The most accurate temperature measurements ever made. Probably.

NPL Lecture by Michael de Podesta It is now 25 years since the establishment of the International Temperature Scale of 1990. The scale has been extremely successful in enabling accurate and consistent temperature measurement around the world. However, it has become clear that the thermodynamic temperature estimates on which ITS-90 is based were in error, even at temperatures close to the triple point of water. The discovery and elucidation of this error is largely due to the development of acoustic thermometry. Over the last decade, the development of combined microwave and acoustic resonators for the measurement of the Boltzmann constant … Continue reading

New references for high temperature measurements

Summary of work reported for high temperature measurements from NPL As a culmination of an eight-year research programme an international collaboration has developed robust reference fixed points, studied their sensitivity to impurities and external conditions and finally measured their melting transition temperature. This talk describes how 100+ measurements made by nine different NMIs have been combined to assign low-uncertainty thermodynamic temperatures to the melting transition of Re-C, Pt-C and Co-C metal-carbon eutectics. At the simplest level, these fixed-points will provide new temperature references for the calibration of pyrometers at temperatures above the freezing point of silver (1234.93 K) and will … Continue reading

The Significance of Thermowells

Consider relevant factors and standards Online — In a May/June 2013 article in InTech Magazine “Basics of thermowell design and selection”, author Ehren Kiker describes why thermowells are important and how their key parameters can be determined for a particular use situation. The article begins: “When planning for a temperature measurement application, a fair amount of consideration is typically given to sensor selection (e.g., thermocouple vs. RTD) and wiring of the output (e.g., transmitter vs. direct wiring), and how these factors will affect the measurement. Often, by comparison, relatively little consideration is given to the mechanical components of the sensor … Continue reading

Wake Frequency Calculator by TempSens Instrument

Plus two additional Calculators An online resource calculator for estimating the Wake Frequency of a thermowell in a flowing stream. According to the website: “TEMPSENS WAKE FREQUENCY CALCULATOR is easy to use and it also ensures that thermowell is designed within the dimensional limits of PTC19.3, 2010. This calculator establishes the practical design considerations for Thermowell installations in power and process piping, which also incorporates the latest theory in the areas of natural frequency, Strouhal frequency, in-line resonance and stress evaluation.” The same webpage provides a Temperature Calculator to convert the Emf (mV)/Ohms generated by thermocouple & RTD to the … Continue reading

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, This new article from R.P. Reed is published … Continue reading

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 … Continue reading

New ASTM Standard For Digital Thermometers

ASTM E2877, Guide for Digital Contact Thermometers W. Conshohocken PA, USA — A new ASTM International standard provides a variety of recommendations for the manufacture and selection of digital thermometers. ASTM E2877, Guide for Digital Contact Thermometers, was developed by Subcommittee E20.09 on Digital Contact Thermometers, part of ASTM International Committee E20 on Temperature Measurement. Included in ASTM E2877 is a set of accuracy classes for digital thermometers. These classes pertain to the temperature interval from -200 °C through 500 °C, an interval important for many thermometry applications. In order to qualify for a specific accuracy class, a thermometer must … Continue reading

Mercury Thermometers & Alternatives in the USA

Thermometer Image: Courtesy & mistermong USA — The USA’s National Institute for Standards and Technology (NIST) began an active mercury-reduction campaign in 2007, and stopped calibrating Mercury (Chemical symbol: Hg) thermometers entirely on March 1, 2011. A full range of thermometric calibration services continues for non-mercury devices according to the special NIST webpage at: Mercury is a potent neurotoxin, and every thermometer that contains it is a potential environmental threat. In the 21st century, however, that is a risk that no one needs to take, and a worldwide effort is underway to deploy substitute devices (alternatives) in consumer, … Continue reading

The Pros & Cons of RTDs & Thermocouples – By Jim Pinto

One useful resource on RTD and Thermocouple sensors was found at Jim Pinto’s Writings section of his website, borrowed from the original article that he wrote for Instruments & Control Magazine in June 2000, at: In the article Jim takes particular care to describe the likely errors that can occur with less-than-perfect cold junction correction in some electronic thermocouple instruments (i.e. signal conditioners, displays, controllers and transmitters) He prefaces his remarks by saying: Resistance temperature detectors and thermocouples can be used for some of the same measurements, but each has strengths and weaknesses that must be carefully matched to … Continue reading

NPL’s Beginner’s Guides to Temperature & Humidity & More…

The Guide to temperature is an introductory guide which aims to help first-time users who have no experience of how to measure temperature beyond what they may have picked up in school, college or everyday life. You can visit the Comment Page on this provisional Guide by Richard Rushby online at the comment webpage for the Temperature guide at: … Continue reading