Ultrasonic Flow Meter Transit Time Determination
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Solution Overview
Problem
The accuracy of transit time measurement in ultrasonic flow meters is costly and dependent on indirect compensation of sound speed variations, necessitating a method to reliably determine transit time with low costs and independence from receive signal amplitudes.
Innovation Solution
The method involves using two transmit signals of different frequencies to generate receive signals with characteristics used to determine transit time, where time differences are calculated using a function that includes pairs of time differences and times, with zero crossings or their equivalents being used to simplify the measurement, avoiding the need for separate trigger circuits and being insensitive to signal shape changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high accuracy equipment is used to determine transit time, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent uses two transmit signals with different frequencies to create receive signals with different characteristics. By analyzing the time differences between corresponding characteristics (such as zero crossings) of these signals, the system determines transit time through mathematical relationships rather than requiring expensive high-precision timing equipment. This changes the measurement approach from direct high-precision timing to frequency-based differential measurement.
2Device complexity
If indirect compensation methods are used for sound speed variations, then measurement complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent employs a feedback mechanism where the system measures the actual transit time using the two-frequency method, which inherently accounts for sound speed variations. The measured transit time directly reflects the current acoustic conditions without requiring separate temperature measurements or lookup tables, creating a self-correcting measurement system that adapts to changing sound speeds.
3Object-affected harmful factors
If zero crossings are used as the characteristic, then sensitivity to signal amplitude changes is reduced, but measurement precision requirements increase
Solution Approach 1:
The patent uses zero crossings as an intermediary characteristic that is less sensitive to amplitude variations and noise. By focusing on the timing of zero crossings rather than absolute amplitude values, the system creates a more robust measurement that is insensitive to signal strength fluctuations. The differential measurement approach further filters out common-mode noise affecting both signals.
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 allows for accurate transit time determination with reduced costs, as it directly compensates for sound speed variations and is less sensitive to noise and signal amplitude changes, making it a cost-effective solution for ultrasonic flow meters.
Implementation Method 1
The transit times of sound bursts transmitted upstream and downstream, between two transducers placed oppositely in a flow tube are measured
Implementation Method 2
The flow speed is directly proportional to the difference between the upstream transit time and the downstream transit time
Data Source
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AI summary
A method for determining a transit time (tt) of an ultrasonic burst, in particular in an ultrasonic flow meter is described, said method comprising generating a first transmit signal having a first frequency and detecting a first receive signal, generating a second transmit signal having a second frequency different from the first frequency and detecting a second receive signal. Such method should allow to reliably detect the transit time with low costs. To this end a function of time based on characteristics of the two receive signals (10, 11) is used for determining the transit time.