Coriolis Flowmeter Asymmetry Detection to Stop False Totalizing
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Solution Overview
Problem
Coriolis flowmeters experience false totalizing due to asymmetric mass or damping caused by bubbles or solid particles, leading to inaccurate flow measurements, especially in multiphase flows, which existing solutions like raising low-flow thresholds or density cutoffs are inadequate or complex.
Innovation Solution
A method and device that measures parameters such as pick-off sensor voltage differences, drive current, and flow tube mass/stiffness to detect asymmetry and halt totalizing when these parameters deviate from predetermined thresholds, eliminating the need for external devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the low-flow threshold is raised to prevent false totalizing, then false flow registration is reduced, but real low-flow measurements may be missed
Solution Approach 1:
The invention segments the detection parameters into multiple independent measurements (delta-t, drive gain, pickoff voltage ratios) rather than relying on a single threshold. This allows the system to analyze different aspects of flow tube behavior separately and combine them for more accurate false flow detection without missing real low-flow conditions.
Solution Approach 2:
The invention changes from using a single low-flow threshold parameter to monitoring multiple parameters simultaneously (delta-t, drive gain, pickoff voltage ratios). By analyzing changes in multiple parameters together, the system can distinguish between false flow caused by asymmetry and real low-flow conditions more reliably.
2Reliability
If density cutoff is implemented to stop totalizing, then false totalizing is prevented, but the solution becomes complex and density does not always behave as expected with entrained gas
Solution Approach 1:
The invention uses the existing flowmeter's internal parameters (delta-t, drive gain, pickoff voltages) that serve multiple functions in normal operation to also detect false flow conditions. This eliminates the need for separate external devices or complex additional systems, as the flowmeter itself performs both flow measurement and false flow detection using its existing sensor capabilities.
Solution Approach 2:
The flowmeter system monitors its own operational parameters (drive gain, pickoff voltage ratios, delta-t) to detect false flow conditions. The system uses self-generated diagnostic information from its existing sensors to identify and prevent false totalizing, rather than requiring external monitoring devices or complex additional systems.
3Reliability
If drive gain is used to detect entrained gas, then some detection is achieved, but drive gain only increases a small amount even when false totalizing is occurring at a harmful level
Solution Approach 1:
The invention specifically targets asymmetry in the flow tube system by comparing pickoff voltage ratios between opposite sides of the flow tube. False flow caused by entrained gas or particles creates asymmetric mass distribution, which manifests as unequal pickoff voltage ratios. By focusing on this asymmetry rather than overall drive gain changes, the system achieves much higher detection sensitivity for false flow conditions.
Solution Approach 2:
The invention adds a new dimension to detection by comparing pickoff voltage ratios from multiple locations around the flow tube cross-section. Instead of relying on a single drive gain measurement, the system analyzes spatial distribution of vibrations across different pickoff points, creating a multi-dimensional detection approach that is far more sensitive to asymmetric false flow conditions.
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
Accurately prevents false totalizing by detecting asymmetry, ensuring precise flow measurements without additional hardware, thus maintaining meter accuracy in multiphase flows.
Implementation Method 1
Vibrating conduit sensors, such as Coriolis mass flowmeters... Mass flow rate may be determined by measuring time delay or phase differences between motions at the transducer locations
Implementation Method 2
Excitation is typically provided by a driver, e.g., an electromechanical device, such as a voice coil-type actuator, that perturbs the conduit in a periodic fashion
Implementation Method 3
motion of the conduit is measured at points spaced along the conduit... Two or more such transducers (or pickoff sensors) are typically employed in order to measure a vibrational response of the flow conduits
Data Source
AI summary
A method for eliminating false totalization in a flowmeter involves flowing a process fluid through flow tubes and vibrating the flow tubes with a driver positioned between a first and second pickoff sensor. The first pickoff sensor is closer to the inlet and the second pickoff sensor is closer to the outlet of the flow tubes. The method includes measuring the mass flow rate of the process fluid, totalizing the process fluid flow, and measuring voltages from the first and second pickoff sensors. A difference in amplitude of vibration greater than a predetermined threshold is detected between the inlet and outlet, indicated by the measured amplitude difference between the first and second pickoff sensor voltages. This difference signifies asymmetric damping due to uneven distribution of bubbles or solid particles. Consequently, the measured mass flow rate is set to zero, halting totalization and preventing false flow readings in a no-flow condition.