Principle Of Operation:
When exposed to radiation, the temperature of the blackened horizontal surface rises. Heat is lost from the blackened surface by conduction, convection and radiation. The equilibrium temperature reached is a measure of radiation. This temperature is measured by a thermocouple array. The net radiometer uses polyethylene protective domes which are transparent to radiation in the region of 0.3 to 60 microns. The net radiometer uses two identical blackened surfaces, one facing downwards and the other facing upwards.
Two thin metallic films blackened with a special paint (which has about 98 % absorption in the entire range) stuck on the top and bottom of a former about 1 cm thick constitute the sensor. A multi element copper Constantin thermocouple precisely measures the difference of temperature between the top and bottom surfaces. This difference of temperature is a measure of the net radiation. The blackened surfaces are protected from rain and dust by very thin polyethylene domes which are kept inflated to hemispherical shape by a constant stream of dry air supply. A small pump is used for supplying dry air through silica-gel container.
Spectral response 0.3 to 60 microns
Sensitivity 40 UV/watt/sq.m
Sensing element Two blackened surfaces with a thermopile in between
Wind shield Polyethylene domes
Carrying arm Approx 1 m long aluminum tube