# Setting for Accuracy

## Blackbody and Emissivity

### Blackbody

An ideal object which absorbs all incident light (electromagnetic wave) and reflects none.

### Emissivity

The ratio of the radiation emitted by an object surface to the radiation emitted by a blackbody at the same temperature. According to Kirchhoff’s law of thermal radiation, an emissivity of an object is equal to a radiation absorption rate of it.

“emissivity ε” (= absorption rate) = 1 - “reflectance” - “transmittance”

If a reflectance and a transmittance are zero, such an object must be a blackbody and an emissivity is 1.

*Object examples of an emissivity close to 1

Pottery  --- Emissivity 0.90

Concrete --- 0.94

*Typically a transmittance of metal is zero and its reflectance is large.
Therefore, an emissivity of metal is relatively small.

Example: Aluminum (Oxide surface) --- Emissivity 0.2 to 0.4

Copper (Oxide surface)     ---         0.4 to 0.8

Iron (Oxide surface)         ---         0.5 to 0.9

An emissivity of metal has a range of values.
Because the metal surface oxidizes in the air and therefore the reflectance changes according to its surface condition.

## Infrared thermometer and Emissivity

The infrared thermometer does not detect all of the radiant light, but actually IT-480 detects infrared light with wavelengths from 8 to 14 microns. HOR team defines that the ideal object which is zero reflectance and zero transmittance for the infrared light with 8 to 14 microns is the blackbody i.e. emissivity ε=1 for an infrared thermometer; IT-480.

### Temperature measurement of a low emissivity object

• Firstly, emissivity setting of IT-480 must be adjusted to the suitable value.
• If a reflectance of the object to be measured is high, non-negligible errors may occur depending on mixing radiant infrared lights from the surrounding objects to a radiant infrared light from the object to be measured. Similarly, if a transmittance of the object is high, radiant infrared lights from objects behind the object to be measured propagate through the object and are mixed in a radiant infrared light from the object.
• In the case of an emissivity is 0.1, ninety percent of the detected infrared light by the IR detector of IT-480 is background infrared light. And in this case, for example, if a surface temperature of the object to be measured is 100ºC, actual measured temperature value becomes close to room temperature.
• Temperature measurement with a demo unit is strongly recommend to confirm the applicability at the measurement site.

### Emissivity Setting Error and Temperature Measurement Error

Following plot is an example of theoretical calculations about HOR infrared thermometers.