Maybe a line was specified in Allen-Bradley and your plant standard is Siemens, or an obsolete Rockwell processor is forcing a decision. Either way, the first question is which Siemens platform corresponds to your Allen-Bradley one. Here's a family-level map and an honest account of what a cross-platform move actually involves.
Family-level equivalents
There is no part-for-part catalog swap between the two systems, but the product tiers line up reasonably well by capability:
- ControlLogix (1756) - large/high-performance rack systems - maps to Siemens SIMATIC S7-1500.
- CompactLogix (5370/5380, 1769) - mid-range - maps to S7-1500 (compact) or a high-end S7-1200.
- MicroLogix (1100/1400) and Micro800 - small machine control - map to the Siemens S7-1200.
- SLC 500 and PLC-5 - legacy, now obsolete - are typically migrated to S7-1500 as part of a modernization.
- POINT I/O and FLEX I/O (distributed) - map to Siemens ET 200SP / ET 200M distributed I/O.
Why it is a migration, not a swap
The two ecosystems differ in ways that matter well beyond the CPU:
- Programming software: Rockwell uses Studio 5000 / RSLogix; Siemens uses TIA Portal. Logic must be re-engineered, not copied.
- Addressing model: Logix is tag-based; older Siemens and many programs are address-based - the data model has to be rethought.
- Networks: Allen-Bradley centers on EtherNet/IP; Siemens centers on PROFINET. Drives, HMIs and remote I/O on the network usually change too.
- I/O wiring: terminal layouts and module form factors differ, so field wiring is re-terminated or adapted.
How to plan one
Inventory the existing system (CPU, I/O count and types, networks, HMI, drives), pick the matching Siemens tier from the table above, then budget for software conversion and commissioning time - that engineering effort, not the hardware, is usually the biggest line item. For a phased approach, distributed I/O can sometimes be reused or bridged while the processor is replaced first.
Need either side sourced?
Whether you're keeping an obsolete Allen-Bradley processor alive until a planned migration, or buying the Siemens hardware to replace it, we can quote both. Send us the catalog numbers and we'll respond within two business days, with availability, condition and price where we have them and a full quote once confirmed. We are an independent reseller and not affiliated with Rockwell Automation or Siemens; both brand names are used here only for identification.