Heat Transfer Handbook part 93. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 916 EXPERIMENTAL METHODS 40 35 30 25 1 20 15 10 0 5 10 15 20 T C Figure Voltage AE versus temperature T measurements from a thermocouple system exhibiting hysteresis. When measuring an increase in T continuous line the sensitivity of the instrument is uniform and equal to mV C. When measuring a decrease in T dashed line the sensitivity is nonuniform and equal to mV C. Calibration All measuring instruments must be calibrated for determining their accuracy a. The accuracy quantifies an instrument s ability to measure a known value or standard. Standards define units of measurement and are essential in building measuring scales. Standards for measuring temperature and heat flow using different scales are maintained in the United States by the National Institute of Standards and Technology NIST . The International Temperature Scale of 1990 ITS-90 is defined with several fixed temperature points or standards listed in Table . This scale evolved from the pioneering work of Lord Kelvin who in 1884 proposed an absolute temperature scale the Kelvin scale for measuring temperatures. The Kelvin temperature scale with only positive values is an absolute scale because the scale covers the entire range of possible temperatures as established by the second law of thermodynamics. When calibrating a thermometer for instance the experimentalist compares the measured temperature value at a certain state to the standard temperature value set FUNDAMENTALS 917 TABLE Some Fixed Temperature Points Used as Standards for Defining the ITS-90 State T K Triple eqailibriam state of hydrogen Triple equilibrium state of neon Triple equilibrium state of oxygen Triple equilibrium state of argon Triple equilibrium state of water Solid-liquid equilibrium of galium at 1 atm Solid-liquid equilibrium of tin at 1 atm Solid-liquid equilibrium of zinc at 1 atm Solid-liquid equilibrium of silver at 1 atm Solid-liquid equilibrium of gold at 1 atm Solid-liquid
