Multiphasic Overreading Correction in Process Variable Transmitters
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Solution Overview
Problem
In process installations with multiphasic fluids, such as wet steam and natural gas, the presence of liquid in the gas stream leads to significant errors in gas flow measurement due to overreading, which is difficult to correct without additional hardware or complex calibration.
Innovation Solution
A multivariable process variable transmitter that can obtain temperature, reference pressure, and differential pressure information to calculate and correct for overreading, using a method that iteratively adjusts for the Lockhart Martinelli parameter and converges on accurate gas flow rates without requiring additional hardware or complex initial characterization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional hardware is added to correct overreading in multiphasic fluid measurement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces physical hardware additions with a computational correction system. The microprocessor uses algorithms that incorporate the Lockhart Martinelli parameter and differential pressure readings to calculate correction factors, substituting mechanical complexity with software-based solutions that maintain measurement precision without adding physical components.
Solution Approach 2:
The system changes operational parameters by introducing correction factors based on the Lockhart Martinelli parameter (X), differential pressure (dp), and absolute pressure (P). These parameter transformations allow the system to compensate for overreading errors through mathematical relationships rather than hardware modifications, resolving the contradiction between precision and complexity.
2Measurement precision
If complex calibration procedures are implemented to correct overreading, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The transmitter performs self-correction by automatically calculating overreading errors using the Lockhart Martinelli parameter and differential pressure measurements. The microprocessor executes correction algorithms without requiring external calibration equipment or technician intervention, making the system self-sufficient and maintaining ease of operation while improving precision.
Solution Approach 2:
The system implements continuous feedback by monitoring differential pressure and Lockhart Martinelli parameter values, then automatically adjusting flow measurements based on calculated correction factors. This closed-loop approach eliminates complex manual calibration procedures while maintaining high measurement precision through ongoing automatic correction.
3Measurement precision
If dedicated technician time is required for overreading correction, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The transmitter is designed to perform overreading correction autonomously without requiring dedicated technician time. The microprocessor automatically calculates correction factors using real-time differential pressure and Lockhart Martinelli parameter data, eliminating the need for manual calibration activities and thereby maintaining productivity while achieving high measurement precision.
Solution Approach 2:
The system performs preliminary correction calculations continuously in the background using pre-programmed algorithms. By preparing correction factors in advance and applying them automatically to flow measurements, the system eliminates the need for time-consuming post-installation calibration procedures, thus improving both precision and productivity.
Data Source
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AI summary
A process variable transmitter (10, 102) is operably coupleable to a source (14) of multiphasic process fluid flow. The process variable transmitter (10, 102) is configured to obtain information relative to temperature, a reference pressure, and differential pressure across a differential pressure producer (12) in the multiphasic process flow. The process variable transmitter (10, 102) is configured to calculate and/or correct for overreading based upon the reference pressure, the differential pressure and the temperature.