Magnetic-Inductive Flowmeter Conductivity Determination
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Solution Overview
Problem
The accuracy of determining the conductivity of a medium using conductive measuring cells is dependent on the actual conductivity of the medium, leading to inconsistencies in measurement precision.
Innovation Solution
A method involving the generation of electrical signals at two distinct frequencies, with impedance and phase analysis to determine resistance, allowing for the use of alternative formulas based on phase ratios to calculate conductivity, thereby reducing dependence on medium conductivity for accurate measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single frequency signal is used to measure conductivity, then the measurement process is simple, but the accuracy of conductivity determination depends heavily on the actual conductivity of the medium
Solution Approach 1:
The patent applies periodic action by using signals with at least two different frequencies to excite the measuring cell. This multi-frequency periodic excitation allows the system to capture frequency-dependent impedance phase changes, enabling more accurate conductivity determination across varying medium conductivities without increasing structural complexity
Solution Approach 2:
The patent changes the frequency parameter of the excitation signal to resolve the technical contradiction. By measuring impedance phase at multiple frequencies and detecting the phase difference, the system achieves accurate conductivity determination independent of the medium's actual conductivity value, while maintaining a relatively simple measurement apparatus
2Measurement precision
If impedance phase analysis at multiple frequencies is performed, then conductivity determination accuracy is improved, but the measurement process becomes more complex
Solution Approach 1:
The patent employs feedback by using the detected impedance phase difference at different frequencies to select the appropriate evaluation formula. The system measures the phase difference, compares it against predetermined thresholds, and automatically selects the corresponding conductivity calculation formula, simplifying the operational process while maintaining high measurement precision
Solution Approach 2:
The measurement system performs self-service by automatically selecting the appropriate evaluation formula based on the measured impedance phase difference. The system self-adjusts the conductivity calculation method according to the detected phase characteristics, eliminating the need for manual intervention and maintaining measurement simplicity
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 precision of conductivity determination by accounting for frequency-dependent impedance phase changes, improving measurement accuracy across varying medium conductivities.
Implementation Method 1
The measuring cell has a cell constant, a first electrode, and a second electrode. The first and second electrodes are in direct contact with the medium. Therefore, the measuring cell is a conductive measuring cell.
Implementation Method 2
In one step, a first voltage (U 1 ) between the first and the second electrode and a first current (I 1 ) through the medium for the first frequency of the signal and a first impedance (Z 1 ) from the first voltage and the first current are determined.
Implementation Method 3
A magnetic-inductive flowmeter measures the flow of a medium through the measuring tube. For this to happen, the medium must be electrically conductive. A magnetic-inductive flowmeter typically has an electromagnet configured in such a way that a magnetic field generated by it at least partially penetrates the medium in the measuring tube, and the flow of the medium in the measuring tube induces a voltage in the medium.
Data Source
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AI summary
A method for determining the conductivity (σ) of a medium (7) is presented and described, comprising a controller (2) and a measuring cell (15), wherein the measuring cell (15) has a cell constant (k), a first electrode (4), and a second electrode (5), and wherein the first electrode (4) and the second electrode (5) are in direct contact with the medium (7). The invention solves the problem of reducing the dependence of the accuracy of the determination of the conductivity (σ) of a medium (7) on the actual conductivity of the medium (7). This problem is solved by the controller (2) performing the following steps: - Generating a signal (S) with a first frequency (f1) and a second frequency (f2) and injecting the signal (S) into the first electrode (4) and the second electrode (5).- Determine a first voltage (U1) between the first electrode (4) and the second electrode (5) and a first current (I1) through the medium (7) for the first frequency (f1) of the signal (S) and a first impedance (Z1) from the first voltage (U1) and the first current (I1), - Determine a second voltage (U2) between the first electrode (4) and the second electrode (5) and a second current (I2) through the medium (7) for the second frequency (f2) of the signal (S) and a second impedance (Z2) from the second voltage (U2) and the second current (U2), - Determine and compare a phase (ϕ1) of the first impedance (Z1) with a phase (ϕ2) of the second impedance (Z2), - Determine, if the phase (ϕ1) of the first impedance (Z1) is smaller than the phase (ϕ2) of the second impedance (Z2), a resistance (R) of the medium (7) determine according to a first formula R=ReZ2−ImZ2⋅ReZ2−ReZ1ImZ2−ImZ1, -if the phase (ϕ1) of the first impedance (Z1) is equal to or greater than the phase (ϕ2) of the second impedance (Z2), the resistance (R) can be determined according to a second formula R=Z1cosϕ1 and a conductivity (σ) of the medium (7) can be determined using the resistance (R) and the cell constant (k).