longitude, date, water depth, etc. on the head- 

 ing of tlie log slieet. Enter observation time in 

 Time column. Enter depth below the surface of 

 the water that each meter is suspended in Depth 

 of Meter column. 



Step 2. Label the speed marks (S) and the 

 direction marks (D). At each fifth revolution 

 of the impeller, a sliced signal is produced by 

 tlie meter, and at each tenth revolution, a di- 

 rection signal is produced. 



Step o. Select a section of the tape where 

 the speed and direction signals consistently fol- 

 low the alx>ve pattern. Niunber the speed sig- 

 nals in the section and enter the number minus 

 one in the Number of Rors. column. Enter the 

 number of seconds in the section in the Ti7ne in 

 Seconds column. 



Step 4. Divide the "Time in Seconds" by 

 the "Number of Revs."' to obtain the enti-y for 

 the Time Tnterval column. 



Step 5. Speed in knots is determined from 

 the "Calibration Data for Meters" tables using 



the time interval. Enter in Velocity hy Meter 

 column. 



Step 6. Count the number of direction sig- 

 nals in the .section of tape selected and enter 

 this number in Number of Dir. Signals column. 



Step 7. Place the direction scaling template 

 ()° and 360° lines at the base of the leajding edge 

 of two sjjeed signals on the tape that have a 

 direction signal between them. Read off the 

 direction and enter it in the Dir. hy Meter col- 

 umn. NOTE : A special case sometimes occurs 

 when the direction signals and the speed sig- 

 nals overlap at 0° (North) (Fig. M-7F). 



Stejo 8. Correx!t the Dir. hy Meter column 

 entry by using the local compass variation to 

 obtain the entry for the Dir. of Current True 

 column. Deviation caused by the ship's hull 

 should be considered if the meter is in the mag- 

 netic field of the ship. 



M-17 Maintenance of Roberts Radio Cur- 

 rent Meter. — During current measuremenit 

 operations, the meter should be inspected peri- 



TIME = 40 SECONDS 



NUMBER OF REVS. = 9-1=8 



[7) 



(8) 



P S S D S 



NUMBER OF DIRECTION SIGNALS = 4 



TIME 



TIME 



INTERVAL - NUMBER OF REVS. 



CALIBRATION 



(abstract of) 

 DATA FOR 



METERS 



Figure M-11. Computing current speed and direction Roberts radio current meter. 



Change 1—1970 



M-9 



