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Programmable Safety Solutions Overview
Programmable Safety Solutions Overview
Safety PLC systems bring the programmability and flexibility of traditional PLC systems to complex safety applications. Their programmable nature means that safety applications can now be solved in software rather than hard-wiring large, cascaded relay systems. This makes activities such as zone control and simplified machine access procedures much easier to achieve. Safety I/O modules are connected to Safety PLCs via safety certified networks, reducing wiring costs and allowing for advanced diagnostic information to be monitored by the safety PLC and shared with HMI systems. This results in reduced costs associated with wiring, troubleshooting and managing production equipment.
Benefits of safety PLCs include:
- Flexibility. Safety PLCs are programmable systems. This allows control engineers to easily design applications in which the behavior of the safety system can be flexible and based on the mode that the machine is currently operating in, the zone of the machine being accessed or the task that an operator or maintenance person is performing. This means that Safety PLCs can be used to help solve applications that are difficult if not impossible to solve with traditional safety relay systems.
- Productivity. The flexible programming of Safety PLCs permits control engineers to create maintenance modes of operation with “limited shutdown” capability, allowing for quicker access to production equipment and faster restart times, which help to reduce downtime. The extensive diagnostics also aid in the troubleshooting and repair of the system, improving MTTR (Mean Time to Repair) and further reducing downtime and improving productivity.
- Wiring Simplification. Safety input and output devices are wired directly to Safety I/O modules. These modules communicate to Safety PLCs via a single network cable. In applications that require logic or have safety devices distributed around equipment, Safety PLC systems can reduce the amount of wiring and commissioning effort required to install and start up production equipment.
- Diagnostics. Safety PLC systems perform internal and external diagnostics checks many times per second. Safety I/O modules also perform checks on their connected input and output devices. This information can be made easily available to operators and service personnel meaning that the exact source of a safety event can often be quickly identified and appropriate action taken, reducing MTTR, getting a machine back into production sooner.
- Integration. Safety PLCs enable machine makers to think of safety as part of the normal control of the machine, not just a piece that is added on at the end. Because safety PLCs communicate on standard automation networks, they allow for easy interlocking between the standard control system and the safety system. Some safety systems are so integrated, they can perform all of the standard machine control (sequential, motion, …) plus safety control, all from one unit.
- Reliability. Safety PLC systems are designed specifically for very high MTBF (Mean Time Between Failure) and very low PFD (Probability of Failure on Demand).
- Expandability. Safety PLC systems are easily expanded. Additional I/O modules can be added to the system and application code can be easily modified and expanded by control engineers.
- Security. All safety PLCs have a “Safety Signature” associated with them, a unique identifier that changes whenever any part of the safety configuration or program is changed. This allows for quick spot checks to determine that the safety system is still the way it was when commissioned. Also, some safety PLCs have multiple layers of password protection to allow only qualified personnel to make changes.
- Safety Certification. Safety PLCs are designed to meet stringent standards for programmable safety systems. To demonstrate their compliance, they are certified by professional testing agencies that they meet the appropriate standard. All Rockwell Automation safety systems are certified by the TÜV Rheinland Group for use in applications up to SIL 3 per IEC 61508 and Category 4 per EN 954-1.
Typical applications for safety PLCs include (i) perimeter access control of production cells, robotic systems and complex manufacturing processes and lines, (ii) point of operation control for press and manual loading applications, and (iii) maintenance simplification, alternative methods for lockout/tagout and other applications where users want to streamline the service procedures for production equipment. Safety PLC systems typically consist of (i) a safety PLC where the user-designed application code is executed, (ii) safety I/O which is where safety input and output devices are wired, and (iii) a safety network that allows the safety PLC to communicate with the safety I/O and with each other. The safety PLC system provides you with an environment to write and execute application code with a very high safety integrity. You generate the application code that is executed in the safety PLC system and then, as part of the commissioning process, validate (test) that the safety PLC system mitigates the safety hazards that it was designed to monitor and control.