What temperature measurement device consists of a pair of wires of different metals or alloys welded together at a point to form a junction to…

A thermocouple is a temperature-sensing device that operates on the thermoelectric principle known as the Seebeck effect. It consists of two wires made from different, dissimilar metals joined at one end to form a measuring junction. When this junction is exposed to a temperature different from the other end (the reference junction), a small, predictable voltage is generated. This voltage is proportional to the temperature difference between the two junctions. By maintaining the reference junction at a known temperature (often electronically compensated), the measured voltage can be accurately calibrated to indicate the temperature at the measuring junction.

A. Liquid Expansion Thermometer: This device operates on the principle of thermal expansion, where a liquid's volume changes predictably with temperature within a calibrated glass tube.

B. Bimetallic Thermometer: This device uses a strip of two bonded metals with different thermal expansion rates, causing it to bend mechanically as temperature changes.

D. Pyrometer: This is a non-contact device that infers temperature by measuring the thermal radiation emitted from an object's surface.

1. NFPA Fire Protection Handbook, 21st Edition. National Fire Protection Association, 2023. Section 2, Chapter 7, "Heat Transfer," Subsection "Temperature Measurement," p. 2-120. The text describes a thermocouple as "two wires of dissimilar metals joined at the ends. A temperature difference between the junctions produces a small electromotive force (voltage)."

2. DiNenno, P. J. (Ed.). (2016). SFPE Handbook of Fire Protection Engineering (5th ed.). Society of Fire Protection Engineers. Section 2, Chapter 12, "Instrumentation for Heat and Smoke Measurement," Subsection "Temperature," p. 688. This section details that "Thermocouples are the most common temperature transducers used in fire testing" and explains their principle of operation based on the Seebeck effect.

3. MIT OpenCourseWare. (2009). Course 2.671: Measurement and Instrumentation, Lecture 15 - Temperature Measurement. Massachusetts Institute of Technology. The lecture notes describe a thermocouple as a sensor where "a voltage is produced when two dissimilar wires are joined at both ends and the two junctions are at different temperatures." It explicitly details the Seebeck effect and the use of a reference junction.