National Instruments NI 9426 - Manual (Page 8)

NI 9426 Operating Instructions and Specifications 8 ni.com
Figure 2. Connecting a Device to the NI 9426 (Three-Wire Device Shown)
The NI 9426 channel registers as ON when the sinking-output
device drives the input below V
sup
and meets the input ON range.
The channel registers as OFF when the device does not drive the
input low and is in the input OFF range. If no device is connected
to the DI pin, the channel registers as OFF. Refer to the
Specifications section for more information about the ON and
OFF states.
NI 9426
+
_
DI
Vsup
Sinking-Output
Device
External
Power
Supply