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• Small objects with medium and high temperatures can also be easily and
accurately measured.
• When measuring materials with low specific heat, a non-contact method does
not induce heat loss which would distort the temperature reading (as is the
case with contact temperature probes). Non-contact temperature detection
is ideal with corrosive molten materials for which the use of thermocouples is
hardly feasible.
• Last but not least it is also possible to measure the temperature of voltage-car-
rying objects.
16.2 Measurements at Black Bodies (Cavity Radiators)
A black body or a black radiator is used to calibrate radiation pyrome-ters. This
black body is designed in a way that its radiation does not
depend on material characteristics, but only on its temperature. A black body emits
at any wavelength the maximum energy possible for the specific temperature. Real
bodies do not have this ability. In other words, a black body completely absorbs
the radiation without reflection or transmission losses. The spectral emissivity
coefficient e(*) of a black body is equal to 1 or 100 %. The emissivity coefficient
indicates the ratio of radiation of a real body (target) to the radiation of an ideal
black body.
ε(λ): Emissivity coefficient of the object's surface (targeted spot) at wavelengh λ
M:
radiant energy actually emitted by a real object
M
: radiant energy emitted by a black body (perfect radiator)
S
Most burning, annealing and hardening furnaces emit a radiation of nearly ‚1'
which corresponds to the conditions of a black body if the aperture through which
the measurement is made is relatively small.
16.3 Measurements of Real Radiators
Real radiation sources are characterized by the relation of the emitted radiation to
the radiation of a black body with the same temperature. Measurements outside a
37
Operating instructions
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