Digital Contact Thermometers
A new ASTM International standard provides a variety of recommendations for the manufacture and selection of digital thermometers. 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 E2877 is a set of accuracy classes for digital thermometers. These classes pertain to the temperature interval from -200 through 500 C, an interval important for many thermometry applications. In order to qualify for a specific accuracy class, a thermometer must measure correctly to within a specified value over this interval or the subinterval in which the thermometer is capable of making measurements.
Digital thermometers, which are used for measuring temperature in many laboratories and industrial applications, are being increasingly seen as environmentally safe alternatives to mercury-in-glass thermometers, particularly since U.S. Environmental Protection Agency efforts to phase out mercury thermometers are under way. According to Christopher W. Meyer, a physicist at the National Institute of Standards and Technology, and an E20 member, the petroleum industry and others have used mercury thermometers for decades.
"These industries wish to convert to digital thermometers, but until now there has been no ASTM standard for them," says Meyer. "Also, there has been no set of defined accuracy classes that could help specify the type of thermometer needed for a given application. E2877 is necessary for instructing these industries in the basics of digital thermometers and for providing a standard that can be used in operation protocols."
The new standard describes three types of sensors used in digital thermometers: platinum resistance sensors, thermistors and thermocouples.
"E2877 describes the various types of contact digital thermometers that are on the market and discusses the relative characteristics of each," says Meyer. "It also defines a set of accuracy classes for digital thermometers that may be used to help specify the type of digital thermometer needed for an application. It will allow industries that have previously specified mercury thermometers in their protocols to use digital thermometers."
All interested parties are invited to join in the standards developing activities of E20.09.
CONTACT Technical Information: Christopher W. Meyer, National Institute of Standards and Technology • Gaithersburg, Md. • Phone: 301-975-4825 | ASTM Staff: Christine DeJong • Phone: 610-832-9736 | Upcoming Meeting: May 20-21 • May Committee Week • Indianapolis, Ind.