12
|
ni.com
|
NI 9437 Getting Started Guide
because the threshold reference is 2/3 the supply voltage on the V
SUP
pin. With any one pin—V
SUP
, COM, or a single DI—shorted to earth
ground, the NI 9437 operates normally and returns valid data.
You can also use a power supply with the NI 9437 that requires a
connection to earth ground for normal operation. When using this
type of power supply, there is always a connection between COM
and earth ground and you will not have protection against ground
faults from V
SUP
-to-earth ground or from DI-to-earth ground.
LED Indicators
The NI 9437 has eight LEDs to display the ON/OFF state of the
eight channels. When an LED is lit, the corresponding channel is
ON and data is being read from the NI 9437. When an LED is dark,
the corresponding channel is OFF.
Note
If V
SUP
is not connected, the LED does not
indicate the state of the channel.
