Rockwell Automation Publication 1791ES-UM001G-EN-P - November 2016 19
Safety Function Operation Chapter 1
Dual-channels, Complementary
In Complementary mode, the inputs of a pair are typically in the opposite
(complementary) state. When a transition occurs in one channel of the pair
before the transition of the second channel of the pair, a discrepancy occurs. If
the second channel transitions to the appropriate state before the discrepancy
time elapses, the inputs are considered complementary.
If the second transition does not occur before the discrepancy time elapses, the
channels fault. The fault state of complementary inputs is the even-numbered
input turned off and the odd-numbered input turned on. If faulted, both
channel status bits are set low. When configured as a complementary
dual-channel pair, the data bits for both channels are sent to the controller in
complementary, or opposite states.
Figure 7 - Complementary, Normal Operation and Fault Detection (not to scale)
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
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