Six years. That's how long I've been managing the automation procurement budget for a mid-sized packaging operation in the Midwest. Every year, I negotiate with somewhere between 15 and 20 vendors. Every quarter, I review the line-item totals in our ERP. And in total, I've approved somewhere north of $180,000 in PLC hardware, programming software, and related infrastructure.
So when I say the following, it's not from a slide deck or a manufacturer's brochure. It's from watching what happens after the invoice gets paid.
I believe Siemens PLCs—particularly the S7-1500 series and the S7-1500F safety PLC—are the most cost-effective automation platforms we buy, even though they're rarely the cheapest option on the quote.
Let me explain why, because "35% cheaper up front" almost cost us a lot more down the road.
Around 2023, I got curious whether we were overpaying for the Siemens name. So for a non-safety-critical conveyor application, I requested quotes from three alternative PLC vendors. The hardware savings were real: roughly 30% below the comparable S7-1200 setup.
Then I put together a TCO comparison. Not just the CPU price, but:
When I added those numbers up, the "cheap" option was $8,400 more expensive over a three-year lifecycle. And that's before the intangible cost of maintaining a second engineering ecosystem. I want to say the final comparison was $31,700 versus $40,100 in total expected cost—but don't quote me on the exact figures; the spreadsheet has been revised since.
That experience changed our procurement policy. Now, any alternative to a Siemens PLC has to be quoted with a full TCO model, not just a unit price.
Here's where I used to be skeptical. The S7-1500F safety PLC costs more than the standard S7-1500. The safety-rated I/O is pricier, the engineering is more restricted, and the certification overhead is real. I remember thinking, "We'll just be more careful with our regular PLC."
Then we installed a 1500F on a form-fill-seal machine with a dangerous jaw closure mechanism, and it changed my view.
Not because we had an accident that the safety functions prevented (thankfully, we haven't). But because the integrated safety diagnostics cut our troubleshooting time dramatically. Before, a safety circuit fault meant sending an electrician through a labyrinth of relays and checking continuity one line at a time. With the 1500F, the safety program tells you exactly which zone failed and why. What I mean is: the fault message doesn't just say "stop" — it says "light curtain 2 on zone 3 was interrupted during a non-guarded cycle."
That granularity saved us an estimated 200 hours in fault-finding over two years. At $65/hour, that's $13,000. Per machine. The safety premium was about $4,200. Do the math.
And yes, the S7-1500F also complies with IEC 62443 security requirements, which is becoming a non-negotiable for our larger OEM customers. I'm not 100% sure when that certification became a must-have, but it started appearing in our RFQs about two years ago, and it's now in nearly every one.
Here's the angle that surprised me: power quality for remote PLCs.
We operate three remote monitoring stations with no grid power available. They run on solar panels, batteries, and a small PLC sending tank levels and pump status over a cellular modem. For years, we used a conventional lead-acid battery bank and AC charger. It worked, but the voltage sagged during long overcast stretches, and we'd lose communications to the site intermittently.
(Lost comms on a remote tank isn't a huge deal—unless the pump runs dry and burns out. That's a $4,000 repair and a weekend trip to the site.)
In Q2 2024, I approved the upgrade to a solar lithium battery charger and lithium bank on all three sites. The upfront cost was about $2,400 more per site than replacing like-for-like. The result: no voltage sag below 24.2V in the past year, zero brownout restarts, and no truck rolls for comms failures. I can't say statistically that the lithium setup is always worth it—our sample size is still three sites and one winter—but the trend is obvious.
If you're about to ask "what is the best solar generator to buy" for a remote PLC project, step back. Figure out your average daily load and your worst-case cloudy-week generation first. The generator is the easy part. The power budget is where projects normally fail. I'd rather check the wiring diagram before ordering equipment than watch the green LED flicker through a VPN at 2 a.m.
Preventive maintenance isn't just about tightening terminals. It's about knowing the early warning signs. I've learned to review each PLC's fault buffer and cycle time trend monthly, the same way a mechanic uses a lean spark plug reading chart. It's not about one reading—it's about the pattern.
For example, when cycle time on our S7-1500s creeps up by more than 5% across several weeks, it's usually a failing HMI panel redrawing screens inefficiently. The PLC isn't dead; the health is just shifting. Catching that before it becomes a full-blown restart saves the "phantom fault" call at 2 a.m. that ends in an unnecessary CPU swap.
We did one unnecessary CPU swap last year. I called it "vendor testing." The technician charged us for the replacement before realizing the real problem was a damaged SD card. We were irritated, but that mistake taught us to check the simplest things first. Which, put another way, is the same lesson as the 5-minute check that saves a 5-day shutdown.
Look, I hear that every single year. And sometimes, it's true.
If you have a simple standalone machine, no safety requirements, an electrician who's never seen TIA Portal and doesn't plan to learn it, and zero need for remote support—then the cheapest controller is the right choice. At least, that's been my experience with low-complexity applications. We've installed other brands in those roles, and I'd do it again.
But if you're building a production line with multiple stations, a fleet of machines covered by IEC 62443 requirements, a maintenance team that's already fluent in Siemens, and an owner who counts downtime in thousands per hour, then the TCO math flips. The S7-1500's integrated PROFINET, the TIA Portal engineering efficiency, the depth of Siemens technical documentation (I still check the SIMATIC S7-1500 PLC product page after years)—those aren't marketing bullet points. They're cost avoidance mechanisms.
And no, I'm not saying Rockwell or Mitsubishi make bad products. They don't. We evaluated Rockwell on a project in 2022, and their integration with our existing drives was actually excellent. But switching an entire installed base means retraining, spare parts, and parallel engineering libraries. That's a cost almost no one includes in the comparison—until they're living it.
So when someone asks me whether we should switch to a cheaper PLC vendor, my answer is simple: build a TCO sheet that includes training, integration, support response time, and unplanned downtime risk. If the numbers still favor the budget brand, go for it. In six years of doing this, that has never happened.
I've spent the last six years watching which decisions caused budget overruns. It's rarely the hardware purchase. It's the corner cutting—skipping the safety PLC, undersizing the battery backup, ignoring the early warning signs, buying a "cheaper" controller without modeling the full cost. The cost of prevention is always lower than the cost of the fire. In my opinion, that's what Siemens delivers better than anyone.
So yes, I'll keep approving Siemens purchase orders. Not because they're the cheapest. Because they're the most predictable. And predictability is the entire game in industrial production.