Future-proofing safety control
By Alex Dahm22 October 2010
Keeping up with the requirements of the latest standards is particularly important in the field of electronic control and safety systems for cranes.
EN 954-1 is the current standard for functional safety of machine applications but it is being replaced by EN 13849-1 Safety of machinery - Safety related parts of control systems - Part 1: General principles for design. In anticipation of this, Hirschmann has improved its Scalable Mobile Control System (SMCS) for mobile applications to provide the performance level c (SIL 1) or d (SIL 2) in accordance with the new EN ISO 13849-1 standard.
The new SMCS is designed to the new standard to offer more reliable hardware and software. It also uses a new safety rating system. So-called performance levels (PL) are used as index for the grade of functional safety. The performance level value is determined by quantitative factors, for example: MTTFd (Mean Time to dangerous Failure), DC (Diagnostic Coverage), CCF (Common Cause Failure) and system design categories, and by qualitative factors.
The qualitative assessment is covered by a well documented development process which proves the appropriateness of the safety application and assures its correct implementation. Risk assessment and probabilistic approach are derived from IEC 61508 (Functional safety of electrical / electronic / programmable electronic safety-related systems), which uses different probabilistic parameters (PFH/PFD, SFF, DC, HFT) and a rating scheme called Safety Integrity Level (SIL).
In summary, the main progress in the new European safety standard is the incorporation of both a probability analysis for a safety system failure and the introduction of a functional safety management system.
The SMCS security architecture for the performance level c (SIL 1) and d (SIL 2) consists of a security controller, a security protocol developed by Hirschmann, plus a Security Task, which monitors the main processor and the main control circuit of the application program. Using different 32-bit CPUs (central processor unit), the whole performance range is covered, from low-end to high-end controls.
Using the integrated communication interfaces, including Ethernet (10/100 BASE-TX), CANopen/CANopen Safety and USB, the system can be integrated with data and/or safety communication networks. An additional safety feature is that each input is tested periodically with a self test signal on operation. All diagnosis data is available as variables to the user and can be analysed in the control program.
The Scalable Mobile Control System can be programmed by CoDeSys (IEC 61131-3) or "C". Hirschmann offers, in addition, complete system integration, including the application software, or libraries of specialized pre-programmed control and safety functions.
Any system is only as strong as the weakest link in the chain so integrating the sensors into the overall concept was important to Hirschmann. The failure probability of a linear combination of sensors, controls and actuators - which can be calculated - highlights very quickly that also sensors, for example, load cells, inclination sensors and pressure transducers, have to provide more or less the same safety ratings as the safety controller itself if they are used within a functional safety application.
With the new Scalable Mobile Control System and the new line of safety sensors, Hirschmann Automation and Control said it aims "to deliver efficient, future-proof control solutions to meet current and up-coming requirements of any mobile machine application."