Capacitive Liquid Level Sensing Touch Noise Filtering
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Solution Overview
Problem
Capacitive liquid level measurement systems are susceptible to noise and errors due to perturbations such as hand touches on the container, leading to inaccurate liquid level determinations in applications requiring high precision.
Innovation Solution
A capacitive liquid level measurement system that filters out changes in capacitance caused by touches using a processing unit to compare sensor values over time, determining a threshold for touch detection and interpolating liquid levels based on overlapping receiver electrodes, allowing for accurate liquid level determination despite external interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If capacitive sensing is used for liquid level measurement, then contactless measurement is achieved suitable for medical and industrial applications, but the system becomes susceptible to noise from container perturbations such as hand touches
Solution Approach 1:
The system performs preliminary sampling of capacitance values at multiple discrete points along the container before determining the final liquid level measurement. This preliminary action creates a baseline set of measurements that can be used to detect and filter out anomalies caused by touches or perturbations on the container exterior.
Solution Approach 2:
The system continuously monitors capacitance changes at multiple discrete sampling points and uses this feedback to detect when a touch perturbation occurs. When a touch is detected at any sampling point, the system adjusts its measurement strategy to exclude affected measurements, thereby maintaining measurement precision while preserving contactless operation.
2Reliability
If discrete sampling points are used along the container, then touch detection capability is improved, but the complexity of the sensing system increases
Solution Approach 1:
The sensing system divides the container into multiple discrete sampling points along its length, with each point independently measuring capacitance. This segmentation allows the system to detect touches at specific locations without requiring a fully continuous sensing system, balancing reliability with manageable complexity.
Solution Approach 2:
The same set of discrete sampling points serves dual functions: they both detect liquid level changes and detect touch perturbations on the container. This multi-functionality eliminates the need for separate detection systems, reducing overall device complexity while maintaining high reliability for both measurement tasks.
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
The system effectively filters out touch-induced noise, maintaining the accuracy of liquid level measurements and providing precise determination of liquid levels within containers, outperforming some ultrasonic and capacitive systems without overlapping electrodes.
Implementation Method 1
a transmitter capacitive sensor projects an electric sensing field into a container
Implementation Method 2
measuring the capacitance between a receiver electrode and a ground terminal or between the receiver electrode and another electrode
Data Source
AI summary
An apparatus for filtering touches and disturbances of a container comprises a processing unit (PU) and computer-readable storage devices storing machine instructions. The PU obtains and sums together sensor values for a first sampling time from electrodes affixed to the container. The PU determines a difference between the sum for the first sampling time and a sum for a second sampling time, which is compared to a threshold representative of a change in capacitance due to a touch on the container. The PU determines whether the touch on the container has occurred at the first sampling time based on the comparison. If a touch occurred, the PU continues to obtain additional sensor values for additional sampling times and determine whether a touch on the container has occurred at the additional sampling times, until determining no touch occurred. The PU determines liquid level for the container after determining no touch occurred.