Capacitive Sensor Fluid Cup Alignment for Fill Level Accuracy
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Solution Overview
Problem
Existing fluid level detection systems in solid-production systems, such as consumer ice-makers, face inaccuracies due to measuring the sides of the compartment rather than the fluid surface, leading to inconsistent filling as they do not account for surface tension, resulting in incorrect fill level determination across the compartment.
Innovation Solution
A capacitive sensing system where the capacitive sensor is positioned a distance-separated and parallel to the top surface of the fluid in a fluid cup, using a sensor pad that forms a plate of a capacitor with the fluid as the dielectric, allowing for precise measurement of fill level changes based on capacitance variations, with the sensor distance ranging from 0.5 mm to 2.5 mm from the fluid surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitive sensor is positioned adjacent to the compartment of the fluid tray to measure the sides of the compartment, then the sensor can detect fill level changes, but the measurement is inaccurate due to surface tension effects causing higher fluid levels at the sides compared to the center
Solution Approach 1:
The patent introduces an intermediary mechanism by using the fluid cup itself as part of the capacitive sensor assembly. The fluid cup is moved into alignment with the capacitive sensor, and the bottom of the fluid cup serves as a reference plane for measurement. This intermediary approach allows the sensor to measure the fluid level relative to the cup bottom rather than measuring the compartment walls directly, thereby eliminating surface tension errors.
Solution Approach 2:
The patent transitions from a two-dimensional side-wall measurement approach to a three-dimensional alignment approach where the fluid cup is movably aligned with the sensor. By introducing the dimension of movable alignment and using the cup bottom as a reference plane, the system achieves more accurate measurements that are independent of surface tension effects at the compartment walls.
2Ease of manufacture
If the sensor measures the sides of the compartment, then the sensor structure is simple and easy to install, but the fill level determination is inconsistent across the compartment
Solution Approach 1:
The fluid cup acts as an intermediary that moves into alignment with the sensor. This intermediary mechanism allows the system to maintain a simple fixed sensor structure while achieving reliable and consistent measurements by referencing the cup bottom rather than the compartment walls.
3Measurement precision
If the capacitive sensor is positioned closer to the fluid surface to improve measurement sensitivity, then the measurement precision increases, but the sensor may be affected by fluid pressure and splashing
Solution Approach 1:
The bottom of the fluid cup serves as an intermediary reference plane that is positioned a controlled distance from the capacitive sensor. This intermediary reference allows the sensor to operate at an optimal distance that balances measurement sensitivity with protection from harmful fluid effects like pressure and splashing.
Solution Approach 2:
The patent establishes a controlled spatial relationship in the vertical dimension between the sensor and the fluid cup bottom. By positioning the sensor at a specific distance (0.5 mm to 2.5 mm) from the cup bottom, the system optimizes measurement sensitivity while maintaining a buffer that protects the sensor from direct fluid pressure and splashing effects.
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 enables precise and consistent filling of fluid to a predetermined threshold level, independent of fluid pressure, eliminating issues related to premature or overfilling and allowing the system to operate over a wider pressure range, and enables immediate determination of fill levels, reducing downtime after power outages.
Implementation Method 1
the capacitive sensor comprises a sensor pad that forms a plate of a capacitor having a dielectric comprising the fluid in the fluid cup, the capacitor having a capacitance that is a function of at least the distance the surface facing the fluid of the capacitive sensor pad is separated from the top surface of the fluid, the capacitance being variable with the distance and thereby the fill level of the fluid in the fluid cup
Implementation Method 2
the capacitive sensor comprises a sensor pad that forms a plate of a capacitor having a dielectric comprising the fluid in the fluid cup
Data Source
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AI summary
A capacitive sensing system may include a fluid cup configured to receive a fluid, and processing circuitry and a capacitive sensor coupled to one another, the capacitive sensor is a distance separated from and in parallel with a top surface of the fluid in the fluid cup, the distance the capacitive sensor is separated from the top surface of the fluid being variable with a fill level of the fluid in the fluid cup. The capacitive sensor and the fluid in the fluid cup may form elements of a capacitor with a capacitance that is a function of at least the distance the capacitive sensor is separated from the top surface of the fluid. The processing circuitry may be configured to measure a change in signal corresponding to a change in capacitance of the capacitor and determine the fill level based on a magnitude of the change in signal.