The pyrheliometer LP PYRHE 16 is based on a new passive thermopile sensor. The sensitive surface of the thermopile is coated with a matt black paint, which makes the instrument not selective to the different wave lengths. The spectral range of the pyrheliometer is determined by the transmission of the quartz window, whose function is to protect the sensor from dust and water. A special quartz allows to perform
a 200nm-4000nm non-selective measurement.
The adopted sensor allows the response time to be lower than ISO9060 requirements for the classifi cation of fi rst class pyrheliometers (the response time is under 9 seconds while the standard requires a response time lower than 20 seconds). Radiant energy is absorbed by the blackened surface of the thermopile, thus creating a difference in temperature between the hot junction and the cold junction of the pyrheliometer, which acts in this case as a cold junction. Thanks to the Seebeck effect, the difference in temperature between hot and cold junction is converted into a Difference of Potential.In order to reduce the variations of sensitivity depending on temperature and to fall within the specifi cations requested to a secondary pyrheliometer, the LP PYRHE 16 is provided with a passive compensation circuit.