Rockwell Automation Allen-Bradley 1734-IB8S, User Manual

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28 Rockwell Automation Publication 1734-UM013J-EN-P - July 2014
Chapter 2 Safety Inputs, Safety Outputs, and Safety Data
Dual-channel, Equivalent
In Equivalent mode, both inputs of a pair should be in the same (equivalent)
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 equivalent. If the second transition does not occur before
the discrepancy time elapses, the channels will fault. In the fault state, the input
and status for both channels are set low (OFF). When configured as an
equivalent dual pair, the data bits for both channels will always be sent to the
controller as equivalent, both high or both low.
Figure 8 - Equivalent, Normal Operation and Fault Detection (not to scale)
ON
OFF
IN0
Safety Input 0
Data
IN1
Fault Detected
Discrepancy Time
Safety
I/O
Network
Data Sent
to the
Controller
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
IN0
Safety Input 0, 1
Status
IN1
Fault Detection
ON
OFF
ON
OFF
ON
OFF
Discrepancy Time
Safety Input 0, 1
Status
Safety Input 1
Data
Safety Input 1
Data
Safety Input 0
Data
Normal Operation
Safety
I/O
Network
Data Sent
to the
Controller