3. Evaluation Principle

Normally, the measuring distance is determined by below principle;

Aperture Diameter of Blackbody = Nominal Spot Size At That Distance × 2

Description of Symbols (1).A = S × 2 (2).A means the "Aperture Diameter of Blackbody" (3).S means the "Nominal Spot Size at Distance D" (4).D means the "Measuring Distance" between TN and Blackbody

4. Lens Cleaning before Measurement

Blow off loose particles using clean compressed air.

5. Note for Low Temperature Blackbody

While using the low temperature blackbody at room environment, the surface of the blackbody is very easy to get frost that will change the surface emissivity of the blackbody.

6. Thermal Shock

7. The effect of different Emissivity setting between target and Thermometer

Most of the thermometers of ZyTemp have a default emissivity setting of 0.95.
The surface emissivity of a material is measured by the amount of energy emitted when the surface is directly observed.
Please refer to http://www.zytemp.com/tutorial/emissivity.asp for the detail emissivity table of metal and non-metal materials.
When the emissivity setting of the thermometer and target surface are different, please adjust the emissivity setting of the thermometer to the proper value as the same as the target. If the emissivity of the thermometer is fixed at some value( such as 0.95 ) and can't be changed, please consult with ZyTemp for how to judge the reading accuracy of the thermometer.
The calculation is based on Stephen-Boltzmann's law:

E=k*e*(Tobj^4-Tamb^4)

Where:      E=infrared radiation energy
k=constant
e=emissivity
Tobj= target surface temperature in Kelvin

8. How to evaluate the emissivity of a target surface?

One can discover the emissivity of an object with two thermometers or one dual functions thermometer such as TN4xxLC or TCT series from ZyTemp. Simple use the contact surface type probe to touch that object to get the (contact) temperature, then use the non-contact sensor(infrared) to obtain that surface temperature. Later, adjust the emissivity until the infrared thermometer displays the same temperature as the contact type thermometer. Now you know the correct emissivity of the object.