error-producing process applies to all know temperature measuring instruments
except infrared thermometers. All conventional thermometers require a probe to
touch the object being measured, which is usually at a different temperature.
Consequently, heat transfer occurs. After equilibrium occurs, the temperature
measurement is said to have “come up,” but the object is now either colder or
warmer than it was before the probe “intruded upon it”. The amount by which the
object is cooler or warmer than the probe is a part of the error of measurement.
Infrared thermometers produce no “intrusion error.” A hot object “target”
is radiating its infrared radiation in all directions whether or not the
infrared thermometer is there taking its temperature. The object’s
radiation characteristics, and hence its temperature, are not disturbed by the
presence of the infrared thermometer.
Assume that the instrument is the cooler of the two objects and that its front
end optical “telescope” is the area that is exposed to sight from the hotter
object being measured.
then collect this sample of infrared radiation from the hot object being
measured and focus it on the tiny infrared detector. The detector, in turn,
converts it to a proportional electrical signal, which is the exact electrical
analog of the incoming infrared radiation, and hence the hot object’s
electrical signal is then amplified in the preamplifier as shown in Figure 4,
converted to a digital signal, and digitally linearized (to change the T4
radiation characteristics to a perfectly linear voltage-temperature
relationship). After linearization and further conditioning, the resultant
temperature number is shown on the display of the instrument.