Mercury Thermometer Alternatives: Training

The NIST Alternative Thermometer tutorials are designed for educating various industrial user groups about the upcoming and current changes that ban the use of mercury products. The slides convey the choices available to industry on the different types of alternative thermometers, how to select an alternative thermometer and some results of an in the field test comparing mercury and alternative thermometers. Dawn Cross is leading the NIST efforts to assist U.S. industry in their transition from mercury thermometers to safer alternative thermometers.

Past NIST Training Events

Selecting and Using Alternative Thermometers
Sept. 19-20, 2012, NIST, Gaithersburg, MD

Frequently Asked Questions

Can a NIST–traceable thermometer be calibrated by using another NIST‐traceable thermometer? And what distinguishes reference thermometers from traceable instruments?

a. Any calibrated thermometer that maintains metrological traceability can be used to calibrate any other thermometer, thus continuing the maintenance of metrological traceability.

b. A "traceable" thermometer can be used to calibrate any thermometer as long as the definition of metrological traceability is met (i.e., result plus uncertainty).

c. A NIST reference thermometer is a special thermometer that is used only at NIST to calibrate other thermometers for a customer. Thermometers that are designated as reference thermometers can be of different types (e.g., platinum resistance, thermocouple, thermistor).

d. A calibrated customer thermometer is used to either calibrate other thermometers or determine temperature for an application. A thermometer calibrated for a customer becomes the customer reference thermometer.

e. A NIST "traceable" thermometer is any thermometer that maintains metrological traceability to the SI through NIST. The NIST "traceable" thermometer can be used to calibrate other thermometer (e.g., customer reference, NIST "traceable", off the shelf) regardless of the type (e.g., platinum resistance, thermocouple, thermistor, analog) as long as the results are associated with uncertainties.

f. The type of thermometer does not define the status (e.g., reference versus traceable); the traceability is critical.

g. Any thermometer that is not a defining instrument (Standard Platinum Resistance Thermometer) of the International Temperature Scale of 1990 (ITS‐90) is an industrial thermometer (e.g., Industrial Platinum Resistance Thermometer, Thermocouple Thermometer, Analog Thermometer, Thermistor Thermometer).

h. A digital thermometer is a display unit plus thermometer of any type.

Can a NIST‐traceable thermometer incremented in 0.2 °C be used to calibrate a NIST‐traceable thermometer incremented in 0.1 °C?

1. Resolution (or increment) and accuracy are not the same thing.
2. Resolution is the number of digits displayed (e.g., digital thermometer) or read (e.g., analog thermometer increment)
3. Accuracy refers to the uncertainty of the measurement made with the thermometer relative to the unit (e.g., °C) through the maintenance of traceability. In most cases, the resolution is better than the accuracy (uncertainty). This will depend on whether the thermometer relies on a tolerance band (e.g., ASTM E1137) to determine an accuracy value or whether the thermometer was calibrated with a stated uncertainty.
4. Calibration and Performance Band (Tolerance) Testing are not the same thing.
5. A calibrated thermometer means that unique coefficients are derived that define how the thermometer interpolates between the calibration points to within a specified uncertainty.
6. A Performance Band (Tolerance) Tested thermometer is measured against a calibrated thermometer. The reading difference divided by the root sum square of the tolerance band and measurement uncertainty should be less than 1 for a pass condition.

Training Documents

Alternative Thermometer Overview - This presentation highlights the general issues and considerations to be made when replacing mercury thermometers with alternative instruments such as liquid-in-glass thermometers, thermistors, thermocouples, or platinum resistance thermometers.

The advantages, disadvantages, uncertainty, calibration range, calibration method, temperature range, and  calibration cost range of each of the various alternative thermometer types are compared to help organizations decide which thermometer type is appropriate for their needs.

ASTM D02 Presentation - Efforts are being made to further the transition from Hg thermometer use (banned by the United Nations Environmental Program's International Treaty of which America is a contributing signatory) to the use of alternative thermometers. This presentation to ASTM's Committee D02 on Petroleum Products and Lubricants outlines the general issues in switching to alternative thermometers. Topics include: advantages and disadvantage of the various alternative thermometers; a tutorial on electronic-based industrial thermometer sensors; and details and results from a pilot study on the use of alternative thermometers in the field.

American Petroleum Institute Presentation - This presentation highlights efforts to further the use of non-mercury thermometers in petroleum field industries. In addition to the considerations to be made when replacing Hg thermometers with alternative technologies, topics include details and results from the first two phases of the pilot study by NIST, the EPA, and a Petroleum Distribution Center on the use of alternative thermometers in the field.

Non-Hg Thermometers for Petroleum Facilities - In 2006, the Quicksilver Caucus, a coalition of State environmental associations, requested that United States government agencies and standards organizations collaborate to reduce the industrial and laboratory use of Hg thermometers. NIST and the EPA are providing science-based support to assist in the promulgation of ASTM standards to allow for the use of alternative thermometers. As part of that support, the EPA and NIST completed a pilot study to phase out the use of Hg thermometers in petroleum field activities. The poster outlines the principal findings.

Organic Liquid-in-Glass Poster - NIST Industrial Thermometer Calibration Laboratory (ITCL) investigated the viability of organic liquid-in-glass thermometers as possible replacements to mercury liquid-in-glass thermometers. The results were presented at ITS9. The poster shows the calibration and in-use uncertainties of organic liquid thermometers over the temperature range from –196 C to 250 C. Measurement capabilities of the organic thermometers are compared to mercury thermometers.