thermocouple
DESCRIPTION
tcTRANSCRIPT
Chapter 6
Electrical Thermometers
Thermocouples • Resistance Temperature Detectors (RTDs) •
Thermistors • Semiconductor Thermometers
Thermocouples • Resistance Temperature Detectors (RTDs) •
Thermistors • Semiconductor Thermometers
•The Seebeck effect causes an electrical potential when two dissimilar wires are joined and the end is heated.
•The Thomson effect causes heating or cooling when there is current flow through a temperature gradient in a wire.
•The law of intermediate temperatures states that the temperature at the end of the wires determines the electrical potential regardless of the inter-mediate temperatures.
•The law of inter-mediate metals states that other metals may be used in a thermocouple circuit as long as the junctions are at the same temperature.
•A complete thermocouple circuit includes extra junctions from the copper wire in the leads to the voltmeter.
•A modern digital thermo-couple system includes a voltage to temperature conversion, cold junction compensation, and a digital readout of the temperature.
•A swamping box uses resistors in each thermocouple circuit to eliminate errors when measuring an average reading of a set of thermocouples.
•A resistance temper-ature detector (RTD) contains a resistor with a resistance that varies with temperature.
•RTDs consist of precision wires wrapped around an insulator and encapsulated in a protective sheath.