[Music]
welcome to the temperature emissivity of
non black bodies
please note before viewing this lesson
please review the learning object ratio
pyrometers radiation pyrometer
temperature measuring devices operate on
the assumption that the total energy
emitted by a body or physical object is
the result of its temperature
however energy is also radiated by being
reflected and transmitted by passing
light is a fiber optic strandos these
two types of energy are not affected by
temperature
the target object radiates emitted II
reflected our and transmitted T energy
to the measurement detector the total
energy radiated from an object is the
sum of emitted energy e reflected energy
R and transmitted energy T it is
represented by the formula radiated
energy equals e + R + T
if an object only radiated emitted
energy resulting from its temperature
alone it would be called a blackbody and
its formula would be radiated energy e
equals 1 R equals 0 and T equals 0 for a
non blackbody object the value of e
would also be 1.0 but it's R and T
values would be greater than 0 because
there is reflected and transmitted
energy radiated
to account for the reflected and
transmitted energy from an object a term
called emissivity must be considered
when making measurements emissivity is
the ratio of total energy radiated by an
object to the emitted energy of a
blackbody made of the same material at
the same temperature based on this
definition the emissivity values are
black body equals 1.0 nan black body
equals 0.12 0.9 emissivity values are
used to compensate for the reflected and
the transmitted energy received by the
radiation pyrometer when making
temperature measurements suppose the
temperature of the non blackbody carbon
is 76 degrees Fahrenheit since it
radiates more energy than a blackbody at
the same temperature because the carbon
radiates reflected and transmitted
energy the radiation pyrometer will
measure a higher reading than 76 degrees
by incorporating the R and T values that
are greater than zero into the radiated
energy formula the emissivity value
which becomes less than one is
determined for non blackbody carbon the
emissivity value is 0.8 this number is
used to compensate for the unwanted
reflected and transmitted energy
received by the pyrometer that adds to
the actual temperature emitted energy by
setting an emissivity adjustment knob to
0.8 on the radiation pyrometer the
pyrometer will electronically calculate
the proper temperature emitted by the
object the emissivity setting required
for most materials is obtained from the
tables electronic and paper data that
were developed in a research laboratory
the tables were created by drilling
holes into various materials to form
black bodies only emitted energy comes
from the holes not reflected or
transmitted energy radiated energy is
then measured from non black bodies made
of the same materials the radiated
energy of black bodies and non black
bodies measured in the laboratory is
then used to calculate the emissivity of
each material and entered into the table
now let's check your understanding feel
free to pause the video if you need more
time to figure out the answer
radiated energy from an object comes
from emitted reflected and transmitted
energy
which type of radiated energy is the
result of an object's temperature
the answer is a emitted energy
the radiated energy of a blackbody is
one
to compensate for the effect of
reflected and transmitted energies the
temperature of an object can be
determined by using an emissivity
calculation
the emissivity value of a non-black body
is less than one
congratulations you have completed this
activity temperature emissivity of non
black bodies