B) is enclosed in a watertight main body of the 

 meter, and the rotation of the impeller is trans- 

 ferred to the gears through the bulkhead by 

 magnetic drive. As the impellei- turns, two de- 

 vices in the mechanism make and bi-eak (cut C) 

 an electrical circuit to produce the speed and 

 direction signals (cuts D and E). One device is 

 fixed relative to the meter ; the otlier is connected 

 with a built-in magnetic compass. The fixed 

 device makes contact at each fifth turn of tlie 

 impeller, the other at every 10th turn. The 

 frequency of the contacts serves as a measure of 

 current speed, and the time relationship of the 

 contacts serves as a measure of current direction. 

 Speed and direction signals are relayed via 

 watertight cable either to a buoy or to a ship. 

 If the current meters are suspended from an 

 anchored ship, the cable can be brought aboard 

 and meters can be monitored directly. If the 

 current meters are suspended from a buoy, the 

 signals are transmitted by radio and received 

 at a i-emotc-monitoring base station. 



M-14 Operating the Roberts Radio Cur- 

 rent Meter. — The Roberts radio current meter 

 can be suspended from a buoy and monitored 

 from a remote base station, or it can be sus- 

 pended from the side of an anchored survey 

 ship. Figure M-8 shows a buoy-operated .system 

 with a diagrammatic sketch of the remote base 

 station. Figure M-9 shows a shipboard-operated 

 system with a diagrammatic sketch of the ship 

 recording station. When operating and main- 



taining the Roberts radio current meter, refer 

 to "Roberts Radio Current Meter Manual," 

 first (1964) edition, publication 30-2, Depart- 

 ment of Commerce, Washington, D.C. 



M-15 Recording Roberts Radio Current 

 Meter Data. — Roberts radio current meter 

 data can lie recorded on any analog recording 

 instrument that will record the make and break 

 electrical contact signals relative to time. Ordi- 

 narily, these current data are recorded for a 

 period of approximately 1 minute each 15 or 

 30 minutes during the time the current sta- 

 tion is being monitored. Station number, date, 

 time (local or G.M.T. can be used but should be 

 si>ecified), and meter depth are annotated on 

 the aiialog record at the beginning of the ob- 

 servation. During the observation, the monitor 

 adjusts the tape si^eed to ensure that the make 

 and break signals on the tape can he distin- 

 guished clearly when the tape is analyzed. 

 After the meters at a station are monitored, the 

 analog tape is analyzed for current speed and 

 direction, and this information is then entered 

 in the record of current meter observations for 

 Roberts radio current meter (fig. M-10). 



M-16 Determination of Current Speed and 

 Direction. — To detennine current speed and 

 direction, analyze the analog tape as follows 

 (fig.M-11): • 



Step 1. Enter current station nimiber, gen- 

 eral locality, location of station, latitude and 



BUOY AND 

 TRANSMITTER 



i 



I to 3 METERS 



RELAY BOX 



ANALOG RECORDER 



HAND 

 KEY 



POWER SUPPLY 



REMOTE MONITORING BASE STATION 



ANCHOR 



Figure MS. Telemetering system for Roberts radio current meters. 



Change 1—1970 



M-7 



