alvuninum holder to provide the gage length desired for the location, 

 usually 15 to 25 feet. Sensing contacts are molded into the 5-foot 

 sections at intervals to provide the incremental accuracy required 

 of the gage. Sensing contacts spaced every 0.2 foot have been found 

 adequate for gages with lengths of 15 to 25 feet. Sensing contacts 

 spaced 0.1 foot have been used on gages of 10 feet or less. 



The sensing unit for the pressure-sensitive underwater wave gage 

 senses the change in pressure produced by the increase (or decrease) in 

 water height as the wave passes over the gage. The change in pressure 

 produced by a wave with an 8-second period with a height of 4 feet on a 

 gage submerged in 30 feet of water will be less than that produced by 

 the same wave on the same wave gage submerged in 10 feet of water. A 

 wave with a period shorter than 8 seconds and with a height of 4 feet 

 will produce less pressure at both the 30-foot and 10-foot depths than 

 the 8-second wave. This phenomena is referred to as a pressure gradient 

 condition produced as a function of wave height versus wave period versus 

 water depth to the sensing element. 



The pressure-sensing element used by the CERC is designed for use 

 in locations where the total water depth (stillwater depth plus height 

 of wave crest) is less than 50 feet. Sensing elements with similar 

 characteristics that are interchangeable with the CERC model except for 

 the d.c. power requirements are available from commercial sources. One 

 of these is Fairchild Semi-Conductor Corporation Model TF 150 series. 

 These sensors are available in a variety of pressure ranges and may be 

 used in water depths greater than the 50-foot total range of the CERC 

 model. However, use of a pressure-sensitive gage in water depths greater 

 than 30 feet is not advised due to the depth-period attenuation factor 

 of recordings taken from such an installation. 



Figure 1 shows a block diagram of the components used in a series- 

 type step-resistance wave gage for use in fresh water. 



Figure 2 shows a block diagram of a parallel-type step-resistance 

 wave gage for use in salt water. 



Figure 3 shows a block diagram of a relay-operated step-resistance 

 wave gage for use in water of varying salinity. 



Figure 4 shows a block diagram of a pressure-sensitive wave gage. 



