The laboratory reference for temperature is a standard platinum resistance thermometer, SPRT (Rosemount model 162CE, S/N 1563). The SPRT's nominal characteristics are 25 ohms at the triple point of water, 0.01 C and 0.385 ohms/C. The SPRT is normally sent back to NIST for routine calibrations; however, NCAR has the ability to do a check at 2 primary temperature points, triple point of water and the melting point of galinum, 29.22279 C.
A Hart Scientific
Model 1575
(S/N 36002) Super Thermometer is used to
measure the resistance of the SPRT with resistance bridge
accuracy. The unit allows the user to load in calibration coefficients
which converts the resistance value to temperature. The International
Temperature Scale (ITS-90) adopted in 1990 algorithm is used.
The SPRT is used in combination with a
Hart Scientific
Model 7040
circulating oil bath
which provides a stable temperature medium over the range of -25 C to
50 C. Control of the temperature is done manually with coarse and fine
potentiometers. The SPRT is not used to control the oil bath
temperature.
