Capacitive Level Sensor Temperature Compensation
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Solution Overview
Problem
Capacitive level sensors used in vehicles face imprecision and environmental disturbance due to temperature variations, especially in conditions where liquids in tanks are at different temperatures, such as when a urea solution is partially frozen and partially thawed, leading to inaccurate capacitance and impedance measurements.
Innovation Solution
A level-sensor device with an array of capacitive elements and a control circuit that includes temperature compensation methods, where each electrode's temperature is compensated using a virtual temperature sensor from the adjacent electrode, reducing the need for multiple temperature sensors and enhancing measurement accuracy across temperature gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive level sensor is used to detect liquid level in a tank, then the level measurement function is provided, but the measurement precision deteriorates under temperature variations and freezing conditions
Solution Approach 1:
The patent applies parameter changes by using temperature sensors to detect temperature variations and dynamically adjusting the capacitance threshold values based on temperature compensation algorithms. This allows the sensor to adapt to different temperature conditions and maintain measurement precision despite thermal effects on the capacitive elements and liquid permittivity.
Solution Approach 2:
The patent implements feedback mechanisms through temperature sensors that continuously monitor the environmental conditions and feed this information back to the control circuit. The control circuit then adjusts the capacitance thresholds in real-time based on the temperature feedback, creating a closed-loop system that compensates for temperature-induced measurement errors.
2Measurement precision
If multiple temperature sensors are installed at each electrode to compensate for temperature effects, then the measurement accuracy improves, but the device complexity and cost increase
Solution Approach 1:
The patent applies partial action by installing temperature sensors at only two strategic locations (top and bottom of the detection part) rather than at every electrode position. The control circuit then uses these partial temperature measurements to calculate and compensate for temperature effects across all electrodes through mathematical modeling, reducing the number of required sensors while maintaining compensation accuracy.
Solution Approach 2:
The patent makes the temperature sensors serve multiple functions: they not only provide temperature compensation data but also help identify the liquid level by detecting temperature gradients, and assist in diagnosing sensor malfunctions. This multi-functionality reduces the need for separate components and simplifies the overall system design.
3Reliability
If temperature compensation algorithms are implemented, then the measurement reliability under thermal stress improves, but the computational requirements and processing time increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing temperature compensation lookup tables during the manufacturing process. These pre-computed compensation values are stored in memory and directly applied during operation based on the measured temperature, avoiding the need for complex real-time calculations and reducing processing time while maintaining compensation accuracy.
Solution Approach 2:
The patent uses simplified approximation algorithms for temperature compensation that prioritize speed and reliability over extreme precision. The control circuit employs straightforward mathematical models that provide sufficient accuracy for practical applications while minimizing computational burden and processing time, effectively trading minor precision losses for significant gains in response speed.
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 solution provides precise and reliable level measurements despite temperature variations, minimizing environmental disturbances and maintaining accuracy in diverse temperature conditions, thus improving the sensor's operational reliability and cost-effectiveness.
Implementation Method 1
capacitive level sensors... based upon the measurement of electrical quantities, such as conductivity/resistivity or capacitance
Implementation Method 2
the values of capacitance or impedance detected via the capacitive elements of the sensor vary as a function of temperature
Implementation Method 3
the level sensor comprises at least one temperature sensor, used for detecting environmental conditions and for possibly compensating mathematically the information on the measurement of level
Data Source
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AI summary
A capacitive level- sensor device, for detecting the level of at least one medium (L, A, I) contained in a container (1) comprises at least: - a detection part (11) that includes an array of capacitive elements, the array of capacitive elements comprising at least one set of electrodes (Ji-Jn) on a substrate (20), the electrodes (Ji-Jn) being set at a distance from one another according to a level-detection axis (X), the detection part (11) including at least one insulating layer (16) for electrically insulating the electrodes (Ji-Jn) with respect to the medium (L, A, I); and - a control circuit (24) having a plurality of first inputs (INi-INn), electrically connected to which are the electrodes (Ji-Jn). The control circuit (24) is prearranged for carrying out a sequential sampling of the inputs of the plurality of first inputs (INi-INn) and for comparing a value representing the capacitance associated to each electrode (Ji-Jn) with at least one corresponding reference threshold, in particular for deducing the medium (L, A, I) facing each electrode(Ji-Jn) and/or the level thereof. The detection part (11) further comprises at least one temperature sensor (27), connected to at least one respective second input (INTS) of the control circuit (24). The control circuit (24) is moreover prearranged for carrying out a compensation of at least one of the following: - the value representing electrical capacitance associated to each electrode (Ji-Jn;); - a value indicating the medium (L, A, I) facing each electrode(Ji-Jn); and - the at least one reference threshold, according to information representing at least one temperature value acquired on the at least one second input (INTS).