Table Top Emissivity Apparatus

Table Top Emissivity Apparatus

TPRL, Inc. has developed a compact method for measuring emissivity. It consists of a series of thin samples, which are be held at a constant temperature (T_s), measured by thermocouples on the surface of the isothermal plate (see Figure 1 for location of samples and isothermal plate). An IR detector located below the samples senses radiation from the samples. Stray radiation on the detector is minimized by a flat optical black coating on the inner surface of the shield and both faces of the aperture plate and by cooling the shield and aperture plates. The shield temperature is monitored by two type-K thermocouples embedded in its walls. Thermocouple and detector voltages are fed to an A/D module and attached to a personal computer. The emissivity is calculated by the equation:

ε=Sσ(T_std⁴ - T_sh⁴)/((1+S)(T⁴ - T_sh⁴))

where S = (V - V_sh)/(V_std - V) and V is the detector voltage, T is the temperature, the subscripts s and sh refer to the emissivity standard and the shutter, respectively. The emissivity standard measurements are readings of the blackbody and cold chamber. They are taken before and after the sample readings and are averaged to cancel detector drift effects.