Electromechanical Liquid Level Gauge Density Compensation
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Solution Overview
Problem
Conventional electromechanical liquid level servo gauges (ESGs) are sensitive to liquid density variations, which poses challenges for custody transfer and legal metrology applications, especially when products have wide variance in composition or purity, and installation limitations restrict the use of larger displacers.
Innovation Solution
The implementation of a software-based automatic density compensation method using a processor to continuously adjust the displacer's immersion depth based on measured density changes, allowing for accurate level measurement even with smaller diameter displacers, by comparing a programmed apparent weight setpoint with the measured value and using a density compensated algorithm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a larger displacer cross-sectional area is used to reduce density sensitivity, then measurement precision is improved, but device complexity and installation difficulty increase due to restricted tank access and small nozzle areas
Solution Approach 1:
The patent replaces the mechanical approach of using a larger displacer to reduce density sensitivity with an electronic/software-based solution. The processor continuously calculates density compensation factors based on measured density variations and adjusts the apparent weight setpoint accordingly, eliminating the need for mechanical displacement of the displacer position to compensate for density changes.
Solution Approach 2:
The patent changes the parameter of the apparent weight setpoint dynamically based on measured density variations. Instead of using a fixed setpoint, the system continuously adjusts the setpoint by applying density compensation factors, allowing accurate level measurement across varying liquid densities without changing the physical displacer dimensions.
2Ease of operation
If a smaller displacer is used to accommodate installation limitations, then ease of installation is improved, but sensitivity to density changes increases reducing measurement precision
Solution Approach 1:
The patent replaces the mechanical approach of using a larger displacer to reduce density sensitivity with an electronic/software-based solution. The processor continuously calculates density compensation factors based on measured density variations and adjusts the apparent weight setpoint accordingly, eliminating the need for mechanical displacement of the displacer position to compensate for density changes.
Solution Approach 2:
The system implements a feedback mechanism where the measured density is continuously used to adjust the apparent weight setpoint. The processor compares the measured density with reference values and applies compensation factors to maintain accurate level measurement despite using a smaller displacer with higher inherent density sensitivity.
3Measurement precision
If density compensation is implemented through continuous adjustment of displacer position, then measurement precision is improved, but wear on ESG components increases
Solution Approach 1:
The patent replaces the mechanical approach of continuously adjusting displacer position to compensate for density changes with an electronic/software-based solution. The processor calculates and applies density compensation factors to the apparent weight setpoint, eliminating the need for continuous mechanical movement of the displacer and thereby reducing wear on ESG components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces the sensitivity to density changes, enabling accurate level measurement in tanks with varying liquid densities, allowing for the use of smaller displacers and enhancing the range of applications, including custody transfer and legal metrology, while reducing wear and tear on the ESG components.
Implementation Method 1
The displacer being more dense than the density of the product in the tank is basically kept at the same level using Archimedes law which indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.
Data Source
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AI summary
A method of measuring liquid level in a tank. An electromechanical liquid level gauge (ESG) is provided including a processor, a displacer suspended on a wire from a grooved drum having a servo motor coupled thereto to rotate the drum for balancing the displacer. A change in liquid level causes a change in a counterforce to move the ESG out of balance. The processor monitors a torque sensor output, and controls movement of the motor using a programmed apparent weight (AW) setpoint to raise or lower the displacer based on an AW derived from the torque. An associated memory stores a density compensated fixed immersion depth level gauging algorithm. The algorithm implements obtaining a density reading for the liquid, continuously corrects an immersion depth of the displacer for changes in density to provide an essentially fixed immersion depth, and calculates the liquid level from the density reading and immersion depth.