Table I. 



Temperature 

 (°C) 







5 



10 



15 

 200 



25 



Double Bridge Temperature 



Coefficient (fo/°C) 



R s =0 R s =120 R s =2000 



3.069 

 2.763 

 2.505 

 2.286 

 2.099 

 1-935 



3.020 

 2.73^ 

 2. 1+92 

 2.286 

 2.108 

 1.952 



2. 



2.71^ 



2.W 



2.286 



2.111+ 



1.963 



Sea Water Temperature 

 Coefficient ($/°C) 



2.999 

 2.708 

 2A81 

 2.286 

 2.118 

 1.976 



SALINITY 

 ERROR 

 P.P.T. 



y 



DIFFERENCE 



%/°C 4-0.02 



0.00 



-0.02 



-0.04 



10 20 



TEMPERATURE 



Rs:INF 



Rs:120n 



Rs=0 



5 10 15 20 25 

 SEA WATER TEMPERATURE °C 



Fig. h. Compensation errors for circuit shown 



in Fig. 3 and difference in temperature 

 coefficient "between circuit in Fig. 3 

 and sea water. 



small as 50 psi an error equivalent to 0.01 parts 

 per thousand in salinity results . Also, the 

 pressure effect is quite dependent on tempera- 

 tures!" as shown in Fig. 6. The effect of pres- 

 sure at 0°C is twice as great as at 30°C. Con- 

 sequently, any pressure compensating device must 

 take into account the temperature. Fig. 7 shows 

 a circuit that has been designed to provide an 

 input-output relationship that closely simulates 

 the changes in conductivity due to changes in 

 pressure. 



The loading effect of Ro on the pressure 

 potentiometer is adjusted so that the relation- 

 ship between E and the pressure applied to the 

 pressure potentiometer closely simulates the con- 

 ductivity pressure relationship of sea water. 

 The reduction in the pressure coefficient with 

 increasing temperature is closely simulated by 



PERCENT 



INCREASE 



IN 



CONDUCTIVITY 



10 12 14 16 



HYDROSTATIC PRESSURE PSIG 

 (x 1000) 



Fig. 5- Change of conductivity of sea water. 



1.6 



1.4 



PRESSURE 1-2 



COEFFICIENT 

 OF ELECTRICAL 10 

 CONDUCTIVITY 

 (10" 5 DECIBAR H ) 0.8 



0.6 



TEMPERATURE °C 



Fig. 6. Effect of temperature on pressure 

 coefficient at 1,500 psig. 



the change in resistance of a thermistor resistor 

 combination, Rjjj and R-j_. By adjusting Rj_, Rg and 

 R3, the effect of pressure on the conductivity of 

 sea water can be simulated with an overall accu- 

 racy of 1$> at temperatures below 10°C. At 



22 



