The HMI or Human Machine Interface provided by Seven Sensor is programmed in Macro codes and designed with three screens:

Soiling Ratio screen: This screen allows to see the soiling ratio in (%). If the difference between the two sensors is greater than 10% (this value can be changed as per buyer requirements), the Red LED lights up to warn the user to clean the panels, Otherwise the Green LED lights up.

Data Recorder: This screen allows the end user to retrieve all the data recorded during the measurement, either in PDF or Excel format.

Data can be taken for 1 hour, 6 hours, or more.

After recording the Data, retrieve them either in PDF Format or Excel Format.

Soiling Ratio Graph; This screen allows to view the results of the soiling Ratio in graphical form.


The soil monitoring system is tested before delivery. The two Irradiance sensors were calibrated under natural sunlight and compared with a calibrated reference cell at Fraunhofer-institut für Solare Energiesysteme ISE, Germany. As per the IEC 61724-1 the Soiling Ratio Calibration should be repeated at least annually.


The communication between the two irradiance sensors and the PLC is done through a Modbus RTU protocol, so that the data collected goes directly from the sensors to the PLC. The diagram below explains how to install the soil monitoring system: