Electromagnetic Flow Meter Conductivity Measurement
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Solution Overview
Problem
Capacitive type electromagnetic flow meters face challenges in measurement precision and stability due to increased impedance between fluid and electrodes, leading to interference between magnetic excitation current and AC signal, and difficulty in miniaturization when combined with electrical conductivity measurement functions.
Innovation Solution
The design incorporates a non-contact electrode with a high-frequency AC signal and a contact electrode connected to common potential, using filters to attenuate interfering frequency components, allowing for separate frequency bands for flow rate and conductivity measurements, reducing electrode count, and incorporating a shield cover to minimize noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If capacitive type electromagnetic flow meter is used to avoid electrode deterioration, then ease of maintenance is improved, but measurement precision and stability deteriorate due to increased impedance between fluid and electrodes
Solution Approach 1:
The patent segments the electrode system into multiple electrodes (first electrode, second electrode, third electrode) with distinct functions. The first and second electrodes measure flow rate, while the third electrode measures electrical conductivity. This segmentation allows each electrode to be optimized for its specific function, improving measurement precision while maintaining the capacitive type's maintenance advantages.
Solution Approach 2:
The patent introduces a shield cover as an intermediary element between the electrodes and the external environment. The shield cover reduces noise interference and stabilizes the electrical field, thereby improving measurement precision without requiring direct contact between electrodes and fluid, maintaining the maintenance-free advantage of capacitive type meters.
2Reliability
If frequency of magnetic excitation current is increased to reduce noise interference, then measurement stability is improved, but mutual interference between magnetic excitation current and AC signal increases when conductivity measurement is added
Solution Approach 1:
The patent employs periodic action by using different frequencies for magnetic excitation current and AC signal for conductivity measurement. The magnetic excitation current operates at one frequency while the AC signal operates at another frequency, allowing both measurements to be performed periodically without mutual interference. This frequency separation enables stable flow rate measurement and accurate conductivity measurement simultaneously.
3Adaptability or versatility
If multiple electrodes are added to enable conductivity measurement function, then versatility is improved, but device complexity and difficulty in miniaturization increase
Solution Approach 1:
The patent applies universality by designing the third electrode to serve dual purposes: it functions as an electrode for electrical conductivity measurement and simultaneously serves as a reference electrode for the capacitive measurement system. This multi-functionality reduces the total number of electrodes needed while maintaining both flow rate and conductivity measurement capabilities.
Solution Approach 2:
The patent merges the conductivity measurement function with the existing electrode structure. The third electrode is integrated into the measurement tube wall, combining the conductivity sensing function with the structural component, thereby reducing device complexity and facilitating miniaturization while maintaining versatility.
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 configuration enhances measurement precision and stability while enabling miniaturization and reducing manufacturing costs by preventing interference and minimizing errors from electrode adhesion or corrosion.
Implementation Method 1
a magnetic excitation coil (Lex) disposed outside the measurement tube for generating a magnetic field according to a supplied AC current (Iex)
Implementation Method 2
measures an electromotive force generated between the electrodes while alternately switching a polarity of an magnetic excitation current flowing to the magnetic excitation coil to measure a flow rate of a fluid
Implementation Method 3
a voltage detecting portion (5) that measures voltages of a signal generated in the third electrode (2) by inputting an AC signal to the other end of the resistor (R1)
Data Source
AI summary
An electromagnetic flow meter comprises a magnetic excitation coil, first and second electrodes which are disposed opposite to each other on an outer peripheral surface of a measurement tube, an amplifying circuit that amplifies an electromotive force generated between the first electrode and the second electrode, a flow rate calculation portion that calculates a flow rate of the fluid, a third electrode formed on the outer peripheral surface of the measurement tube separated from the first electrode and the second electrode, a fourth electrode which is in contact with the fluid, a resistor in which one end is connected to the third electrode, a voltage detecting portion that measures voltages of a signal generated in the third electrode by inputting an AC signal to the other end of the resistor, and an electrical conductivity calculating portion that calculates electrical conductivity of the fluid.