Information

2 Fluke Corporation Infrared Temperature Calibration 101
Converting input
temperature to radiance
The measurement surface of
a calibrator acts as a trans-
ducer by converting thermal
energy into thermal radiation.
The intensity of a portion of
the infrared radiation emitted
by the measurement surface is
measured by the infrared ther-
mometer to calculate a tempera-
ture. The measurement surface
is analogous to the sensor of
an RTD which transduces ther-
Infrared temperature
calibration
Temperature source
In spite of our experiences with
seeing temperature, confidence
in IR temperature measurement
usually requires the use of cali-
brated instruments. Calibration
can be defined as a set of oper-
ations, performed in accordance
with a definite, documented
procedure, which compares the
measurements performed by
an instrument to those made
by a more accurate instrument
or standard, for the purpose
of detecting and reporting,
or eliminating by adjustment,
errors in the instrument tested.
An IR temperature calibra-
tion starts with a measurement
surface that acts as a tempera-
ture source, which may be a
flat plate or cavity that func-
tions as the standard or refer-
ence. Calibration geometry,
which includes the size of the
measurement surface and its
distance from the thermom-
eter being calibrated plays an
important role in the measure-
ment result. Also critical are
the temperature stability and
uniformity and the physi-
cal properties of the emitting
surface such as its emissivity.
Calibration is easy with the 4180 Series Precision Infrared Calibrator.
Temperature uniformity is important for infrared thermometer and thermal imager calibrations.
Amplitude
Wavelength
mal energy into a resistance
that is measured by a readout
device and used to calculate a
temperature. It is interesting to
note that the sensor is respon-
sible for most of the error in
a temperature measurement,
which explains the importance
of calibrating the temperature
sensor. One of these sources
of error in the measurement
surface and perhaps the largest
in an infrared temperature cali-
bration is emissivity.