Nano-powder of a negative temperature coefficient (NTC) ceramic with a spinel structure of Mn-Ni-Cu-Co-La-O composition was prepared by the Pechini method. A type of NTC thermistor sensor (3.0 mm diameter × 1.5 mm high) was designed by the in situ lead wire attachment method (ISAM) and made using the synthesized powder. NTC thermistors were packed in the glass-sealed package. Six independent NTC thermistors were calibrated using a cryostat, a standard platinum resistance thermometer, and a Fluke 1590 super thermometer meter over the temperature range from 18 K to 120 K. The data were interpolated to obtain calibration tables at 2 K intervals from 18 K to 30 K, and at 5 K intervals from 30 K to 120 K. These tables were fitted with the equation:Aging, thermometric characteristics, fitting of calibrated data, stability of NTC thermistors, and the effect of a magnetic field on NTC thermistors were investigated.

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/R ref ) + 2.46 × 10 −5 ln(R/R ref ) 2 + 9.48 × 10 −7 ln(R/R ref ) 3 − 2.16 × 10 −8 ln(R/R ref ) 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.

Based on the analysis and investigation of calibration systems for high-accuracy low temperature thermometers, a new facility for automatic calibration of high-accuracy low temperature thermometers was developed. Continuous calibration for multiple points can be made automatically with this device. According to the thermophysical characteristics of the constant-temperature block in this device, segmented Fuzzy-PID (proportional-integral-differential) algorithm was applied. The experimental results showed that the temperature fluctuation was smaller than ±0.005 K in 30 min. Therefore, this new device can fully meet the calibration requirement of high-precision low temperature thermometers. calibration, low temperature thermometer, control algorithm Citation:Chen G M, Gao X, Zhang S Z, et al. Development of an automatic calibration device for high-accuracy low temperature thermometers.