The NI ‑ 9421 uses industrial logic levels and signals so it can be connected directly to a wide variety of industrial switch modules, converters, and other devices. Each channel is compatible with 24 V signals and has an LED status display. The NI ‑ 9421 provides isolation between the input channels and ground.
 Product features:
-  Number of pure digital input channels: 8
-  Number of pure digital output channels: 0
-  Number of bidirectional digital channels: 0
-  Logic level of the digital I / O: 24 V 12 V.
-  Maximum update rate: 100 µs
-  Current flow direction: Current sinking input
-  Isolation of the digital I / O: 60 VDC isolation of the channel from ground
-  Connection type front: D-Sub
-  Protective coating: yes
-  With housing: yes
-  Supported hardware platform: CompactDAQ, CompactRIO