the steps of multiplying
(1) a displacement signal D from said sensor, said displacement signal being adjusted according to a transfer function H for said sensor, and (2) a signal representative of the sensor temperature, the sensor temperature signal being adjusted according to a temperature function of the sensor, to obtain an adjusted displacement signal representing the amount of displacement of said bellows unit, said displacement signal being adjusted for a transfer function of said bellows unit, resulting in obtaining a pressure signal, said pressure signal being adjusted by a determined density value to obtain a height signal representative of the height of the measured fluid, and comparing said height signal to known stored values to obtain a geometric volume-dependent signal representing the number of gallons in the tank.
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15. A method for determining storage tank fluid inventory quantity in a system comprising a detection device for location at a bottom of the tank and in contact with the fluid, the device including a bellows unit immersed in the fluid, and a displacement sensor for detecting displacement of the bellows and for issuing an output signal representative of the detected bellows displacement, and a processor unit for monitoring said sensor output signal and for correlating such output signal with changes in the mass of the fluid, for determining fluid quantity and loss rate of the stored fluid, the method comprising the steps of
obtaining a sensor displacement signal which is adjusted with a transfer function signal, resulting in a displacement signal representing displacement of the bellows unit, said displacement signal being adjusted with a bellows unit transfer function, said adjusting resulting in a pressure value signal, said pressure value signal being adjusted with a determined density value signal, said density value signal being adjusted with a high resolution transfer function to obtain a height signal representative of the height of the measured fluid, and said height signal being converted to a signal representative of gallons as a function of height reflecting the particular geometric volume dependency on the height of the fluid in the tank, and a series of said gallon signals being obtained and then compared to obtain a loss rate in gallons per hour.
Specification