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Letter - R
Radiance temperature

The temperature of a black body which has a radiance equal to the radiance of the object at a particular wavelength or wavelength band.

Radiant energy

The electromagnetic energy emitted by an object due to its temperature.

Radiation thermometer

A device used to measure the temperature of an object by quantification of the
electromagnetic radiation emitted therefrom. Also, a radiometer calibrated to indicate a
blackbodys temperature.

Rankine or R

The absolute temperature scale related to Fahrenheit in the equivalent manner Kelvin is
to Celsius. R = 1.8 x K, or also R = F + 459.67.

Reference junction or cold junction

Refers to the thermocouple junction that must be known in order to infer the temperature
of the other or thermocouple measurement junction.


The ratio of the radiant energy reflected from a surface to that incident on the surface.

Reflected energy compensation

A variable used to achieve greater accuracy by compensating for background IR energy that is reflected off the target into the instrument. If the temperature of the background is known, the instrument reading can be corrected.

Relative humidity

The dimensionless ratio of the actual vapor pressure of the air to the saturation vapor pressure (abbreviated RH). Percent relative humidity is expressed as the product of RH and 100 %. For example an RH of 0.30 is a percent relative humidity of 30 %.


The degree to which a single instrument gives the same reading on the same object over successive measures under the same ambient and target conditions. The ASTM standard E 1256 defines it as the sample standard deviation of twelve measurements of temperature at the center of the span of the instrument. Generally expressed as a temp difference, percent of full scale value, or both.


See temperature resolution, optical resolution, or spatial resolution.

Response time

The time for an instrument-s output to change to 95 % of its final value when subjected to an instantaneous change in target temperature corresponding to the maximum temperature the instrument can measure (per ASTM E 1256).


Recommended Standard (RS) 232 is a standard developed by the Electronic Industries Association (EIA) that governs the serial communications interface between data processing and data communications equipment and is widely used to connect microcomputers to peripheral devices. [Ref. 1] The present revision is EIA-RS-232-D, which defines the interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) employing serial binary data interchange. The standard does not define the protocol or format of the binary stream. The standard comprises three parts: electrical characteristics, interface mechanical characteristics, and functional description of the inter change circuits. The equivalent international standard is Comite Consultatif International Telegraphique et Telephonique (CCITT) V.24.


A recommended standard developed by EIA that defines a balanced interface and is an
expansion of RS-423 that increases the data rate to 10 Mbps.


A recommended standard developed by EIA that defines an unbalanced interface and
is an expansion of RS-232 and provides improvements included increased connecting cable lengths, increased data rates, and use of multiple receivers on line.


A recommended standard developed by EIA that is an improvement over RS-422 in that
it allows an increase in the number of receivers and transmitters permitted on the line.

RTD resistance temperature device

A contact measurement device whose resistance varies with temperature.

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