240-100 Net Radiometer

The 240-100 Net Radiometer contains a high-output, 60-junction thermopile with a nominal resistance of four ohms and linear calibration. The thermopile generates a millivolt signal that is proportional to the net radiation level. The thermopile is mounted in a glass-reinforced plastic frame with a built-in level. A ball joint on the stem facilitates leveling. The thermopile and surrounding surfaces are painted black to reduce internal reflections within the instrument, thus providing more uniform performance over reflective and non-reflective surfaces. The black paint used on these radiometers has superior absorption properties and durability compared to previous versions.

A hemispherical polyethylene windshield protects sensor surfaces from excessive convective cooling. Polyethylene was chosen as the material for the windshield because it is transparent to both long- and short-wave energy. The heavy-duty, self-supporting windshield eliminates the need for pressurization. O-ring seals are included to facilitate windshield replacement. The support arm contains a desiccant supply to keep the air spaces inside the windshield dry. The instrument and its support arm contain purge ports. A mounting bracket is included for attachment to horizontal or vertical pipes.

The net radiation values determined by the 240-100 may not be comparable to those calculated using pyranometer and pyrgeometer combinations if the other radiometers lack proper windshield temperature correction algorithms. Extensive research has been conducted to better understand the effects of windshield temperatures on radiation measurements. The 240-100 radiometers are designed and calibrated to minimize errors caused by windshield temperatures.