104 



HYDROGRAPHIC MANUAL 



P*K>ro &v Ch«««o«M« Bay instiluM 



Figure 43. — Chesapeake Bay Institute ICTI. 



water in which the transformer is immersed. 

 This current is measured by the second core, 

 and the output signal is transmitted, along 

 with a reference voltage derived from a sec- 

 ondary winding on the first core, through the 

 cable to the indicator aboard ship, where the 

 information is automatically processed and 

 actuates a counter so that conductivity is 

 read directly. The conductivity reading and 

 the simultaneously observed temperature are 

 used to enter tables from which salinities are 

 extracted. 



The temperature sensing element is a re- 

 sistance thermometer, made from about 25 

 feet of enameled nickel wire wound around 

 a tube and connected to the cable. The tem- 

 perature measuring circuit is a modified 

 Wheatstone bridge. Temperature is shown 

 directly on a dial to 0.01° C. 



3-134 Salinometer (salinity bridge). — 



The Salinometer, or salinity bridge (Fig. 44) 



is an instrument for the determination of 

 salinity of sea water aboard ship or in the 

 laboratory by an electrical conductivity meth- 

 od. The first apparatus of this kind was con- 

 structed by the National Bureau of Standards 

 in 1930 and is known as the Wenner-Smith- 

 Soule Salinity Bridge. Several improvements 

 have been made in the equipment, the most 

 recent being described in Technical Report 

 No. 61 published by the University of Wash- 

 ington in 1958. 



The equipment consists of the bridge-oscil- 

 lator detector unit, a refrigerated oil-tight 

 constant-temperature bath, seven conductiv- 

 ity cells mounted in the bath, a refrigerator 

 unit and controls, a proportional-type tem- 

 perature controller, a constant-voltage sup- 

 ply for the electronic parts, and a suction 

 system for emptying the cells. 



The salinometer is calibrated in the labora- 

 tory by a lengthy series of measurements of 



