To perform soiling measurements with RDE300, the soiled PV device ("PV2") must be calibrated or normalized against the clean PV device ("PV1"). Note that PV1 and PV2 may be either modules or cells, depending on your RDE300 model number.

Calibration for soiling measurement means determining the Isc_Ref and Pmax_Ref values for PV2 that will cause soiling ratio to equal 1.00 when the PV2 device is clean.

The RDE300 Series User Guide explains soiling calibration of RDE300 in more detail. See Chapter 11. 

For most users we recommend using Method 1 in Chapter 11, described in section 11.2.1. Please refer to this section for more details.

Sometimes when performing the procedure users will find that the "Last Reading" values for Soiling Ratio Isc and/or Soiling Ratio Pmax show NAN instead of the expected numerical values as shown in the example below.

The table below lists several possible causes of NAN values in the Last Reading fields and how to troubleshoot them.

ProblemExplanationHow to Check It and Fix It
Irradiance is too lowMinute-by-minute soiling ratio values are not calculated when irradiance is below the user-set threshold.
On the System tab, go to Soiling Analysis Settings. Check the Minimum Irradiance. We recommend using 500 W/m2. If the value is incorrect, adjust it.

On the PV Channel 2 tab, go to Output Data, Check the Irradiance reading. If the value is below the Minimum Irradiance threshold, you must wait for sunnier conditions to perform the calibration.
Time of Day is incorrectMinute-by-minute soiling ratio values are only calculated when time on the unit's clock is within the user-set window.
On the System tab, go to Soiling Analysis Settings. Check the Time Window (Hours +/- Noon). We recommend 2 hours. This means soiling will be calculated between 10:00 and 14:00.

On the System tab, go to System Clock. Check the time. Confirm that the clock is set correctly, according to local time. If not, adjust the clock.

For using Method 1 for Soiling Calibration (RDE300User Guide 11.2.1), confirm that the time is within the analysis time window. If not, wait until the time is within the time window before attempting the procedure.
Temperature is not being read correctly
Calculation of soiling ratio requires valid temperature readings for the PV2 device (soiled PV module or cell).
On the PV Channel 2 tab, check the Last Reading for Temperature. Confirm that there is a reading in the valid range, and that the temperature does not display NAN.

If the temperature is not correct or is NAN, check the RTD cabling and setup. See Troubleshooting RDE300 series RTD temperature sensors

After correcting the problem, perform the soiling calibration procedure again, following instructions in the RDE300 Series User Guide section 11.2.