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CHAPTER II 

 CONCEPTS OF A DIFFERENTIAL PRESSURE GAUGE SYSTEM 



A. DPG Response to Surface Waves 



As previously mentioned, it is the difference in pressure 

 between points that must be considered in the determination of wave 

 direction. Differential pressure transducers generate an electrical 

 voltage proportional to the fluid pressure difference on opposite 

 sides of a mechanical diaphragm. Absolute (or gage) pressure 

 transducers report only the fluid pressure at one point. Using 

 absolute (or gage) transducers, the difference in pressure between 

 two points must be arithmetically created by subtracting the 

 pressures reported at each of the two points of interest. Since the 

 differential transducer measures pressure differences directly, the 

 differential gauge can be considered to be an inherently more 

 effective instrument for determining wave direction. Furthermore, 

 the response with depth of the differential pressure is a maximum 

 over a range of frequencies that is more representative of typical 

 ocean gravity waves. For a pressure transducer located at height s 



