Ultrasonic Flow Meter Digital Signal Processing for Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ultrasonic fluid velocity measurement techniques face challenges in accuracy and cost due to limitations in analog processing and variability in ultrasonic signal velocity, which affects the measurement of fluid velocity in pipes.
Innovation Solution
A method involving the sampling and cross-correlation of ultrasonic signals to calculate the differential time of flight (ΔTOF) using advanced signal processing techniques, including parabolic interpolation and cross-correlation, to improve measurement accuracy and reduce errors associated with sampling and transducer mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog processing is used for ultrasonic signal measurement, then device complexity is reduced, but measurement precision deteriorates due to limitations in analog processing and variability in ultrasonic signal velocity
Solution Approach 1:
The patent replaces analog signal processing with digital signal processing. Specifically, ultrasonic signals are captured by transducers and processed through digital signal processing techniques including cross-correlation algorithms and parabolic interpolation methods to determine time of flight measurements. This substitution of digital for analog processing resolves the contradiction by providing superior measurement precision through computational methods while maintaining manageable device complexity through standard digital processing components.
Solution Approach 2:
The patent changes the processing parameter from analog domain to digital domain. By converting ultrasonic signals to digital form and applying digital signal processing techniques, the system achieves higher measurement precision. The digital approach allows for flexible parameter adjustment including sampling rates, correlation window sizes, and interpolation coefficients, enabling optimization of measurement accuracy without proportionally increasing device complexity.
2Measurement precision
If temperature compensation is implemented to account for ultrasonic signal velocity variability, then measurement precision improves, but device complexity and cost increase due to additional temperature sensors and compensation circuits
Solution Approach 1:
The patent implements self-service temperature compensation where the system uses its own ultrasonic signal measurements to compensate for temperature effects. By measuring the speed of sound through cross-correlation of upstream and downstream signals, the system automatically compensates for temperature variability without requiring separate temperature sensors or external compensation devices. This resolves the contradiction by achieving temperature compensation through the measurement process itself, maintaining measurement precision while avoiding additional device complexity.
Solution Approach 2:
The patent uses the ultrasonic signal itself as an intermediary to compensate for temperature effects. Rather than using a separate temperature sensor as an intermediary, the system leverages the ultrasonic waves traveling through the fluid to carry temperature information. By comparing upstream and downstream travel times, the system extracts temperature-compensated flow velocity data, eliminating the need for additional temperature measurement components.
3Measurement precision
If cross-correlation and parabolic interpolation techniques are used to calculate differential time of flight, then measurement precision improves, but device complexity increases due to advanced signal processing requirements
Solution Approach 1:
The patent segments the signal processing into distinct modular steps: (1) capturing upstream and downstream ultrasonic signals, (2) applying cross-correlation to determine initial time differences, (3) using parabolic interpolation to refine the time of flight measurements, and (4) calculating differential time of flight. This segmentation of the processing algorithm into discrete, manageable stages resolves the contradiction by making the complex signal processing systematic and implementable through standard digital signal processing components, thereby achieving high measurement precision without excessive device complexity.
Solution Approach 2:
The patent applies preliminary cross-correlation processing to the ultrasonic signals before performing the final differential time of flight calculation. By pre-processing the signals through cross-correlation to identify peak alignments and estimate time differences, the system prepares refined input data for the subsequent parabolic interpolation step. This preliminary action resolves the contradiction by breaking down the complex measurement task into preparatory and final computation stages, making the overall process more manageable while achieving superior measurement precision.
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 of fluid velocity measurement by reducing measurement errors and system noise, thereby improving the overall precision and cost-effectiveness of ultrasonic fluid flow measurement systems.
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 sampling a first ultrasonic signal (r21) to produce a first sampled signal (y1(i)) and sampling a second ultrasonic signal (r12) to produce a second sampled signal (y2(i)). A first time (LEAD_LAG) is determined between a time the first sampled signal crosses a threshold (θ1) and a time the second sampled signal crosses the threshold. The first sampled signal is cross correlated with the second sampled signal to produce a second time (SAMP_OFFSET). The time difference is calculated in response to the first and second times.