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configuration. This analysis technique is discussed in Appendix E. 



C. Selection of Transducers and Gage Length 



The selection of the gage length between the two points to be 

 compared by the differential pressure transducers is dependent upon 

 three criteria: (1) the characteristics of the transducer, (2) the 

 error in approximating the water surface slope as a linear function 

 between two sampled points, and (3) reasonable size limitations of 

 the instrument. The third criterion limits the gage length per 

 transducer to a maximum of about five feet if one imposes a design 

 constraint of easy instrument manageability. At such small spacings, 

 the maximum error in linearly approximating the water surface slope 

 between sample points is less than one and one-half percent for the 

 shortest waves of interest, (say, 3.2 seconds). 



Having satisfied the second and third criteria, the first 

 criterion remains. In the selection of the differential transducers, 

 one must consider the physical size, ruggedness, cost, and 

 availability of a transducer that can measure small "wet" 

 bidirectional pressure fluctuations. The desired rated capacity of 

 the transducer is a function of the maximum wave height expected and 

 the ability of the transducer to detect and report a pressure 

 difference of a minimum wave condition beyond the ambient and 

 electrical noise level. One might determine the rated capacity by 



