The CR1000X is a popular data logger unit manufactured by Campbell Scientific. At the link below we provide example code for CR1000X to demonstrate logging Mars Soiling Sensor using Modbus RTU (RS485). Download the example code and adapt it as needed to suit your system.
See wiring instructions here: RS485 connections to Campbell Scientific CR1000X data logger. Note that the wiring instructions and wiring comments in the example code refer to the 810230-20 model of Mars sensor when used with the 830303 cable series, and other models and cables may have different wiring requirements or colors.