Tank Fill Level Sensor with Temperature-Compensating Electrodes
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Solution Overview
Problem
Existing sensor arrangements for determining the filling level of liquid reducing agents in vehicles, such as urea solutions, face challenges with corrosion resistance, temperature fluctuations, and malfunction due to chemical aggression and varying temperatures.
Innovation Solution
A sensor arrangement with corrosion-resistant, temperature-compensating measuring electrodes and a compact design, featuring a circumferential groove for axial locking and encapsulation in plastic, along with a secondary spray coating and integrated temperature sensor for robust and fail-safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measuring electrodes are directly exposed to the liquid reducing agent for filling level detection, then the sensor arrangement can accurately determine the filling level, but the measuring electrodes are subject to corrosion and chemical aggression
Solution Approach 1:
A carrier made of chemically resistant material (such as plastic or PTFE) is introduced as an intermediary between the measuring electrodes and the liquid reducing agent. The carrier encapsulates the electrodes and provides chemical protection, allowing the electrodes to function without direct exposure to corrosive substances. This mediator enables both accurate measurement and corrosion resistance simultaneously.
2Reliability
If the sensor arrangement is designed to be compact and sealed, then it is protected against chemical influences, but temperature compensation becomes more difficult
Solution Approach 1:
The temperature sensor is nested inside the sealed carrier, positioned in thermal contact with the measuring electrodes but protected from direct exposure to the liquid reducing agent. This nested arrangement allows the temperature sensor to measure the temperature of the electrodes for compensation purposes while remaining protected within the chemically resistant carrier structure.
3Stability of the object's composition
If the measuring electrodes are fixed rigidly in the carrier, then the sensor arrangement is mechanically stable, but temperature fluctuations cause expansion and contraction leading to malfunctions
Solution Approach 1:
The measuring electrodes are designed with dynamic fixation features such as circumferential grooves or locking means that allow axial movement. This dynamic design enables the electrodes to expand and contract with temperature changes while maintaining electrical contact and functional integrity, preventing malfunctions caused by rigid constraints during thermal cycling.
4Reliability
If multiple sensors (filling level and temperature) are integrated in a separate housing, then they are protected from chemical aggression, but the overall device complexity and space requirement increase
Solution Approach 1:
The filling level sensor and temperature sensor are merged into a single integrated sensor arrangement with a common carrier structure. Both sensors share the same protective carrier and sealing system, eliminating the need for separate housings and reducing overall device complexity while maintaining protection against chemical aggression for both sensors.
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
Ensures reliable and accurate filling level detection while protecting against corrosion and temperature fluctuations, ensuring safe and continuous operation in chemically aggressive environments.
Implementation Method 1
The sensor arrangement has a first measuring electrode and a longer, second measuring electrode arranged parallel to one another, which are designed as metal pins
Implementation Method 2
The sensor arrangement or the tank is robust and fail-safe with respect to the considerable temperature fluctuations that occur in continuous operation
Implementation Method 3
provide a circumferential groove on the measuring electrodes as a locking means, which locks them axially on one side
Implementation Method 4
use a secondary spray coating area on the side of the sensor arrangement facing away from the tank interior to provide a secondary spray coating that shields it from harmful chemical influences
Implementation Method 5
integrate a temperature sensor in the carrier of the filling level sensor, which, with a compact design and sealed against the liquid, can promptly register temperature changes in the tank
Data Source
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AI summary
The invention relates to a sensor arrangement for determining a tank fill level of a liquid (7), especially a reducing agent for removing nitrogen from the exhaust gases of an internal combustion engine, which liquid is contained in a tank (5), at least two electrically conductive measuring electrodes (14, 16) of different length being arranged substantially parallel relative each other and being adapted to be arranged substantially perpendicular in the tank. The measuring electrodes are at least partially embedded in a carrier (8, 32) that is produced of an electrically non-conductive material. The measuring electrodes are rigidly fastened relative to the carrier (32) on one side (17) by locking means (38) and are radially held on the other side by radial holding means (42) of the carrier in such a manner as to compensate a heat-induced variation in length of the measuring electrodes (14, 16) relative to the carrier by an axial compensating movement of the measuring electrodes (14, 16) relative to the holding means (42) on the other side (19). The invention also relates to a method for producing said sensor arrangement.