Emissivity; Definition; Determination Of Unknown Emissivity - B+B Sensors DM-Compact Series Operating Manual

OPEARTING MANUAL
9

Emissivity

9.1

Definition

The intensity of infrared radiation, which is emitted by each body, depends on the temperature as well as on the radiation features of the surface
material of the measuring object. The emissivity (ε – Epsilon) is used as a material constant factor to describe the ability of the body to emit infrared
energy. It can range between 0 and 100 %. A "blackbody" is the ideal radiation source with an emissivity of 1,0 whereas a mirror shows an
emissivity of 0,1.
If the emissivity chosen is too high, the infrared thermometer may display a temperature value which is much lower than the real temperature –
assuming the measuring object is warmer than its surroundings. A low emissivity (reflective surfaces) carries the risk of inaccurate measuring
results by interfering infrared radiation emitted by background objects (flames, heating systems, chamottes). To minimize measuring errors in such
cases, the handling should be performed very carefully and the unit should be protected against reflecting radiation sources.
9.2

Determination of unknown Emissivity

► First, determine the actual temperature of the measuring object with a thermocouple or contact sensor. Second, measure the temperature with
the infrared thermometer and modify the emissivity until the displayed result corresponds to the actual temperature.
► If you monitor temperatures of up to 380 °C you may place a special plastic sticker (emissivity dots – part number: ACLSED) onto the
measuring object, which covers it completely. Now set the emissivity to 0,95 and take the temperature of the sticker. Afterwards, determine the
temperature of the adjacent area on the measuring object and adjust the emissivity according to the value of the temperature of the sticker
► Cover a part of the surface of the measuring object with a black, flat paint with an emissivity of 0,98. Adjust the emissivity of your infrared
thermometer to 0,98 and take the temperature of the colored surface. Afterwards, determine the temperature of a directly adjacent area and
modify the emissivity until the measured value corresponds to the temperature of the colored surface.
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