The Research And Design Of Pulsed Eddy Current Receiving System For Ferromagnetic Material

Ferromagnetic materials of casing, pipeline and pressure vessel often sufferthickness reduction from corrosion in the long term load operation process, forming apotential safety hazard. Various depth of detection can be detected effectively forferromagnetic pressure equipment, the Pulsed Eddy Current technology has became anew type of nondestructive testing (NDT) technology in recent yearsThe paper designed the low noise, low power consumption weak signalconditioning circuit according to the characteristics of the PEC signal for thickness offerromagnetic materials pressure equipment such as low SNR, interference easily,difficulty receive effectively;enhanced the SNR of Pulsed Eddy Current testing system,improved the accuracy of the detection.To get the signal high-resolution acquisition under the large dynamic range forpulsed eddy current testing, a time-sharing, dual channel data system is designed for thePEC signal with the characteristics of weak, large dynamic range and accurateacquisition.Analyzed the detecting coil output response characteristics under differentdamping state, optimized the parameter for excitation source and designed theimpedance matching circuit, obtained high sensitivity detection coil output.High and low voltage clamping circuit was designed, the late time delay signalwhich is rich of various detection information, was selected from the whole of PECtesting signal, to design special weak signal conditioning circuit according to thecharacteristic of the signal.Improving the noise performance of the pulsed eddy current detecting receivingsystem, the balanced differential preamplifier circuit and high order low pass filtercircuit were designed.Set up data acquisition platform with the LabVIEW software and NI multi-functiondata acquisition card, designed multistage programmable amplifier circuit based on thedigital output signal from data acquisition platform; through programmable amplifiercircuit which is controlled by data acquisition platform, adopting the method ofsynchronous data acquisition and multiple superimposed on average, improving theresolution of pulsed eddy current testing signal effectively.Analyzed the characteristics of each frequency band and the noise source from the receiving system including internal and external, restrained the noise of the receivingcircuit and components through the reasonable choice of circuit components, the lowripple linear floating voltage source designing and reasonable shielding and groundingtechnology.Tested and analyzed the main performance of receiving system, a series ofexperiments were taken on ferromagnetic pips with different artificial detects, thenanalyzed the detect ability of the PEC receiving systems through processed data. Theexperiment results show that this pulsed eddy current receiving system forferromagnetic materials can detect0.5mm area corrosion thickness difference onoutside pipes, effective detecting wall thickness range from1.5mm to8mm under5.7mm inner pipe wall thickness with internal through type detection probe.