Rockwell Automation 1715-OF8I Redundant I/O System User Manual - Manual (Page 89)

Rockwell Automation Publication 1715-UM001C-EN-P - March 2014 89
Installation Instructions Chapter 2
Command packets are received from the processor module via the EtherNet/IP
network. The output switch control units decode and vote the output data
addressed to them and set the output FET switches accordingly. The output
voltages are produced from the 24V DC field power input voltages by a power
combiner circuit. Each output channel has a pair of FET switches arranged in a
series that are independently controlled. Load current and voltage monitoring is
provided for each switch. Output channel protection ensures the output circuit is
switched off when the channel load current exceeds a safe limit.
A reverse voltage protection circuit ensures that externally applied voltages to any
output channel do not generate current flow backwards into the module outputs.
In Duplex redundant mode, the two fail-safe output switches per channel are
combined in a parallel arrangement so that they automatically form a fault-
tolerant output configuration. In this configuration, removal and of an output
module is possible without any disruption to a live system.
The module has a range of self-checking functionality. Short circuit and open
circuit line monitoring is provided on all outputs. In addition, each output
channel is tested and checked for ‘stuck-on’ and ‘stuck-off ’ conditions on the
output switch pairs.