What this base unit is
The Mitsubishi FX3S-30MR/DS is a base-unit PLC from the FX3S family, configured as 16 DC inputs with relay outputs for basic sequencing and discrete control panels. It sits in the PLCs & HMIs class as a PLC Expansion Module entry, which means it functions as a standalone controller rather than a backplane add-on.
Where it lands in a panel
As an FX3S base, it carries its own I/O on-board and is sized for small machines, conveyor cells, and standalone sequence work where a compact relay-output controller is enough.