There is no legislation to control of the proper functioning of pyranometers used to measure solar radiation installed in the PV field. The control can be effectively carried out with portable instruments suitable to avoid uninstalling pyranometers set in areas normally inaccessible as placed at the side of panels. A quick test on the field assesses whether a good maintenance is sufficient to obtain a reliable measurement of the solar radiation or if it is necessary to send radiation sensors to the manufacturer...