## 6 Evaluation and Demonstrator Use Cases
### Smart Factory Demonstrator  
In contrast to the smart home demonstrator, the smart factory demonstrator is a so-called brown-field scenario. Such scenarios are often found in practice, as industrial environments commonly contain legacy devices [61; 62]. These devices are used for specific steps in processing. They are spatially distributed and difficult to upgrade as upgrades are mostly rolled out via physical medium [61; 62]. Legacy and proprietary protocols are used that need to be integrated into the environmental context [61; 62]. Due to the cost of downtimes, these machines often run around the clock and are seldomly maintained or updated from a software-perspective. This fact in conjunction with the increase in interconnectivity in industrial areas, creating the IIoT, creates an abundance of vulnerabilities [16; 61].  
For this demonstrator, a fischertechnik smart factory was employed with the pre-implemented process scenario [63]. It consists of a high-bay warehouse, a crane with vacuum grabber for moving the materials around, a processing as well as a sorting station. Material can be delivered to and from the factory. A picture of this smart factory is shown in Figure 7.  
For the smart factory demonstrator, the available system model from fischertechnik was employed to emulate a brown-field scenario. This system uses a Siemens S7-1500 to take in, store, process, and deliver materials. This Programmable Logic Controller (PLC) provides OPC UA-support. OPC UA is an industrial data model that provides connectivity and descriptions of devices and allows, among other features, for M2M communication. An Asset Administration Shell (AAS) can be integrated. This OPC UA functionality was used to notify the SBT dashboard of changes in the output connectors of the PLC. Additionally, an SBT component was set up that measured the electrical current consumed by different parts of the factory. With this sensor-fusion approach, deviations of expected behaviour can  
Figure 6: Micro-controller architecture in the smart home demonstrator scenario.  
be discovered. The electrical current sensors were controlled by an ESP32 micro-controller, which was integrated into the system. Data points describing the current in terms of value and unit were used to generalise monitoring. The features of the SBT allow for the integration of OPC-UA values and the retrofit of external sensors, such as the ESP32 used in this scenario. This is especially interesting as the base functionality of the smart factory was already implemented on the PLC. The possibility to integrate that into an IIoT with standardised interfaces enables flexibility. To simulate wear of devices, rubber bands were employed to mimic increasing mechanical load as it occurs in practice when lubrication of housing of rotating parts degrades, or when the tools grow dull due to wear and require more force. While the OPC UA state clearly shows that the correct outputs for the processing steps were set, the electrical current sensor is capable of differentiating between zero, one, and two rubber bands. A comparison is shown in Figure 8. It shows that the current required to move a motor is nearly linearly dependant on the number of rubber bands added to the motor. The addition of rubber bands in this case simulates wear of a motor due to degradation of an attached tool or the lubricant used.  
Figure 8: OPC UA state as well as current sensor with zero, one, and two rubber bands influencing the process.  
Figure 7: Picture of fischertechnik smart factory.  
That indicates the value of retrofit sensors and shows their usability. A framework to quickly and easily set up IIoT sensor networks can prove significantly useful in detecting and predicting faults and, consequently, leading to stable operation.