Digital Expansion Units These look similar to FX2N Base Units and are available in 32 and 48 I/O formats. They attach to the right hand end of the Base Unit or Digital Expansion Blocks, and require an external supply of 100 – 240Vac. All inputs are opto-isolated, 24Vdc sink or source selectable to suit NPN or PNP sensors, and all outputs are relay type. Within Maximum I/O limitations, more than one of these may be used with an FX1N or FX2N Base Unit. They can be further expanded using Digital Expansion Blocks (see Digital Expansion Blocks above).