PROPERTIES AND USES OF THERMISTORS 



175 



Curves 1 and 2 are for Materials No. 1 and No. 2 which have been ex'ten- 

 sively used to date. Material No. 1 is composed of manganese and nickel 

 oxides. Material No. 2 is composed of oxides of manganese, nickel and 

 cobalt. The dashed part of Curve 2 covers a region in which the resistance- 

 temperature relation is not known as accurately as it is at lower tempera- 

 tures. Curve 3 is an experimental curve for a mixture of iron and zinc 



2 



U 10- 



2 



5 

 y 10- 



3.0 



xiO'' 



temperature: °k 



Fig. 3. — Logarithm of the si)ecific resistance of two thermistor materials as a function 

 of inverse absolute temperature. See equation (1). 



oxides in the proportions to form zinc ferrite. From Fig. 2 it is obvious 

 that neither the resistance R nor log R varies linearly with T. 



Figure 3 shows plots of log p versus l/T, for Materials No. 1 and No. 2. 

 These do form approximate straight lines. Hence 



BlT 



Pooe or p = poe 



(,bIt)-{bitq) 



(1) 



where T = temperature in degrees Kelvin; p„ — p when T = oo or \/T = 0; 

 P{i = p when T = To ; e = Naperian base = 2.718 and 5 is a constant equal 

 to 2.303 times the slope of the straight lines in Fig. 3. The dimensions of B 



