36 Rockwell Automation Publication 1734-UM013N-EN-P - September 2017
Chapter 2 Safety Inputs, Safety Outputs and Safety Data
You can configure a tolerance range, called a deadband, to work with process
alarms. This deadband lets the process alarm status bit remain set, despite the
alarm condition disappearing, as long as the data remains within the deadband of
the process alarm.
Figure 13 - Alarms
Using a Single-channel Sensor
You must address the following requirements to meet SIL 3 with a single-channel
sensor.
• The module’s ±10V and ±5V analog input modes must not be used for
SIL 3 with a single-channel sensor because 0V falls within the valid input
range. Therefore, a stuck at ground fault cannot be detected.
• In a single-channel sensor system, you must use other methods to make
sure a channel-to-channel short cannot occur because these faults cannot
be detected.
• If you are using a 3-wire sensor, you must verify its behavior to make sure
that if it loses its ground connection, the signal is 0 (safe state) at the
module input when the fault occurs.
If you are using the safety application instructions with a GuardLogix
controller, do not use the process alarm of the module. Instead, perform analog
range checking in your application logic.
High High alarm turns OFF. High alarm remains ON.
High High alarm turns ON. High alarm remains ON.
High alarm turns
ON.
High alarm turns OFF.
Normal input
range
Low alarm turns
ON.
Low alarm turns
OFF.
Low Low alarm turns OFF. Low alarm remains ON.
Low Low alarm turns ON. Low alarm remains ON.
Alarm deadbands
High High Alarm
High Alarm
Low Low Alarm
Low Alarm
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