Characteristics of a Type of NTC Thermistors for Cryogenic Applications

A new type of miniature negative temperature coefficient (NTC) thermistors has been developed and manufactured with Mn-Ni-Cu-Fe oxides. The prepared NTC thermistors were calibrated in the temperature range from 77 K to 300 K with 1 μA exciting currents. The automatic calibration apparatus as well as thermometric characteristics, stability, calibration equations and interchangeability of the manufactured thermistors were investigated. A mean fit equation was obtained: 1/T = 8.60 × 10−4 + 6.54 × 10−4 ln(R/Rref) + 2.46 × 10−5 ln(R/Rref)2 + 9.48 × 10−7 ln(R/Rref)3 − 2.16 × 10−8 ln(R/Rref)4. All the prepared NTC thermistors agreed with this fit with an error of 1.5 K. If the greater accuracy is required, a calibration is necessary, and the calibration accuracy is estimated to be ±10 mK.