Measurements Of Real Radiators - Siemens MPA 1 Series Instruction Manual

s
body emits at any wavelength the maximum energy possible for the spe-
cific temperature. Real bodies do not have this ability. In other words, a
black body completely absorbs the radiation without reflection or trans-
mission 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.
 
( ) 
M:
M ::
S
Most burning, annealing and hardening furnaces emit a radiation of
nearly '1' which corresponds to the conditions of a black body if the aper-
ture through which the measurement is made is relatively small.
15.3

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 furnace - which applies to all other self-
contained targets - always, show a reading which is too low. Considera-
ble errors can occur at targets with reflecting, polished or bright surfac-
es, e.g. molten steel and metal without oxide layer and ceramic materi-
als. Exact results can only be obtained when the emissivity coefficient is
correctly adjusted on the pyrometer.
The spectral emissivity coefficient of a body does not represent an exact
material constant, but is also largely dependent on the surface proper-
ties. For different materials the spectral emissivity coefficient  for the
spectral ranges  = 8 - 14 m (MPA 10),  = 1.1 – 1.7 m (MPA 20) and
 = 0.8 - 1.1 m (MPA 30) is shown in the following tables:
M
M
S
 (  ): Emissivity coefficient of the object's surface (targeted
spot) at wavelengh 
radiant energy actually emitted by a real object
radiant energy emitted by a black body (perfect radiator)
Operating Manual MPA
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