©
National Instruments Corporation
25
NI WSN-3212 User Guide and Specifications
Digital I/O Protection
Each digital I/O channel has overcurrent protection specifically to prevent damage due to short circuit faults.
Understanding Short Circuit Protection
A short circuit fault at the DIO.
x
terminal may cause a resettable fuse internal to the digital I/O channel to
increase in resistance preventing damage to the equipment. Whether the fuse increases in resistance depends
on factors such as the current level, the temperature, and power supply voltage. High inrush currents that
exist for a short time do not trip the fuse. Refer to the
section for more information about the
maximum continuous output current, short circuit behavior, and short circuit trip time.
Preventing an Overcurrent Condition
Follow these recommendations to prevent an overcurrent condition:
•
Do
not
connect DIO PWR to ground.
•
Do
not
ground unused terminals.
•
Do
not
exceed the output current rating of the channel.
Detecting a Overcurrent Condition
If the node has detected an overcurrent condition, it immediately stops driving the DIO line, goes to
a safe power down state, and blinks a four blink error code. The node must be manually reset or
power-cycled to resume operation. A DIO line can be in overcurrent if it is driving high, or driving low,
but not if it is tristated. To identify which DIO line tripped the overcurrent protection, set all the DIO
lines to tristate and one by one set them to the desired drive mode and value until the protection is
tripped.
Resetting Channels After an Overcurrent Condition
After you have identified and removed the cause of the overcurrent condition, to resume normal
operation, you must reset the node by pressing the RESET button or by removing and reapplying power
to the node.