Rockwell Automation 1756-SPESMNRMXT GuardLogix Controllers User Manual - Manuel (Page 74)

74 Rockwell Automation Publication 1756-UM020I-EN-P - August 2012
Chapter 5 Add, Configure, Monitor, and Replace CIP Safety I/O
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
Delay. This method can be used on an input or output connection. After the
system has been run for an extended period of time through its worst-case loading
conditions, record the Maximum Observed Network Delay.
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%