Safety Manager Safety Manual - Tuv-fs.com

SafeNet communication
The maximum response time equals the sum of:
• the application cycle time of the Node ID plus
• the application cycle time of the Peer ID plus
• the expected communication delay.
The Node ID periodically sends data to the Peer ID systems and initiates a request
for data from the Peer IDs. A correct answer must be provided for within the
time-out period; when not received in time, the link is regarded faulty.
A new data transmission and request for a Peer ID are initiated after the Peer ID
reply to the previous request has been received. This could be equal to the
time-out time, but usually it is shorter.
SafeNet time-out time
All systems within the network monitor the operation of a communication link by
means of a time-out.
• The time-out can be set for each individual logical link and must be chosen
such that it stays within the Process Safety Time (PST) for the Safety
Instrumented Functions (SIFs) involved.
• The time-out time set must be at least 2x the calculated response time.
Ethernet communication
When communicating via Ethernet you should be aware of the following:
• “Ethernet communication risks” on page 43
• “Ethernet bandwidth and response time calculation” on page 44
Ethernet communication risks
Attention:
USIs running 3 rd party protocols may be vulnerable to communication overflow, causing
USI outages and communication shutdown.
If communication overflow is a potential risk, we recommend to allocate all SafeNet links
on dedicated USIs (not running vulnerable 3 rd party protocols).
When devices communicate via an Ethernet based local area network (LAN),
their information is contained and sent in packets. This is no different when using
SafeNet through Ethernet. However, Ethernet has far less timing restrictions and,
when sending SafeNet packets together with other application packets, some
packets may suffer critical delay or get lost if a network gets congested.
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