Eddy Current Sensor Triaxial Cable Segmented Coil Drift
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Solution Overview
Problem
Long-term accuracy of eddy current sensors is compromised by output signal drift due to environmental factors and parasitic capacitances in the measuring circuit, which are difficult to compensate.
Innovation Solution
The use of a triaxial transmission cable with a voltage follower to isolate line capacitance from the sensor coil, combined with a segmented sensor coil design where multiple winding layers are connected in series, reduces the influence of parasitic capacitances and improves measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional sensor coil with continuous windings is used, then the sensor structure is simple, but the self-capacitance of the coil is high causing output signal drift
Solution Approach 1:
The sensor coil is divided into multiple coil segments (s1-sn) with consecutive windings arranged in superimposed winding layers. These segmented coils are connected in series and arranged side by side along a coil axis, which reduces self-capacitance while maintaining the required sensing performance
Solution Approach 2:
The patent transitions from a single-layer continuous coil to multi-layer superimposed winding structures. By stacking multiple winding layers vertically and connecting them in series, the design achieves reduced self-capacitance while preserving the coil's inductive properties
2Measurement precision
If a standard coaxial cable is used for transmission, then the cable structure is simple, but the line capacitance affects the sensor coil causing long term drift
Solution Approach 1:
A voltage follower circuit is introduced as an intermediary between the sensor coil and the transmission cable. This buffer circuit isolates the cable's line capacitance from the sensor coil, preventing capacitance coupling while maintaining signal integrity
Solution Approach 2:
The patent employs a triaxial cable with distinct functional layers: center conductor for signal transmission, inner shield for electromagnetic shielding, and outer shield for additional protection. Each layer serves a specific quality function to minimize capacitance effects
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 effectively minimizes signal drift and enhances long-term measurement accuracy by isolating cable capacitance and reducing self-capacitance, leading to more reliable distance measurements.
Implementation Method 1
An eddy current sensor comprises means for generating an eddy current in an electrically conducting test object and a sensor coil for the detection of the magnetic field of this eddy current
Implementation Method 2
the base portion of the sensor circuit comprises a voltage follower connected between the center conductor and the inner shield to isolate the line capacitance of the cable from the sensor coil
Data Source
AI summary
The invention pertains to an eddy current sensor with a sensor circuit having a head portion, including a sensor coil, a base portion and a transmission cable connecting the head portion to the base portion. The transmission cable is a triaxial cable and the sensor coil is connected between the inner conductor and the outer shield of this cable. The base portion of the sensor circuit comprises a voltage follower connected to buffer the voltage of the center conductor and apply it to the inner shield of the triaxial cable in order to isolate the cable's line capacitance from the sensor coil. The invention further concerns a sensor coil for an eddy current sensor, having a segmented winding structure with a particularly low self-capacitance. In a preferred embodiment, the triaxial transmission cable is combined with a sensor coil having this segmented winding structure.