156 



LAWRENCE R. PROUTY AND JAMES D. HARDY 



temperature characteristic that fits the apphcation for which the 

 thermometer is to be used. 



Semiconductor Resistance Thermometers (Thermistors). 

 Oxides of manganese, nickel, cobalt, copper, and uranium belong 

 to the class of chemical compounds known as semiconductors which 

 are extremely sensitive to relatively minute temperature changes. 

 A new series of resistance units known as "thermistors" has been 

 developed by the Bell Telephone Laboratories and may further ex- 



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t 



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 — 

 in 



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 o 



UJ 

 Q. 



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•100 100 200 300 



TEMPERATURE. "C. 



400 



Fig. 9. Resistance-temperature relationships of three ther- 

 mistor materials compared to platinum. (Courtesy Bell Tele- 

 phone Laboratories.) 



tend the use of resistance thermometry for biophysical tempera- 

 ture determination (23). Essentially, a thermistor consists of an 

 oxide or mixture of oxides with a high temperature coefficient of re- 

 sistivity (Fig. 9), a method of mounting and protecting the oxides, 

 and electrical leads. Over thirty variations in the prototype are 

 now available. All are small, inexpensive, flexible in application, and 

 undergo practically no change in resistance properties with continual 

 use. They are available in three basic shapes (Fig. 10) — discs, rods, 

 and beads. Various mixtures of the oxides can be used to provide 

 the resistance-temperature relationships desired for the particular 

 application. 



