Eddy Current Test Setup Digital Filtering Scan Rate Reduction
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Solution Overview
Problem
Existing eddy current test setups for non-destructive flaw detection in devices face challenges in achieving high accuracy due to limitations in signal processing and analysis, particularly in reducing noise and enhancing flexibility with varying excitation frequencies.
Innovation Solution
The proposed test setup incorporates an excitation coil, a receiving coil, an analog-digital converter, a filter arrangement, and a demodulator, enabling digital filtering and scan rate reduction to enhance accuracy. This setup allows for high converter scan rates, band-pass filtering, and adjustable scan rate reduction, facilitating precise demodulation and analysis of eddy current signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high converter scan rate is used to overscan the coil signal for high accuracy detection, then measurement precision is improved, but device complexity increases due to the need for band-pass filtering and scan rate reduction
Solution Approach 1:
The system performs preliminary digitalization of the coil signal at a high converter scan rate before demodulation, ensuring that the signal is captured with sufficient resolution. This preliminary high-rate sampling allows subsequent scan rate reduction without losing measurement accuracy, as the essential signal information has already been captured in detail.
Solution Approach 2:
The patent introduces a band-pass filter arrangement as an intermediary component between the analog-to-digital converter and the demodulator. This filter serves as a mediator that reduces the scan rate by filtering out unnecessary frequency components while preserving the essential signal characteristics needed for accurate flaw detection.
2Ease of manufacture
If digital filtering and scan rate reduction are implemented, then analog component costs are reduced, but processing time increases
Solution Approach 1:
The patent replaces expensive analog filtering components with digital filtering implemented in software or digital signal processing hardware. The band-pass filter arrangement operates in the digital domain after analog-to-digital conversion, eliminating the need for complex analog filter circuits while achieving the same signal processing objectives.
Solution Approach 2:
The system uses periodic sampling at the converter scan rate that is synchronized with the excitation frequency. By sampling at specific intervals and applying scan rate reduction, the system processes signals efficiently in periodic batches rather than requiring continuous high-rate processing, thereby reducing overall processing time.
3Measurement precision
If the converter scan rate is set high to satisfy Nyquist-Shannon sampling theorem, then measurement precision is improved, but productivity decreases due to increased data processing load
Solution Approach 1:
The band-pass filter arrangement extracts only the relevant frequency components from the oversampled signal by removing unnecessary high-frequency and low-frequency content. This extraction process reduces the data volume that needs to be processed by the demodulator while preserving the essential information needed for accurate measurement.
Solution Approach 2:
The system performs excessive sampling at a converter scan rate higher than the minimum required by the Nyquist-Shannon theorem, then applies scan rate reduction to achieve the desired processing efficiency. This partial use of the oversampled data ensures measurement precision while the reduction factor optimizes processing efficiency.
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 achieves high accuracy in detecting flaws by maintaining Nyquist-Shannon sampling theorem compliance, allowing for flexible selection of scan rates corresponding to excitation frequencies, and enabling further processing with a slow-operating digital demodulator, thus improving the precision of eddy current analysis.
Implementation Method 1
An excitation signal can be sent to the excitation coil (14) to act on the device under test (16) with an electromagnetic alternating field
Implementation Method 2
Eddy currents form in the device under test and are picked up. Changes in these eddy currents around the flaw are analyzed
Implementation Method 3
The receiving coil (17) is designed to generate a coil signal that is a function of the flaw in the device under test
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A test set-up (10) for non-destructive detection of a flaw in a device under test by means of an eddy current comprises an excitation coil (14), to which an excitation signal (SE) can be provided to act on the device under test (16) with an electromagnetic alternating field, a receiving coil (17) to generate a coil signal (SP), which is a function of the flaw in the device under test (16), an analog-digital converter (21), which is coupled to the receiving coil (17) on the input side, a filter arrangement (22), which is coupled to the analog-digital converter (21) on the input side and is designed for band-pass filtering and scan rate reduction, and a demodulator (27), which is coupled to an output of the filter arrangement (22) on the input side.