Impedance Sensor Detecting Deposit Type in Liquid Media
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Solution Overview
Problem
Existing methods for detecting and measuring deposit layers on surfaces in contact with liquids, such as those in water pipelines and heat exchangers, cannot distinguish between inorganic and biological deposits, leading to ineffective intervention or treatment.
Innovation Solution
A method using a pair of electrodes positioned on the surface, sending a signal frequency higher than the zero frequency determined by the double-layer capacitance and liquid resistance, allowing for the measurement of the resistive impedance to discern between inorganic and biological deposits by observing the inverse behavior of resistivity with thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capacitance measurement is used to detect deposit layer thickness, then the measurement is simple and cost-effective, but the method cannot distinguish between different types of deposits (scale vs. biofilm)
Solution Approach 1:
The patent changes the measurement parameter from capacitance (which cannot distinguish deposit types) to impedance measurement at multiple frequencies. By measuring impedance at both low frequency (where capacitive effects dominate) and high frequency (where resistive effects dominate), the system can differentiate between scale and biofilm based on their distinct electrical properties, while maintaining measurement simplicity
2Measurement precision
If refractive index measurement is used to detect scale layer thickness, then real-time measurement is achieved, but the instrumentation is costly and cannot distinguish between scale and other deposit types
Solution Approach 1:
The patent replaces the optical measurement system (refractometer) with an electrical measurement system (impedance sensor). This substitution maintains real-time measurement capability while significantly reducing instrumentation cost and enabling deposit type discrimination through frequency-dependent impedance measurements that reveal different electrical characteristics of scale versus biofilm
3Ease of operation
If thermal conductivity measurement is used to detect scale layer, then the measurement is straightforward, but the method cannot distinguish between scale and other types of layers
Solution Approach 1:
The patent changes from single-parameter thermal conductivity measurement to multi-parameter electrical impedance measurement at different frequencies. This allows the system to maintain ease of operation while extracting multiple pieces of information (deposit thickness and deposit type) from the frequency-dependent impedance response, since scale and biofilm exhibit different resistive and capacitive behaviors
4Measurement precision
If low frequency impedance measurement is used to detect biofilm growth, then the capacitive part can be detected, but the sensor is not suitable for dynamic environments with flowing liquid and cannot directly measure layers in contact with the electrode
Solution Approach 1:
The patent implements a dynamic measurement approach by using multiple frequency points (low and high frequency) within the same measurement cycle. This allows the system to adapt to dynamic environments with flowing liquid, as the high frequency measurement captures the resistive properties of deposits in direct contact with the electrode, while the low frequency measurement provides biofilm-specific capacitive information, making the sensor versatile for both static and dynamic conditions
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
Enables targeted intervention by accurately measuring the thickness and nature of deposits, allowing for appropriate chemical treatment, such as acid release for inorganic or disinfectant release for biological layers, improving maintenance and reducing operational costs.
Implementation Method 1
sensing the impedance between the at least one pair of electrodes, wherein the signal frequency is chosen so as to measure the resistive part of the impedance
Implementation Method 2
the signal frequency being greater than or equal to the zero frequency given by the double layer capacitance and by the resistance of the liquid medium
Data Source
Figure 1~2
Figure 3
Figure 4a~4b
AI summary
The present invention relates to a method (100) for detecting and measuring a layer deposited on a surface in contact with a liquid medium, able to discern the nature of the deposit, comprising the steps that consist of positioning at least one pair of electrodes (11) arranged at a mutual distance (D) on the surface in contact with a liquid medium; sending to the at least one pair of electrodes (11) a signal having signal frequency (f); and detecting the impedance (Z) between the at least one pair of electrodes (11) and it is characterised in that the signal frequency (f) is selected in such a way as to measure the resistive component of the impedance (z), the signal frequency (f) being greater than or equal to the zero frequency (f0) given by the double layer capacitance (CDL) and by the resistance (RSOL) of the liquid medium in which the measurement takes place.