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Technical Discussions
Timothy MacInnis
Senior NDT Engineer
SAIC/Ultra Iamge International, USA, Joined Dec 1999, 10

Timothy MacInnis

Senior NDT Engineer
SAIC/Ultra Iamge International,
USA,
Joined Dec 1999
10
07:21 Dec-10-1999
Piezo-Composite UT Elements

I am currently using a piezo-composite element with a positive going square wave pulser. The units have been failing in a slowly, within hours, deteriorating fashion. I have spoke with various xdcr manufacturers and found that the polarization of the element requires a negative going pulse. I have always been able to just pick up a transducer and not worry about pulse polarity. Questions I have: can the elements be selectively polarized upon manufacture? Is there an industry standard stating all pulsers be negative going? Is their an industry standard for the polarization of elements?
Any response will be greatly appreciated.


    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1219

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1219
08:49 Dec-10-1999
Re: Piezo-Composite UT Elements
A positive going spike for a pulser is a bit non-standard but it is still
odd that it should cause a depolarisation (especialy so fast).
Is the voltage of the pulse especially high?
Is the duration of the pulse very long?
Are there a lot of cycles in the pulse?
Usually a fairly high temperature would need to be associated with a "depolarising voltage".
Are you running the experiment in a heat experiment?

Ed
: I am currently using a piezo-composite element with a positive going square wave pulser. The units have been failing in a slowly, within hours, deteriorating fashion. I have spoke with various xdcr manufacturers and found that the polarization of the element requires a negative going pulse. I have always been able to just pick up a transducer and not worry about pulse polarity. Questions I have: can the elements be selectively polarized upon manufacture? Is there an industry standard stating all pulsers be negative going? Is their an industry standard for the polarization of elements?
: Any response will be greatly appreciated.




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

Paul Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
09:16 Dec-10-1999
Re: Piezo-Composite UT Elements
Hi Tim,
The factors causing dpolarization of a piezoelectric material are electric field, temperature, and time. There are many different piezoelectric materials used in transducer construction and some are more capable of tolerating reverse fields than others. As Ed points out high reverse fields at high temperatures are especially damaging. It's also possible that high rep rates can increase the internal temperature of the probe even though the environment isn't hot. Higher frequency probes use thinner piezoelectric elements which increase the field for the same pulse voltage.
If you can't reverse the pulsed field, you can probably have your probe supplier reverse the piezoelectric element to avoid this effect.
Regards,
Paul

: I am currently using a piezo-composite element with a positive going square wave pulser. The units have been failing in a slowly, within hours, deteriorating fashion. I have spoke with various xdcr manufacturers and found that the polarization of the element requiresa negative going pulse. I have always been able to just pick up a transducer and not worry about pulse polarity. Questions I have: can the elements be selectively polarized upon manufacture? Is there an industry standard stating all pulsers be negative going? Is their an industry standard for the polarization of elements?
: Any response will be greatly appreciated.




    
 
 

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