1. Comparison with contact thermometers
A contact thermometer such as a thermocouple or resistance is used to measure the surface temperature of the material being measured. Next, radiation thermometer with emissivity set to 1 is used to measure the surface temperature of the material. Gradually change emissivity of radiation thermometer until the contact thermometer reading and radiation thermometer reading are the same. emissivity when both thermometer readings are the same is emissivity of the material being measured.
2. How to use blackbody tape
Affix a piece of blackbody tape (or paint) with a known emissivity to the object to be measured. Set emissivity of radiation thermometer to emissivity of blackbody tape (e.g. 0.94) and measure the area where blackbody tape is attached.
Next, measure the area where blackbody tape is not attached.
Adjust emissivity so that the measured value is the same as the value where blackbody tape is attached.
