Data For The Digital Twin

More flexible production, fewer downtimes, higher quality: Digitalization in production and logistics promises key competitive advantages for companies. The basic concept: A digital twin maps each real object in the IT system, thus enabling accurate planning, documentation and control of all processes. But how to feed the digital twin with field data? This article describes some concepts for digital connectivity in brief.

A core element of the digital infrastructure is the networking layer, which provides the necessary connections between the sensors in the field and the cloud-based applications. The requirements placed on this layer are high: Besides the typical industrial capability (high availability and guaranteed quality of service), the IIoT (Industrial Internet of Things) is primarily concerned with ensuring flexibility and data security. The flexibility of the architecture is so important because the requirements in the IIoT can change relatively quickly: For each new application, it may be necessary to tap new data sources without effecting changes to the automation landscape.

Data Highway Towards The Cloud

Modern networks provide for connectivity between all units of the automation landscape. To meet the increased requirements of industrial applications, a network architecture with several layers and segments is recommended.At the machine or cell layer (controllers, distributed I/O modules, inverters, operating units), horizontal communication predominates, i.e. the exchange of small data packets within or between machines (machine-to-machine, M2M) and cells; the transmission distances are mostly short (not exceeding 100 meters). Occasionally, communication must be simultaneously deterministic, fail-safe, highly available and protected from unauthorized access. Standard in this field are the Ethernet-based protocols TCP/IP and Industrial Ethernet, as well as specialized protocols such as PROFINET. OPC UA is suitable for manufacturer-independent data exchange or the transmission of data for analysis and further processing in cloud-based systems.

To get the required information out of the field devices, also some kind of protocol conversion is needed. Therefore, Siemens had introduced a new intelligent gateway called Simatic CloudConnect 7. This module collects data from the field level (e.g. from PLCs) via Simatic communication, OPC UA, or (in an upcoming release) via Profibus and send these date by the use of MQTT to cloud platforms or other IT Systems.

The core idea of CloudConnect 7 is that most sensor data are already available on the PLC level, including some semantics like data types, names etc. A direct connection from the sensors to the Cloud seems neither possible in most cases (different physical transmission and protocol standards) nor reasonable due to machine and network layouts. However, with CloudConnect 7, the benefits of the digial twin are available also for legacy machines and plants.

In such an environment, cyber security is essential to protect the available of the Network as well as the confidentiality of information. This is best accomplished with dedicated security modules, such as from the SCALANCE SC-600 Family by Siemens, which feature standardized mechanisms including firewall protection and VPN encryption. The individual cells then form more or less self-sufficient segments in the production landscape.

Wireless communication

Wired networking, however, can only be used to transfer data to the cloud if the corresponding field device possesses a communication port. But big data is also interesting for objects such as transport containers, tools or the actual products. This is where various wireless technologies come into play, which can close the gap between (Ethernet) communication networks and real production objects. A distinction is made between wireless LAN (WLAN), radio frequency identification (RFID) and real-time locating systems (RTLS).

Wireless technologies allow to bridge the gap between the IIoT and the rising number of mobile production equipment.

WLAN networks are already widespread and suitable for a variety of tasks, which can also be simultaneously implemented on the same wireless network – subject to the bandwidth requirements. The products in the SCALANCE W family fulfil the industrial requirements for ruggedness, flexibility and performance particularly well, and also offer options for the realization of safety applications (wireless safety). As a counterpart to the wireless networks, WLAN-enabled sensors are needed. Depending on the plant situation, they can be used to realize different benefits. For one, WLAN-enabled sensors save cabling costs, which can be quite substantial, especially if no communication infrastructure exists at certain points in the plant (e.g. outdoors). Another advantage results from data transmission from mobile objects to the cloud, where cabling is simply not feasible.

As a second technology for the IIoT, RFID systems have been in use for many years in production control and logistics applications. Here, all relevant objects are equipped with small radio chips (transponders), which RFID readers can read and write to by radio. Depending on the process, RFID transponders can be directly inserted into the actual product, like an electronic rating plate, or affixed to workpiece carriers, for example, for multiple use.

Last but not least, real-time locating systems (RTLS) have also begun their triumphant march into factory halls. Similar to RFID, all relevant objects are furnished with a transponder, which – unlike RFID – comes with its own energy source. By means of a network of anchors (comparable to access points in WLAN), the transponders can be located in three dimensions, as often as every second if necessary. The position data goes from there to a locating manager, which in turn distributes the data to the various target systems. At the same time, real-time locating systems such as the SIMATIC RTLS also provide a feedback channel, which enables the depiction of location-dependent information on a paper-ink display integrated in the transponder.

Optimal use of technology

First-class network components alone, however, do not make a first-class industrial communication network. At least as important is a network design that is tailored to the specific requirements. Siemens therefore offers a comprehensive range of services for all aspects of industrial communication – from training through consulting and design, to integration and implementation. The combination of future-oriented technology and its optimal use is already creating the prerequisite for new digital applications in manufacturing companies today.