Last year, our team had to standardize on one PLC platform for a 12-line packaging retrofit. Budget: around $3.2 million across hardware, programming, and commissioning. We had vendors pitching both Siemens and Allen-Bradley, naturally.
I'm the quality compliance manager at a mid-sized system integrator. I review every PLC spec and panel build before it ships—roughly 50 projects annually. In 2023, I rejected 12% of first deliveries due to wiring violations, incorrect firmware, or documentation gaps. So when I say this comparison is grounded in real-world audit data, I mean it.
Here's what we found comparing Siemens PLC (S7-1200, S7-1500, TIA Portal) vs Allen-Bradley (CompactLogix, ControlLogix, Studio 5000).
We defined five dimensions before touching any brochures:
No surprises so far, except maybe the cybersecurity angle. More on that later.
We had two senior controls engineers each commission a simple conveyor station: 8 digital inputs, 8 outputs, one VFD over Profinet. Time was measured from opening a blank project to a running program with basic HMI screens.
Siemens S7-1200 with TIA Portal V18: roughly 4.5 hours including online connection hiccups. The drag-and-drop device configuration and unified tag database saved maybe 40 minutes vs older tools. Most productive moment? The shared tags between PLC and HMI—no double entry. Most frustrating part? The licensing portal. You'd think buying software in 2024 would be straightforward, but Siemens still uses a dongle-based license model. Took 20 minutes just to authorize.
CompactLogix 5380 with Studio 5000 V35: just over 6 hours. The environment is mature and rock-solid, but add-on instructions (AOIs) require more manual mapping. Also, the tag database is not shared with HMI (FactoryTalk View), so you're essentially maintaining two lists. To be fair, Rockwell has improved this with PlantPAx, but for a standalone machine, you feel the friction.
Our take: Siemens wins this round for pure engineering speed. But don't hold me to this—if your team is deeply experienced in Rockwell, the gap narrows significantly.
I'm going to spoil something: the cheapest hardware is not always from Siemens. Not anymore.
We priced a typical mid-range system—something like a 50-I/O controller with Profinet/EtherNet/IP, remote I/O rack, and a 7-inch HMI:
That's a ~$350 delta, about 19% higher for A-B. Then we factored in our typical spares strategy: one spare CPU and one spare HMI per 10 machines. Spread across a 12-line project, that's roughly $4,200 extra for Allen-Bradley.
So yes, Siemens is cheaper upfront. But—and this is the kicker—we also looked at TCO over 5 years including tech support. Siemens annual support is around $800 per seat. Rockwell's TechConnect is ~$1,200. Get 5 seats? That's $2,000 extra per year. Over 5 years? $10,000. Not negligible.
Our take: Siemens is measurably cheaper for hardware and support, at least in this size class. But if you're already deeply invested in Rockwell's ecosystem, switching costs will kill any savings.
This one surprised us. We assumed both had solid security. But when we checked, only Siemens had IEC 62443-4-1 (product development lifecycle) certification for TIA Portal and S7-1500 controllers as of May 2024.
Rockwell's current line of CompactLogix and ControlLogix had self-declared conformity but not independent certification last time I checked—I'm not 100% sure, but their official documentation as of Q3 2024 still said 'in progress' for full certification. Take this with a grain of salt, because it might have changed.
For our clients in automotive and food & beverage, IEC 62443 compliance is increasingly a procurement requirement. One OEM we work with rejected a ControlLogix-based bid explicitly because of this gap. The cost to them? A $240,000 order lost to a competitor using Siemens.
Our take: If your industry requires explicit security certification, Siemens holds the edge. Period.
You might expect Siemens to dominate here too. But honestly? Allen-Bradley's diagnostic buffer in Studio 5000 is cleaner for troubleshooting logic errors. The cross-reference and tag monitoring is snappier. On the other hand, Siemens has better physical I/O diagnostics—you can visually trace exactly where a signal breaks on the topology map.
Here's where personal preference matters. Our lead controls engineer—a guy with 18 years of Siemens experience—said: "The A-B diagnostics are easier to read, but the Siemens diagnostics are more complete." Both have their strengths. I'd call this a draw, unless you specifically value one style over the other.
This one's not close. Siemens is more open than people think, but Rockwell is more proprietary.
Example: Profinet is an open standard with thousands of certified devices from dozens of vendors. Siemens PLCs talk to any Profinet device without issue. EtherNet/IP is also open, but Rockwell's implementation often requires additional configuration for third-party devices—and some features (like device-level ring) are proprietary.
We had a project where an A-B PLC needed to control a Danfoss VFD over Ethernet. Simple enough, but the EDS file setup took an extra day of troubleshooting. With Siemens and a Siemens drive, it was literally plug-and-play.
Our take: If you need flexibility to mix vendors, Siemens is friendlier. If you're all-in on Rockwell, lock-in won't hurt you.
Here's my honest advice, based on the real data we collected:
If you're starting from scratch with a greenfield project? I'd lean Siemens. The development speed and TCO advantages are real. But if you're maintaining existing machines that are already A-B, switching just for the shiny new thing is rarely worth the headache.
Either way, don't just look at the PLC itself. Look at the ecosystem you'll be living in for the next 5-10 years. The PLC is just the start. The programming environment, the support model, the spare parts pipeline—that's where the real cost (or savings) lives.