Flow Velocity Measurement Using Pressure Fluctuation Analysis
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Solution Overview
Problem
The accuracy of flow velocity and mass flow measurements using differential pressure methods is limited by measurement errors such as temperature drift, mechanical stresses, and non-linearities in sensors, leading to significant errors, especially at small flow rates and high pressure losses, which are common in applications like air mass measurement in internal combustion engines.
Innovation Solution
The method involves measuring continuous reference values in a measuring tube with a narrowed section, determining reference value fluctuations through mathematical functions or signal analysis, and using these fluctuations to calculate the absolute flow rate, which is independent of offset drifts and other influencing variables, allowing for improved accuracy by correlating statistical variables with flow velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential pressure measurement is used to determine flow velocity, then flow rate can be measured, but measurement accuracy deteriorates due to offset drift and sensor errors
Solution Approach 1:
The system continuously monitors the differential pressure signal and uses feedback mechanisms to distinguish between actual flow velocity variations and sensor offset drift. By analyzing the temporal characteristics and statistical properties of the signal, the system can separate genuine flow information from sensor artifacts, thereby maintaining measurement accuracy despite sensor unreliability.
Solution Approach 2:
The patent replaces direct mechanical differential pressure measurement with a signal processing approach that uses statistical analysis and mathematical functions to extract flow velocity information. Instead of relying solely on the mechanical sensor output, the system uses computational methods to process the signal, substituting mechanical measurement with informational processing to overcome sensor limitations.
2Measurement precision
If throttle device is installed to create pressure difference, then flow rate can be determined, but permanent pressure loss increases
Solution Approach 1:
The system uses a minimized throttle device that creates only the necessary pressure difference for measurement, rather than a full-scale throttle. By applying partial action (small pressure difference) and using sophisticated signal processing to extract accurate flow information, the system achieves measurement precision without the excessive pressure loss that would result from a traditional throttle device.
3Adaptability or versatility
If smallest effective pressures are measured at low flow rates, then measurement range expands, but measurement accuracy deteriorates due to sensor uncertainty
Solution Approach 1:
The patent transitions from measuring absolute pressure values to measuring pressure fluctuations and statistical characteristics (standard deviation, variance, frequency). By moving to another dimension of analysis - the temporal and statistical properties of the signal rather than the absolute magnitude - the system can accurately measure low flow rates where absolute pressure differences are small, as the fluctuation patterns remain detectable and characteristic.
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 measurement accuracy by isolating the influence of offset drifts and other errors, enabling precise determination of flow rates even at low flow velocities and reducing the impact of sensor noise, thus extending the applicability to smaller flow rates and reducing permanent pressure losses.
Implementation Method 1
The measuring principle is based on the installation of the throttle device (e.g. an orifice plate, a nozzle or a Venturi tube) in a pipeline through which the flow is full. The installation of the throttle device creates a Difference in static pressure between the plus pressure tapping in the inlet and the minus pressure tapping in the narrowest throttle cross-section or in the outlet.
Implementation Method 2
A known method in this regard is the vortex/eddy counting method. For this purpose, a bluff body is placed in a stirring piece. which causes a vortex to form in the flow (Karmann vortex street). As a result, periodic vortices are released. The shedding frequency of the vortices is a measure of the flow velocity.
Data Source
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AI summary
The method involves measuring continuous reference values, where each individual reference value is in a direct physical relationship to the flow rate. Reference value fluctuations are determined, and absolute flow rate (Va) is calculated or mapped as a function of a numerical and/or statistic evaluation of the reference value fluctuations for generating a fluctuation value selected from amplitude, a standard deviation, and a variance of the reference value fluctuations. Existence of flow is checked by comparison of the reference value fluctuations with a limit value. An independent claim is also included for a measuring device.