4. Induction- conductivity- temperature indicator 



A development which seeks to avoid the complications of elec- 

 trodes is the induction-conductivity-temperature indicator developed 

 at the Chesapeake Bay Institute. This device operates through the 

 inductive measurement of an electric current which has been induced 

 in a sea water path. The sensing head consists of two iron-core toroidal 

 windings potted in an insulating resin. One winding is excited by a 

 115- volt, 60-c.p.s. electrical signal; the sea water path through the hole 

 in the center of this toroid acts as a one-turn secondary of a trans- 

 former and, consequently, has about 0.2 volt induced in it. The amount 

 of current flowing depends primarily upon the length and diameter 

 of the hole and upon the conductivity of the water in the hole. The 

 current flowing in the sea water is measured by means of the second 

 toroid which is mounted adjacent to and coaxially with the existing 

 toroid. 



No sea- water-to-metal contact exists in this system, so the prob- 

 lems inherent to electrodes are eliminated. The system is essentially 

 independent of line frequency variations over a moderate range of 

 several cycles per second. Stability of the instrument depends wholly 

 upon the dimensional stability of the resin "doughnut and the stabil- 

 ity of the electrical components. 



Laboratory tests have shown this device to be capable of measuring 

 conductivity to ±0.02 millimho (±0.02%« of salinity) over the entire 

 ranges of temperature and salinity encountered in estuarineand marine 

 envir onment s . 



5. Sound velocity meter for in situ salinities 



The Hydrographic Office has several models of the sound velocity 

 meter developed at the National Bureau of Standards. This meter has 

 an inherent accuracy of ±0.1 foot per second, but the present read-out 

 system allows an accuracy of only ±1.0 foot per second. A read-out 

 accuracy of ±0.2 foot per second coupled with the simultaneous 

 measurement of temperature to ±0.02°C would provide in situ salinity 

 of ±0.05%o. 



6. Vibrating rod densitometer 



William S. Richardson of the Woods Hole Oceanographic Institu- 

 tion has described a vibrating rod densitometer for measuring density 

 in situ. If such a device were developed, it is conceivable that it 



IV- 6 



