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- since 1996 -

Sonotron NDT
Original developer and manufacturer of advanced ultrasonic instruments
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Technical Discussions
Eli Brosh
Eli Brosh
04:18 Mar-10-2003
Pulsed Eddy Current : advantage over conventional EC

What is the advantages of pulsed eddy current over conventional EC ?
Does Pulsed eddy current provide better lift-off compensation than conventional eddy current ? Can Pulsed eddy current be used with larger lift-off or larger lift-off variations than conventional EC ?


 
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Dave Forsyth
R & D
TRI/Austin, USA, Joined Nov 2001, 41

Dave Forsyth

R & D
TRI/Austin,
USA,
Joined Nov 2001
41
02:13 Mar-10-2003
Re: Pulsed Eddy Current : advantage over conventional EC
All answers IMHO...

: What is the advantages of pulsed eddy current over conventional EC ?
Inherently more information is available in pulsed EC. This can be a disadvantage.

: Does Pulsed eddy current provide better lift-off compensation than conventional eddy current ?
There is no automatic lift-off compensation. It is possible to do so lift-off compensation successfully, and has been demonstrated by many groups including one in which I participate.

:Can Pulsed eddy current be used with larger lift-off or larger lift-off variations than conventional EC ?
This is a good question. I would think the answer would be yes, at least in theory.

It is probably simpler to use multiple single frequencies to mix out liftoff in cases where liftoff is regular (i.e. due to well defined geometry). Then one can highly optimize the mixing.

In other cases where liftoff can vary unpredictably over a large range, the liftoff compensation schemes used in many pulsed EC implementations are likely superior. For example, we developed a liftoff compensation algorithm for inspection of aircraft fuselage splice joints, where manufacturing and corrosion-induced deformations make for varying and unpredictable tilt and liftoff. Our algorithm works well over a large range of liftoff values for this case.

One of my colleagues was able to do a pretty good job of compensation in the same case using three frequencies, but it was a lot more difficult.

Regards, Dave



 
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Tom Bloodworth
Consultant, R&D
Bloodworth Consulting Limited, United Kingdom, Joined Aug 2002, 12

Tom Bloodworth

Consultant, R&D
Bloodworth Consulting Limited,
United Kingdom,
Joined Aug 2002
12
09:20 Mar-11-2003
Re: Pulsed Eddy Current : advantage over conventional EC
: What is the advantages of pulsed eddy current over conventional EC ?
: Does Pulsed eddy current provide better lift-off compensation than conventional eddy current ? Can Pulsed eddy current be used with larger lift-off or larger lift-off variations than conventional EC ?
.

Despite having worked in ECT for many years, I was never sure what advantages pulsed eddy currents gave. Now working with metal detectors - I know that pulsed detectors are supposed to be less influenced by the susceptibility of the soil. The idea is that the response is sampled after the initial pulse (strongly dependent on the soil susceptibility) has died away. Unfortunately things are more complicated than this as the susceptibility is complex (freq. dependent) so it does not quite work...

So my follow-up question is; is pulsed eddy current intended to be less dependent on the magnetic characteristics of the metal?



 
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