PLC Capacity Selection in 2026: I/O, Memory, Scan Time, Program Size
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PLC Capacity Selection in 2026: I/O, Memory, Scan Time, Program Size
is still the entry filter, but in 2026 budget 20% spare points AND 30% spare rack slots for safety I/O expansion.
Detail
has split into code size + tag-database size; a Logix Designer project can hit the tag ceiling before code ceiling.
is now bounded by task model: a 1756-L8x periodic task at 4 ms still beats a 1756-L7x at 5 ms on equivalent ladder.
should be quoted in KB of source (ladder + AOI) AND runtime tag-bytes, not "lines of code".
In short: size on four axes (I/O, memory, scan, program), pick a CPU with at least 30% headroom on every axis, and confirm the spare-parts pipeline covers the next 10 years.
. We quote active, EOL, and hard-to-find modules across Allen-Bradley, Siemens, Mitsubishi, Omron, Fanuc, Schneider, Yaskawa, Panasonic and KEYENCE within 24 hours.
Plan for 20% spare digital points, 25% spare analog, 30% spare rack slots, and a separate 10-15% safety I/O reserve for future Profisafe or CIP Safety additions.
No. Modern platforms expose a task model. Spec the worst-case periodic task (often 4 ms for safety), then verify the event-task interrupt latency separately from the vendor.
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