Virtual commissioning is the practice of testing control software, the PLC program, HMI screens, robot paths and safety logic, against a simulated model of the machine or line before the real equipment is ready. The code is the same code that will run on site; only the machine is virtual. Bugs that would normally surface during a tense week of site commissioning are found at a desk, weeks earlier, when they are cheap to fix.
It is not a new idea, but it has become practical for ordinary projects because emulated controllers and behaviour models are now affordable and fast. A 2020 article in ISA InTech describes it simply as moving the debugging of PLC code into a virtual environment before it reaches physical equipment.
How virtual commissioning works
Every virtual commissioning set-up has three parts. First, the controller: either the real PLC on a bench (hardware-in-the-loop) or an emulated controller such as Siemens S7-PLCSIM Advanced, TwinCAT in simulation mode or a CODESYS soft PLC (software-in-the-loop). Second, the plant model: a behaviour model of the sensors, actuators, drives, kinematics and material flow. Third, the coupling: an I/O map that ties every PLC input and output to a signal in the model, synchronised closely enough that timing faults show up.
| Set-up | What runs the code | Best for |
|---|---|---|
| Software-in-the-loop (SIL) | Emulated PLC on a PC | Early logic testing, remote teams, many test runs |
| Hardware-in-the-loop (HIL) | The real PLC and I/O on a bench | Timing-critical motion, safety PLCs, network load |
| Mixed | Real PLC, simulated field devices | Panel FAT with a virtual machine attached |
What the model needs to contain
The model only needs enough fidelity to exercise the logic. Over-modelling is the most common way to blow the budget. For a typical packaging or assembly line we model:
- Every digital sensor and actuator, with realistic travel and switching times
- Drives and axes at the level the PLC sees them (speed, position, ready, fault)
- Product flow: parts appearing, jamming, being rejected
- Fault injection: a sensor that sticks, a cylinder that never reaches its end position, a drive trip
- Operator actions: e-stop, guard door open, mode changes, restart after a stop
Virtual Commissioning with NX MCD and PLCSim Advanced
Siemens Knowledge Hub
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Watch on YouTubeWhat the evidence says about commissioning time
Published results are encouraging, though most come from vendors or single case studies, so treat them as indications rather than promises.
| Result reported | Context | Source |
|---|---|---|
| Design phase cut by 10%, commissioning time by 25% | Machine builder Tronrud Engineering | ISA InTech, 2020 |
| Software quality up from 37% to 84%; real commissioning time down 75% | Academic field study on a small PLC-controlled system (2007) | Visual Components |
| On-site commissioning time cut by 70% | Brownfield engine assembly line, Wipro PARI | Siemens blog, 2022 |
| Real commissioning up to 70% faster | Vendor service claim for machine tools | Siemens |
The study summarised by Visual Components is worth reading because it measured software quality, not only time. The Wipro PARI case is useful for brownfield teams: the project went from design to shop-floor commissioning in three months against an estimated six to eight.
Where virtual commissioning pays back fastest
- Brownfield changes with a short shutdown window. If you have a 48-hour Christmas stop to swap a line's controls, every hour of on-site debugging is expensive.
- Complex sequences and interlocks. Robot-to-PLC handshakes, multi-station transfer lines and recipe-driven batch steps hide the bugs that hurt most.
- Repeat machines. Machine builders who ship the same platform with options can reuse the model and test every variant.
- Long-lead equipment. When the conveyor or press arrives two months late, the software team can still finish and test.
- Distributed teams. A model on a shared server lets engineers in different countries test the same build.
Where it is not worth the effort
A standalone machine with twenty I/O and a simple sequence rarely justifies a full 3D model. A signal-level simulation in the PLC itself, or a well-run bench test, will do. Be wary too of projects where the mechanical design is still moving: you will rebuild the model three times. Start virtual commissioning once the layout and I/O list are stable.
A step-by-step plan for a first project
- Pick one cell or line section with a known history of commissioning pain.
- Freeze the I/O list and functional specification for that section.
- Build the behaviour model from CAD and the I/O list; resist modelling what the PLC cannot see.
- Connect an emulated controller and run the normal sequence end to end.
- Write fault and recovery test cases from the specification and run them all.
- Hold a virtual factory acceptance test with the end user, then log every change.
- On site, compare the issue log with a previous similar project to measure the gain.
Virtual FAT and what customers now expect
The ISA article notes that end customers have started to ask for virtual factory acceptance tests. That changes the conversation with a machine builder: instead of a single day in the builder's workshop, the customer can test sequences and fault recovery remotely, and repeat the test after changes. We cover the wider difference between factory and site tests in our FAT vs SAT guide.
How we approach it at Wartens
We build machine and line models from CAD at 1:1 scale and drive them with the PLC program that will run on site, so logic, interlocks and sequences are tested before anyone travels. Engineering is done at our India centre; you review and test the result remotely before site work, and the same model can later serve as an operator training or operations twin. For background on the model itself, read digital twin vs simulation.
If you have a line or machine coming up for commissioning, send us the I/O list and a layout and we will tell you honestly whether virtual commissioning is worth it. Start with our digital twins and virtual commissioning service or contact the team.
