Work out plc io count instantly with clear inputs, formula shown and shareable results.
IO counts are sized with spare capacity because adding a module later means rack space, wiring and often a rebuild of the address map. Twenty percent spare on each type is the usual allowance, and module counts round up since partial modules do not exist.
IO sizing
points required = actual x (1 + spare); modules = ceil(points / channels per module)
20% is standard, more on a first-of-type installation. It is far cheaper to fit a module now than to extend a rack in a live plant.
Usually yes. Analogue additions are more common during commissioning, and each channel needs its own scaling and alarm configuration.