Strain Gage Flowmeter DC Drift Cancellation
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Solution Overview
Problem
Strain gages in vibrating flowmeters face challenges in accurately measuring strain on thick metal flow tubes due to small tension and compression forces from fluid flow, leading to difficulties in resolving Coriolis forces and susceptibility to DC drift, which affects the accuracy of mass flow rate measurements.
Innovation Solution
The use of strain gages with varying placements and orientations connected to bridge circuits, combined with a high-pass filter to mitigate DC drift, allows for effective signal amplification and background cancellation, enabling accurate strain detection and mass flow determination in flowmeters originally designed for coil/magnet type pickoffs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If strain gages are used to measure strain on thick metal flow tubes, then the flowmeter can operate in industrial conditions with high pressures and temperatures, but the small tension and compression forces from fluid flow make it difficult to resolve Coriolis forces and detect strain accurately
Solution Approach 1:
The patent changes the measurement parameter from direct strain measurement to measuring the difference in strain between two locations on the flow tube. By using differential measurement of strain at different positions, the system can detect the small Coriolis forces even when operating with thick metal tubes in high-pressure and high-temperature industrial conditions.
2Productivity
If strain gages are used in vibrating flowmeters, then the device can measure mass flow rate, but DC drift in the strain gage signals affects the accuracy of measurements
Solution Approach 1:
The patent extracts and removes the DC drift component from the strain gage signals through differential measurement. By measuring the difference between two strain gage signals, the common-mode DC drift is eliminated, leaving only the AC Coriolis signal that contains the mass flow information.
3Stress or pressure
If strain gages are placed on thick metal flow tubes, then the flowmeter can handle high pressures, but the strain signals from Coriolis forces become too small to resolve accurately
Solution Approach 1:
The patent combines the signals from two strain gages placed at different locations on the flow tube. By merging these differential measurements, the system amplifies the Coriolis signal while canceling out common-mode noise and drift, making it possible to detect small Coriolis forces on thick metal tubes.
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 configuration enhances the accuracy of mass flow measurements by effectively addressing the limitations of strain gages in thick metal tubes, reducing the impact of DC drift and enabling reliable operation in industrial conditions with high pressures and temperatures.
Implementation Method 1
Two or more strain gages configured as pickoff sensors are coupled to the one or more rigid flow tubes and oriented to sense at least one of a tension and compression in the one or more rigid flow tubes
Implementation Method 2
A driver coupled to the one or more rigid flow tubes. The driver is oriented to induce a drive mode vibration in the one or more rigid flow tubes
Implementation Method 3
A high-pass filter is configured to eliminate DC offset of the output of the one or more bridge circuits
Implementation Method 4
As a material begins to flow through the fluid tubes, Coriolis accelerations cause each point along the fluid tubes to have a different phase with respect to other points along the fluid tubes
Data Source
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AI summary
A flowmeter is provides that includes a sensor assembly and meter electronics. The flowmeter comprises one or more rigid flow tubes, a driver coupled to the flow tubes that is oriented to induce a drive mode vibration in the flow tubes. Two or more strain gages are coupled to the one or more rigid flow tubes and oriented to sense tension and compression of the flow tubes. One or more bridge circuits is in electrical communication with the two or more strain gages, wherein outputs of the bridge circuits are proportional to a strain detected by at least one of the strain gages.