Damir Ilid, Ivan Leniček, Luka Ferkovid
USE OF HIGH-RESOLUTION DIGITAL MULTIMETERS FOR THE CALIBRATION OF TEMPERATURE SENSORS
The calibration of precise negative temperature coefficient resistors (NTCRs), which have resistance RN = 10000 Ω at a temperature of 25 °C and limits of error ±0,2 °C in the range from 0 °C to 70 °C, by means of the reference platinum resistance thermometer Pt-25 (with the resistance of ≈ 25,5 Ω at 0 °C) in the range of (23 ± 4) °C, and the high-resolution digital multimeters (up to 8.5 digits), is described. The influence of the resolution of the digital multimeter is investigated, as well as the influence of the self-heating of NTCRs and the measurement on different ranges and with different currents during the comparison of different type of sensors. The analysis of the resistance-versus-temperature (R - T) dependence is done by using the least-squares method and the two-parameter approximation curve for NTCRs. The results have shown that, in the range of (23 ± 4) °C, which is useful for the laboratory applications, NTCRs can be calibrated by means of Pt-25 thermometer and high-resolution digital multimeters with an uncertainty of a few millikelvin, which is very convenient for their wide application as precise and sensitive temperature sensors.