ABSTRACT
Temperature and moisture measurements are important in process control, both as direct indications of system or product state and as indirect indications of such factors as reaction rates, energy flow, turbine efficiency, and lubricant quality. Filled thermal systems, which traditionally have been used most in the food, paper, and textile industries, consist of sensors connected through capillary tubing to pressure or volume sensitive elements. These systems are simple and inexpensive and generally have fast dynamic responses. A thermocouple consists basically of two dissimiliar metals, such as iron and constantan wires, joined to produce a thermal electromotive force when the junctions are at different temperatures. Parallel connection of thermocouples for average temperature measurement is advantageous because the instrument construction and calibration can be the same as that for a single thermocouple. Resistance thermometry is based on the change of electrical conductivity with temperature.
