Benefits of a Digital Twin in Control System Implementation

The cost of a control system implementation in large-scale projects across various sectors can range from 5% to 15% of the total project cost. While these figures are rough estimates, and actual costs can differ based on various factors, what remains clear is that delays during the commissioning stages can incur a significantly higher cost. It’s not uncommon for delays to result in additional costs of up to 25% or even more of the total project cost.? One way to avoid such delays is ensuring a comprehensively tested control system software.

Before deploying any PLC software (referred to as PLC logic), thorough testing is imperative, regardless of the complexity. This is a sentiment shared among all control systems engineers, each employing their own testing techniques.

Some readers might recall panels adorned with switches, potentiometers, LEDs, and indicators. While effective for altering inputs and observing outputs, the associated costs (in terms of time, space, and hardware) make this solution impractical for all but the most repeatable PLC logics.

Another approach is crafting a specialized SCADA system for input and output manipulation. This, too, incurs significant costs and suits scenarios where applications can be deployed multiple times with minimal modifications.

Some opt for forcing program inputs and inspecting output statuses through built-in tools in the PLC programming software. However, this method presents challenges, as it requires swift adjustments to inputs once an output is triggered to simulate real-world scenarios—an arduous task for most cases.

An alternative option is embedding logic within the PLC to simulate process behaviour. While effective, it introduces irrelevant logic into the PLC, potentially leading to oversight during deployment. To address this, logic is segregated within the PLC and activated only when needed—during testing and deactivated or removed during plant deployment.

Yet, we propose going beyond these methods with a powerful approach we call "virtual commissioning." This method allows us to simulate real commissioning from the comfort of our office, eliminating the risks associated with on-site environments and significantly enhancing testing comprehensiveness.

Before delving into our method, let's introduce another term: Digital Twin. In our context, a Digital Twin is a software representation of the real process, intricately connected to our PLC as if communicating with the actual plant. A PLC communicates with the real plant through its Inputs and Outputs. In contemporary control system architectures, these inputs and outputs are often stationed remotely, connected to the PLC through a fieldbus. A Digital Twin not only uses the same protocol but replicates the data exchange telegrams, making the Digital Twin indistinguishable from real remote stations for the PLC.

Our approach in building this Digital Twin is a simulation box capable of generating the same telegrams as real remote stations. Furthermore, this simulation box can be programmed to simulate reactions directly from outputs to inputs, maintaining the PLC's seamless interaction. The simulation box is connected to software serving as an engineering station for simulation logic and a human-machine interface. This software supports fast development with predefined logic and HMI objects, offering interfaces for data exchange with other software applications.

The dynamic created during Factory Acceptance Tests (FAT) with our Digital Twin has been remarkable. Collaborating with operators, process engineers, and mechanical engineers has enriched knowledge exchange and discussions, leaving our customers confident and satisfied.

Our tool is not limited to virtual commissioning; it has proven versatile in various scenarios, including operator training, reverse engineering PLC logics, validating third-party control components, and supporting SCADA system migrations.

Our chosen product for this Digital Twin is SIMIT by 西门子 , utilizing simulation boxes for Profibus and Profinet fieldbuses. SIMIT can be used as a software-only solution, accompanied by their Virtual Controller or PLC SIM. We've even employed SIMIT with non-Siemens PLCs using Modbus-TCP or Ethernet-IP drivers.

If commissioning delays sit high on your project delivery worry list, comprehensive and flexible testing is something that you should demand from your system integrator partner. Virtual Commissioning with the development of a Digital Twin is the best approach for this.