Fig. 3. Data logging package from central tube 

 of subsurface buoy. 



SENSOR MEASUREMENTS 



The digital clock in the system uses a 100 

 Kcps crystal and has an operation cycle of 

 2.63 seconds. Consider a Savonius rotor speed 

 pulse input to the system of Fig. 2. When the 

 stepping switch is in the proper position (deter- 

 mined by the digital clock) the sensor output 

 will pass into a wave shaping circuit where the 

 shape of the wave form is altered so that it will 

 operate the digital logic. From there, the sig- 

 nal proceeds into an interval detector that pro- 

 duces a square wave out of the time interval 

 occurring between switch pulses. This square 

 wave is mixed with a standard frequency of 

 3,125 cps. The frequency burst from the interval 

 detector passes through other portions of the 

 stepping switch in the sequence of events and 

 through the proper gating circuits before it is 

 impressed upon the count accumulator from which 



is formed the 12 bit binary. At the proper time 

 the information is transferred from the count 

 accumulator to the tape heads. The 12 bit lines 

 are fed into each individual head through gates 

 and determine the presence or absence of a signal 

 on a particular head. 



The tape is not moving when current passes 

 through the tape heads. After the information 

 is transferred a step function is sent to the 

 stepping motor of the tape drive and the tape 

 moves about O.O36 inch to be ready for the next 

 data cycle. During the cycling time a pulse is 

 sent back to the interval detector and the count 

 accumulator for complete reset prior to the next 

 sample sequence. 



The method of measuring resistance differs 

 slightly. A vane for measuring water current 

 direction moves a microtorque resistance element 

 which is referenced to a magnetic compass device. 

 The resistance is proportional to the clockwise 

 rotation angle between magnetic north and the 

 vane direction. This input is put into an analog- 

 to-frequency converter which is located in the 

 buoy system. From here, the signal passes through 

 portions of the stepping switch and through the 

 proper gates and logic and is impressed on the 

 count accumulator. The reset and stepping func- 

 tions of the tape motor take place in the same 

 manner as discussed above. 



The stepping switch turns the system off on 

 its last position and waits for the master timer 

 to again activate the circuit. Twenty-five input 

 channels are sampled in each data cycle but these 

 are not all sensor channels as there is a 3- 

 point calibration function for the direction 

 measuring devices and a 5-point calibration func- 

 tion for the temperature devices. This internal 

 calibration is to determine the stability of the 

 data logging system over a long period of time 

 when voltage variations are liable to affect the 

 accuracy of the data. 



The tape recorder of this system performs 

 digital recording in a static or stationary mode, 

 i.e., the tape is motionless when the heads are 

 magnetized. There are several precautions that 

 have to be taken in this type of recording to 

 insure reliable noise-free data. All of these 

 seem to have been overcome and the system pro- 

 duces extremely clean signals that are not diffi- 

 cult to program into computer format. Thus, a 

 full data tape is acquired in the field system 

 with decimal information that is calibrated and 

 in readily interpretable engineering units. 



DATA TRANSCRIPTION 



A duplicate tape is made from the original 

 that effectively increases the spacing between 

 frames by a factor of 3 . A scanning process is 

 used during constant speed playback from which a 

 punched paper tape is eventually produced. The 

 punched tape is fed to the 160^ computer with 

 calibrations in IBM format that produces a cali- 

 brated decimal output in the proper format. 



