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Technical Discussions
A K Das
A K Das
07:39 Sep-26-2003
Bandwidth of UT equipment required for driving a probe

Dear Members of this forum,

I would like to have technical help on the following issue:

-What should be the bandwidth (narrow, broad) for driving a UT probe in genral

-Can a UT equipment having 20 MHZ 3 dB bandwidth be used for driving a 25 MHz straight beam probe with delayline. In case it could be used, then with what limitations?

Wish to have your valuable guidance on this issue
thanks to you all

Anil.


    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1235

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1235
05:01 Sep-27-2003
Re: Bandwidth of UT equipment required for driving a probe
Mr. Das:
By "driving" a probe I think you mean to pulse it with a voltage. Pulsers are usually of 3 types, spike, squarewave or tone-burst. The latter 2 usually have some "tuning" ability so you can match the piezo element displacement timing with the applied voltage cycle(s). By tuning closely to the natural mechanical vibration you can optimise element displacement. Thereby, the transmitted pulse provides a maximum particle displacement. This usually results in a smaller frequency content in the pulse. By tuning longer or shorter voltage durations than the natural resonance of the element you reduce the maximum displacement in the element but increase the frequency content (i.e. increase bandwidth).

The 3dB bandwidth of the "instrument" you refer to seems to relate to the receiver portion of the circuit. This would suggest that the centre frequency of the receiver is located at 20MHz, or perhaps the range between the upper and lower frequency region between the 3dB drop points is 20MHz.

In anycase, this sounds like the receiver could also be sensitive to the pulse generated by a "nominal" 25MHz probe. Most maunfacturers assess probe frequency content in an immersion setup. If you were to do on FFT on the interface signal of the delayline to air you would probably find that the centre frequency has already dropped to well below the nominal 25MHz as a result of higher frequencies being absorbed in the delayline. If the electrical matching between the probe and instrument are adequate you should be able to use the probe with the instrument and get useful signals.
Ed
----------- Start Original Message -----------
: Dear Members of this forum,
: I would like to have technical help on the following issue:
: -What should be the bandwidth (narrow, broad) for driving a UT probe in genral
: -Can a UT equipment having 20 MHZ 3 dB bandwidth be used for driving a 25 MHz straight beam probe with delayline. In case it could be used, then with what limitations?
: Wish to have your valuable guidance on this issue
: thanks to you all
: Anil.
------------ End Original Message ------------




    
 
 
Edi Suranta Perangin-angin
NDT Inspector
PT. Growth Asia, Indonesia, Joined May 2003, 1

Edi Suranta Perangin-angin

NDT Inspector
PT. Growth Asia,
Indonesia,
Joined May 2003
1
00:16 Oct-06-2003
Re: Bandwidth of UT equipment required for driving a probe
----------- Start Original Message -----------
: Mr. Das:
: By "driving" a probe I think you mean to pulse it with a voltage. Pulsers are usually of 3 types, spike, squarewave or tone-burst. The latter 2 usually have some "tuning" ability so you can match the piezo element displacement timing with the applied voltage cycle(s). By tuning closely to the natural mechanical vibration you can optimise element displacement. Thereby, the transmitted pulse provides a maximum particle displacement. This usually results in a smaller frequency content in the pulse. By tuning longer or shorter voltage durations than the natural resonance of the element you reduce the maximum displacement in the element but increase the frequency content (i.e. increase bandwidth).
: The 3dB bandwidth of the "instrument" you refer to seems to relate to the receiver portion of the circuit. This would suggest that the centre frequency of the receiver is located at 20MHz, or perhaps the range between the upper and lower frequency region between the 3dB drop points is 20MHz.
: In anycase, this sounds like the receiver could also be sensitive to the pulse generated by a "nominal" 25MHz probe. Most maunfacturers assess probe frequency content in an immersion setup. If you were to do on FFT on the interface signal of the delayline to air you would probably find that the centre frequency has already dropped to well below the nominal 25MHz as a result of higher frequencies being absorbed in the delayline. If the electrical matching between the probe and instrument are adequate you should be able to use the probe with the instrument and get useful signals.
: Ed
: : Dear Members of this forum,
: : I would like to have technical help on the following issue:
: : -What should be the bandwidth (narrow, broad) for driving a UT probe in genral
: : -Can a UT equipment having 20 MHZ 3 dB bandwidth be used for driving a 25 MHz straight beam probe with delayline. In case it could be used, then with what limitations?
: : Wish to have your valuable guidance on this issue
: : thanks to you all
: : Anil.
------------ End Original Message ------------




    
 
 

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