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Technical Discussions
Lirin Philip
,
VALDEL , India, Joined Sep 2019, 10

Lirin Philip

,
VALDEL ,
India,
Joined Sep 2019
10
06:34 Sep-09-2019
How to select Rectifier in Ultrasonic testing.

Selection of Rectifier in ultrasonic testing ,like full wave,half wave positive ,half waves negatives or radio frequency ,what is criteria selection of that mainly doing operation on carbon composite material. We are using Omni scan sx by olympus.

 
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nick bublitz
Other,
VeriPhase, USA, Joined May 2010, 137

nick bublitz

Other,
VeriPhase,
USA,
Joined May 2010
137
15:04 Sep-09-2019
Re: How to select Rectifier in Ultrasonic testing.
In Reply to Lirin Philip at 06:34 Sep-09-2019 (Opening).

Generically-
Full wave for angle beam flaw detection where maximum echo response is of most importance. RF to visualize phase shift- bond testing etc. Half wave for thickness testing/corrosion testing.
You can search for and apply conventional ut principles on these displays to phased array.

from Olympus tutorial on UT:
Received echoes can be displayed either as an unrectified RF signal, as half wave positive or half wave negative rectified signals, or with full wave rectification. Raw echoes are initially processed as RF waveforms with both positive and negative peaks. The RF display mode is useful when working with very thin test pieces and in cases where echo phase or polarity is of interest. Half wave positive rectification shows only the positive peaks, while half wave negative rectification shows only the negative peaks, flipped to the positive side of the baseline. Half wave rectification can in some cases improve signal-to-noise by reducing spurious peaks. Full wave rectification displays both positive and negative echo lobes together on the positive side of the baseline and is the most commonly used format in flaw detection applications

3
 
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Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 253

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
253
15:18 Sep-09-2019
Re: How to select Rectifier in Ultrasonic testing.
In Reply to Lirin Philip at 06:34 Sep-09-2019 (Opening).

zoom image



Further to Nick's comments, half-wave is best used in thickness testing to ensure that measurements are always made on wave lobes of the same polarity.

If you use full wave rectification, it is impossible to tell whether your gate is triggering on a positive or negative lobe (see attached image). This may be inconsequential if your measurement resolution requirements are relatively low (i.e. if you don't care about the nearest 0.005" or 0.010", then full wave may be fine!).

But if you are doing very fine, precise work (e.g. pen probe or small diameter high frequency dually) then you are definitely better off using half wave.

Use RF mode to start, find out which wave lobe is the best, then calibrate off that and go for it.
2
 
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Lirin Philip
,
VALDEL , India, Joined Sep 2019, 10

Lirin Philip

,
VALDEL ,
India,
Joined Sep 2019
10
10:17 Sep-10-2019
Re: How to select Rectifier in Ultrasonic testing.
In Reply to Paul Holloway at 15:18 Sep-09-2019 .

I'm working in the field of composite materials and the maximum thickness of composite parts comes around less than 5mm.

 
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