The Allen-Bradley 1772-SD-A Remote I/O Scanner is a solid-state memory device that allows for the connection of remote distribution racks into the Allen-Bradley Bulletin 1772 PLC-2 Mini Programmable Logic Controllers. These distribution racks can be located at up to 10,000 feet (3048 meters) away from the remote scanners, and they are used for collecting information from the field sensors and delivering the processor commands to the field actuators. The distribution racks are called Remote I/O Adapter Modules and they are connected to the 1772-SD Remote I/O Scanners such as the Allen-Bradley 1772-SD-A Remote I/O Scanner by using a special type of communication wiring called Twinaxial cables. All the information moving through the system is encoded and transmitted via serial communication protocols.

With an Allen-Bradley 1772-SD-A Remote I/O Scanner, it is possible to collect information from up to 896 I/O points. The data collected from the field sensors is processed in the Mini PLC-2 central computer and the responses are transmitted through the Twinaxial Cable and interpreted by the Remote I/O Adapter Modules where they are passed on to the appropriate signal transducers that will command the field actuators. Using serial communication systems creats significant savings when compared to the deployment of the same control structure by hard wiring. Central troubleshooting capabilities and the simplification of the application system are some of the advantages of using serial communications instead of traditional technologies. Only properly trained technicians should be allowed to perform maintenance, troubleshooting, or repair work to the PLC-2 processor systems, their accessories, and their corresponding serial networks. The Allen-Bradley 1772-SD-A Remote I/O Scanner is an ESD sensitive device, so using a protective ESD wrist strap while servicing it is strongly recommended.