With industrial environments becoming noisier due to variable frequency drives and wireless devices, the 2021 iteration includes integrated ferrite beads and a redesigned PCB layout. This results in in electromagnetic interference rejection, particularly in the 10 MHz to 1 GHz band.
The label is not arbitrary. It signifies the year of a major revision or certification update for the SSIS351 product line. Below are the critical enhancements introduced in the SSIS351 2021 models: ssis351 2021