Magnetic-Inductive Flow Meter Filtering for Zero-Point Error Reduction
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Solution Overview
Problem
Magnetic-inductive flow meters experience zero-point errors due to parasitic effects during transitions between alternating magnetic field strengths, leading to inaccuracies in flow rate determination.
Innovation Solution
The method involves averaging and normalizing measurements, filtering out parasitic effects by subtracting averaged measurement points, and using pseudo-flow values to determine flow rate, while considering the direction of the magnetic field to correct flow direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If alternating magnetic field strengths are used for measurement, then measurement capability is improved, but zero-point errors occur due to parasitic effects during transitions
Solution Approach 1:
The control unit discards initial measurement points at the beginning of each sub-interval where parasitic effects are still present. This preliminary filtering action removes corrupted data before averaging, preventing zero-point errors from affecting the final flow rate calculation while maintaining the benefits of alternating magnetic field measurement
Solution Approach 2:
The control unit continuously monitors measurement points during transitions and dynamically adjusts which points are included in the averaging calculation. By providing feedback on the presence of parasitic effects and adjusting the measurement window accordingly, the system maintains accurate flow rate determination while operating with alternating magnetic field strengths
2Productivity
If measurement points are taken during transitions between magnetic field strengths, then measurement frequency is improved, but parasitic effects cause measurement errors
Solution Approach 1:
The measurement process is segmented into distinct phases: transition phases where parasitic effects occur and steady-state phases where accurate measurements are taken. By segmenting the measurement intervals and selectively using only steady-state measurement points for calculation, the system achieves both high measurement frequency and high accuracy
Solution Approach 2:
The control unit uses the known timing and characteristics of parasitic effects during transitions to its advantage. By deliberately excluding measurement points taken during transition periods and only averaging points from stable measurement phases, the system converts the predictable harmful effect into a manageable parameter that does not compromise measurement accuracy
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
Reduces zero-point errors and improves the accuracy of flow rate determination by mitigating parasitic effects, ensuring precise measurement and control of fluid flow.
Implementation Method 1
the magnetic field generator generates a magnetic field that alternates between a first target magnetic field strength in the first sub-intervals and a second target magnetic field strength in the second sub-intervals. This induces a measuring voltage between the two measuring electrodes into the medium flowing in the measuring tube
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
A method for determining the flow rate of a medium (10) using a magnetic-inductive flowmeter (2, 17) is presented and described. The flowmeter (2, 17) comprises a measuring tube (7), a magnetic field generator (8), two measuring electrodes (9), and a control unit (4, 18), and a medium (10) flows through the measuring tube (7). The method reduces the zero-point error of the flow rate. For this purpose, intervals (12) with first sub-intervals (13) and second sub-intervals (14) are generated by the control unit (4, 18) and a magnetic field (15) alternating between a first target magnetic field strength (B1) in the first sub-intervals (13) and a second target magnetic field strength (B2) in the second sub-intervals (14) is generated by the magnetic field generator (8), so that a measuring voltage (u) applied between the two measuring electrodes (9) is induced in the medium (10) flowing in the measuring tube (7).Furthermore, in each of a number of measurements (N) of the intervals (12), the controller (4, 18) performs a first measurement (an) with a number of measurement points (M) of the measured voltage (u) in the first sub-intervals (13) and a second measurement (dn) with a number of measurement points (M) of the measured voltage (u) in the second sub-intervals (14), wherein the controller (4, 18) performs the following procedure steps at least for one of the intervals (12): - Determining an averaged first measurement ( a→‾) with a last averaged measurement point (aM) from several of the first measurements and determining an averaged second measurement ( d→‾) with a last averaged measurement point (dM) from several of the second measurements.- Determining a normalized first measurement (bn) by subtracting the last averaged measurement point of the averaged first measurement from the averaged first measurement, and determining a normalized second measurement (en) by subtracting the last averaged measurement point of the averaged second measurement from the averaged second measurement. - Determining a filtered first measurement (cn) by subtracting the normalized first measurement from the first measurement, and determining a filtered second measurement (ƒn) by subtracting the normalized second measurement from the second measurement. Furthermore, the controller (4, 18) determines the flow rate of the medium (10) through the measuring tube (7) using the filtered first measurements (cn) and the filtered second measurements (ƒn) determined for at least one interval (12).