Capacitance Probe Foam Discrimination via Discharging Current
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Solution Overview
Problem
Conventional liquid level detection methods, especially those using capacitance changes, struggle to reliably distinguish between bulk liquid and foam, leading to potential pipetting errors in automated clinical analyzers, and high-frequency impedance measurements are costly and prone to electromagnetic interference.
Innovation Solution
A method and system utilizing a probe with electric capacitance that repeatedly charges and discharges to measure the discharging current, allowing for discrimination between bulk liquid and foam based on changes in electric resistance, enabling accurate positioning of the probe within the bulk liquid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capacitance change measurement is used for liquid level detection, then the detection method is simple and low-cost, but foam causes capacitance change similar to bulk liquid leading to unreliable discrimination
Solution Approach 1:
The patent changes the measurement parameter from capacitance to impedance by applying high-frequency voltage signals (1 MHz to 1 GHz). This parameter change enables reliable discrimination between foam and bulk liquid because foam exhibits different impedance characteristics at high frequencies compared to its capacitance behavior at low frequencies.
Solution Approach 2:
The patent employs periodic high-frequency voltage signals to repeatedly measure the impedance of the probe. By periodically charging and discharging the probe and measuring the discharging current, the system can distinguish foam from bulk liquid based on their different impedance responses to these periodic signals.
2Reliability
If high-frequency impedance measurement is used to discriminate foam from bulk liquid, then discrimination accuracy improves, but sophisticated equipment and high cost are required
Solution Approach 1:
The patent replaces complex mechanical foam detection systems with an electrical impedance measurement system. By using electrical signals to probe the sample and measuring the resulting current, the system achieves accurate foam discrimination without requiring sophisticated mechanical or optical equipment.
Solution Approach 2:
The patent utilizes the frequency-dependent impedance characteristics of foam and bulk liquid to achieve discrimination. By measuring impedance at high frequencies rather than using complex mechanical or optical systems, the patent simplifies the device while maintaining high discrimination accuracy.
3Reliability
If high-frequency voltage signals are applied for impedance measurement, then foam discrimination capability improves, but electric interference effects occur reducing electromagnetic compatibility
Solution Approach 1:
The patent uses periodic charging and discharging cycles with high-frequency voltage signals. By applying voltage periodically rather than continuously, the system reduces electromagnetic interference while maintaining the ability to measure impedance differences between foam and bulk liquid effectively.
Solution Approach 2:
The patent applies high-frequency voltage signals that rapidly charge and discharge the probe capacitance. This rapid cycling allows the measurement to be completed quickly, minimizing the time during which electromagnetic interference can occur, thus reducing overall interference effects.
4Reliability
If probe tip is positioned just below liquid surface for pipetting, then cross-contamination is minimized and cleaning is facilitated, but reliable liquid level detection is required which is compromised by foam
Solution Approach 1:
The patent implements feedback-based liquid level detection by continuously measuring impedance changes as the probe approaches and enters the liquid. The system uses the measured impedance signal to provide feedback on probe position, enabling automatic adjustment to maintain the probe tip just below the liquid surface despite the presence of foam.
Solution Approach 2:
The patent replaces mechanical or optical liquid level detection methods with electrical impedance measurement. This substitution enables accurate liquid level detection through foam by measuring the electrical properties of the liquid, which differ significantly from foam, thus allowing precise probe positioning for contamination-free pipetting.
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 allows for reliable discrimination between bulk liquid and foam, reducing pipetting errors and improving the accuracy of liquid volume extraction by using the distinct electric resistances of bulk liquid, foam, and residuals, even in the presence of foam on the liquid surface or on the vessel walls.
Implementation Method 1
A method and system utilizing a probe with electric capacitance that repeatedly charges and discharges to measure the discharging current
Implementation Method 2
allowing for discrimination between bulk liquid and foam based on changes in electric resistance, enabling accurate positioning of the probe within the bulk liquid
Data Source
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AI summary
The present invention pertains to method for discriminating bulk liquid from foam and/or residuals of said bulk liquid of a sample contained in a sample vessel, comprising the following steps: providing a probe having an electric capacitance; moving said probe into said sample; repeatedly performing a pair of consecutive steps of charging and at least partially discharging said probe to generate a discharging current; measuring a quantity indicative of said discharging current for each pair of consecutive steps of charging and at least partially discharging said probe; analyzing said quantity in a manner to determine an electric resistance (Rmess) of said sample via said probe; discriminating said bulk liquid from said foam and/or said residuals of said bulk liquid based on a change of said electric resistance (Rmess) of said sample occuring when said probe contacts said bulk liquid. It further pertains to an automated system for discriminating bulk liquid from foam and/or residuals of said bulk liquid of a sample contained in a sample vessel.