skip to Main Content
Letter - T

The object upon which the temperature is determined.

Target size effect

See Size-of-Source Effect.


Teflon® is a brand name and a registered trademark of DuPont.


A property of an object which determines the direction of heat flow when the object is
placed in thermal contact with another object (i.e., heat flows from a region of higher
temperature to one of lower temperature).

Temperature coefficient

The change in accuracy of an instrument with changes in ambient temperature from
that at which the instrument was calibrated. Usually expressed as the percent change in
accuracy (or additional error in degrees) per change in ambient temperature. For a rapid change in ambient conditions, refer to Thermal Shock.

Temperature resolution

The minimum simulated or actual change in target temperature that gives a usable change in output and/or indication.

Temporal drift

See Temperature Coefficient.

Test temperature

The test temperature, Tt, is the gas temperature at the measuring Location.

Test pressure

The test pressure, Pt, is the total pressure in the gas at the measuring location. The specification defines it as the absolute pressure against vacuum.

Thermal Detector

Detector in which the photons of incident radiation are converted to heat and then into a signal from the detector. Thermal detectors include pyroelectric, bolometer, and thermopile types.

Thermal Drift

See temperature coefficient.

Thermal Radiator

An object that emits electromagnetic energy due to its temperature.

Thermal Shock

An error due to a rapid change in the ambient temperature of an instrument. Expressed
as a maximum error and the time required for performance to return to prescribed


A semiconductor material whose resistivity changes with temperature.


A set of two junctions of two dissimilar metals used to measure temperature by means of the Peltier effect, whereby heat is liberated or absorbed by the flow of electrical current
through a junction of two dissimilar metals such that an electrical potential develops
between two such junctions in proportion to the difference in temperature of the junctions.
A variety of types exist including:
J   (Fe / constantan)
K   (chromel / alumel)
T   (Cu / constantan)
E   (chromel / constantan)
R   (Pt / Pt – 30 % Rh)
S   (Pt / Pt -10 % Rh)
B   (Pt – 6 % Rh / Pt – 30 % Rh)
G   (W / W – 26 % Re)
C   (W – 5 % Re / W – 26 % Re)
D   (W – 3 % Re / W – 25 % Re)

Thermoelectric (TE) Cooling

Cooling based on the Peltier effect. An electrical current is sent through two junctions of two dissimilar metals. One junction will grow hot while the other will grow cold. Heat from
the hot junction is dissipated to the environment, and the cold from the other junction is used to cool.


A thermal photograph generated by scanning an object or scene.


A number of similar thermocouples connected in series, arranged so that alternate junctions are at the reference temperature and at the measured temperature, to increase the
output for a given temperature difference between reference and measuring junctions.

Time Constant

The time it takes for a sensing element to respond to 63.2 % of a step change at the target.

Transfer Standard

A precision radiometric measurement instrument with NIST traceable calibration in the USA (with other recognized standards available for international customers), used to calibrate radiation reference sources.


The ratio of IR radiant energy incident on an object to that exiting the object.

Triple Point

The condition of temperature and pressure under which the gaseous, liquid, and solid phases of a substance can exist in equilibrium. For water at atmospheric pressure, this
is typically referred to as its freezing point.

Two-Color Thermometry

A technique that measures the energy in two different wavelength bands (colors) in order to determine temperature. The 2 color technique has been shown to be effective for correcting errors due to partial blockage of the target caused by dust particles.

Back To Top