Digital TVG Gain Circuit for Backwall Flaw Detection
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Solution Overview
Problem
Existing ultrasonic flaw detectors face challenges due to their complex analog front ends, which result in calibration difficulties, reliability issues, and inconsistent results, particularly with matching input impedances, backwall attenuation, and DC offset errors, leading to reduced sensitivity and accuracy in detecting flaws near the backwall of objects.
Innovation Solution
A digital ultrasonic inspection system with a logarithmic time variable gain (TVG) device and tunable digital filters is implemented, simplifying circuitry and calibration processes, and using digital signal processing to enhance gain control and noise reduction, thereby improving the detection of flaws near the backwall and reducing the need for multiple filters and analog components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If complex analog front ends with multiple switches and amplifiers are used, then gain control flexibility is improved, but device complexity and calibration difficulty increase
Solution Approach 1:
The patent replaces the mechanical analog switching system with a digital signal processing approach. Instead of physically switching between multiple analog amplifiers with different gain values, the system uses a single analog amplifier followed by digital gain adjustment in the signal processing stage. This substitution eliminates the complexity of analog switching networks while maintaining full gain control flexibility through software-controlled digital processing.
Solution Approach 2:
The patent extracts the gain control function from the analog front end and relocates it to the digital signal processing stage. By separating the analog amplification stage from the gain control functionality, the system maintains simple analog circuitry while achieving flexible gain adjustment through digital processing of the captured echo signals.
2Adaptability or versatility
If multiple analog amplifiers with different gain values are switched in and out, then gain range is improved, but matching input impedances and maintaining frequency response becomes difficult
Solution Approach 1:
The patent implements a universal single analog amplifier that serves all gain requirements through one device. This amplifier is designed with a flat frequency response characteristic that remains consistent across all operating conditions. The previously needed multiple specialized amplifiers are replaced by this single multi-functional amplifier combined with digital gain control, eliminating impedance matching issues between different amplifier stages.
Solution Approach 2:
The patent makes the gain value dynamic by implementing time-variable gain control through digital processing. Instead of static gain settings requiring physical amplifier switching, the system dynamically adjusts gain values in software based on the time-of-flight of ultrasonic signals, allowing continuous gain adjustment without changing the physical amplifier configuration or affecting frequency response consistency.
3Adaptability or versatility
If analog circuits are switched in and out of the signal path, then adaptability is improved, but calibration accuracy and DC offset errors increase
Solution Approach 1:
The patent performs preliminary DC offset measurement and correction before the main measurement process. The system includes a DC offset nulling circuit that automatically measures and compensates for DC offsets in the analog circuits prior to signal acquisition. This preliminary action ensures that subsequent measurements are not affected by DC offset errors, maintaining high measurement precision while allowing flexible signal path configuration.
4Measurement precision
If the entire dynamic range of the instrument is utilized, then sensitivity is improved, but gain linearity calibration becomes more difficult
Solution Approach 1:
The patent changes the parameter space by implementing logarithmic compression of the signal amplitude in the digital processing stage. This allows the system to utilize the entire dynamic range of the analog-to-digital converter while representing the data in a logarithmic scale that simplifies gain linearity calibration. The logarithmic transformation compresses the large dynamic range into a manageable scale where linear calibration relationships are maintained, avoiding the complexity of calibrating across the full exponential dynamic range.
Data Source
AI summary
In a non-destructive test instrument, there is provided a time variable gain (TVG) amplifier wherein the gain of the amplifier is dynamically changed to optimize the amplitude of a flaw echo signal. The TVG digital memory for a given TVG curve specifies and controls not only the start gain value, and the end game value, but the gain rate of change slope as well to generate TVG curve line segments.