I/O Protection
The NI-9474 provides short-circuit protection.
Each channel has circuitry that protects it from current surges resulting from short
circuits over 14 A.
Note
Refer to the device datasheet at
for maximum
continous output current, short-circuit behavior, and short-circuit trip time
specifications and information about conditions that may damage the
module.
Note
Refer to the IEC 61131-2 standard for more information about short-
circuit-proof devices.
Note
Because the NI-9474 includes internal flyback diodes, you do not
need to add external diodes when connecting to switching devices that
store energy.
Power Supplies and Overcurrent Conditions
If a short circuit occurs, the current through DO can exceed the current rating for the
power supply and the maximum continuous output current for the NI-9474.
If the power supply you are using with the NI-9474 cannot supply more than 14 A,
the module may be damaged if a short circuit condition occurs.
Detecting an Overcurrent Condition
If a device connected to the module is not working while the channel is on, the
module channel may be in an overcurrent state. Neither the software nor the
module LEDs indicate if an overcurrent condition occurs. A channel LED may be on
even if the channel is off because of an overcurrent condition.
To determine if the channel is in an overcurrent state, measure the voltage between
DO and Vsup. If the voltage is equal to the voltage of the external power supply
connected to the module, the channel is in an overcurrent state.
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10
NI-9474 Getting Started