Auto Reset Operation; Short Circuit/Overload Current Diagnostics; Recovery From Channel Shutdown - Allen-Bradley 1746-IA4 Installation Instructions Manual

Auto Reset Operation

IMPORTANT

Short Circuit/Overload Current Diagnostics

If a short circuit or overload current condition occurs on an output channel:
• the E-FUSE LED indicator will illuminate provided that power is applied to
the module. Power required: 5V dc via backplane and load power via an
external supply.
• all other channels continue to operate as directed by the CPU (processor)
module.

Recovery from Channel Shutdown

1. Remove the SLC 500 system power and correct the conditions causing the
short circuit or overload current condition.
2. Restore the SLC 500 system power.
The module automatically resets and resumes control of the output channel
and associated load.
The 1746-OB6EI and 1746-OB16E modules perform auto-reset under
overload conditions. When an output channel overload occurs, that channel
will limit current within milliseconds after its thermal cut-out temperature
has been reached. While in current limit, the output channel can cool below
the thermal cut-out temperature allowing the module to auto-reset and
resume control of the output channel as directed by the processor until the
thermal cut-out temperature is again reached.
Removing power from an overloaded output channel would also allow the
output channel to cool below the thermal cut-out temperature, allowing
auto-reset to occur when power is restored. The output channel would
operate as directed by the processor until the thermal cut-out temperature is
again reached.
To avoid auto-reset of an output channel under overload conditions, an
external mechanical fuse can be used to open the circuit when overloaded.
Digital I/O Modules
Publication 1746-IN027C-EN-P - August 2008
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