Thermocouple Junctions Are Not Voltage Sources!

by R. P. Reed, Ph.D, PEret

NOTE: The following is a brief overview of a special article written and 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 semi-retired, yet still a contributing member of the ASTM International Committee E20 on Temperature Measurement. He has written and presented many professional and peer-reviewed articles on temperature sensors, notably thermocouples in his long career.

His list of publications is on another page on this website, http://www.temperatures.com/resources/temprefs/publications-presentations-of-r-p-reed/.

This new article from R.P. Reed is published with his permission and is in downloadable format.

It is in Adobe PDF format and its size is about 310 kb.

Here’s a sample of the initial paragraph of the article:

“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.”

Link to a full Introduction to the article and the download link Link: http://www.temperatures.com/thermocouples are not voltage sources!/

TI Temperature Measurement Videos

TI, or Texas Instruments, is one of the world’s most prolific and largest makers of temperature sensors. They make all kinds but their sensors are mostly in the form of Integrated Circuit semiconductors.

TI also does an exceptional job in educating users how their devices work and how they can be interfaced and incorporated in measurement systems. Especially useful are the videos showing how some of their other integrated circuit modules can be used with external temperature sensors, like Thermocouples, RTDs and Thermistors.

Here’s an example of an interesting one:

Developed through TI’s expertise in MEMS technology, the TMP006 is the first of a new class of ultra-small, low power, and low cost passive infrared temperature sensors. It has 90% lower power consumption and is more than 95% smaller than existing solutions, making contactless temperature measurement possible in completely new markets and applications.

Check out their Video Channel on YouTube, especially the long list of videos already published about “Temperature Measurement”. It very straightforward; just go to: https://www.youtube.com/user/texasinstruments/search?query=%22temperature+measurement%22

Acoustic Gas Thermometry Review Article

Metrologia Cover Image

Metrologia Cover Image

Online  —  Acoustic gas thermometry (AGT) is not a very well known temperature measurement technique; several have been reported in the past.

This featured review article in Metrologia (Acoustic gas thermometry M R Moldover et al 2014 Metrologia 51 R1) by six authors from six different  NMIs around the world provides a modern update on the technology and its significance in helping determine values of physical reference temperatures points on the International Temperature Scale of 1990 (ITS-90).

Acoustic Gas Thermometry

Authors: M R Moldover1, R M Gavioso2, J B Mehl3, L Pitre4, M de Podesta5 and J T Zhang6

Review Article ABSTRACT

We review the principles, techniques and results from primary acoustic gas thermometry (AGT). Since the establishment of ITS-90, the International Temperature Scale of 1990, spherical and quasi-spherical cavity resonators have been used to realize primary AGT in the temperature range 7 K to 552 K. Throughout the sub-range 90 K < T < 384 K, at least two laboratories measured (T − T90). (Here T is the thermodynamic temperature and T90 is the temperature on ITS-90.) With a minor exception, the resulting values of (T − T90) are mutually consistent within 3 × 10−6 T. These consistent measurements were obtained using helium and argon as thermometric gases inside cavities that had radii ranging from 40 mm to 90 mm and that had walls made of copper or aluminium or stainless steel. The AGT values of (T − T90) fall on a smooth curve that is outside ±u(T90), the estimated uncertainty of T90. Thus, the AGT results imply that ITS-90 has errors that could be reduced in a future temperature scale. Recently developed techniques imply that low-uncertainty AGT can be realized at temperatures up to 1350 K or higher and also at temperatures in the liquid-helium range.

The complete article can be obtained online at: http://iopscience.iop.org/0026-1394/51/1/R1/article.

About Metrologia

It is the leading international journal in pure and applied metrology, published by IOP Publishing on behalf of Bureau International des Poids et Mesures (BIPM), the International Bureau of Weights and Measures. It is published by the Institute of Physics (IOP) in The United Kingdom.

Online at: http://iopscience.iop.org/0026-1394
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1 Sensor Science Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
2 Thermodynamics Division, Istituto Nazionale di Ricerca Metrologica, 10135 Turin, Italy
3 36 Zunuqua Trail, PO Box 307, Orcas, WA 98280-0307, USA
4 Laboratoire Commun de Métrologie LNE-Cnam (LCM), 61 rue du Landy, 93210 La Plaine Saint-Denis, France
5 National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK
6 National Institute of Metrology, Beijing 100013, People’s Republic of China

Precision & Accuracy in Measuring Surface Temperatures

A subject rife with errors, no matter how you look at it.

There’s a classic pair of books on temperature measurement that are hopelessly out of print. We are fortunate to have both in our little library. They are:

1. “Temperature Measurement in Engineering“, Volume I, by H.D Baker, E.A. Ryder and N.H. Ryder, John Wiley & Sons, Inc. New York and Chapman & Hall, Limited, London (Copyright 1953) Library of Congress Catalog Card Number 53-11565, and

2. “Temperature Measurement in Engineering“, Volume II, by H.D Baker, E.A. Ryder and N.H. Ryder, John Wiley & Sons, Inc. New York and London (Copyright 1961) Library of Congress Catalog Card Number 53-11565. Continue reading

The EarthTemp Network

 

Online — EarthTemp is a network to stimulate new international collaboration in measuring and understanding the surface temperatures of Earth. This will involve experts specialising in different types of measurement of surface temperature, who do not usually meet.

Their motivation is the need for better understanding of in situ measurements and satellite observations to quantify surface temperature as it changes from day to day, month to month.

Knowing about surface temperature variations matters because these affect ecosystems and human life, and the interactions of the surface and the atmosphere. (for more details, see motivations and objectives and scientific context – http://www.geos.ed.ac.uk/research/earthtemp/objectives.html and http://www.geos.ed.ac.uk/research/earthtemp/context.html).

The network is organised around three themes over three years.

In the first year (2012), they focused on Taking the temperature of the Earth: Temperature Variability and Change across all Domains of Earth’s Surfacehttp://www.geos.ed.ac.uk/research/earthtemp/themes/1_in_situ_satellite.

This is an inclusive question, designed to bring together research communities and develop a full picture of common research needs and aspirations.

The second year (2013) discusses Characterising surface temperatures in data-sparse and extreme regions (with an Arctic focus – http://www.geos.ed.ac.uk/research/earthtemp/themes/2_data-sparse).

EarthTemp People

Management group

Chris Merchant (Principal Investigator)
Dr. Chris Merchant is Reader in Earth Observation in the School of GeoSciences (University of Edinburgh). His principal expertise is use of thermal and reflectance imagery from satellites for observing surface temperature for climate applications, with interests also in lakes, aerosols, clouds, air-­sea fluxes and the radiation budget.

John Remedios (Co-Principal Investigator)
Prof. John Remedios is Professor of Earth Observation Science (EOS) in the Space Research Centre (University of Leicester). His research interests include surface temperatures and atmospheric correction; climate trends; measurements, retrievals and exploitation of tropospheric pollution and stratospheric composition; and validation and calibration of satellite instrument data.

Nick Rayner (Co-Principal Investigator)
Dr. Nick Rayner is a scientist at the Hadley Center (Met Office) where she leads the analysis of marine climate observations. Her expertise includes sea surface temperature, marine air temperature and sea ice observations, and the the statistical reconstructions of historical climate data.

Stephan Matthiesen (Project manager)
Dr. Stephan Matthiesen is a physicist and works as project manager and researcher at the School of GeoSciences (University of Edinburgh). He is also a freelance translator and editor of scientific texts.

Steering group

Jacob L. Høyer, Danish Meteorological Institute (DMI)
Phil Jones, University of East Anglia (UEA)
Folke Olesen, Karslsruhe Institute of Technology (KIT)
Hervé Roquet, Centre de Météorologie Spatiale, MeteoFrance
José Sobrino, University of Valencia
Peter Thorne, National Oceanic and Atmospheric Administration (NOAA)

Website support: Science and Engineering at The University of Edinburgh

Website: http://earthtemp.org/

News Feed: http://www.google.com/reader/public/atom/user/15733979554046153349/state/com.google/broadcast