Once the end-cap was removed, the thiTd channel demonstrated 

 sinusoidal output with the expected IT/2 phase difference to the 

 absolute signal as predicted by Equations 2.1 and 2.2. The 

 unexpected characteristics of the first and fourth differential 

 channels, however, remained unexplained. Both channels indicated the 

 passage of a trough, as expected, but did not report the actual crest 

 passage — instead suggesting the passage of two crests ir/A before 

 and after the actual passage. This phenomenon was noted in both 

 orientations of the DPG tested. It is thought that the unexpected 

 characteristics of these differential channels could have been due to 

 the poor positioning of the sensors at the unprotected ends of the 

 PVC arms. It is also possible that the arm tubings were broken at 

 the time of the tests or that the sensitive differential gauges were 

 adversely influenced by the return flow pipes to which the cradle was 

 attached. 



The instrument was originally positioned such that the dPl 

 and dP3 arms were aligned approximately 55 degrees from the 

 centerline of the tank, or wave ray. The cradle and instrument were 

 next rotated about 20 degrees such that arms 1 and 3 were 

 approximately 35 degrees from the wave ray. Figures V-8 and V-9 are 

 strip chart recordings from each of the configurations, respectively. 

 The rotation of the DPG was restricted between these two positions 

 because of the pipes that surrounded either side of the cradle. 

 These pipes, however, off erred the only structure to which the cradle 



