nections while the third strand, a steel piano 

 wire, supports the meter. This cable should be 

 inspected frequently for breaks. Extreme care 

 must be taken to insure watertight connections 

 of the cable to the contact chamber gland. 

 Should the piano wire require replacement, 

 /^2-inch stainless steel wire rope (bathythermo- 

 graph wire) may be substituted. 



9-48 The Vanes and Supporting Rod. — 

 The meter is kept facing into the current by 

 two tail vanes set at right angles and a stream- 

 lined lead weight at the bottom of the vertical 

 supporting rod. Proper balance of the meter 

 is made by adjusting a small movaole weight 

 on one of the vanes. 



9-49 The Stopwatch. — Whenever taking 

 observations directly with the earphones, it is 

 necessary to have a reliable stopwatch. Be sure 

 to check the stopwatch against a chronometer 

 of known rate before using it. In the past, much 

 time and data have been lost because of faulty 

 stopwatches. 



9-50 Recording the Data. — The method of 

 recording the Price current meter data directly 

 by earphone is simple. At the instant the signal 

 is heard start the stopwatch and count a pre- 

 determined number of clicks. When the last 

 click is heard, stop the watch and record the 

 number of seconds elapsed in the Record of 

 Current Observations for Price Current Meter, 

 PRNC-NHO-1506. The calibration or rating 

 table is then used to convert to current speed. 



Special emphasis should be placed upon the 

 collection of supporting meteorological data. 

 Visual observations should be made of surface 

 wave and current directions and conditions. 

 The data, ship's name and position, Greenwich 

 mean time, depth to the bottom, and depth 

 of the meter must be recorded also. 



9-51 Care and Maintenance of the Price 

 Current Meter. — Prior to lowering the meter 

 into the water, a close inspection of all splices 

 and connections should be made to prevent 

 loss of the instrument or parts. Loose splices 

 and worn cables must be replaced. Electrical 

 connections should be soldered wherever pos- 

 sible. The cup shaft bearings should be kept 

 clean and well oiled. To prevent corrosion of 

 the contact points, the contact chamber should 

 be filled with a light oil when in use. The meter 

 should be rinsed in fresh water and all moving 

 parts oiled after use. 



9-52 INSTRUCTIONS FOR OPERATING 

 THE ROBERTS RADIO CURRENT ME- 

 TER. — The Roberts Radio Current Meter is an 

 instrument designed specifically to record sub- 

 surface current speeds accurately and simulta- 



neously indicate the direction of the flow. The 

 basic components consist of a buoy from which 

 1 to 3 meters may be suspended, an automatic 

 radio-transmitting system within the buoy, and 

 a ship- or shore-based radio-receiving monitoring 

 system which can monitor up to 15 meters. 

 The buoys usually are anchored in bays, rivers, 

 channels, or other relatively shallow areas. 

 Meters have been operated successfully at 

 depths as great as 2,500 meters from anchored 

 ships. 



A current study of an area, employing 

 Roberts meter and associated equipment, is a 

 large-scale field operation, requiring approxi- 

 mately 10 men including experienced tech- 

 nicians and observers. A vessel capable of 

 handling the survey equipment and shore 

 facilities for repair of the gear is necessary for 

 efficient operation. 



9-53 The Principle of Operation. — The cur- 

 rent meter is suspended at any desired depth 

 from a buoy of special design which contains a 

 battery-powered radio transmitter and select- 

 ing device, and supports an antenna and warn- 

 ing lights (fig. 9-5). The meter aligns itself to 

 the direction of the current flow. The current 

 drives an impeller, or screw, in the nose of the 

 meter. The impeller is connected by a mag- 

 netic drive through a watertight bulkhead to 

 an enclosed mechanism which makes and breaks 

 an electrical circuit by means of two contacting 

 devices. One device makes a contact at each 

 fifth turn of the impeller and the other at every 

 tenth turn. The frequency of the contacts 

 serves as a measure of velocity. The first con- 

 tacting device is connected with a built-in mag- 

 netic compass and the second is fixed relative to 

 the position of the meter body. The contacting 

 mechanisms are so arranged that when the 

 instrument is heading south both contacts 

 will close at the same time. When the meter 

 heads in any other direction the time relation 

 between the two sets of contacts changes with 

 the meter heading. This serves as a measure of 

 direction. The contact makes and breaks, 

 relating to direction and speed, are relayed via 

 watertight electrical cable to the buoy where 

 the transmitter is keyed to produce radio 

 signals on a designated frequency. The operat- 

 ing frequency is controlled by a crystal selected 

 for maximum results in the specific area. These 

 signals are received, amplified, and recorded on 

 tape by means of a chronograph at the ship- or 

 shore-based monitoring station. Observers at 

 the monitoring station record the signals on 

 tape from several current meter stations by 

 adjusting the receiver to different frequencies 

 at timed intervals. Up to five stations can be 



H. O. 607 



95 



