Ultrasonic Pipetting Needle 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, which affects the precision and accuracy of pipetting operations.
Innovation Solution
The use of ultrasonic pulses transmitted through the pipetting needle to detect the contact and position of the liquid surface, allowing for reliable detection even when the needle pierces a cover or passes through foam, and enabling the minimization of penetration depth into the liquid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive level sensor is used to detect liquid level, then liquid level detection is achieved under normal circumstances, but it fails when needle pierces vessel closure or encounters foam
Solution Approach 1:
The patent replaces capacitive sensing (electrical field-based) with ultrasonic sensing (acoustic wave-based). The ultrasonic transducer emits sound waves through the needle, and the reflected waves are detected to determine liquid level. This mechanical/acoustic approach works reliably through foam and vessel closures where capacitive sensors fail, as acoustic waves can penetrate these media without being misled by their presence.
Solution Approach 2:
The pipetting needle itself serves as an intermediary medium for transmitting ultrasonic waves from the transducer to the liquid surface. By using the needle as the transmission path, the system achieves reliable detection while the ultrasonic method provides the mediator capability to distinguish actual liquid contact from foam or closure interference.
2Manufacturing precision
If pipetting needle penetration depth is minimized to reduce carryover, then pipetting accuracy is improved, but liquid level detection becomes more difficult under abnormal conditions
Solution Approach 1:
The patent replaces capacitive detection with ultrasonic detection to enable reliable liquid level identification even with minimal needle penetration. The ultrasonic time-of-flight measurement can accurately determine when the needle tip contacts the liquid surface, allowing the system to stop penetration at the precise moment of contact, thus minimizing carryover while maintaining detection reliability.
Solution Approach 2:
The ultrasonic detection system provides real-time feedback on needle position relative to the liquid surface. By continuously monitoring the reflected ultrasonic signal during needle approach, the system can detect liquid contact immediately and provide feedback to stop further penetration, enabling precise control with minimal penetration depth.
3Measurement precision
If ultrasonic pulses are used instead of continuous waves, then time of flight can be used to determine contact position, but system complexity increases
Solution Approach 1:
The system uses periodic ultrasonic pulse emission instead of continuous waves. By emitting short pulses at regular intervals and measuring the time until reflection returns, the system achieves precise position determination. The pulse timing and measurement electronics, while adding some complexity, provide accurate time-of-flight data that continuous waves cannot deliver without additional modulation complexity.
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 accurate detection of the liquid surface, verifies the presence and integrity of the pipetting needle, and measures the penetration depth, ensuring precise control and minimizing carryover during pipetting operations.
Implementation Method 1
Ultrasonic pulses are generated e.g. by applying pulses of short duration of an electrical signal having a suitable frequency to a piezoelectric transducer
Implementation Method 2
ultrasonic pulses are transmitted through the pipetting needle and pulses reflected at the fluid delivery tip of the pipetting needle are detected
Implementation Method 3
it is possible to use the time of flight of an ultrasonic pulse to determine the contact and the position or distance at which contact occurs
Data Source
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AI summary
A level sensor apparatus for detecting contact of a pipetting needle with a liquid contained in a vessel. The apparatus comprises a pipetting needle (11) made of a material suitable for transmitting ultrasonic waves, a needle holder for holding the pipetting needle, a electromechanical transducer (15) for generating ultrasonic pulses to be transmitted towards the needle, for receiving echo pulses reflected at the tip (17) of the needle, and for generating an electrical output signal representative of the echo pulses, electronic circuit means (31) for generating a driving signal and for applying this signal to the electromechanical transducer (15), which generates corresponding ultrasonic pulses which are transmitted to the pipetting needle (11) towards the tip (17) thereof, and for monitoring the electrical output signal in order to detect the position of the needle (11) at which the tip (17) of the pipetting needle (11) contacts the free surface (14) of the liquid (12) contained in the vessel (13), and transport means (21, 22) for automatically transporting the needle holder and said needle, for positioning the needle (11) at a pipetting position and for moving the tip (17) of the needle (11) towards the free surface (14) of the liquid (12) contained in the vessel (13).