The Allen-Bradley 1720-L004 is a four-input gates circuit card (PC board) designed as a plug-in add-on for legacy Allen-Bradley PLC systems. It provides four independent input gating channels on a single module, enabling simple combinational logic to process digital inputs within the backplane. Listed in distributor catalogs as 1720-L004, the card is described as a four-input gate module in the 1720 family and is noted as discontinued by the manufacturer. In practical use, engineers historically employed this card to implement gate-level logic for input signals in older Rockwell Automation control cabinets without requiring separate external logic modules.
