Rockwell Automation 1756-L7x GuardLogix 5570 Controllers - Manual (Page 64)

64 Rockwell Automation Publication 1756-UM022A-EN-P - November 2012
Chapter 5 Add, Configure, Monitor, and Replace CIP Safety I/O
Timeout Multiplier
The Timeout Multiplier determines the number of RPIs to wait for a packet
before declaring a connection timeout. This translates into the number of
messages that may be lost before a connection error is declared.
For example, a Timeout Multiplier of 1 indicates that messages must be received
during every RPI interval. A Timeout Multiplier of 2 indicates that 1 message
may be lost as long as at least 1 message is received in 2 times the RPI (2 x RPI).
Network Delay Multiplier
The Network Delay Multiplier defines the message transport time that is
enforced by the CIP Safety protocol. The Network Delay Multiplier specifies the
round-trip delay from the producer to the consumer and the acknowledge back to
the producer. You can use the Network Delay Multiplier to reduce or increase the
Connection Reaction Time Limit in cases where the enforced message transport
time is significantly less or more than the RPI. For example, adjusting the
Network Delay Multiplier may be helpful when the RPI of an output connection
is the same as a lengthy safety task period.
For cases where the input RPI or output RPI are relatively slow or fast as
compared to the enforced message delay time, the Network Delay Multiplier can
be approximated by using one of the two methods.
Method 1: Use the ratio between the input RPI and the safety task period. Use
this method only under all of the following conditions:
• If the path or delay is approximately equal to the output path or delay.
• The input RPI has been configured so that the actual input message
transport time is less than the input RPI.
• The safety task period is slow relative to the Input RPI.
Under these conditions, the Output Network Delay Multiplier can be
approximated as follows:
Input Network Delay Multiplier x [Input RPI
÷
Safety Task Period]
Method 2: Use the Maximum Observed Network Delay. If the system is run for
an extended period of time through its worst-case loading conditions, the
Network Delay Multiplier can be set from the Maximum Observed Network
EXAMPLE Calculate the Approximate Output Network Delay Multiplier
If:
Input RPI = 10 ms
Input Network Delay Multiplier = 200%
Safety Task Period = 20 ms
Then, the Output Network Delay Multiplier equals:
200% x [10
ч
20] = 100%