Rockwell Automation 1791ES-IB16 Guard I/O EtherNet/IP Safety Modules - Manual (Page 22)

22 Rockwell Automation Publication 1791ES-UM001D-EN-P - May 2013
Chapter 2 Understand the Operation of Safety Functions
Set Dual-channel Mode and Discrepancy Time
To support redundant channel safety devices, the consistency between signals on
two channels can be evaluated. Either equivalent or complementary can be
selected. This function monitors the time during which there is a discrepancy
between the two channels.
If the length of the discrepancy exceeds the configured discrepancy time
(0…65,530 ms in increments of 10 ms), the safety input data and the
individual-safety input status turns off for both channels.
IMPORTANT The dual-channel function is used with two consecutive inputs that are
paired together, starting at an even input number, such as inputs 0 and 1, 2
and 3, and so on.
IMPORTANT Do not set the discrepancy time longer than necessary. The purpose of the
discrepancy time is to allow for normal differences between contact
switching when demands are placed on safety inputs. For this testing to
operate correctly, only a single demand on the safety input is expected
during the discrepancy time. If the discrepancy time is set too high, and
multiple demands occur during this time, then both safety input channels
will fault.