Expanding Allen-Bradley® with Intelligent Remote I/O 

Intelligent Remote I/O
In a  PLC based system the programmable logic controller does all the work: it scans all points, solves the logic, and then writes to all points. The speed with which it can do so is usually critical to the system.  Depending on how busy the PLC is, adding new I/O points-or new functions such as heavy analog signal processing-may slow down scan rates to an unacceptable level, requiring that an additional PLC be added and programmed to provide more processing power.

A PLC-based system with intelligent remote SNAP I/O works in a differnt way, however: like a distributed control system (DCS), it distributes control.  The PLC doesn't do all the work, but instead parcels out some of it to remote I/O processors.  These processors provide communication, like a bus coupler, but also do more.  Although they are not programmable like a PLC, they have built-in functions that automatically run once the I/O is configured.  This distributed processing takes some of the load off the PLC, so that adding points or functions has much less of an impact on system performance.

Intelligent remote I/O works like this:   
  • Scans its own I/O and processes most functions related to it.
  • Holds the data the PLC needs and sends it out as requested.
  • Continues to process local I/O even if communication with the PLC is lost .