Capacitive Sensing Noise Compensation via Periodic Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive sensing systems face limitations due to temperature, humidity, and electrical noise, which affect accuracy and reliability in measuring capacitance changes, particularly in human interfacing applications.
Innovation Solution
The implementation of a capacitive sensing system that uses a constant current source for linear charging and discharging of capacitances, incorporates noise measurement and compensation mechanisms, and employs a-periodic measurement techniques to reduce noise sensitivity and variability, ensuring improved accuracy and robustness against environmental and electrical interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive measurement methods are used, then capacitance can be measured, but the system is susceptible to temperature, humidity, and electrical noise interference
Solution Approach 1:
The patent employs periodic measurement cycles with alternating phases: a first measurement phase where the capacitive sensor is connected to a measurement circuit to capture capacitance data, and a second measurement phase where electrical noise is measured. By periodically switching between these phases and avoiding capacitance measurements during high-noise intervals, the system achieves more reliable measurements while reducing susceptibility to electrical interference, temperature variations, and humidity effects.
2Measurement precision
If measurement is performed continuously, then capacitance changes can be detected, but noise sensitivity and variability increase
Solution Approach 1:
The patent implements a feedback mechanism where electrical noise levels are continuously monitored during measurement phases. Based on the measured noise levels, the system dynamically adjusts its measurement strategy by comparing capacitance measurements taken at different times and identifying measurements taken during low-noise periods. This feedback-driven approach enhances measurement precision by selectively utilizing high-quality measurements while filtering out noisy data.
Solution Approach 2:
The measurement system dynamically adapts its operation based on real-time noise conditions. Instead of using fixed measurement parameters, the system adjusts measurement timing, averaging windows, and selection criteria based on the measured electrical noise levels. This dynamic adaptation allows the system to maintain high measurement precision even in varying electromagnetic environments by automatically optimizing measurement parameters.
3Loss of time
If linear charging and discharging is used, then charging time can be controlled, but time spent near reference voltage thresholds increases noise sensitivity
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitive sensor to a voltage close to, but not exceeding, the upper reference voltage threshold before the actual measurement phase. This preliminary charging reduces the time the sensor voltage spends near the threshold during the measurement phase, thereby minimizing noise sensitivity. The sensor is then allowed to discharge naturally or through a controlled path, and the capacitance is measured during the discharge phase when the voltage passes through the thresholds more quickly.
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 accuracy and noise immunity of capacitive sensing systems by reducing the time spent near reference voltage thresholds, allowing for more reliable detection of capacitance changes and improved resistance to periodic and radiated noise, thereby improving overall system performance.
Implementation Method 1
Capacitive sensing measures a capacitance resulting from two or more conductive surfaces separated by a dielectric
Implementation Method 2
Capacitive sensing measures a capacitance resulting from two or more conductive surfaces separated by a dielectric
Data Source
AI summary
A capacitive sensing system includes a controller, a node connected to one side of a capacitance, the controller configured to measure the capacitance by measuring a time for a voltage across the capacitance to reach a predetermined reference voltage, a noise measurement circuit configured to measure electrical noise on the node, and the controller receiving the measurement of noise from the noise measurement circuit.