Coaxial Fill-Level Probe Galvanic Isolation Design
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Solution Overview
Problem
Classic fill level measuring devices using coaxial probes face challenges in maintaining galvanic isolation between the inner and shield conductors while ensuring the shield conductor is at a reference potential, essential for both capacitive and transit time measurements, especially in conductive media and explosion protection applications.
Innovation Solution
A fill level measuring device with a coaxial probe design featuring a galvanically isolated inner conductor and a shield conductor electrically connected to a reference potential through a conductive annular disk and spring elements, ensuring reliable electrical contact and insulation, even under temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a coaxial probe is used for fill level measurement, then measurement independence from installation situation is improved, but galvanic isolation between inner conductor and shield conductor becomes difficult to maintain
Solution Approach 1:
The probe is divided into functionally independent segments: the inner conductor (13) is completely surrounded by an insulating layer (15) that extends into the container, separating it from the shield conductor (5). This segmentation maintains galvanic isolation while preserving the coaxial structure's measurement independence.
Solution Approach 2:
An insulating body (17) acts as an intermediary element between the inner conductor (13) and the shield conductor (5). This insulating body completely surrounds the inner conductor and maintains galvanic isolation, while still allowing the coaxial structure to function independently of installation conditions.
2Reliability
If the shield conductor is electrically connected to reference potential, then measurement reliability is improved, but power loss and interference increase
Solution Approach 1:
The shield conductor (5) is electrically connected to the reference potential only at specific locations (e.g., through the fastening device (7) and counterpart (9)), rather than being continuously connected throughout the entire probe. This localized connection maintains measurement reliability while minimizing power loss and interference in the measurement section.
3Reliability
If insulating layer completely surrounds inner conductor, then galvanic isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The insulating layer (15) and insulating body (17) are combined to form a complete galvanic isolation system. The insulating layer completely surrounds the inner conductor (13), and the insulating body (17) extends this insulation into the container, merging two insulation elements to achieve complete galvanic isolation while managing manufacturing complexity.
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
Enables accurate capacitive and transit time measurements with reduced power loss and interference, suitable for a wide temperature range and safe operation in conductive media, maintaining high signal quality and compliance with explosion protection standards.
Implementation Method 1
at least one in the ring disk outside of a covered area of the insulating body of the same on a spring element fixed electrical contact element through which the shielding conductor is electrically conductively connected to the fastening device
Implementation Method 2
an inner conductor completely surrounded by an insulating layer, which in measuring operation through the annular disk is guided through into the container, an insulating body adjoining the insulating layer, which coaxially surrounds the inner conductor
Implementation Method 3
The fill-level measuring device generates electromagnetic signals, which it sends into the container along the measuring probe, which in this case serves as a waveguide
Implementation Method 4
the measuring probe serves as a capacitive probe or as an electrode. It is inserted into the container and a capacitance of a capacitor formed by the probe and the container wall surrounding it is measured
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a fill-level measuring device for measuring the fill level of a filling material in a tank (1) capacitively and/or according to the propagation time principle, comprising a coaxial measuring probe, the inner conductor (3) of which is galvanically isolated from the shield conductor (5) of said coaxial measuring probe and the shield conductor (5) of which is electrically at a reference potential, having a fastening device (7) electrically at a reference potential for fastening the measuring device to a tank opening (11) equipped with a counterpart (9) that corresponds to the fastening device (7), an annular disk (13) that is made of an electrically conducting material and that is clamped between the fastening device (7) and the counterpart (9) during measuring operation, an inner conductor (3) that is completely surrounded by an insulating layer (15) and that is fed through the annular disk (13) into the tank (1) during measuring operation, an insulating body (17) that is connected to the insulating layer (15), coaxially surrounds the inner conductor (3), and comprises an annular disk-shaped section (19) that is clamped between the fastening device (7) and the annular disk (13), a shield conductor (5) that coaxially surrounds the inner conductor (3) and is connected to the annular disk (13) mechanically and in an electrically conducting manner, and at least one electrical contact element (23), which is fixed on a spring element (25) in the annular disk (13) outside an area of the annular disk covered by the insulating body (17) and by which the shield conductor (5) is connected to the fastening device (7) through the contact element (23) and the annular disk (13) in an electrically conducting manner.