by R. P. Reed, Ph.D, PEret
NOTE: The following is a special article written published here by a noted authority on thermocouples. Dr. Ray P. Reed. Dr. Reed is a retired researcher from Sandia Laboratories in New Mexico, USA.
He is a long time contributing member of the ASTM International Committee E20 on Temperature Measurement and has written and presented many professional and peer-reviewed articles on temperature sensors, notably thermocouples. His extensive list of publications is on another page on this website, .
This new article from R.P. Reed is published with his permission and is in downloadable format. The link is shown below. Merely click on it to download.
It is in Adobe PDF format and its size is about 310 kb.
Here’s a sample of the opening to the article (The numbers in brackets are the references listed at the end of the paper):
“Thermocouples, based on the Seebeck effect, remain the simplest, most widely used, electrical sensor of temperature. Thermocouples consist only of thermoelectrically dissimilar conductor legs connected at junctions. The Seebeck emf occurs only in the legs. Therefore, commonplace calibration and thermometry errors relate to degraded thermoelements, not to junctions. A yet commonplace implicit Junction-Source Model incorrectly asserts that Seebeck emf occurs only in junctions. That erroneous concept hides problems that are commonplace in consequential thermometry.
“Thermocouple applications range widely. Some are of casual indication of moderate temperatures of benign environments. Many now are for critical monitoring and consequential control of extreme temperatures under harsh conditions of industrial process applications. Modern circuits now range from the initial simple loop of only two thermoelectrically dissimilar electrical conductors to distributed complex networks and of several different materials. [ 1-3 ]
“Properly understood and applied, thermocouples now are capable of accurate and reliable thermometry. However, as now often misunderstood, they have concealed very costly and consequential error.
“The physical nature of thermoelectric phenomena is complex but now is very well understood. [ 4,5 ] Peculiarly, however, the history, terminology, and simple principles essential for use in thermometry are yet very widely misrepresented in current literature at all levels of sophistication. An initial brief summary of thermocouple history suggests here why confusion has persisted for so long. This article then briefly reviews aspects of a decades-old comprehensive, simple, authentic, practical model, the Functional Model of Thermoelectric Circuits. [ 6 ]”
Download Link: Thermocouple Junctions Are Not Voltage Sources!
Citing this work:
Reed, R.P. “Thermocouple Junctions Are Not Voltage Sources!” Temperatures.com. Temperatures.com, Inc. Tues. 21 Oct.. 2014. Web. <http://www.temperatures.com/thermocouple junctions are not voltage sources!/>