Fig. 8. Power supply. 



CONDUCTIVITY MEASURING SYSTEM 



The conductivity measuring system with which 

 the probe was originally used is shown in 

 Fig. 9. This is essentially a conductivity devi- 

 ation circuit, i.e., the variable resistor in 



WATER 

 I RESISTANCE — 



~1 



POWER 

 SUPPLY 



I 



BATHYSAL1NOMETER 

 PROBE 



X 

 X 



ID 



PHASE 

 SENSITIVE 

 DEMODULATOR 



NULL 

 ADJUST 



CALIBRATED 

 NULL ADJUST 



CALIBRA 

 NULL AOJ' 



Fig. 9- Conductivity deviation measuring system. 



the bridge circuit was set for a null at a par- 

 ticular value of water conductivity and the output 

 signal was a measure of deviation from this par- 

 ticular value. A more sophisticated system is 

 diagrammed in Fig. 10. Here, a two-phase servo 

 motor drives the bridge circuit to a null setting. 

 Since the circuit is always driven to null, errors 

 due to variations in transformer magnetizing reac- 

 tance and core loss and in power supply frequency 

 and voltage are largely avoided . 



TO NULL ADJUST POT 

 AND READOUT DEVICE THROUGH GEAR REDUCER 



Fig. 10. Servo null balance conductivity 

 measuring system. 



Trial runs of the induction conductivity probe 

 mounted in the nose of the underwater vehicle 

 have been made at moderate depths. Additional 

 laboratory and field tests will be made to more 

 completely evaluate this technique for salinity 

 measurements . 



ACCURACY 



It is difficult to establish a definite 

 accuracy figure for the instrument since this will 

 depend on the type of measuring system and data 

 recording systems used and on the environmental 

 conditions encountered. The effects of the tem- 

 perature and hydrostatic pressure on cell sta- 

 bility have not been fully evaluated but investi- 

 gations made to date show these effects to be 

 small, particularly where the servo null balance 

 system is used. Since the output of the induction 

 conductivity cell is a low level signal, careful 



16 



