Schelt Technology

The pyrheliometer is an instrument that measure the direct solar irradiance (W/m2
). The receiving surface must be
positioned perpendicularly to sun’s rays, via a solar tracker or else.LPPYRHE16 is a Class B pyrheliometer with a field of view of 5° and a slope angle of 1° in accordance with ISO9060:2018 standard and with the criteria of the WMO.The working principle is based on a passive thermopile sensor. The sensitive surface of the thermopile is coated witha matt black paint, which makes the pyrheliometer not selective to the different wave lengths. The spectral range ofthe pyrheliometer is determined by the transmission of the quartz window, whose function is to protect the sensorfrom dust and water. A special quartz allows to perform a nonselective measurement from 200 nm to 4000 nm.The adopted sensor allows the response time to be even lower than ISO 9060:2018 requirements for theclassification of class B pyrheliometers. Radiant energy is absorbed by the blackened surface of the thermopile, thuscreating a difference in temperature between the hot junction and the body of the pyrheliometer, which acts in thiscase as a cold junction. Thanks to the Seebeck effect, the difference in temperature between hot and cold junction isconverted into a Difference of Potential.In order to reduce the variations of sensitivity depending on temperature and to fall within the specifications requestedto a class B pyrheliometer, LPPYRHE16 is provided with a passive compensation circuit. Deviations are calculatedstarting from sensitivity measured at 20 °C.Sensors are supplied with their own Calibration Report.