Rockwell Automation 1791DS-IBxxxx Guard I/O DeviceNet Safety Modules - Manual (Page 31)

Rockwell Automation Publication 1791DS-UM001J-EN-P - May 2013 31
Understand the Operation of Safety Functions Chapter 2
equivalent dual pair, the data bits for both channels will always be sent to the
controller as equivalent, both high or both low.
Figure 15 - Equivalent, Normal Operation and Fault Detection (not to scale)
Dual-channels, Complementary
In Complementary mode, the inputs of a pair should typically be in the opposite
(complementary) state. When a transition occurs in one channel of the pair prior
to the transition of the second channel of the pair, a discrepancy occurs. If the
second channel transitions to the appropriate state prior to the discrepancy time
elapsing, the inputs are considered complementary.
If the second transition does not occur before the discrepancy time elapses, the
channels will fault. The fault state of complementary inputs is the even-
numbered input turned off and the odd-numbered input turned on. Note that if
faulted, both channel status bits are set low. When configured as a
ON
OFF
IN0
Safety Input 0
IN1
Fault Detected
Discrepancy Time
Remote
I/O
Data
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
IN0
Safety Input
Status 0, 1
IN1
Fault Detection
Remote
I/O
Data
ON
OFF
ON
OFF
ON
OFF
Discrepancy Time
Safety Input
Status 0, 1
Safety Input 1
Safety Input 1
Safety Input 0
Normal Operation