User Manual

SAFETY
Safety handbook page - 44 -
PNSPO
8.0 Safe networks
Due to technical progress it is possible to have safe data communication on serial
networks. For standard communication Networks as DeviceNet, ASI, Ethernet etc. are
established systems to have a high reliable communication.
The connection of safety related information to a network was not possible in the past.
Some European and international standards still insist on “hard wired“ realisation of
safety systems. The revisions of these standards will also allow to use safe data
communication instead. The main requirement is that the system provides the same
integrity and safety as a hard wired system.
8.1 Background of safety networks and bus systems
To ensure an appropriate level of safety, this systems must be designed to detect
failures caused by several reasons to prevent an unsafe condition of the system:
-
Message repetition - Incorrect sequence
- Message loss - Message corruption
-
Message insertion - Message delay
- Coupling of safety and standard information
-
Coupling of safety and safety information
To ensure high safety special measures must be implemented in the communication
protocol to reach an appropriate “ Safety Integrity Level”.
- Control of time with time stamp
- Identification of producer and consumer
- Multiple CRC checking
Safe networks are defined in several categories:
1) Proprietary systems that are owned and developed by one major company
2) Open networks that are owned and developed by multiple companies
A) Safety only networks that are only dedicated to handle safety functions
B) Mixed (hybrid) networks that allow standard (non safety) and safety communication
on the same network
In the past mainly “1A” networks were released and are used in safety dominated
application like press lines. Since several years the networks got more open and were
designed as safety extension to the standard functions. (2A)
Safety networks offer a lot of benefits and new functionality.
-
Easy design and wiring, safe time in engineering and mounting
- Additional functionality increases safety of the application
-
Reduced possibility to defeat or manipulate safety measures
- Transparency , the condition of all safety device can easily be monitored
- Possibility of rooting within several safety related networks (Depend on system)
Safety networks are able to provide safety up to SIL 3 ( safety integrity level, EN
61508) that represent a similar failsafe level as Category 4 ( EN954-1).