©
National Instruments Corporation
23
NI WSN-3202 User Guide and Specifications
Connecting Digital Inputs
Tristate Mode
Use this mode to configure the channel as digital input, or for contact to ground sensing, as shown in
Figure 23. In Tristate mode, when DIO.
x
terminal is read, a weak pull-up resistor to internal 3.3 V is
enabled for about 1 ms.
Figure 23.
Example of Using the NI WSN-3202 in Tristate Mode
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.
Cont
a
ct
S
witch
TTL
S
ign
a
l
NI W
S
N-
3
202
DI.
x
(Intern
a
l)
DI.
x
(Intern
a
l)
DI.
x
(Intern
a
l)
Extern
a
l
Power
Su
pply
Device
D GND
DIO.
x
DIO.
x
DIO.
x
D GND
D GND
+
–
