Presentation / operationABB Control - AC 31 Page 1-31SBC 260400 R1001-b 06.992. General setup rulesAn ABB AC 31 system always includes an AC 31 central unit. There are three types of centralunits:- The 40 series central unit, with a local inputs / outputs extensions interface- The 50 series central unit, with a local inputs / outputs extensions interfaceand a CS 31 bus interface- The 90 series central unit, with a CS 31 bus interfaceEach central unit incorporates a specific number of binary inputs / outputs and occasionallyanalog. It is possible, depending on the central unit, to increase the number of inputs / outputs,to add input / output extensions connected directly to the central units or remote input / outputunits via the CS 31 twisted pair.
