Temperature Transducers 



The two most widely used temperature transducers are the resistance 

 thermometer and the thermocouple or thermoelement. Of these, the 

 resistance thermometer (2-11) has potentially the highest sensitivity; 

 it permits the detection of temperature variations in the order of 

 1/10,000 of one degree centigrade, at room temperature. One form 

 of the resistive temperature transducer, the platinum resistance 

 thermometer, forms the basis of the International Temperature 

 Scale from —190 to +660°C. Metallic resistance thermometers 

 (2-1 la) can be used in the range from approximately —270 to more 

 than 1000°C. Semiconducting resistance thermometers (thermistors, 

 2-116) are generally used in a range from —100 to +300°C, although 

 special materials have been employed for very low temperatures from 

 0.15 to 20°K (carbon) and also at very high temperatures between 

 800 and 1100°C. The sensitivity (change of resistance per unit 

 change of temperature) of thermistors is usually considerably higher 

 than that of metals, but their stability and accuracy are generally less 

 than those of metallic resistance thermometers. The electrolytic 

 transducer (2-1 lc) is of limited practical importance but may be 

 useful for some biological applications. The application of the 

 ionized-gas transducer (2-1 Id) is limited to the range of very high 

 temperatures, exceeding 4000°C. 



Two forms of inductive temperature transducers have been used 

 (2-12): The first (2-12a), based on susceptibility variations of para- 

 magnetic salts, is applicable in the range below 4°K; the other, 

 (2- 126), based on susceptibility variations of ferromagnetic materials, 

 has apparently found only one practical application in the range 



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