PROPERTIES AND USES OF THERMISTORS 



199 



ture range. In practice however, the compensating thermistor is associated 

 with parallel and sometimes series resistance, so that the com.bination gives 

 a change in resistance closely equal and opposite to that of the circuit to be 

 compensated over a wide range of temperatures. See Fig. 18. 



2000 



-40 



-20 20 40 60 



TEMPERATURE IN DEGREES CENTIGRADE 



80 



Fig. 18. — Temperature compensation of a copper conductor by means of a thermistor 

 network. 



A copper winding having a resistance of 1000 ohms at 25 degrees centi- 

 grade can be compensated by means of a thermistor of 566 ohms at 25 

 degrees centigrade in parallel with an ohmic resistance of 445 ohms as shown 

 in Fig. 18. The winding with compensator has a resistance of 1250 ohms 

 constant to ± 1.6 per cent over the temperature range —25 degrees centi- 

 grade to -t-75 degrees centigrade. Over this range the copper alone varies 

 from 807.5 ohms to 1192.5 ohms, or ± 19 per cent about the mean. The 



