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Platforms·7 min read·

Virtual PLCs: control logic without the controller

Running the PLC as software on standard hardware is now a real product from major vendors, and the tradeoffs are clearer than the marketing suggests.

Short answer

A virtual PLC runs the control logic as software on an industrial PC or server, usually in a container on a real-time Linux kernel, with the I/O still on the plant floor. Siemens ships the S7-1500V, and Audi has production lines running on it. The gain is decoupling hardware from software; the cost is that the platform becomes an IT asset with an IT lifecycle.

Which protocol sits whereENTERPRISEOPC UAMQTTCONTROLEtherNet/IPPROFINETModbus TCPDEVICEIO-LinkPROFIBUS DPModbus RTUEthernet carries most of it now, which is why the layers blur.

The idea is old and the products are new: run the control logic as software on standard hardware, and keep the I/O where it is.

What ships today

Siemens' SIMATIC S7-1500V runs as a container on an industrial PC with a real-time Linux kernel, under Industrial Edge. Audi has production running on it, which moves this out of the demonstration category.

What it buys

  • Logic decoupled from hardware, so it can be versioned, backed up and moved like software.
  • Consolidation, with several controllers on one machine.
  • Replacement by deploying an image rather than configuring a device.

What it costs

The platform becomes an IT asset. Patching, imaging, hardware refresh cycles and somebody who owns it.

The reliability question does not disappear, it moves. Instead of trusting controller firmware you are trusting a real-time kernel, a hypervisor and a server, and each needs the same discipline the controller used to get for free.

Where it makes sense first

New lines, high controller counts, and plants that already run a competent IT function on the OT side. Retrofitting a single machine gains little and inherits all of the new obligations.

Common questions

Is a virtual PLC as reliable as a hardware PLC?
It can be, on a properly specified real-time platform, and Audi runs production on one. The reliability question moves rather than disappearing: instead of trusting controller firmware you are trusting a real-time kernel, a hypervisor and a server, each of which needs the same lifecycle discipline.
What are the benefits of a virtual PLC?
Control logic stops being tied to a specific piece of hardware, so it can be backed up, versioned, moved and scaled like software. Several controllers can consolidate onto one machine, and commissioning a replacement becomes deploying an image rather than configuring a device.

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