Equipment 



Hydrophone Description. 



The hydrophone impact test equipment consisted of: 



• a Bruel and Kjaer (B&K) hydrophone and safety case 



• a voltage supply source for the hydrophone (B&K) 



• a Piezotronic (PCB) instrumented hammer 



• a programmable digital oscilloscope (Tektronix model 7854) 



• a computer (Tektronix model 4052), printer, and tape drive 



The hydrophone and voltage supply source are shown in Figure 20. This 

 equipment was selected based on availability, economic constraints and 

 desired characteristics. 



The B&K hydrophone had the desired characteristics and was readily 

 available at NCEL. The hydrophone parameters are: 



• Piezoelectric transducers 



• Frequency range of 1 Hz to 125 Hz 



• Flat frequency response up to 70-80 kHz 



• Omnidirectional 



• Sensitivity of -184 db Ref lV/uPa 



• Built-in, solid state preamplifier 



Instrumented hammer kits are commercially available for behavior 

 testing of a wide variety of structures. PCB Piezoelectronics Incorpo- 

 rated manufactures and supplies hammer kits as complete calibrated sys- 

 tems. A technical representative from PCB Piezotronics recommended the 

 General Purpose impulse hammer. This impulse hammer was selected because 

 structures (like timber pilings) could be tested at low, medium, and 

 high frequencies. The impulse hammer contains a built-in accelerometer 

 (Figure 21) designed to measure the impact generated by the specific 

 hammer. The impulse hammer parameters are: 



• Forced transducer range of 0-500 lbf 



• Sensitivity of 10 mV/lbf 



• Resonant frequency of 70 kHz 



• Hammer mass of 0.3 lb 



• Tip diameter of 0.5 inch 



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