Magnetic-inductive Flowmeter Admittance Empty Tube Detection
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Solution Overview
Problem
Magnetic-inductive flowmeters face challenges in accurately measuring flow rates in partially filled tubes due to measurement errors caused by varying liquid levels and conductivity, and are influenced by thin liquid films and conductive adhesions, making it difficult to distinguish between adequate and inadequate filling levels.
Innovation Solution
The implementation of an admittance measuring device with a detector, counter-electrode, and ac signal source operating at frequencies between 50 MHz and 200 MHz, which uses planiform electrodes and a capacitance-based measurement principle to determine liquid levels independently of conductivity, and is designed to differentiate between complete and partial filling, including adhesions and air bubbles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional electromagnetic induction measurement is used in partially filled tubes, then flow rate measurement is possible, but measurement errors occur due to varying liquid levels and conductivity
Solution Approach 1:
The patent introduces an intermediary capacitance measurement system that indirectly detects liquid level and filling conditions. Instead of directly measuring flow in partially filled tubes with electrodes, a capacitor formed by the measuring tube wall and conducting layer serves as a mediator to detect filling level, which then enables correction of flow measurements.
Solution Approach 2:
The patent replaces direct electromagnetic induction measurement with capacitance-based detection for liquid level sensing. The capacitance measurement system substitutes for direct flow measurement in partially filled conditions, providing indirect but more accurate detection of filling level that can then be used to correct flow measurements.
2Productivity
If measuring electrodes are used to detect flow rate, then flow measurement is enabled, but detection of thin liquid films and conductive adhesions becomes difficult
Solution Approach 1:
The patent replaces direct electrode-based flow measurement with capacitance measurement for detecting liquid films and adhesions. The capacitance sensor can detect thin conducting layers on the tube wall that would be invisible to conventional flow measurement electrodes, enabling detection of these problematic conditions.
Solution Approach 2:
The patent changes the measurement parameter from direct voltage measurement (electromagnetic induction) to capacitance measurement. This parameter change enables detection of thin liquid films and conductive adhesions that do not significantly affect electromagnetic induction but do affect capacitance between the tube wall and conducting layer.
3Measurement precision
If correction values based on conductivity are used, then measurement accuracy in partially filled tubes improves, but dependence on medium conductivity increases
Solution Approach 1:
The patent substitutes capacitance measurement for conductivity-based correction methods. Instead of using conductivity variations to determine filling level and apply corrections, the capacitance sensor directly measures the filling level and adhesion conditions, providing correction information that is independent of the medium's conductivity properties.
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 solution allows for reliable detection of empty tubes and accurate measurement of liquid levels, reducing measurement errors and enabling precise determination of flow rates even in partially filled conditions, with minimal influence from conductivity changes or surface adhesions.
Implementation Method 1
the electrode of the detector and the counter-electrode, which are made planiform, are located essentially opposite one another on the outer surface of the measuring tube... an admittance measuring device with a detector, a counter-electrode, an ac signal source and an evaluation unit, wherein the detector has an electrode which is connected to the ac signal source
Implementation Method 2
a magnetic field generating apparatus for generating an especially changing magnetic field which permeates the measuring tube essentially perpendicular to the longitudinal axis of the measuring tube... two measuring electrodes which are especially conductively coupled to the medium for tapping a measuring-circuit voltage which has been induced in the flowing medium
Data Source
AI summary
A magnetic-inductive flowmeter with a nonconductive measuring tube, a magnetic field generating apparatus, two measuring electrodes conductively coupled to the medium for tapping a measuring-circuit voltage induced in the flowing medium, and with a measuring device for detecting an empty tube. Detection of an empty tube is obtained by the measuring device being an admittance measuring device having a detector, a counter-electrode, an ac signal source and an evaluation unit, the detector having an electrode connected to the ac signal source so that the electrode is exposed to an ac signal in the range of roughly 50 MHz-200 MHz and then an electrical field extends from the electrode into the medium. The electrode of the detector and the counter-electrode planiform shaped and are located essentially opposite one another on the outer surface of the measuring tube above and underneath the longitudinal axis of the measuring tube, respectively.