PROCESSWEST Magazine Online

Solutions for a Simple and Safe Focus on Control Technology

Don Horne   


As the demands on plant and machinery rise, so too does the level of automation. Control technology has a key role in processing the digital and analogue signals from the sensors and input devices and sending them to actuators, drives and control devices. As the processes required to do this becomes increasingly complex the number of relationships within a machine is rising and the level of networking is growing. In many sectors people are moving closer to the process. Where man-machine interaction is as close as possible, it can help to improve plant availability and increase productivity. Accordingly, safe automation is becoming increasingly important. With intelligent, safe control architectures, users have the freedom for customized implementation of the safety requirements for design, operating and service concepts, as well as operator regulations.

Standardizing safety
The determining factor when selecting the appropriate safety system is the plant’s function range. For example, by their very nature, stand-alone machines have fewer safety functions than interlinked machines and do not need an overriding safety function, such as a safety area shutdown. Configurable control systems are particularly suitable for this type of application. The Pilz PNOZmulti configurable control system supports all common fieldbus and Ethernet-based communication systems, so machine operators can choose the operational control system that best suits their individual needs. Both manufacturers and users benefit from this standardization of safety, in terms of troubleshooting, machine design and training. Ease of use is one of the strengths of the configurable control system. Instead of carrying out the wiring manually, the user creates a safety program quickly and simply using the PNOZmulti Configurator software tool and the certified function blocks for safety-related functions stored within it. Compared with conventionally wired solutions, users save time and money on design, configuration, commissioning, diagnostics and maintenance. The system is powerful enough to assume complete machine control on smaller machines. As a result, the machine builder has no need for an additional control system and saves hardware costs, space in the control cabinet and procurement and stock holding costs.

Safety and standard in one system
Increasingly, safety is no longer just dominated by static events, such as the actuation of an emergency stop mechanism or the opening of a guard door, but must be capable of reacting to sometimes multifaceted situations or to the results of complex calculations. Dynamic safety concepts, such as different operating modes or torque monitoring based on the position of one or more axes, will continue to find their way into the control architecture in the future. Increasingly, that requires more complex relationships with the individual elements in the overall process chain. Machine data – whether for standard or safety – must be capable of being processed together. The trend is for standard and safety functions to use a common control architecture, or to functionally merge the two areas. Hybrid designs are catching on, especially in distributed systems, in order to minimize cabling complexity and interface problems. One common periphery system is needed for the important control-related process signals as standard I/Os and the I/Os for the safety functions. Thanks to the openness of the safety control system, additional encoder systems, interface problems or adapter solutions are consigned to the past. Here Pilz can offer the PSSuniversal multi control system. These continue the philosophy of the configurable control systems and can implement local safety functions as well as recording and forwarding standard periphery signals. The system illustrates the importance of synergies for visualization, diagnostics, servicing, maintenance work and engineering when functional and safety-related parts of a machine control system can be considered together. As they are fully-fledged programmable logic controllers (PLCs), users can choose whether to program using the standardized editors in accordance with EN/IEC 61131-3 for standard and safety tasks or configure using the Program Editor PASmulti, which continues the configuration philosophy of the PNOZmulti Configurator. Pilz offers a wide range of safe, certified function blocks.

Distributing intelligence
Both the PSSuniversal multi and PSSuniversal PLC are control systems in the PSS 4000 automation system. The idea is to merge standard automation and safety. Process or control data, failsafe data and diagnostic information are exchanged and synchronized via the Ethernet-based SafetyNET p. For the control function, it makes no difference where the respective program section is processed. Instead of a centralized control system, a user program distributed in runtime is made available to the user within a centralized project. All network subscribers are configured, programmed and diagnosed this way. So for all control tasks, the user maintains a centralized view of distributed systems. If the intelligence is distributed in the machine components, there is greater availability due to local error reactions and higher productivity as a result of shorter reaction times across the whole system. Dividing the intelligence into smaller machine components also leads to improved scalability.


by Kevin Pauley, National Sales Manager,
Certified Machinery Safety Expert


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