©
National Instruments Corp.
7
NI 9426 Operating Instructions and Specifications
Each channel has a DI pin to which yo
u
can connect a digital inp
u
t
signal. The NI 9426 has fo
u
r s
u
pply pins, V
s
u
p
, that are internally
connected to the isolated reference of the mod
u
le.
The NI 9426 has so
u
rcing inp
u
ts, meaning the DI pin so
u
rces
c
u
rrent from V
s
u
p
to the sinking o
u
tp
u
t device. The NI 9426
internally limits c
u
rrent signals connected to DI. For more
information abo
u
t inp
u
t c
u
rrent levels, refer to the
section.
Yo
u
can connect 2-, 3-, and 4-wire sinking-o
u
tp
u
t
devices to
the NI 9426. A sinking-o
u
tp
u
t device provides a path from the
DI pin to a voltage below V
s
u
p
. An example of a sinking-o
u
tp
u
t
device is an open collector NPN.
Connect the sinking-o
u
tp
u
t device to the DI pin of the NI 9426.
Connect the positive power s
u
pply lead of the external device to the
V
s
u
p
pin. Refer to Fig
u
re 2 for an ill
u
stration of connecting a device
to the NI 9426.
