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Technical Discussions
Doug Mendes
NDT Inspector, R & D
Imetrix Inc., USA, Joined Oct 1999, 7

Doug Mendes

NDT Inspector, R & D
Imetrix Inc.,
USA,
Joined Oct 1999
7
05:45 Nov-16-1999
Resonance Testing

I'm considering the application of resonance testing for immersion thickness gauging on steel for corrosion, but i'm unsure as to how the frequency of the transducer is selected. I know the instrumentation is tuneable but how do the two relate? Does the thickness of the test speciman govern the frequency? Is there a table that gives a starting point for thinkness vs. frequency selection? Any information would be most helpful and greatly appreciated.
Regards
Doug



    
 
 Reply 
 
Paul A. Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul A. Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
05:58 Nov-16-1999
Re: Resonance Testing
Hi Doug,
One method uses broadband ultrasonic pulses and looks at the frequency content of the entire signal reflected from the layer. If you have the same liquid (for example water) on both sides of the layer, then the reflection factor is zero at frequencies for which the layer is a multiple of one-half wavelength thick. If the frequency spectrum of the probe is in this range you will see a depression or notch in the reflection because those frequencies are totally transmitted. You select the probe so that its center frequency will be close to one-half wavelength in the layer.
You can achieve the same effect using tone-burst excitation and sweeping the frequency of the source. Using this method you generate the same spectrum one component at a time.
I hope this helps.
Regards,
Paul

: I'm considering the application of resonance testing for immersion thickness gauging on steel for corrosion, but i'm unsure as to how the frequency of the transducer is selected. I know the instrumentationis tuneable but how do the two relate? Does the thickness of the test speciman govern the frequency? Is there a table that gives a starting point for thinkness vs. frequency selection? Any information would be most helpful and greatly appreciated.
: Regards
: Doug




    
 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 302

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
302
09:18 Nov-17-1999
Re: Resonance Testing
: I'm considering the application of resonance testing for immersion thickness gauging on steel for corrosion, but i'm unsure as to how the frequency of the transducer is selected. I know the instrumentation is tuneable but how do the two relate? Does the thickness of the test speciman govern the frequency? Is there a table that gives a starting point for thinkness vs. frequency selection? Any information would be most helpful and greatly appreciated.
: Regards
: Doug

Dear Doug,
The reply from Krautkramer suggested two techniques, one a broad band excitation and one a swept frequency excitation.
We market the Quasar International Resonant Inspection instrument here in Europe. This may provide a solution.
It could also possibly be used in contact mode, and does not need a couplant.
e-mail me if you need more information.

Godfrey Hands
Godfrey Hands Ltd.
Godfrey@hands-ndt.co.uk


    
 
 Reply 
 

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