Development of Modular Array Eddy Current Online Testing System

Date: April 2022 – present (Master project)

This is my graduate research project. The development of an 8-channel array eddy current testing (ECT) system involves hardware system design and software development.

• Hardware system: Implemented the demodulation of defect signals from the detection coil. Employed analog signal processing and digital filtering to amplify the defect signal, initially at the 0.1V level, to a 1V level. Utilized ZYNQ-7000 with a network interface for efficient data transmission to the host computer.
• Software development: Utilized CPLD and STM32 to excite coils and demodulate defect signals. Incorporated a DSP chip to execute infinite impulse filter (IIR) and digital-to-analog (DA) outputs. Leveraged the ZYNQ (FPGA + Arm) platform to control the variable gain amplifier and ensure efficient transmission of analog-to-digital (AD) data to the host computer.

Methodology

These are the three steps of detection, the PCB design is shown in Fig 1:

1. Eddy current excitation and detection signal preprocessing module: This module is mainly composed of STM32 and CPLD. The STM32 controls the CPLD to generate a sinusoidal excitation signal and send it to the probe. The detection coil picks up the detection signal excited by the probe and demodulates the defect signal through phase-sensitive detection (PSD).
2. Digital filtering and gain control module: The detected weak defect signal (peak-to-peak value is about 100mV) is digitally filtered in DSP(TMS320F28377D) and amplified by an variable gain amplifier (AD8338) to obtain a high SNR defect signal.
3. Main control module: The module uses ZYNQ-7000 to control AD acquisition chip to obtain defect signal, and communicates with the host computer based on network interface, uploads defect signals, and obtains control information of the system from host computer.

Result

The PCB currently supports processing speeds of up to 8 channels at 200kHz. The Fig 3 is the acquisition result of testing the hole defects of copper tubes by means of through-type eddy current testing. The hole sizes range from 0.3 mm-1.15 mm.