The System and Method of Ultrasonic TestingBased on Linear-Frequency-Modulation Technique

Jiaying ZHANG, Tie GANG, Sen CONG

State Key Laboratory of Advanced Welding and Joining,

Harbin Institute of Technology, China

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Founded in 1920, Harbin Institute of Technology (HIT),

with science, engineering and research as its core, encompassing management and liberal arts, economy and law,

is now developing into an open, multi-disciplinary and world-class university.

Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

CONTENTS

Experiments

Introduction

Design and Realization of The System

Evaluation of The System Performance

4

1

2

3

Conclusions5

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Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

INTRODUCTION

� Ultrasonic testing used widely

� A problem existing

A conflict between the propagation distance and the time resolution

The exciting signal The echo signal

Average power

Propagation distance

Lower

Higher

Shorter

Longer

Time resolution

Smaller

Larger

� To solve the problem

The power of the exciting signal

The time resolutionControl respectively

f 1/f

Time DomainFrequency Domain

Introduce the theory of LFM(Linear Frequency Modulation ) and pulse compression in radar system into ultrasonic testing

Ultrasonic system Pulse compression

Higher average power

Longer propagation distance

Smaller time resolution

The LFM exciting signal The echo signal� Make the LFM ultrasonic system smaller in size

The system used in the lab

composed of waveform generator and so on

The developed system

composed of integrated circuit and so on

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Smaller in size and convenient to be used

Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

DESIGN AND REALIZATION

The signal generation section

The signal acquisition section

Pulse compression section

Results

Time width: 1µs-1msBandwidth: 1MHz-20MHzVoltage:5V-600VCommunication with host computer: USB 2.0

Sampling rate: 50MSPSSampling resolution: 8 bitDual channels

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Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

The signal generation section

� General design block diagram

DESIGN AND REALIZATION

Double micro-processor chips

51 series microcontroller

CPLD(Complex Programmable Logic Device)

The exciting signal is stable and can be controlled in real time

Based on DDS(Direct Digital Synthesizer) techniqueCore chip: AD9910

Realization of the filter: analog circuitUSB2.0 techniqueCore chip: CY7C68013A

Linear

� Flow chart

� Physical map of this section

The power amplifierThe waveform generation and the filter

and the double microprocessors

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Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

The signal acquisition section

� General design block diagram

DESIGN AND REALIZATION

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Dual channels for data acquisition

Sampling rate: 50MSPS

Sampling resolution: 8bit

The No.1 module

of data acquisition

The No.2 module

of data acquisitionThe synchronizing signal

Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

Pulse compression section

� Realization

( ) ( )* ( )y t s t h t====

FFT{ ( )* ( )} ( ) ( )s t h t S f H f= ⋅= ⋅= ⋅= ⋅

( ) FFT{ ( )}S f s t====( ) FFT{ ( )}H f h t====

1FFT { }y S H−−−−

= ⋅= ⋅= ⋅= ⋅

s(t): the received signal

h(t): the frequency-domain response of the matched filter(the reference signal through the conjugate and turning)

DESIGN AND REALIZATION

� Flow chart

� Matlab simulation

The exciting signal The TOFD echo signalThe result of pulse

compression

0 1 2 3 4 5-1

0

1

Time(µs)

Norm

alized A

mplitu

de

0 5 10 15-1

0

1

Time(µs)

Norm

alized A

mplitu

de

0 5 10-1

0

1

Time(µs)

Norm

alized A

mplitu

de

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Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

� Selection of the system parameters� The signal at the boundary

� Evaluation of the system

EVALUATION

� Evaluation of the exciting signalB

an

dw

idth

:20M

Hz

Time width: 1µs

Ban

dw

idth

:1M

Hz

The developed system The waveform generator Matlab simulation

� The signal used in the experiments

Time width: 5µs Bandwidth:11MHz

The developed system The waveform generator Matlab simulation

Time width: 5µsBandwidth: 11MHzFrequency Range: 1MHz-12MHzExcitation voltage: 110V

0 1 2 3 4 5-1

0

1

Time(µs)

Norm

alized A

mplitu

de

Testing sample: 30mm-thicknesscarbon steel

Flaw depth: 28.1mmSampling rate: 50MSPSExcitation voltage: 110VTime width: 5µsBandwidth:11MHz

Flaw

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� Summarize the differences between the two systems

The system used in the lab

The system developed in this paper

� size

� cost

� Data acquisition

� reference signal

� pulse compression

larger smaller

more expensive cheaper

single channel double channels

can not change can change anytime

different

The system used in the labThe system developed in this paper

composed of waveform generator and so on

composed of integrated circuit and so on

Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

EXPERIMENTS

� Samples

Testing sample 1: 20mm-thickness carbon steelFlaw depth: 12.0mm

Testing sample 2: 20mm-thickness stainless steelFlaw depth: 15.0mm and 12.0mm

Testing sample 3: 20mm-thickness stainless steel weldFlaw depth: 14.7mm and 7.4mm

Sample 3 (flaw depth: 14.7mm) Sample 3 (flaw depth: 7.4mm)

� Compared with the conventional TOFD testing

The results of testing carbon steel with12mm-depth flaw

The conventional TOFD testing The LFM system developed in this paper

Lateral waveDiffracted wave

Back wall echoLateral wave

Diffracted wave

Back wall echo

� Compared with the system used in the lab

The system used in the lab The system developed in this paper

The results of testing carbon steel with12mm-depth flaw

Different pulse-compression algorithm

Dual-channel data acquisitionSignal-channel data acquisition

Lateral wave

Lateral waveFlaw diffracted

wave

Flaw diffracted

wave

Back wall echo

Back wall echo

� Results of testing 20mm-thickness stainless steel

The depth of the flawAbsolute

error(mm)

Relative error(%)

Actualvalues(mm)

Measured values(mm)

15.0 15.2 0.2 1.3

12.0 12.2 0.2 1.7

Parent material weld

The depth of the flawAbsolute

error(mm)

Relative error(%)

Actualvalues(mm)

Measured values(mm)

14.7 14.3 0.4 2.7

7.4 7.7 0.3 4.1

Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining

CONCLUSIONS

� A real-time ultrasonic testing system has been developed based on LFM technique

� The system is portable and stable and convenient to be used in the construction site

� The time width of the exciting signal produced by the system ranges from 1µs to 1ms, and the bandwidth ranges from 1MHz to 20MHz

� The absolute error is no more than 0.4mm and the relative error is less than 5% when testing stainless steel and its weld

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Harbin Institute of TechnologyState Key Laboratory of Advanced Welding and Joining12/12