In September 2023, I signed off on a 14-PLC order that ended up in the trash. Every single unit had the wrong network module for the customer's PROFINET infrastructure. The mistake cost $3,800 in rework plus a two-week delay — and it wasn't the first time I'd paid for not thinking through the full ecosystem before choosing hardware.
I've handled industrial automation orders for eight years. I've documented 11 significant mistakes, totaling roughly $47,000 in wasted budget. When I say "significant," I do not mean typos — I mean rework, delays, and real money. This article is the checklist I wish I'd had back in 2017, when I made my first big selection error.
It's not about which PLC brand is "better." It's about which one fits your situation. I've grouped what I've learned into four scenarios: maintaining an existing Siemens plant, building high-performance machinery, starting out on a tight budget, and managing distributed assets like EV charging or backup power.
Here's what I didn't understand in my first year: PLC selection isn't a spec-sheet comparison. It's an ecosystem decision. The hardware is maybe 30% of the total cost of ownership. Software licenses, training, spare parts inventory, engineer familiarity, compatibility with field devices — those make up the rest.
I only believed that after ignoring it. In 2018, I chose a controller on price alone. The "cheap" option ended up costing 40% more than the "expensive" one once I'd counted the software license, the training time, and the customer's pushback because it didn't integrate with their existing HMI.
These days the two names I get asked about most are Siemens and Beckhoff. Both are excellent. They're also different tools for different jobs. Here's how to figure out which one matches your scenario.
If your facility already runs Siemens controls — whether that's S7-300s from 2005 or newer S7-1500s — I almost always recommend staying in the Siemens ecosystem. This is where I've seen the most costly mistakes, because someone decides to "try something different" without counting the integration cost.
Sticking with Siemens means:
For most of these applications, the S7-1500 is the right call. It's been the workhorse of Siemens' automation line for years, and as of 2025 it remains a strong choice for medium to large processes. It also carries IEC 62443 certification for industrial cybersecurity — worth checking if IT/OT integration is on your roadmap. If your needs are simpler, like a compact machine with basic I/O, the S7-1200 is worth a serious look. The Siemens S7-1200 PLC product page has a useful spec comparator that shows you exactly what you're getting before you commit.
When reviewing that page, check the power supply requirements and the network module options. I've lost count of the engineers who picked the wrong 24V DC variant because they didn't click through to the full datasheet. And if you're doing your own panel wiring, keep a breaker panel diagram within reach. I learned that the hard way when a wiring mistake on a control panel shorted out and destroyed a $600 module.
The mistake I made: In March 2021, I tried to integrate non-Siemens remote I/O into an existing S7-1500 rack because it was 15% cheaper. The integration issues ate that savings in about two weeks of engineering time. I now follow one rule: if the plant speaks PROFINET, the new hardware speaks PROFINET.
If you're a machine builder designing custom equipment — especially servo-driven, high-speed, multi-axis systems — Beckhoff's TwinCAT and EtherCAT architecture is genuinely impressive. As of 2025, benchmark tests I've reviewed (and one I ran myself on a demo system) show Beckhoff handling motion control loops that would strain a traditional PLC scan cycle.
Here's my transparency confession: I've recommended Siemens in scenarios where Beckhoff was arguably the better technical fit, simply because I was more comfortable with TIA Portal. That bias cost me. One customer's machine builder spent months fighting the platform's strengths because I steered them the wrong way.
The numbers said the I/O count was small and the S7-1500 would handle it. My gut said the servo update rate was the real test. I went with the numbers. Turns out the machine could barely reach 60% of its rated throughput. We upgraded the CPU mid-project, which meant redoing the panel layout and reordering parts. That single decision cost roughly $9,000 and three weeks of schedule delay.
But Beckhoff isn't the right answer for everyone either. To be fair to Siemens, the S7-1500 with Motion Control is a capable system in its own right, and the TwinCAT learning curve is real. If your team has zero IEC 61131-3 structured text experience, expect a rough first few months.
The mistake I made: In 2020, I under-specified a controller because I focused on I/O count and ignored the task cycle time. The lesson: calculate your worst-case cycle time before choosing a CPU, not after.
If you're just getting started with PLCs — or supporting a small shop with basic automation needs — the Siemens S7-1200 is where I tell most people to start. Not because it's the cheapest, but because the cost structure is transparent and the ecosystem is forgiving.
With the S7-1200, you can get a genuine Siemens PLC plus the basic version of TIA Portal for a modest investment compared to the S7-1500 line. The community support is unmatched. When I was learning, I spent many late nights on Siemens support forums, and the answers were almost always there.
But "transparent cost structure" doesn't mean "cheap." I've seen plenty of people burned by not reading the fine print on software versions. Compare the full cost — controller, software license, programming cable, training. If a quote looks too good to be true, ask "what's NOT included?" before you celebrate.
One thing I tell every beginner: don't overbuy. Your first project doesn't need a redundant CPU setup unless it's safety-critical. Start with a compact S7-1200 and a small I/O module. Get one project running successfully. Then expand.
The mistake I made: In 2017, I spec'd an S7-1500 for a simple conveyor with 12 inputs and 8 outputs. The S7-1200 would've handled it with room to spare. I spent over $2,000 more than necessary and waited a month for backorder. Match the controller to the application, not to your ego.
This scenario has become more common in the last few years. I've helped customers set up monitoring for EV charging stations, backup power systems, and remote pump stations.
For these applications, the PLC's connectivity matters more than raw speed. You're collecting data and sending it to a central SCADA system, not running high-speed motion control. Both Siemens and Beckhoff handle this fine. Your real decision factors:
I'm seeing more industrial sites install EV charging infrastructure. The chargers themselves are typically not user-programmable, but the load management logic that coordinates charging with the plant's electrical demand often lives in a PLC. That's where Siemens S7-1200 or S7-1500 units with OPC UA support shine — they talk to the building management system without much friction.
And when grid instability hits, I get calls about backup power. I've had plant managers ask me where to buy portable generators as a stopgap while waiting on permanent transfer switch installation. In those situations, the PLC choice comes down to one question: which platform can your team have running in an afternoon? Familiarity beats features when the lights are out.
The mistake I made: During a site outage in February 2024, I spent 45 minutes configuring a newer Beckhoff controller I wasn't fully familiar with, while the customer's operations team waited for us to bring backup systems online. We got it running — barely. Now we maintain standard configuration templates for every platform we deploy.
If you're still unsure which category fits, ask yourself these questions in order:
Choosing between Beckhoff and Siemens in 2025 isn't about picking a winner. The winner depends on your situation. What eight years of documented mistakes taught me is this: the most expensive choice is almost never the hardware itself. It's the cost of not thinking through the ecosystem.
There's something satisfying about a well-executed PLC selection — when the commissioning goes smoothly and the customer's machinery runs from day one. After all the stress of past mistakes, getting it right never gets old.
If you're new to this, start with the S7-1200. Open the product page, check the specs, download the trial version of TIA Portal, and build something small. If you make a mistake, you'll make it on a few hundred dollars' worth of hardware instead of a few thousand.