Appendix: Determining an Unknown Emissivity | C |
In Appendix A, we showed how emissivity is an important parameter in calculating the temperature of an object via infrared means. In this section we discuss how to determine a specific emissivity value. If you know the material of the object, use Table B- 1 in Appendix B to look up its approximate emissivity. Most organic materials such as plastics, cloth, or wood have an emissivity of about 0.95. For this reason, we use 0.95 as the default emissivity setting in the OS530 Series Thermometer.
For objects of unknown material or for very precise measurements, use one of the following methods to determine a specific emissivity value.
Method 1
1.Measure and record the temperature of the object using a contact temperature probe such as a thermocouple or RTD.
2.Aim the thermometer at the object.
3.Adjust the emissivity until the temperature reading of the thermometer equals the temperature measured in Step 1.
Method 2
1.Heat the object (or at least a sample of the object material) on top of a heating plate to a known temperature. Make sure the thermometer and the air surrounding the heating plate are at the same temperature.
2.Measure the temperature of the object material with the thermometer. Make sure that the object fills the FOV of the thermometer.
3.Adjust the emissivity until the temperature reading of the thermometer equals the known temperature of Step 1.