Mercury Thermometers & Alternatives in the USA

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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, professional, and industrial applications.

New analog thermometers with safe filling materials are in production at several companies and recent ASTM standards have been developed to cover them. See ASTM Standards E1 ( and E2251 (

For more information on each, click each standard’s title (above).

Digital thermometry technologies are plentiful, trials versatile, and generally superior to modern variations on the mercury-in-glass design. Many of these digital devices have wider effective temperature ranges, and nearly all of them equilibrate about 10 times faster than Mercury-filled devices.

There are three classes of sensors that produce signals which can be converted into a digital temperature read-out: thermistorsplatinum resistance thermometers and thermocouples. For more information on each, click on the name on on their name.

Each sensor type used is digital thermometers uses a slightly different aspect of a well-characterized relationship between temperature and electrical resistance or induced voltage in certain materials.

The term “thermometer,” when used in the context of digital equipment, refers to electronic systems that capture signals from the sensors, convert them into temperatures using conversion methods compatible with ASTM and/or ITS-90 standards, and then display the result in some format.

The accuracy of digital thermometers thus depends on the sensor type used, the sensor’s quality, its calibration, and conformance to specified standards. Plus,  the conversion system’s electronics, it’s calibration and conversion technique used and the unit’s sensitivity to ambient temperature and other conditions result additional sources needing traceable calibration.

In many modern devices, these details can be transparent to the user and summary details are described in the unit’s ‘System” calibration certification.

If not, then it is the responsibility of the user to assure that all major components of the measuring system have certified, traceable calibration and then perform the required calculations to determine the system’s measurement capability and combined measurement uncertainty.

This is not always an easy task, but is quite straightforward, as described in the NIST Publication: NIST/SEMATECH Engineering Statistics Handbook (

Reference webpage: Selection of Alternatives to Liquid-in-Glass Thermometers

Promoting alternatives to mercury thermometers



Ref: ASTM E230 / E230M – Standard Specification and Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples

Platinum Resistance Thermometers (PRTs)

Standard Specification for Industrial Platinum Resistance Thermometers:
ASTM E1137 / E1137M – 08

Verification Methods for Alternative Thermometers

Background References & Links
(Laws and Regulations),

EPA’s Mercury home page — (

State Regs: 2005 Mercury Compendium

The Environmental Council of the States
50 F Street NW Suite 350,
Washington, DC 20001

Tel: +1  202-266-4920
Fax: +1 202-266-4937
Email: ecos (at) ecos (dot) org

Dewpoint & Humidity Vendors

Humidity and dewpoint temperature device vendors supply a wide range of equipment for the many types of conditions under which the parameters need to be measured.

Below is a listing arranged by type of sensor. Recall, here we are focusing on those uses commonly understood as moisture levels in gaseous media, e.g., air, combustion gases, process gases.

Thanks for visiting. Click on the links below to learn more details from the equipment suppliers and manufacturers.

  • Chilled Mirror Dewpoint Meters

    Cosa Instrument
    Models MBW.-accuracies claimed to be better than 0.2°C

    Claimed accuracies to ±0.2°C.

    General Eastern
    The Humidity Experts See their site to get the General Eastern Humidity Handbook-loaded with lots of useful details and technical tables-like vapor pressure of water vs temperature .

    Kahn Instruments, Inc.
    Two and three stage Optical devices with accuracies claimed to ±0.1 °C.

  • Other Types of Dewpoint Meters
  • Meaco (UK)
    The Home of Humidifiers, Damp & Humidity Monitoring and Control.

    Vaisala Inc. (USA)
    Producer of a wide variety of unique RH and Dewpoint meters based on their special sensing technology for portable, on-line, calibration, low temperatures, high temperatures and metrology as well as industry.

  • Hygrometers

Some NMIs

National Standards Custodians (NMIs) & Governmental Services

NIST’s Calibration Service Users Guide
Direct calibrations by the USA custodian of temperature (and other) standards

NIST MEASUREMENT SERVICES: Radiance Temperature Calibrations>
An online technical description, in great depth, about the (a) realization and dissemination of ITS-90 above 700°C, (b) a description of the facilities in the NIST Radiance Calibration Laboratory, (c) A discussion of the the wavelength calibration, size of source and linearity issues, (d) An explanation of the use and calibration of radiance temperature standards, and, (e) A summary of the values of stability and uncertainty in the ITS-90 Scale at NIST and the expanded uncertainties for ribbon filament lamp, optical pyrometer and infrared radiation thermometer calibrations. In short, a very complete description of the technology behind the calibration services at high temperatures at NIST.
Read more Some NMIs

Dewpoint & Humidity Software

Plus Psychrometric Charts

There are numerous programs and versions of the psychrometric charts on the Web, just do a search on Find Psychrometric Chart or Humidity Software Suppliers on GlobalSpec, The Engineering Web Search Engine, or Google, and you’ll find plenty.

We’ve already found a few for you, see the list below.

Thanks for visiting. Click on the links below to learn more details, some of which is on this site and some is on others.
Read more Dewpoint & Humidity Software