Wave Gages 



Baylor wave staff gages 



28. Two parallel cable inductance wave gages, manufactured by the 

 Baylor Company, Houston, Tex., were mounted on the FRF pier: gage 615 at 

 sta 6+20 and gage 625 at sta 19+00 (Figure 2). These gages are rugged and 

 reliable, and require little maintenance except to keep tension on the cables 

 and to remove any material which may cause an electrical short between them. 

 These gages were calibrated prior to installation by creating an electrical 

 short between the two cables at known distances along the cable and recording 

 the voltage output. Electronic signal conditioning amplifiers are used to en- 

 sure that the output signals from the gages are within a 0- to 5-V range. 

 Gage accuracy is about 1 percent, with a 0.1 percent full-scale resolution; 

 full scale is 9.4 m for gage 625 and 8.5 m for gage 615. These gages are sus- 

 ceptible to lightning damage, but protective measures have been taken to mini- 

 mize such occurrences. A more complete description of the gage's operational 

 characteristics is given by Grogg (1986). 



Waverider buoy wave gage 



29. A Waverider buoy gage (620) was located 3 km offshore. This gage 

 was manufactured by the Datawell Laboratory of Instrumentation, Haarlem, The 

 Netherlands, and measures the vertical acceleration produced by the passage of 

 a wave. The signal is double-integrated to produce a displacement signal 

 which is transmitted by radio to an onshore receiver. The manufacturer states 

 that wave amplitudes are correct to within 3 percent of their actual value for 

 wave frequencies between 0.065 and 0.5 Hz (15- to 2-sec wave periods). How- 

 ever, calibration curves for one of the two buoys used indicate that the wave 

 heights reported in Part V of this report, for wave periods less than 15 sec, 

 average about 7 percent less than actual values. For wave periods greater 

 than 15 sec, this error increases with wave period. The manufacturer spec- 

 ifies the error can increase to 10 percent for wave periods greater than 



20 sec. Calibration results show errors as large as 15 percent are possible 

 for the very long wave periods. The buoys were calibrated without the mooring 

 system used during deployment, which may introduce additional errors of un- 

 known magnitude. For most engineering applications, a 7 percent error is 

 tolerable; however, a correction procedure is described in Appendix A, which 

 will allow the calibration error to be improved up to 4 percent. 



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