Packet-Based DDS for Eddy Current Testing Noise Reduction
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Solution Overview
Problem
Conventional direct digital synthesizers (DDS) in eddy current instruments suffer from roll-over errors due to numerical differences in consecutive sine waves, leading to noise and reduced sensitivity in measuring small changes in test objects.
Innovation Solution
A packet-based DDS design is employed, where sine waves are packaged into packets with precisely chosen periods to match the start and end of each packet, eliminating roll-over errors and ensuring perfect repeatability of signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional DDS generates consecutive sine waves with different numerical sequences, then frequency control is achieved, but roll-over errors and noise are introduced
Solution Approach 1:
The patent applies periodic action by organizing sine wave data into packets that repeat identically. Instead of generating continuously varying sine waves, the system creates a finite packet of sine wave data points that repeats periodically, ensuring identical numerical sequences in each packet cycle and eliminating roll-over errors at packet boundaries.
Solution Approach 2:
The patent segments the continuous sine wave generation into discrete packets of data points. By dividing the sine wave into finite packets and ensuring each packet contains an integer number of cycles, the system eliminates the problematic continuous accumulation and roll-over behavior while maintaining frequency control through packet repetition rate.
2Device complexity
If conventional DDS uses modular arithmetic with accumulator overflow, then frequency synthesis is simplified, but noise is spread across the spectrum
Solution Approach 1:
The patent extracts and removes the problematic roll-over error component from the signal generation process. By using pre-calculated packets that repeat identically rather than continuous modular accumulation, the system eliminates the spectral noise generated by roll-over errors while maintaining the simplicity of digital frequency synthesis.
3Measurement precision
If eddy current instruments measure very small changes in signal phase and amplitude, then inspection sensitivity is improved, but the unchanging portion of the signal interferes with measurement
Solution Approach 1:
The patent creates a precise copy of the excitation signal through identical packet repetition. This copy serves as a reference that exactly matches the unchanging portions of the received signal, enabling effective nulling and subtraction to isolate the small changes caused by defects while eliminating interference from the dominant unchanging signal components.
Data Source
AI summary
Disclosed are a method of and an apparatus devising a packet based DDS circuitry for performing packet based a direct digital synthesizing (DDS) function within an electronic testing instrument. The circuitry comprising a DDS logic circuit configured to execute direct digital syntheses on a plurality of consecutive packets of sine-like waves, each packet having a length of a period precisely chosen such that the sine wave at the end of one packet matches up with the sine wave at the start of the immediate subsequent packet. Also disclosed is an eddy current testing circuitry using multiple outputs of the single packet based DDS, one of the output is used in a circuit producing reference signals approximating the response signals. With the usage of the packet based DDS, the reference signal can be highly effective in nulling the unchanging portion of the response signals.