Process Instrumentation I Temperature

Abstract

Temperature is the most widely measured quantity in process industry. Its wide range of application and varied environment of operation, call for a variety of engineering adaptations of the temperature transducer [Magison, McGee, Quinn]. Nevertheless, the basic methods of sensing which have proved to be popular, are only a few. As with other physical variables, exotic and novel methods of sensing have been suggested. They are either restricted to highly specialized niche areas or of limited utility. Bimetallic strips and thermistors have been in wide use for local indication, compensation and protection applications. They are used to sense temperature and temperature-changes and effect a local action. These uses are characterized by simplicity and low cost at the expense of accuracy and flexibility. Barring these, thermocouple remains the main temperature sensor accounting for about half of all applications. Resistance Thermometer Detectors (RTD) form about half of the rest (i.e., about 25% of all the applications). Thermistors account for about 10% to 15% of all applications. Semiconductor sensors and different types of radiation pyrometers span most of the rest.