There are several types of thermoelectric pyrheliometer, but their structures are similar. Figure 7.8
shows the structure of the one used by JMA. Copper-plated constantan wire is used as the thermopile in
the sensor portion, which is attached to the bottom of the cylinder at right angles to the cylinder axis. The
cylinder is fitted with diaphragms to direct sunlight to the sensor portion. It is made of a metallic block
with high heat capacity and good thermal conductivity, and is enclosed in a polished intermediate cylinder
and a silver-plated outer brass cylinder with high reflectivity to prevent rapid ambient temperature changes
or outer wind from disturbing the heat flux in the radiation-sensing element. The cylinder is kept dry using
a desiccant to prevent condensation on the inside of the aperture window.