COUPLING RINGS 



• ne WRAPS 



• MOUNTING RING 



■ SUPPORTING RODS 



■ CROSS BRACING 

 ■TRANSDUCERS 

 •CONNECTOR 



COAXIAL CABLE 



Figure 9-2. OSU BASS sensor array and frame 



The BASS transducers transmit and receive 1.75-MHz acoustic pulses with 

 each opposing pair transmitting and receiving twice during one sampling 

 interval. Within the BASS electronics package the two time-of-travel mea- 

 surements from each pair of sensors are subtracted and digitized, and the four 

 resulting velocity measurements from each BASS array are output for storage. 

 The four velocities correspond to four flow direction vectors which intersect at 

 one point within the sampling volume and can thus be trigonometrically con- 

 verted to three orthogonal velocity vectors during the data analysis process. 



Pressure sensor. The hydrodynamic pressure history for each wave run 

 was recorded using a Model ST-420 pressure sensor manufactured by Wika 

 Instrument Corporation (Wika 1989). The instrument has a range of 0-5 psi 

 and is principally used to record the dynamic pressure near the sampling 

 volume of the ACP and BASS array. Another use of the pressure sensor is 

 for the reconstruction of the surface wave climate history. The instrument 

 simply measures the instantaneous ambient pressure at the transducer com- 

 pared to a previously established datum. 



The pressure transducer contains a piezo-resistive sensing element, which 

 is protected from the media by a stainless steel diaphragm, and an isolating 



156 



Chapter 9 The Ohio State University Measurements 



