A moisture control system is provided for a pelletizing process wherein the moisture content of the pellets leaving the pelletizing process is constantly monitored and differences between the measured moisture content of the pellets and a set point indicating the desired moisture content of the pellets are used to regulate variable process controls in the pelletizing process so that the pellets leaving the pelletizing process will have the proper moisture content. Also, a system for protecting a viewing window of an instrument from contaminants is provided.