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Industrial Ethernet Book Issue 102 / 10
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Use of SafetyBridge technology in plastics production

The Chemours company utilized SafetyBridge technology to create a TÜV-certified safety system that is independent of the S7 standard PLC, while still being completely integrated into the existing factory network. The new system offers both flexibility and simultaneous conformity with the latest safety guidelines.

IF SAFETY CONTROL SYSTEMS have to be integrated in large-scale applications, specialised know-how is typically required. Only like that all relevant requirements can be considered completely so that the machine operators are reliably protected against dangerous situations. Solutions like SafetyBridge technology prove to be advantageous because it combines the simplicity of a configurable system with the benefits of I/O modules distributed within the automation network.


Retrofitting safety functions can be a daunting task, and needs to be both carefully planned and coordinated.

Decentralized control systems

Chemours′ Dordrecht site in the Netherlands is their largest production facility in Europe and is focused on the production of plastics (fluoropolymers) for applications such as non-stick coatings and refrigerants with the core brands produced being Te on, Opteon and Viton.

At the widespread Dordrecht plant, all operations in different factories are controlled and monitored from a central control room that has access to all mission critical data as it comes from each production process. The final stages of the factories, where the products are finished and automatically packaged before dispatch, are controlled locally by PLCs that use either Pro net or Profibus as the communication backbone across the automated machines.

Operators have access to process information that is presented on HMIs at various locations that also allow them to control and, if necessary, correct process non-conformities. The production philosophy is to react on alarms by adjusting process parameters centrally from the control room.

Separation of safety and control

When it came to the safety-related parts of the machine control systems, while the main process was controlled via a dedicated safety PLC, the finishing and packaging parts were still based on rigid, hardwired systems. As a result, a project was initiated in order to modernize the outdated safety control systems with the goal of providing more flexibility, whilst still ensuring that the processes complied with strict plant safety procedures and directives.

Johan Sterrenburg, chief engineer for electrical systems and instruments, explains the approach. "From the beginning of the project, we were clear that a major priority was the separation of the safety system from the main control PLC.

After reviewing all possible solutions, we selected Phoenix Contact Inline I/O with the TÜV-certified SafetyBridge Technology protocol. We found that the system could be easily connected to the S7 standard PLC but, at the same time, has its own integrated, on–board safety CPU, so it could be operated completely independently of the standard PLC, while still being completely integrated into the existing network."

Extension by additional I/O modules

As the factory finishing and packaging processes are spread over a wide area with a number of related remote control cabinets, for the first time, the distributed safety I/O could be used to connect the various safety sensors and interlocks positioned throughout the processes. Johan Sterrenburg reports: "Compared with hardwired systems, SafetyBridge offered us a number of advantages. We know our processes very well and try to think ahead as much as possible. For this reason, for the two packaging lines we chose the version 3 LPSDO (logic programmable safe output device) option of SafetyBridge which is future-proof".

In this configuration, Chemours Netherlands B.V. can use one LPSDO to control up to 16 safety input or output terminal blocks remotely across the network. If more safety signals will be needed in the future, the employees can simply add I/O slices or introduce a new LPSDO module with related I/O. This possibility fits exactly to the type of flexibility the chemical company has set as the original project goal.

Safety function blocks

With the safety zones and system interaction clearly defined and specified, the SafetyBridge system offers various safety I/O modules from which a complete system can be assembled. The central control component and heart of each SafetyBridge system is the logic module.

It generates and monitors the SafetyBridge protocol and processes the safe logic. Using the Safeconf configuration software, the user can assign up to 16 different safe I/O modules, each with a unique address, to one, central logic module. For the individual functions, the Safeconf software offers a function-block toolbox that is based on the PLCopen specification and covers all common types of safety sensors and sensor-related functions such as muting.


Safety sensors and interlocks are now integrated into the automation network via SafetyBridge.

The allocated sensor inputs in the hardware can be adapted to the sensor type to create a perfect match, for example, to sensor specific test-pulse filter widths or discrepancy times. Depending on the power control elements, the user can also choose between output modules with semiconductor outputs or floating relay contacts. The hardware modules have a service life of 20 years and can be used up to EN ISO 13849-1 PLe or EN IEC 62061 SIL 3, depending on the configuration and wiring.

Errors excluded by programmers

Once the safety logic is set up, the distribution and physical location of the I/O modules in the network plays no role and does not influence the logic. To implement or retro t the safety logic into an existing standard PLC, the programmer does not need any experience or special training on the subject of functional safety.

From the point of view of the PLC, the SafetyBridge system is seen as a standard I/O and simply ensures the communication backbone for the safety data packages the contents of which cannot be accessed or viewed. The safety modules themselves continually monitor the safety data package contents and if a non-conformity is recognized, the system is immediately transferred to a safe state.

For the Chemours Netherlands B.V. operation, it was also imperative that the status data is fed back to the central control room - another advantage of a network integrated system. Due to the safety mechanisms integrated in the SafetyBridge system, the PLC programmer cannot make any errors or compromise the functional safety. This ensures a worry-free handling of the system in any control and network environment where it ensures a maximum of functional safety.

Simple, functional and flexible

SafetyBridge Technology enables the integration of a functional safety control system into a machine that is independent of both the PLC and the automation network. The system is designed to be as simple as a configurable safety module whilst offering the functionality and flexibility of a programmable PLC with safe I/O terminals that can be distributed across an automation network.

The SafetyBridge system consists of safe input and output modules and so-called logic modules. The input and output modules monitor safety sensor signals and switch off power control elements. The logic module generates and monitors the safety-related SafetyBridge transmission protocol and processes the user-configured safety logic. In addition, the logic modules also have eight safe outputs.

Summary

Retrofitting safety functions to an existing plant can be a daunting task for the project team. The approach needs to be structured, well thought out and can take several months to implement. In accordance with European regulations, the technology also needs to be state of the art. For Chemours, selecting Inline I/O with SafetyBridge technology offered the possibility to use a TÜV-certified safety system at the Dordrecht plant that is independent of the S7 standard PLC while still being completely integrated into the existing factory network.

Simon Davis, Product Marketing Manager Safety, Phoenix Contact Electronics GmbH.


Source: Industrial Ethernet Book Issue 102 / 10
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