Ultra sound test

8/12/2019 Ultra sound test

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mmz 2003

Sound Generation

Hammers (Wheel tapers)

Magnetostrictive

Lasers Piezo-electric

magnetostrictive


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Piezo-Electric Effect

When exposed to an alternating current acrystal expands and contracts

Converting electrical energy into mechanical

- + + - - +


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Piezo-Electric Materials

QUARTZ Resistant to wear

Insoluble in water

Resists ageing

Inefficient converter ofenergy

Needs a relatively high

voltage

Very rarely used nowadays

LITHIUM SULPHATE Efficient receiver

Low electrical

impedance

Operates on lowvoltage

Water soluble

Low mechanical

strength Useable only up to 30CUsed mainly in medical


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mmz 2003

Polarized Crystals

Powders heated to

high temperatures

Pressed into shape Cooled in very

strong electrical

fields

Examples

Barium titanate (Ba Ti O3)

Lead metaniobate(Pb Nb O6)

Lead zirconate titanate

(Pb Ti O3 or Pb Zr O3)

Most of the probes for conventional usage use

PZT : Lead Zirconate Titanate


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Probes


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Probes The most important part of the

probe is the crystal The crystal are cut to a

particular way and thickness to

give the intended properties

Most of the conventional crystal

are Xcutto produce

Compression wave

Z

X

X X

Y


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mmz 2003

Probes

The frequency of the probe depends on

the THICKNESSof the crystal

Formula for frequency:

Ff = V / 2tWhere Ff = the Fundamental frequency

V = the velocity in the crystal

t = the thickness of the crystal

Fundamental frequency is the frequency of the material ( crystal )where at that frequency the material will vibrate.


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mmz 2003

Probes

The Thinnerthe crystal the Higherthe frequency

Which of the followings has the Thinnest crystal ?

1 MHz Compression probe

5 MHz Compression probe

10 MHz Shear probe

25 MHz Shear probe

25 MHz ShearProbe


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mmz 2003

Probe Design

Compression Probe

Normal probe

0

Damping

Transducer

Electricalconnectors

Housing


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Probe Design

Shear Probe

Angle probe

DampingTransducer

Perspex wedge

Backing

medium

Probe

Shoe


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Probe Design

Twin Crystal

Advantages

Can be focused

Measure thin plate

Near surface

resolution

Disadvantages

Difficult to use on

curved surfaces Sizing small defects

Signal amplitude /

focal spot length

Transmitter Receiver

Focusing

lens

Separator /

Insulator


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Sound Intensity

Comparing the intensity of 2 signals

1

0

1

0

P

P

I

I

Electrical power proportional to the

square of the voltage produced

2

1

2

0

1

0

)(

)(

V

V

P

P

2

1

2

0

1

0

)(

)(

V

V

I

IHence


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mmz 2003

Sound Intensity

2

1

2

0

1

0

)()(

VV

II Will lead to large ratios

21

2

0

10..1

0

10.. )(

)(

V

VLog

I

ILog Therefore

dBV

VLog

I

ILog

1

0

10..

1

0

10.. 20

BELS

V

VLog

I

ILog

1

0

10..

1

0

10.. 2


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1

0

10..20

H

HLogdB

2 signals at 20% and 40% FSH.

What is the difference between them in dBs?

2..2020

4020

1010.. LogLogdB

3010.020dB

dBdB 6


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mmz 2003

1

0

10..20

H

HLogdB

2 signals at 10% and 100% FSH.

What is the difference between them in dBs?

10..2010

10020

1010.. LogLogdB

120dB

dBdB 20


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mmz 2003

Amplitude ratios in decibels

2 : 1 = 6bB

4 : 1 = 12dB

5 : 1 = 14dB 10 : 1 = 20dB

100 : 1 = 40dB


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Automated Inspections

Pulse Echo

Through Transmission

Transmission with Reflection

Contact scanning

Gap scanning

Immersion testing


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Gap Scanning

Probe held a fixed

distance above the

surface (1 or 2mm)

Couplant is fed intothe gap


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Immersion Testing

Component is placed in a water filled

tank

Item is scanned with a probe at a fixed

distance above the surface


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mmz 2003

Immersion Testing

Water

path

distance

Water path distance

Front surface Back surface

Defect

Ultra sound test

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