With the latest developments in digital twin concepts and virtual commissioning or virtual FAT, it is very important to have a tool for setting up process simulation. Building a simulation framework into the operational software is simply not good enough anymore for the current way of thinking, as it does not support any of the new digital twin or industry 4.0 concepts. So how can you create a process simulation system that for any Siemens control system, new or old, that can be used now and integrated into a digital twin concept as well?
Simulating a process in a control system used to be done by simply writing simulation logic into the existing object set. This way, it was easy to roll out during engineering, and so it is easy for an engineer to test their programmed functions. The main simulation is often setup as a control input which, when enabled, enables control functions in the PLC that write a simulation value on the inputs used to read the field inputs. So whenever the functions are enabled, the field inputs are ignored, and outputs are written based on the simulation values.
In some cases, this process simulation based on PLC programs, is left in the software, and can still be triggered by engineers. Obviously having this functionality in the operational control system, can be considered a big risk for safety and operational availability. Taking out the PLC program simulation will remove all capabilities to test the functionality in future, and so this way of simulating a process can not be used in a digital twin environment. A separate tool should be used to keep and run the process simulation code, and a connection to the control system should be setup, so that the control system can be linked to this simulation tool in case simulation is required to test the control software.
With the latest Siemens tool sets it is has been made very easy to setup a simulation model for any process. With a tool like Siemens SIMIT, we can very quickly build process simulation in an independent tool, which can then be connected to a Siemens control system like PCS 7 or PCS Neo. SIMIT has the option to run a single, redundant or multi controller simulation by using a virtual PLC system. This Virtual controller can be downloaded to by the PCS 7 engineering system, at which point the simulation and virtual controller are running the simulated process based on the real control logic. This system can now run as if it was a real process system, and can even be visualised by a copy of the real HMI software.
Using this setup for a digital twin is the base for a good industry 4.0 implementation, and will allow the operators and plant managers to test and train themselves on the running software. Using SIMIT to integrate simulation, will also make sure that there is no code needed in the control system that is used specifically for simulation. The removal of simulation code, will make the running control system more stable, and less vulnerable to accidental actions caused by simulation options being left in the system.
Like all good concepts people would like to used this feature on a site that has already been built a long time ago. With the advantages of running a digital twin, it makes sense to do so, and so, with a bit of effort, usually it is not that difficult to get the process simulation working for existing sites. The newer the PCS 7 version on site is, the easier it is to get SIMIT setup, as for instance a direct export and import of control module types can be made, or even of the APL function blocks. This way, we can define simulation functions for a particular APL function or CMT, and import the tags with the predefined simulation function.
If the site uses older PCS 7 libraries, or custom libraries, it will make the simulation engineering a bit more of a process to go through, especially if the PLC side simulation needs to be removed in the process. But the end result of having a software version of you factory and all processes, is usually worth the effort.
Are you interested in creating a digital twin of your plant? or would you like to know more about process simulation? contact us at firstname.lastname@example.org and we will be happy to setup a virtual meeting with you.
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