Radiation Thermometer or Pyrometer
Pyrometer is the older,more common name of these instruments derived from the greek word pyro that means fire.
How it works ?
All object above absolute zero will radiate energy in the form of electromagnetic waves.
The pyrometer measures the object’s temperature by measuring the emitted energy arriving from the target material.
Emissivity is the ability of an object to emit or radiate its temperature energy.
Black Body Radiation Emitter
A perfect emitter something which is able to emit 100% of its energy is known as black body.
In this case the energy within the object move towards the surface the surface,100% of it is emitted,and none is reflected back inside.The emissivity value is 1.
Non Black Body Radiation Emitters
This is an imperfect emitter with an emissivity value of 0.4. As the energy move towards the surface 60% is reflected back inside,and this internally reflected energy is unable to leave by radiative means. Only 40% of the energy is emitted.
Dark,rough surfaces are good absorbers. Shiny surfaces are poor absorbers.
Dark,rough surfaces are good emitters.Shiny,smooth surfaces are poor emitters.
Factors Affect Emissivity
Radiation Pyrometer advantages
Excellent for temperature measurement of moving item.
Measurement of distant items
Doesnt conduct temperature away from or to the surface.
Measurement doesnt contaminate the measured item.
Doesnt wear out like contact measurement device
Provide years of drift free measurements
Measurements are possible in dangerous areas