Pipetting Needle Capacitance Touch Detection
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Solution Overview
Problem
Current touch detection methods in in-vitro diagnostic systems are prone to interference from electrostatic discharges and high-frequency fields, making it difficult to distinguish real voltage pulses from noise, especially when dealing with small liquid volumes.
Innovation Solution
The method involves cyclically charging and discharging the pipetting needle and monitoring the capacitance between the needle and a reference potential, using the time profile of capacitance changes to generate a touch signal, with criteria such as a sudden increase and sustained value to differentiate genuine contact from noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive measurement with voltage pulse detection is used, then touch detection sensitivity is improved, but susceptibility to electromagnetic interference increases
Solution Approach 1:
The patent applies periodic charging and discharging cycles to the pipetting needle, measuring the capacitance changes during each cycle. By analyzing the time profile of multiple periodic measurements and comparing them against predetermined criteria, the system achieves reliable touch detection while filtering out electromagnetic interference that does not follow the expected periodic pattern.
Solution Approach 2:
The system continuously monitors the capacitance between the pipetting needle and reference potential during charging/discharging cycles, compares the measured time profile against predetermined criteria, and generates a touch signal when criteria are met. This feedback mechanism enables real-time distinction between genuine touch signals and electromagnetic interference.
2Measurement precision
If float, inductance or conductivity methods are used for level measurement, then measurement capability is improved, but applicability to small liquid volumes deteriorates
Solution Approach 1:
The patent replaces mechanical float-based level measurement with an electrical capacitance measurement system. The pipetting needle itself serves as the sensing element, measuring capacitance changes between the needle and reference potential as it approaches and touches the liquid surface, enabling accurate detection of very small liquid volumes.
Solution Approach 2:
The pipetting needle is designed to serve multiple functions: both liquid transport and touch detection. By using the needle's inherent capacitance characteristics during its normal charging/discharging operation, the system eliminates the need for separate sensing mechanisms, making the solution particularly suitable for small volume applications.
3Measurement precision
If analog circuit technology with operational amplifiers is used, then touch detection capability is improved, but reliability under interference conditions deteriorates
Solution Approach 1:
The system implements continuous feedback monitoring of the capacitance time profile during charging and discharging cycles. By comparing measured values against predetermined criteria in real-time, the system can reliably distinguish genuine touch signals from interference, significantly improving reliability under electromagnetic interference conditions.
Solution Approach 2:
The patent introduces an intermediate evaluation step that analyzes the time profile of capacitance changes during periodic charging/discharging cycles. This intermediary measurement and comparison process acts as a filter, allowing the system to reject interference signals that do not match the expected temporal pattern of genuine touch events.
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 provides more reliable touch detection, reducing false signals from electromagnetic interference and allowing for accurate liquid handling, while also detecting errors like disconnected or defective needles.
Implementation Method 1
one of a number of measured variables recorded during charging and/or discharging for the current capacitance between the pipette needle and reference potential is determined
Data Source
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AI summary
The invention relates to a method for detecting the touch of a pipetting needle in an in-vitro diagnostic system (1). In an advantageous embodiment of the invention, the pipetting needle (18) is cyclically charged by an electrical voltage or current applied between the pipetting needle (18) and a reference potential and subsequently discharged by electrically connecting the pipetting needle (18) to the reference potential; a characteristic value for the current capacitance between the pipetting needle (18) and the reference potential is determined from a number of measured values acquired during charging and/or discharging; and the temporal profile of this value is continuously monitored based on a number of predetermined criteria, and a touch signal is generated when the predetermined criteria are met.