Perhaps the simplest form, a radiometer a source temperature by measuring the voltage output from a thermopile detector. A schermatic of such a device is shown in รูปที่ 28 The increase in temperature of the thermopile is a direct indication of the temperature of the radiation source. One application of principle is in the measurement of total solar radiation incident upon a suface.8.29 shows a schematic of a pyranometer ,used to measure global salar irradiance. It would have a hemispherical field of view, and measures both the direct or beam radiation, and diffuse radiation . The diffuse and beam components of radiation can be separted by shading the pyranometer from the diret soler radiayion, therby measuring the diffuse component.