Capacitive Sensor Level Measurement Guard Plate Shielding
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Solution Overview
Problem
Capacitive level sensors face challenges such as electromagnetic interference, non-linear responses due to electrode geometry, and varying base capacitance caused by temperature and humidity, leading to inaccurate liquid level measurements in tanks.
Innovation Solution
The capacitive sensor employs a motherboard with multiple layers, featuring linearly distributed measuring electrodes and tracks of uniform shape and length, surrounded by guard and shielding plates to minimize coupling with the medium and external disturbances, and includes interposed ground electrodes to stabilize capacitance measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear electrodes are used to measure liquid level, then measurement resolution is improved, but electromagnetic interference and antenna effects worsen
Solution Approach 1:
The patent divides the continuous linear electrode into multiple discrete electrode segments arranged in a specific pattern. This segmentation reduces the antenna effect by breaking up the continuous conductive path, thereby reducing electromagnetic interference while maintaining measurement resolution through the distributed capacitance measurement of individual segments.
Solution Approach 2:
The patent introduces a guard electrode as an intermediary element between the measuring electrode and the liquid medium. This guard electrode is held at a fixed potential and shields the measuring electrode from electromagnetic interference and parasitic capacitance effects, improving measurement accuracy while reducing susceptibility to electromagnetic noise.
2Object-affected harmful factors
If discrete electrodes are used instead of linear electrodes, then antenna effects are reduced, but connection track coupling and parasitic capacitance worsen
Solution Approach 1:
The guard electrode acts as an intermediary that isolates the measuring electrode from parasitic capacitance effects. By holding the guard electrode at a fixed potential (typically ground or a reference voltage), it creates an equipotential barrier that prevents coupling between the measuring electrode and nearby conductors or the liquid medium, thereby reducing parasitic capacitance.
Solution Approach 2:
The patent employs the guard electrode to create an equipotential region around the measuring electrode. By maintaining the guard electrode at a constant potential, it eliminates potential differences that would otherwise cause parasitic capacitance and coupling effects, stabilizing the measurement signal.
3Measurement precision
If reference electrodes are used to determine liquid level, then measurement accuracy is improved, but non-linearities and complexity worsen
Solution Approach 1:
The patent implements self-service by using the discrete electrode segments themselves to provide reference information. Each electrode segment's capacitance measurement serves as both a measurement point and a reference point, eliminating the need for separate reference electrodes. The system automatically compensates for environmental effects by comparing measurements across multiple segments.
Solution Approach 2:
The electrode segments serve multiple functions: they act as measuring electrodes for capacitance measurement, as reference electrodes for comparison, and as shielding elements when held at fixed potential. This multi-functionality eliminates the need for dedicated reference electrodes, reducing device complexity while maintaining measurement accuracy.
4Ease of operation
If tracks connect measuring electrodes to controller, then signal transmission is enabled, but coupling with liquid and electromagnetic disturbances worsen
Solution Approach 1:
The guard electrode serves as an intermediary barrier between the measuring electrode tracks and the liquid medium/external electromagnetic fields. By holding the guard electrode at a fixed potential, it shields the signal tracks from capacitive coupling with the liquid and reduces susceptibility to electromagnetic disturbances, enabling reliable signal transmission.
Solution Approach 2:
The guard electrode creates an equipotential shield around the signal tracks, maintaining a constant potential that prevents voltage differences from developing between the tracks and surrounding conductors or the liquid medium. This eliminates capacitive coupling and reduces electromagnetic interference with the signal transmission.
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 provides high-precision, immune to electromagnetic noise and temperature/humidity variations, allowing for accurate liquid level measurement without the need for reference electrodes, and is suitable for the automotive industry's demanding standards.
Implementation Method 1
surrounded by at least one guard plate and optionally at least one shielding plate, both made of a conductive material, the guard plate being subjected to a guard voltage to prevent coupling between the tracks with the medium
Implementation Method 2
the shielding plate being connected to ground for the electromagnetic shielding of the tracks
Implementation Method 3
capacitive systems for measuring the level of liquids in tanks based on the arrangement of electrodes submerged in the liquid in the tank and on the measurement of capacitance variation between said electrodes
Implementation Method 4
the capacitance value between the electrodes changes with the dielectric properties of both the medium and the insulating substrate on which the electrodes are placed
Data Source
AI summary
A capacitive sensor for measuring the level of a substance in a tank is provided, which has a motherboard with a plurality of layers (1a, 1b, 1c, 1d, 1e), wherein each layer (1a, 1b, 1c, 1d, 1e) has one or more plates with components, such as measuring electrodes (2), microcontroller (3), and tracks (4) for connecting the measuring electrodes (2) to the microcontroller (3), wherein the capacitive sensor has a first layer (1a) which in turn has a plate having a plurality of linearly distributed measuring electrodes (2), wherein all the tracks (4) for connecting the measuring electrodes (2) to the microcontroller (3) has the same shape and length, and are surrounded by at least one guard plate (8) and optionally at least one shielding plate (7), both made of a conductive material.