CURRENT METERS 



37 



A study of the rating curves of a large number of small 

 Curl* ' < shows that, as a ml* . is made up of two 



Straight I MICH, tin- extension <>i th>- lower one joining the upper 

 "ii. in .in angle between thr \. -I... ities of 8 and 9 ft. At this 

 [mi MI- ! is a slight increase in tli>- ln tion on the bearing! 

 ..! tlf m.-N-r \%lirr| .in.l shaft. Nottoitli-t.iiiiling this break in 



IM-. the observed curve parallel* the theoretical <-.. 

 very closely. The lower part of the curve starts at a velo 

 I If** than 0.1 ft. per second, which is required to start the 

 wheel 



In u-iiij: tin- in. t, r. observation is made of the number of 

 second^ ili \%h. -1 n <|tiires to make a selected number of revo- 

 inn-!-, ore, a rating table in prepared for each m 



1'iMiig the velocities per second corresponding to the numln r 



\nluiioMH. The most convrni' Mt table is prepared for 

 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, and 200 revolu 

 lions, with tin- hmrx ot ili.- runs ranging from 40 to 70 seconds, 

 giving velocities from 0.19 to 11.12 feet per second. 



Rating Table for Use with 



Acoustic Current Meter, No. 616 



This Table in a mean ot the rating* of many different meter*, and will probably give 

 value* within one per cent, for any meter of it* pattern when in good order. 

 The time column i thr number of econd that have rlapved during one 

 revolutions of the wheel, then being ten revolution* to each rap. 



Tin* 



m 



250 

 222 



M 



167 

 154 

 143 



125 

 118 



Velocity 



0.70 



101 



t II 



T1m 



111 



U2 

 143 

 134 

 165 

 1.76 



Velocity 



2.10 



2JI 



. 4. 



2.75 

 U6 



X19 



SJ4 



Timr 



Velocity 



174 



4.11 



512 



SJt 



Time Velocity 



667 



7JJ 

 759 

 7JS 



47 

 Ml 



