counted by a binary counter. At a predetermined count another gate is 

 opened, allowing pulses from a two-megacycl e-per-second clock pulse gene- 

 rator to be counted by a second binary counter. When the first binary 

 counter reaches another predetermined count, both gates are closed and the 

 flow of pulses to the counters is stopped. The time, in half-microseconds, 

 is held as a binary coded number in the second counter and represents the 

 period required for the predetermined number of pulses to flow into the 

 first counter from the pressure sensor. The resolution of the pressure 

 measurement is in direct proportion to the number and is limited only by 

 the time allowed for sampling the sensor. When determined by the sequence 

 control, gates connect the output of the counter to the tape recorder. 



3. Savonius Current Meter 



A current meter has been designed to utilize the digital logic 

 basic to the data acquisition system. Its output is similar to that of the 

 digital wave staff and has the same advantages listed in the discussion of 

 the staff. 



A miniature Savonius rotor was modified to produce 120 electrical 

 pulses for each revolution. Sixty equally spaced holes near the periphery 

 of one rotor end plate interrupt a I ight beam as the rotor turns. One 

 pulse is generated as the beam passes through each hole, and another pulse 

 is generated as the beam is interrupted. 



The digital record of current flow is formed in the same manner as the 

 record of wave height. A sampling interval is selected and a record is 

 made of the number of pulses occurring during this interval. Since the 

 pulses are electronically maintained at constant width, an integrating 

 circuit may be used to form a continuous analog signal for a chart re- 

 corder i-fe desi red . 



Several light sources were tested during the development of the 

 current sensor. The final design incorporated a type LI 5-45 bulb manu- 

 factured by Pinlites, Inc. of Fairfield, New Jersey. 



4, Synchronous Timing Lights 



Accurate synchronization of observations, such as those from an 

 underwater camera, with other measurements of the environment has been 

 attained by providing a synchronous digital time display. Miniature 

 indicator lamps provide a time code which appears in the field of the 

 photograph and can be directly related to the wave and current data re- 

 corded by the data acquisition system. Synchronization is assured by 

 driving the lamps with solid-state electronic switches operated directly 

 from the binary time counter of the data acquisition system (DAS). The 

 lights are arranged in groups of three for rapid visual read-out in an 

 octal numbering system (Figure 12). A lamp is illuminated when a one is 

 to be indicated in the binary bit it represents. The time code shown on 

 the lights is printed out on the computer digital time series read-out 

 and also on the direct analog chart read-out of DAS. An example of the 



