Pipetting Needle Vibration for Liquid Level Detection
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Solution Overview
Problem
Existing liquid level detection methods in pipetting systems fail when the pipetting needle pierces a vessel's closure or encounters foam, leading to inaccurate liquid surface detection.
Innovation Solution
A level sensor apparatus with a sensor head and electromechanical transducer that generates vibrations at a known resonance frequency, allowing for reliable detection of liquid contact by analyzing changes in the vibration signal's amplitude and phase, even when the needle passes through a cover or foam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive level sensor is used to detect liquid surface, then liquid level detection is achieved, but it erroneously detects foam or wet cover as liquid surface
Solution Approach 1:
The patent applies mechanical vibration by causing the pipetting needle to vibrate at its resonance frequency and detecting changes in vibration characteristics when contact with liquid occurs. The vibration signal is generated by an electromechanical transducer attached to the needle, and the system monitors amplitude and frequency changes to distinguish liquid contact from foam or cover contact, resolving the false detection problem of capacitive sensors
Solution Approach 2:
The system changes the detection parameter from electrical capacitance to mechanical vibration characteristics. By monitoring changes in vibration amplitude and frequency of the needle, the system can reliably distinguish between liquid contact (which dampens vibration) and false contacts with foam or covers (which do not produce the same damping effect), thereby improving both measurement precision and reliability
2Ease of operation
If the pipetting needle pierces the vessel closure to reach liquid, then access to liquid is achieved, but liquid level detection becomes unreliable
Solution Approach 1:
The vibration-based detection method works effectively even when the needle pierces the closure because the vibration signal is generated directly on the needle itself. The electromechanical transducer attached to the needle creates vibrations that are unaffected by the closure material, and liquid contact is detected through changes in vibration characteristics, maintaining measurement precision while enabling access to closed vessels
3Ease of operation
If the pipetting needle passes through foam to reach liquid, then liquid access is achieved, but liquid surface detection becomes inaccurate
Solution Approach 1:
The vibration detection method distinguishes between foam and liquid contact by analyzing the damping characteristics of the vibration signal. When the needle contacts foam, the vibration pattern differs from when it contacts liquid, allowing the system to accurately identify the true liquid surface even after passing through foam layers, thereby maintaining measurement precision while enabling access to liquid under foam
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 accurate detection of liquid surface contact and prevents undesirable contacts, such as with the vessel's bottom, improving pipetting precision and reducing carryover.
Implementation Method 1
The sensor head comprises a pipetting needle attached to a needle holder and mechanically connected to an electromechanical transducer. An electrical signal generator is configured to provide a driving signal to the electromechanical transducer.
Implementation Method 2
a measurement device is configured to measure a parameter of an electrical signal provided by the electromechanical transducer. The electrical signal provided by the electromechanical transducer is useful because it is indicative of a vibration of the pipetting needle
Implementation Method 3
A first aspect of the invention provides a level sensor apparatus which is able to reliably detect contact between a pipetting needle with a liquid contained in a vessel... a sensor apparatus that has a sensor head with a known mechanical resonance frequency
Data Source
AI summary
A level sensor apparatus is disclosed for detecting contact of a pipetting needle with a liquid contained in a vessel. The apparatus includes a sensor head made up of a pipetting needle, a needle holder, and an electromechanical transducer. The sensor head also has an associated mechanical resonance frequency. An electrical signal generator is used to generate a driving signal which when applied to the electromechanical transducer causes vibration of the pipetting needle at the resonance frequency. A measurement device is used to measure a parameter of a vibration signal indicative of the mechanical vibration of the pipetting needle when it is driven by the driving signal. An electronic circuit and associated computer software is provided to evaluate variation of the vibration signal with time and thus detect contact of the pipetting needle with a liquid contained in the vessel.