Ultrasonic Flow Meter Digital Signal Processing
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Solution Overview
Problem
Current ultrasonic fluid velocity measurement techniques are limited by cost and accuracy, particularly in determining fluid velocity in pipes using analog processing methods that require precise measurement of ultrasonic propagation times and are sensitive to temperature variations and transducer mismatches.
Innovation Solution
A method involving the calculation of differential time of flight (ΔTOF) using sampled ultrasonic signals from transducers, employing threshold selection, parabolic or linear interpolation to determine alignment points, and averaging to improve accuracy and reduce measurement errors due to sampling and transducer mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If analog processing methods are used for ultrasonic signal measurement, then the system cost is reduced, but the measurement precision and accuracy deteriorate
Solution Approach 1:
The patent replaces analog processing methods with digital signal processing using an ADC (analog-to-digital converter) and microcontroller. This substitution enables more accurate measurement of time of flight differences through digital correlation algorithms, resolving the contradiction by achieving both acceptable cost and improved measurement precision through digital rather than purely analog processing.
Solution Approach 2:
The patent changes the processing approach from analog domain to digital domain by sampling ultrasonic signals at specific rates and processing them digitally. This parameter change allows for more precise measurement of propagation times and fluid velocity while maintaining cost-effectiveness through efficient digital algorithms.
2Measurement precision
If temperature compensation is implemented, then the measurement accuracy is improved, but the system cost increases
Solution Approach 1:
The patent implements self-service temperature compensation by measuring the temperature of the ultrasonic signals themselves and using this information to compensate for temperature effects on sound velocity. The system uses the ultrasonic signals' own temperature characteristics to correct measurements, eliminating the need for separate expensive temperature sensors while maintaining accuracy.
Solution Approach 2:
The patent replaces physical temperature sensors with digital temperature measurement and compensation algorithms. By measuring temperature electronically and compensating through software calculations, the system achieves temperature compensation without adding expensive hardware components.
3Measurement precision
If high-resolution ADC sampling is used, then the measurement precision is improved, but the system cost and complexity increase
Solution Approach 1:
The patent applies partial action by using correlation algorithms that process only the essential features of the ultrasonic signals needed for time of flight measurement. Rather than processing entire high-resolution waveforms, the system extracts and processes only the critical timing information, achieving good measurement precision with reduced computational complexity.
Solution Approach 2:
The patent optimizes the sampling rate parameter to achieve the minimum necessary resolution for accurate time of flight measurement. By carefully selecting the ADC sampling rate and correlation window parameters, the system achieves sufficient measurement precision without the excessive complexity and cost of ultra-high-resolution sampling.
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 approach enhances the accuracy and cost-effectiveness of fluid velocity measurement by reducing measurement errors and system noise, providing a more reliable method for determining fluid flow in pipes.
Implementation Method 1
Two ultrasonic transducers UT1 and UT2 are mounted inside a pipe 100
Implementation Method 2
Propagation time t12 or time of flight (TOF) is the time for an ultrasonic signal to travel from UT1 to UT2 within the fluid
Implementation Method 3
If C is the velocity of the ultrasonic signal in the fluid and V is the velocity of the fluid in pipe 100, these propagation times are given by equations [1] and [2]
Data Source
AI summary
A method of calculating a time difference is disclosed. The method includes receiving a first ultrasonic signal (r21) from a first transducer (UT1) and receiving a second ultrasonic signal (r12) from a second ultrasonic transducer (UT2). The first and second ultrasonic signals are sampled to produce respective first and second sampled ultrasonic signals (502). Points having a value greater than a first threshold are selected from the first and second sampled ultrasonic signals (510). A difference in travel time between the first and second ultrasonic signals is calculated (512) in response to the selected points.