Automation engineer at a small manufacturer. We have 9 machines with Siemens S7-1200s doing interlocks, sequencing and a couple of PID loops. Since we started sending machine data to Hermetry (through a gateway reading the PLCs over Modbus TCP), our founder has the idea that we could replace the PLCs with ESP32 boards, “they’re 50 times cheaper and Hermetry can do the logic”.
I know why I’d keep the PLCs, but I’m too close to it and I come across as defensive. I’d like the argument from someone else’s angle, ideally someone who has seen what goes wrong.
Founder here (not Eric’s!). Honestly I’d have the same instinct. What’s the real argument beyond “PLCs are the industry standard”?
I’m on the data side at a water operator, so I see this argument from the people who want dashboards. Our sites run exactly this split and it’s held up for years.
The PLC does control: it scans I/O every few milliseconds whether the network is up or not, its inputs and outputs are made for 24 V field wiring and noisy cabinets, it has certified safety options, and the night-shift technician can open the ladder logic and see why a pump didn’t start. An ESP32 can do the logic, but you’d be building and certifying all of that yourself, then supporting it for 15 years.
Hermetry does monitoring and supervision: history, alarms, dashboards, operators sending a command. Even Hermetry’s own ready-made water solution keeps it that way, the pump stations’ automatic start and stop stays in the station’s controller and the cloud only switches manual mode and pumps on command. See Water site. If the internet drops, a cloud rule can’t stop a conveyor.
Where ESP32s do make sense: extra sensors the PLC doesn’t have, like vibration on a motor, temperatures in a cabinet, energy meters. Cheap, no risk, and they go straight to Hermetry.
Kevin, the cost question is the one to answer with numbers: one hour of downtime on a line versus the price of an S7-1200.
Used Megan’s split almost word for word with the downtime math. We lose roughly $4,000 an hour when line 2 stops. Founder agreed to keep the PLCs and fund ESP32 vibration and cabinet sensors on all 9 machines instead. Everyone’s happy.
The downtime number is what would’ve convinced me too. Fair.
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