32 Rockwell Automation Publication 1794-UM061B-EN-P - March 2020
Chapter 3 About the FLEX I/O Diagnostic Output Module
The output open-wire current monitor detects a fault condition if the output
OFF-state current drops below 0.1 mA. Output channel shorts are protected by a
current limit and over-temperature thermal sensor that is built into the output
device. For overcurrents, the output device’s internal current limit is tripped and
the output voltage begins to collapse.
For a sustained overcurrent or direct output short the output device’s thermal
limit is tripped and the output is automatically turned off. This shorted
condition is monitored by the on-state output channel short monitor. It detects a
short if the output voltage drops below 2V. If the on-state output channel short is
removed, the output will automatically recover and voltage will appear at the
output, thus driving the attached load on.
Optocouplers isolate FLEX I/O system-side logic voltages from the user power
supply and output channels. This provides protection against field-side voltages
and transients.
Module Protection
Functions
The module protection functions consist of output device short protection,
external power supply reverse voltage protection, and power supply loss detection
Output Device Short Protection
Diagnostic digital outputs have internal electronics to prevent too much current
from flowing through the module. This feature protects the module, attached
wiring, and load from damage. Current limit and over-temperature thermal
sensor that is built into the output device protect against output shorts. For an
overcurrent, the output device’s internal current limit trips and output voltage
collapses. The output device’s thermal limit is tripped and the output is
automatically turned off if an output short circuit is detected. This shorted
condition is monitored by the on-state output channel short monitor. It will
detect a short if the output voltage drops below 2V. Under shorted conditions,
the shorted channels indicator turns red, the module fault indicator turns red and
the short fault bit and module error bit are set. If the on-state output channel
short is removed, the output automatically recovers and voltage appears at the
output, thus driving the attached load on.
ATTENTION: A shorted output channel turns off and de-energizes a
connected load. Following removal of the short the output channel becomes
active and will reenergize a connected load. Be careful for unexpected
machine operation following removal of an active output channel short.
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