For example, a ball in compartment 35 indi- 

 cates a current flowing approximately 350° 

 magnetic. Balls may be found in more than 

 one compartment. In this case, a system of 

 weighted averages will determine the current 

 direction. For example; 



No.: 

 310 

 320 

 330 

 340 



= 930 



= 1, 600 



= 1, 320 



= 2, 380 



19 6, 230 



-^328° current direction (magnetic) 



In computing the current direction, the local 

 magnetic variation must be applied to obtain 

 true direction. 



If it is desirable to resume observations with 

 minimum delay, the second compass-ball recep- 

 tacle may be used. The meter can then be 

 returned to the water immediately after the 

 dial reading has been taken and the instrument 

 prepared for operation. 



9-43 Computing the Current Velocity. — 

 Each meter used for Navy surveys is calibrated 

 to determine the relation of the speed of the 

 current to the speed of rotation of the impeller. 

 Each meter usually is provided with an extra 

 impeller and each is calibrated separately. 

 Either a rating formula for computing current 

 speed is provided for each impeller, or a cali- 

 bration curve is drawn with revolutions per 

 minute and current speed in knots as coordi- 

 nates. 



From the times recorded on the log sheet, 

 the number of revolutions per minute can be 

 calculated. Knowing this, the current speed 

 is obtained either by inspection of the calibra- 

 tion curve or by applving the formula. 



9-44 INSTRUCTIONS FOR OPERATING 

 THE PRICE CURRENT METER.— The Price 

 current meter was originally designed by Assist- 

 ant Engineer W. G. Price, Corps of Engineers, 

 U. S. Army. It is designed to measure current 

 speeds from 0.1 to 11 feet per second (0.06 to 

 6.6 knots). It does not measure current direc- 

 tion. Current direction must be determined by 

 other means when using this instrument. 



The meter consists of a number of cone- 

 shaped cups mounted on a vertical rotating 

 shaft called the cup shaft. For every 1, 5, or 

 10 revolutions of the cup shaft, depending on 

 the model being used, an electrical circuit in a 

 contact chamber is closed and transmits a 

 signal to the observer through a 2-conductor 

 electrical cable and a set of earphones. In 



place of earphones, an automatic recorder 

 with a time-marking system may be connected 

 to the circuit. Power for the circuit can be 

 supplied by dry-cell batteries. The number of 

 revolutions of the cup shaft, when applied to 

 the calibration or rating table, indicates the 

 speed of the current (fig. 9-4). 



X 



METER CONTACT 

 CHAMBER 



Figure 9~ 



Wiring diagram for Price current meter. 



Complete instructions for operating the 

 Price current meter are given in the U. S. 

 Coast and Geodetic Survey Special Pub. 

 No. 215, Manual of Current Observations. 

 Given briefly below are general operating in- 

 structions and recommendations. 



9-45 Price Models. — A number of different 

 models of the Price meter are available for use. 

 The meter generally used for ocean surveys is 

 the deca-count model which transmits a signal 

 for every 10 revolutions of the cup shaft. An 

 old and new model of the single- and penta- 

 count meter is also available. 



9-46 Contact Chamber. — In the old model, 

 the single- and penta-count gears and contact 

 points are housed in separate contact chambers. 

 If it is necessary to change the entire contact 

 chamber in the older type meter to obtain a 

 different count, the small spindle at the top also 

 must be changed. In the new model, the 2 

 gears are contained in 1 chamber and either is 

 made operative by connecting the proper wire. 

 Electric power is supplied by 1 or 2 dry cell 

 batteries. 



9-47 The Cable. — The meter is suspended 

 from a 3-strand, 2-conductor cable. Two insu- 

 lated copper wires provide the electrical con- 



94 



H. O. 607 



