Capacitance Probe Shielding for Fluid Surface Detection
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Solution Overview
Problem
Existing methods for detecting fluid surfaces in clinical analyzers, particularly those based on capacitance changes, face reliability issues due to small capacitance changes and interference from external influences, leading to inaccurate results.
Innovation Solution
The method involves using a probe with an electric capacitance that is activated by a periodic electric signal, and applying a shield signal to nearby conductive regions to minimize interference, allowing for reliable detection of fluid surfaces by analyzing changes in capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capacitance-based probe method is used for fluid surface detection, then the method is simple and cost-effective, but the capacitance change is very small (some ten Femtofarads) leading to low detection reliability
Solution Approach 1:
The patent introduces a shield electrode as an intermediary element between the probe and the external environment. This shield electrode is positioned between the probe and surrounding conductive objects, mediating the electromagnetic field interaction. By placing this intermediary shield, the patent successfully isolates the probe's capacitive measurement from external disturbances while maintaining the simplicity of the capacitance-based detection method.
Solution Approach 2:
The patent converts the harmful effect of external electromagnetic disturbances into a beneficial shielding effect. By intentionally introducing a grounded shield electrode, the patent creates a controlled capacitive division where the shield captures the interfering fields, thereby protecting the probe measurement. The shield's capacitance, which could be seen as an additional interference, is actually used to block external disturbances from reaching the probe.
2Ease of operation
If probe is positioned close to fluid surface for accurate pipetting, then cross-contamination is minimized and cleaning is facilitated, but fluid surface detection accuracy is compromised due to external interference
Solution Approach 1:
The shield electrode serves as a protective intermediary that allows the probe to operate close to the fluid surface without suffering from external electromagnetic interference. The shield is positioned between the probe and surrounding conductive objects, creating a controlled electromagnetic environment that enables both accurate positioning and accurate detection.
Solution Approach 2:
The patent changes the electromagnetic field distribution parameters by introducing the shield electrode. This alters the capacitance measurement parameters in a controlled way, creating a new reference state that is insensitive to external disturbances. The shield modifies the field geometry so that the probe's capacitive signal becomes predominantly sensitive to fluid surface position rather than external objects.
3Measurement precision
If high-frequency voltage signals (1 MHz to 1 GHz) are applied to probe for surface detection, then electric impedances sensitive for surface detection are generated, but sophisticated technical equipment is required and electromagnetic interference effects occur
Solution Approach 1:
The patent changes the frequency parameter from high-frequency (1 MHz to 1 GHz) to low-frequency (lower than 1 kHz) voltage signals. This parameter change maintains the ability to detect surface changes through capacitance variations while avoiding the need for sophisticated high-frequency equipment and eliminating electromagnetic interference problems. The low-frequency signals still produce measurable capacitance changes when the probe approaches the fluid surface.
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 enhances the reliability of fluid surface detection by shielding disturbances, enabling precise positioning of the probe and improving the accuracy of pipetting operations in clinical analyzers.
Implementation Method 1
Another technique is based on a change of the electric capacitance of the probe when the probe is brought in or out of physical contact with the fluid
Implementation Method 2
the probe is repeatedly charged by periodic electric signals, with the capacitance of the probe being measured by analyzing the discharging current
Data Source
Figure 1~2
Figure 3
Figure 4A~4B
AI summary
The present invention pertains to a method for detecting a fluid surface, comprising the following steps: providing at least one probe having an electric capacitance with respect to its ambient; moving the probe into or out of a fluid; charging the probe by applying a periodic first electric signal to the probe for activating the probe; applying a periodic third electric signal to one or more electrically conductive regions different from the probe simultaneously with applying the first electric signal to the probe, wherein the third electric signal corresponds to the first electric signal or an amplified/damped first electric signal; at least partially discharging the probe so as to obtain a discharging current; detecting a second electric signal based on the discharging current; analyzing the second electric signal or a signal derived from the second electric signal with respect to the capacitance of the probe; identifying the fluid surface of the fluid based on a change of the capacitance of the probe. It further relates to a corresponding system adapted to perform the method.