j EXCITING N 



TRANSFORMER 



e 



ei 



eu 



u R 



i — vyvc^ 



PICKUP 

 u -r TRANSFORMER 



R* 



± e 



INDUCTION 



CONDUCTIVITY 



CELL 



Fig. 5- Schematic diagram for null setting proportional to conductivity. 



n 2 Ru 



Hid ^ 



Ni V 



Nc 



nj ns 



5^ei © 



Xm 

 A — nnnm — 4 



-WW- 



Rm 



-WA- 



ifer* fer- 



Fig. 6. Equivalent circuit for null setting 

 proportional to conductivity. 



directly proportional to conductivity, the cir- 

 cuit of Fig. 3 ma-y be modified to the arrange- 

 ment of Fig. 5- The setting of the potentiometer, 

 Rp, in Fig. 5 is directly proportional to the 

 water conductivity providing the impedance of 

 Rp is considerably less than that of R s to mini- 

 mize potentiometer loading. An equivalent cir- 

 cuit is shown in Fig. 6. 



It has been found that a small quadrature 

 (reactive) component may he present in the bridge 

 circuit that interferes with obtaining a sharp 

 null. Compensation for this component may be 

 made with a small variable capacitor connected 

 across Ro. 



PHYSICAL DESCRIPTION 



The tape wound cores used in the transformers 

 are each encased in a rigid housing to give pro- 

 tection from external stresses. The exciting 

 transformer core is wound with tape of approxi- 

 mately 50$> nickel and 50$ iron composition for 

 high saturation flux density and good permea- 

 bility. The pickup core is wound with Super - 

 malloy which has the highest initial permeability 

 and lowest core loss of any commonly available 

 magnetic material. 



Fig. 7 shows the physical layout of the probe. 

 The toroidal head of the probe is 2 l/2 inches in 

 diameter and 2 3/8 inches long. The cores are of 

 the tape wound variety each enclosed in a rigid 

 case. A high strength outer housing constructed 

 of stainless steel tubing and Nylatron GS encloses 

 both transformers . All voids in the conductivity 

 head are filled with a high strength epoxy resin. 

 To eliminate the possibility of crushing pressure 

 being transmitted to the transformer cores, a 

 cushion of foam silicone rubber is placed between 

 the epoxy resin and the wound cores. Magnetic 

 shielding materials are incorporated in the con- 

 ductivity head to eliminate direct magnetic 

 coupling of the transformer cores . 



The temperature sensor is a glass enclosed 

 thermistor probe located in one of the four stain- 



Ik 



