Development Of Pulsed Eddy Current Testing System Excitation Signal Source

Pulsed eddy current testing is a new nondestructive testing technology developed rapidly in recent years.It is based on the principle of eddy current effect, the development of eddy current nondestructive testing technology, enabling rapid detection of surface and sub-surface defects in metal conductors, has been widely used in shipbuilding, aviation, chemicals and other industrial fields.The pulsed eddy current testing system usually consists of a pulse excitation signal source, detection probe and signal data acquisition and data processing system.The eddy current sensor probe is excited by a pulse excitation signal in the pulsed eddy current testing system.The excitation source as one of the key components of the pulsed eddy current testing system, which will affect the performance and stability of the entire eddy current testing system.With the continuous development of pulsed eddy current testing technology, the excitation signal source’s requirements of cost control, space size, performance, stability, and special applications are becoming increasingly high in the actual industrial applications. Therefore,according to the actual demand of the pulsed eddy current testing system,it is particularly important to design an excitation source with good stability and high reliability.Through the contrast analysis of excitation source’s technical parameters and design methods in pulsed eddy current testing system both at home and abroad in this paper,performance of pulsed eddy current testing affected by pulsed excitation parameters is analyzed at first,and the commonly generate ways of pulse signal is compared.Then drawing a design based on the principle of DDS and developing a excitation signal source with the micro controller and field programmable logic devices according to the requirements of indicators and special function by detection system excitation source.MSP430 micro controller used for control chip.FPGA is developed for DDS signal source module and logic function module.The hardware architecture of system is designed in detail which mainly includes digital-analog conversion circuit、low-pass filter circuit、square wave generator circuit and amplifier circuit modules.On the basis of the hardware system,control software and PC software are designed by C language and Labview.High power square waveform、sawtooth waveform and triangle waveform can be generated in the continuous or instantaneous model by controlling the pulsed eddy current testing platform.Integrative design and control of the pulsed eddy current testing system is achieved in the end.Finally,the software and hardware modules of pulse excitation signal source are carried out a series of parameter index test、function test and commissioning test of pulsed eddy current testing system,meanwhile the deviations of the test results are analyzed which point out the improved method.It shows that the excitation signal source system researched in this paper can generate pulse sequence with external burst or timing burst,and it has large output power 、 good stability that frequency accuracy≤±0.5% and amplitude accuracy≤±(2%+10mv) for pulsed eddy nondestructive detection in the results.All the parameters and function meet the design goal of the pulsed eddy current testing system.