Safety PLC simplifies safety engineering for control projects

22 October 2013

ABB has launched a new safety PLC that offers flexible programming facilities designed to speed and simplify the development of safe control solutions for complex control applications.

The safety PLC - the AC500-S - is a new addition to ABB's AC500 PLC range. It features a dual processor architecture that complies with SIL3/PL e functional safety levels. Prior to commercial release, the controller has been extensively field tested over three years in ten pilot applications, including different types of cranes, mining hoists, automatic guided vehicles, and robotics.

The AC500-S includes support for Structured Text (ST) programming, in addition to conventional graphical function block diagram (FBD) and ladder diagram (LD) software. This provides users with a high level programming approach that can simplify the development of solutions for applications that require complex algorithms and mathematics. The feature is complemented by the inclusion of a powerful suite of functions for trigonometric calculations. The mathematical capability is ideal for ensuring safe control of movement in applications involving complex kinematics - such as on cranes, hoists and manipulators.

Existing AC500 PLC users can convert to safety PLC architectures, and start programming applications using the new PLC because ABB includes support for the safety PLC programming in its CODESYS-based integrated development environments for control, motion, robotics and HMI.

The new safety PLC hardware also shares the same look and feel as ABB's standard AC500 PLC family for non-safety applications, as well as identical dimensions to standard ABB CPU and I/O modules, and the same mounting and wiring scheme. Both types of modules may be mixed in the same PLC, allowing it to perform both safety and non-safety functions. This can reduce the complexity and cost of many projects, and open up new options for applications such as direct variable mapping and data exchange between safety and non-safety elements of the control system.

The safety PLC features a separate safety processor. The safety CPU can be configured to work even if the non-safety processor is in STOP or maintenance mode, or during an online change. The dual processor architecture means that users can easily upgrade the performance of a safety PLC during its lifecycle by plugging in a faster non-safety CPU module.

ABB offers a choice of SIL3/PL e certified safety I/O modules including digital input and outputs, and a dedicated analogue current input module covering the 0-20 mA (or 4-20 mA) range. The latter module makes it possible to measure parameters such as pressure, temperature, position and torque on applications directly, without any need for A/D conversion or proprietary electronics. This can simplify the implementation of a wide range of safety-related machinery control applications such as braking systems in hoists and lifting equipment, to positioning systems and temperature control on cranes, and selective shutdown systems on wind power turbines.

To simplify system design, safety-related control modules may be installed as part of the main PLC solution, or be sited in a remote I/O rack linked using the PROFINET/PROFIsafe protocol.

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