Safety Scanner for GuardPLC Controllers User Manual

Publication 1753-UM002A-EN-P - July 2005
1-8 Before You Begin
Communication Rate
The safety scanner supports the following communication rates, but
does not support autobaud:
125 Kbps (default)
250 Kbps
500 Kbps
Physical Layout of the
DeviceNet Safety System
Planning your system helps ensure that you can:
meet safety times
use memory and bandwidth efficiently
fulfill device-specific requirements
leave room for system expansion
Before configuring your 1753-DNSI scanner, you should be familiar
with each of the DeviceNet devices on your network. You should
know each device’s:
system safety time requirements
communication requirements
I/O size
frequency of message delivery
You must also understand and define which data elements can be
treated as safety and which as standard in your intended
configuration.
DeviceNet Safety I/O Performance Factors
Safety nodes have priority on a DeviceNet network, but the
performance of DeviceNet Safety I/O modules can be affected by the:
baud rate of the network (Lower baud rates mean slower
transmissions and slower responses.)
packet size for the various connections (Bigger packets may
result in fragmented messages and slower responses than
single-packet messages, but use fewer resources.)
type and number of connections used (Using point-to-point
connections to make multiple connections to an input node uses
more resources than a multicast connection.)
RPI of the devices (Lower RPIs consume more bandwidth but
lower system reaction time.)