NI WSN-3230/3231 User Guide and Specifications
24
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Connecting Digital Inputs
You can connect a variety of sensors, switches, and industrial devices to the NI WSN-3230/3231 device.
Refer to the
section to ensure compatibility.
24V Sinking
In 24V Sinking mode, the DIO
x
terminal has a low impedance to ground and input thresholds
compatible with 24 V signaling. Select this mode for connection to industrial 24V/IEC1131 sourcing
output devices.
24V Sinking with Power Management
In 24V Sinking with Power Management mode, the DIO
x
terminal is similar to 24V Sinking mode, but
the low impedance path to ground is removed when the inputs are not being actively read. This can
reduce the power consumption of the output device. This mode should only be used with output devices
that have valid output states within 100
μ
s of having a low impedance path presented to the output.
TTL Logic
TTL Logic mode is suitable for most 3 V or 5 V logic signals. The DIO
x
terminal has high impedance
inputs with TTL Logic compatible thresholds.
Contact Closure
Contact Closure mode is suitable for connections to contact switches wired between the input and
ground. The DIO
x
terminal has
compatible thresholds and provides a pull-up resistor to 3 V
when the input is being read. If a contact to ground remains closed while the DIO Notification property
is enabled, the current into the contact switch increases power consumption and can reduce battery life.
Digital I/O Protection
The high side switch on each I/O channel has short circuit protection. The low side switch on each I/O
channel is oversized to be able to withstand higher currents than when in normal operating conditions.
Understanding Short Circuit Protection
The current that flows through the high side switch is continuously sensed. If a current above the trip
limit is detected, the current protection trips and turns off the high side switch. The protection latches in
the tripped state and only resets when the high side switch is given the command to turn off. High inrush
currents that exist for a short time do not trip the short-circuit protection. 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.
•
Do
not
exceed the voltage ratings of the channel.
Detecting a Overcurrent Condition
To check whether or not the short circuit protection is tripped, the logic state of the DIO pin can be read
when driving high using the digital input function. If DO is set to
and Low (Sinking and Sourcing)
modes and a digital value of 1 is written to the channel, a logical 1
should be read from the channel. If a logical 0 is read instead, then the current protection is tripped or a
fault is preventing the high side switch from driving the output high.
