Dual Capacitor Load Cell Linearizing Output Signal
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Solution Overview
Problem
Capacitive load cells face issues with non-linear output and sensitivity due to the change in capacitance as a result of applied force, which affects the accuracy of force measurement.
Innovation Solution
A dual capacitor load cell configuration is introduced, where two parallel plate capacitors share a common deflectable plate, resulting in inverse variation of capacitance with applied force, improving sensitivity and linearizing the output signal by measuring and combining the capacitance values of both capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single capacitor is used in the load cell, then the structure is simple, but the output signal sensitivity and linearity are poor
Solution Approach 1:
The single capacitor is segmented into two separate capacitors (first capacitor and second capacitor) with a common movable plate. Each capacitor independently measures capacitance changes, and their outputs are combined to achieve linearized measurement results, resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The outputs of the two capacitors are merged through addition or subtraction operations. By combining the capacitance change signals from both capacitors, the system achieves linearized output that compensates for the non-linearity of individual capacitors, improving measurement precision while maintaining manageable device complexity
2Measurement precision
If a single capacitor is used in the load cell, then the device complexity is low, but the sensitivity of force measurement is insufficient
Solution Approach 1:
The measurement function is segmented across two capacitors, each contributing to the overall sensitivity. The common movable plate ensures both capacitors respond to the same mechanical displacement, and their combined output amplifies the sensitivity to applied force while keeping the structural complexity reasonable
Solution Approach 2:
The sensitivity contributions from both capacitors are merged through signal combination. The additive or subtractive combination of capacitance changes from the two capacitors produces an enhanced output signal that is more sensitive to small force variations, improving measurement precision without excessive 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 configuration enhances the sensitivity and linearity of the output signal, providing more accurate force measurement by inversely relating the capacitance changes, thereby improving the overall performance of the load cell.
Implementation Method 1
a force responsive deflectable plate including a vertically deflectable main portion resiliently coupled such that the main portion is configured to move vertically in response to a received force
Implementation Method 2
the first capacitive plate and the force responsive deflectable plate form a first capacitor, and the second capacitive plate and the force responsive deflectable plate form a second capacitor, and the capacitance of the first capacitor and the second capacitor change inversely
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A dual capacitor load cell (100) is presented that includes two coupled capacitors (170, 175) with a common plate (125) between them where the common plate (125) is responsive to a force applied to the load cell (100). The capacitance of the two capacitors (170, 175) varies inversely and changes in response to the applied force. The combined capacitance of each capacitor (170, 175) is used to determine the magnitude of the force being applied to the load cell (100).