Ultrasonic Flow Meter Error Cancellation via Inverted Propagation
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Solution Overview
Problem
The propagation period difference method for measuring fluid flow velocity using ultrasonic waves is affected by variations in sound speed due to temperature and other physical quantities, leading to increased measurement errors over time.
Innovation Solution
A fluid measuring apparatus with ultrasonic wave transmitting and receiving means disposed upstream and downstream in a pipe, measuring both propagation periods and canceling errors by deriving flow velocities Va and Vb, allowing for high-precision measurement despite sound speed variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ultrasonic waves are transmitted and received multiple times to enhance S/N ratio, then measurement precision improves, but temperature variation affects speed of sound over prolonged measurement period, increasing measurement error
Solution Approach 1:
The patent applies inversion by measuring propagation periods in reverse order (downstream to upstream instead of upstream to downstream) for alternating measurements. This reverses the direction of ultrasonic wave propagation, causing errors from speed of sound variations to have opposite signs, which enables error cancellation when averaging multiple measurements.
Solution Approach 2:
The patent uses feedback by comparing propagation periods measured in opposite directions and using the difference to cancel systematic errors. The measurement system incorporates feedback loops that adjust based on the observed propagation period differences, allowing continuous correction of temperature-induced speed of sound variations.
2Measurement precision
If measurement period is prolonged to perform multiple measurements, then S/N ratio enhancement is achieved, but temperature variation accumulates, causing speed of sound to vary and increasing measurement error
Solution Approach 1:
By inverting the measurement direction alternately, the patent enables error cancellation within shorter measurement intervals. This allows multiple measurements to be performed more quickly without accumulating significant temperature variations, thus reducing the time loss while maintaining precision.
Solution Approach 2:
The patent employs periodic action by alternating between upstream-to-downstream and downstream-to-upstream measurements in a regular sequence. This periodic reversal of measurement direction creates a rhythm that systematically captures and cancels temperature drift effects, enabling precise measurements over extended periods without prolonged continuous measurement in one direction.
3Device complexity
If speed of sound in fluid is assumed constant for propagation period difference method, then calculation is simplified, but speed of sound actually varies due to temperature and other physical quantities, leading to measurement error
Solution Approach 1:
The patent maintains calculation simplicity while improving precision by using inversion of measurement direction. Instead of complicating the calculation to directly account for speed of sound variations, the method simply reverses the measurement direction alternately, allowing errors to cancel out mathematically while keeping the computational approach relatively simple.
Solution Approach 2:
The patent converts the harmful effect of speed of sound variation into a benefit by measuring in opposite directions. The temperature-induced speed of sound changes that would normally cause errors are transformed into a useful phenomenon where the errors in opposite directions have opposite signs, enabling cancellation and actually improving 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 signal-to-noise ratio and reduces measurement errors by opposing and canceling errors in flow velocity measurements, enabling precise fluid flow velocity measurement even with varying sound speeds.
Implementation Method 1
at least one pair of ultrasonic wave transmitting and receiving means which transmits and receives ultrasonic wave to and from a fluid flowing in a pipe
Implementation Method 2
a period measuring unit which measures the propagation period of ultrasonic wave transmitted and received by the ultrasonic wave transmitting and receiving means
Implementation Method 3
The method utilizes phenomenon in which when ultrasonic waves in one direction along flow of fluid and the other direction against the flow of the fluid are transmitted and received, difference in propagation periods of the ultrasonic waves in the two directions varies depending on flow velocity of the fluid
Data Source
AI summary
A fluid measuring apparatus, including a pair of ultrasonic wave probes in which one is disposed more upstream than the other, a processor, and a non-transitory storage medium containing program instructions therein. The execution of the program instructions by the processor causes the fluid measuring apparatus to provide functions of a period measuring unit that measures a first propagation period during which ultrasonic wave propagates from the one ultrasonic wave probe to the other, and a second propagation period during which ultrasonic wave propagates from the other ultrasonic wave probe to the one ultrasonic wave probe, and a flow velocity measuring unit that derives a flow velocity of the fluid by cancelling errors in a first flow velocity that is derived by measuring the second propagation period after measuring the first propagation period, and a second flow velocity that is derived by measuring the first propagation period after measuring the second propagation period.