Allen-Bradley 1734-OB8S - Safety Inputs (1734-IB8 S)

26 Rockwell Automation Publication 1734-UM013C-EN-P - August 2010
Chapter 2 Safety Functions
Dual-channels, Complementary
In Complementary mode, the inputs of a pair should 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 complementary dual-
channel pair, the data bits for both channels will always be sent to the controller
in complementary, or opposite states.
Figure 9 - Complementary, Normal Operation and Fault Detection (not to scale)
ON
OFF
IN0
Safety Input 0
IN1
Fault Detected
Discrepancy Time
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
IN0
Safety Input
Status 0, 1
IN1
Fault Detection
ON
OFF
ON
OFF
ON
OFF
Discrepancy Time
Safety Input
Status 0, 1
Safety Input 1
Safety Input 1
Safety Input 0
Normal
Operation
Safety
I/O
Network
Data Sent
to the
Controller
Safety
I/O
Network
Data Sent
to the
Controller