Resonant Conductor Fluid Measurement with Phase Lock Loop
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Solution Overview
Problem
Existing methods for measuring fluid viscosity in damped vibratory systems face challenges with DC offset from amplifiers and low-frequency interference, which complicates the measurement process and can lead to inaccurate readings, especially in environments with ambient noise or physical shocks.
Innovation Solution
A method and apparatus that utilize a conductor with a magnetic field to induce vibrations in a fluid medium, incorporating a phase lock loop and a DC and low-frequency integrator to correct for amplifier-induced DC offset and low-frequency noise, allowing for accurate measurement of fluid properties by adjusting the current waveform frequency and using a sensor to detect phase relationships.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a simple high pass filter is introduced to filter out DC offset from the amplifier, then the DC offset is reduced, but transients from switching excitation and sensing periods are amplified by the filter
Solution Approach 1:
The patent divides the measurement process into distinct excitation periods and sensing periods, allowing different processing to be applied to each. During excitation periods, the system can tolerate transient effects, while during sensing periods, the integrator accumulates only the steady-state signal, effectively separating the harmful transients from the useful measurement data.
Solution Approach 2:
The patent applies preliminary action by using the integrator to accumulate signal during excitation periods before the actual sensing begins. This preliminary accumulation allows the system to prepare the signal in a way that filters out DC offset while maintaining the ability to reject transient interference when needed.
2Measurement precision
If the excitation frequency is adjusted to compensate for DC offset, then measurement accuracy improves, but the system becomes more complex and requires additional processing iterations
Solution Approach 1:
The patent implements self-service by using the phase-locked loop to automatically adjust the excitation frequency based on the measured phase difference between the excitation signal and the sensor output. The system self-corrects for DC offset effects without requiring external intervention or complex manual calibration procedures, reducing operational complexity while maintaining high accuracy.
Solution Approach 2:
The patent employs feedback by continuously monitoring the phase difference between the excitation signal and the sensor output, then using this information to adjust the excitation frequency. This closed-loop feedback mechanism automatically compensates for DC offset and other frequency drift effects, improving measurement accuracy while keeping the control logic relatively simple.
3Measurement precision
If the integrator time constant is increased to better filter DC offset, then DC correction improves, but the system responds more slowly to frequency changes
Solution Approach 1:
The patent applies dynamics by making the integrator time constant adjustable rather than fixed. The system can dynamically adapt the time constant based on the measurement conditions - using a longer time constant when DC offset is the primary concern and a shorter time constant when rapid frequency tracking is needed, thus optimizing performance for each specific application scenario.
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
The solution effectively reduces the amplitude of erroneous DC signals and low-frequency vibrations, enabling precise measurement of fluid properties, including viscosity, density, and elasticity, while using less expensive components and reducing system complexity.
Implementation Method 1
A current waveform, having a frequency, is periodically passed through the conductor, so as to cause the conductor to move, due to force exerted on the conductor from interaction of the current and the magnetic field
Implementation Method 2
The phase relationship between the current waveform and the amplified sense signal is measured and the current waveform frequency is adjusted so as to create a phase lock loop
Data Source
AI summary
A method of measuring properties of a fluid that uses a conductor electrically connected to a current source. A magnetic field is created about the conductor and the conductor is introduced into the fluid medium. A current waveform, having a frequency, is periodically passed through the conductor, so as to cause the conductor to move, due to force exerted on the conductor from interaction of the current and the magnetic field. The conductor movement is sensed, producing a sense signal that is amplified into an amplified sense signal. The phase relationship between the current waveform and the amplified sense signal is measured and the current waveform frequency is adjusted to create a phase lock loop. The frequency when the phase lock loop is in lock state is measured as the phase between the excitation and the measured sense signal is varied, and fluid properties are calculated from the measured frequencies.