Allen-Bradley 1734-OBV2S

30 Rockwell Automation Publication 1734-UM013N-EN-P - September 2017
Chapter 2 Safety Inputs, Safety Outputs and Safety Data
Dual-channel, Equivalent
In Equivalent mode, both inputs of a pair must be in the same (equivalent) 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 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 are 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