The PSS programmable protective control system is usually a programmable logic controller (PLC) with special structural elements for receiving, processing, and sending signals, the purpose of which is to guarantee the safety and serviceability of safety-related systems. PSS is a registered trademark of Pilz GmbH & Co KG . PSS management system appeared in the 1990s after approval by the professional association of employers liability insurers. [1] The first safety-related control system actually came about thanks to the desire to flexibly connect functions through programming, similar to how it is done on a programmable logic controller (PLC). [2]
Content
Product History
Protective control systems in essence appeared due to the desire to combine protective functions with the help of programming, as is done in the PLC . Therefore, it is not surprising that the world of PLCs influences the development of protective control systems. First, centralized systems appeared, then decentralized systems combined with protective I / O backbone systems. Programming was carried out according to the same formula, except for the fact that the number of languages was radically reduced from the very beginning for a set of instructions - there are very few of them, in particular, IL (list of instructions) or LD ( multi-link logic / ladder diagram language ). Such measures were taken for safety, since it was believed that the limitation of programming options would ultimately reduce the number of possible errors when creating a program. The original systems were clearly aimed at working with security features. Despite the fact that from the very beginning it was possible to program a protective control system for standard automation , in reality the demand for this applied area was very limited. [3]
Device and work
If we ignore the design features related to safety, the protective control system in its actual functionality differs little from standard automation systems. In essence, the protective control system consists of two PLCs that work in parallel with the application, use the same image of the input-output process and are continuously synchronized. Such a seemingly simple scheme, when examined in detail, is rather complicated. Cross-comparisons, checking the level of input-output, establishing a common, reliable result, etc. are multilayer processes that clearly confirm the internal complexity of such systems. Ultimately, the user is mostly unaware of this; the exception is some specific features, in particular the use of test pulses to detect short intercontact faults. Modern systems behave exactly like other PLCs . [four]
Protective control system device: [3]
- Two separate channels
- Diverse structure with different hardware
- Continuous check of input and output signals
- Constant comparison with user data
- Voltage and time control functions
- Safe shutdown in case of error / danger
Links
- ↑ European Patent EP0808482B1
- ↑ Security Handbook, Chapter 4: Secure Management Technologies, page 115 Archived on March 7, 2013.
- ↑ 1 2 Security Handbook, Chapter 4.3: Security Modern Management Systems, page 149 Archived on March 7, 2013.
- ↑ Security Digest, chapter 4.3: Security Modern Management Systems, page 149 next pages Archived on March 7, 2013.