Pipette Tip Capacitance Sensing for Accurate Liquid Contact Detection
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Solution Overview
Problem
Existing automated laboratory systems face challenges in reliably detecting the contact of a pipette tip with a liquid surface due to interference from different sample liquids and labware, especially in systems with densely spaced measurement channels, leading to inaccurate and delayed detection.
Innovation Solution
A method and device that measure absolute capacitance between the pipette tip and a reference potential, using techniques like median filtering, down sampling, and predictive signal processing to distinguish between capacitance changes caused by liquid contact and electrostatic discharges, ensuring rapid and accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If relative capacitance measurement is used to detect liquid contact, then sensitivity can be achieved, but measurement precision deteriorates due to influence from different sample liquids, labware, and spatial compactness of components
Solution Approach 1:
The patent changes the measurement parameter from relative capacitance change to absolute capacitance measurement. By measuring the actual capacitance value between the pipette tip and reference potential (grounded base plate), the system eliminates dependence on reference potential variations and labware characteristics, achieving consistent detection across different samples and containers
Solution Approach 2:
The patent extracts the harmful influences from the measurement by using absolute capacitance measurement. The measurement circuitry measures capacitance relative to a fixed reference potential (ground) rather than relative changes, thereby removing the influence of varying labware capacitance, container geometry, and liquid properties from the detection signal
2Productivity
If densely spaced measurement channels are used to increase parallelism, then productivity is improved, but measurement precision deteriorates due to mutual influence (capacitive coupling) of adjacent channels
Solution Approach 1:
The patent removes the mutual interference between adjacent measurement channels by using absolute capacitance measurement referenced to a common ground. This eliminates capacitive coupling effects between neighboring channels, allowing densely spaced parallel measurement channels to operate independently with high precision
3Measurement precision
If calibration and parameter adjustment are performed to compensate for labware and liquid variations, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the need for calibration and parameter adjustment by using absolute capacitance measurement. Since the measurement is referenced to a fixed ground potential rather than relative changes, the system becomes inherently independent of labware and liquid variations, eliminating the need for elaborate calibration procedures
Solution Approach 2:
The patent creates a universal measurement approach that works across different sample liquids and labware without requiring specific calibration for each combination. The absolute capacitance measurement system provides consistent detection performance universally across all samples and containers
4Productivity
If fast detection of liquid contact is implemented, then productivity is improved, but reliability deteriorates due to false alarms from electrostatic discharges and noise
Solution Approach 1:
The patent applies feedback through signal processing techniques including median filtering and down-sampling of the capacitance measurement signal. These processing steps provide feedback about the true signal characteristics, enabling the system to distinguish between real liquid contact events and false signals from electrostatic discharges or noise
Solution Approach 2:
The patent performs preliminary signal processing actions by applying median filtering and down-sampling to the capacitance measurement signal before detection. These preliminary actions clean the signal of outliers and noise, preparing it for accurate detection while maintaining fast response capability
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
The method provides reliable and fast detection of liquid contact, reducing false alarms and enabling precise liquid processing without delay, thereby improving system throughput.
Implementation Method 1
measuring an absolute capacitance between the pipette tip and a reference potential, such as a grounded base plate upon which a container with the liquid is arranged
Data Source
AI summary
A method for detecting contact of a pipette tip with a surface of a liquid in a pipetting device is disclosed. The method consists of moving the pipette tip in the direction of the surface of the liquid thereby measuring an absolute capacitance between the pipette tip and a reference potential and generating a sampled output signal. A predicted momentary sample value of the output signal is generated based on a plurality of past sample values of the output signal. A contact signal indicative of the pipette tip being in contact with the surface of the liquid is generated based on comparing a momentary sample value of the output signal with the predicted momentary sample value of the output signal. A corresponding pipetting device capable of performing the method as a laboratory system, in particular an automated liquid processing system, with one or more such pipetting devices are proposed.