NIST Industrial Thermometer Calibration Laboratory

摘要

The NIST Industrial Thermometer Calibration (ITC) Laboratory provides calibrations of industrial thermometers over the range from 196 degrees C to 550 degrees C. The different types of thermometers include liquid-in-glass (LiG), thermistors, thermocouples (<200 degrees C), and industrial platinum resistance thermometers (IPRTs). Calibrations are performed by both comparison with a standard platinum resistance thermometer (SPRT) calibrated on the International Temperature Scale of 1990 and by a limited number of fixed-points. The comparison baths are liquid nitrogen (196 degrees C), alcohol (100 degrees C to 1 degrees C), water (0.5 degrees C to 95 degrees C), oil (95 degrees C to 275 degrees C), and salt (275 degrees C to 550 degrees C). The fixed points used are the melting point of ice (0 degrees C), the triple point of water (0.01 degrees C), and the melting point of gallium (29.7646 degrees C). The temperature measurement system for the reference SPRT it is a commercially-available ac resistance ratio bridge, for the IPRTs and thermistors it is a dc voltmeter with a constant current source, for the thermocouples it is a dc voltmeter, and for the LiGs it is a digital video camera. All of these temperature measurement systems are integrated via three computer-controlled data acquisition systems that semi-automate calibrations. This paper presents the methods, equipment, and uncertainties associated with the calibration of industrial thermometers in the ITC Laboratory.