PXI‑6515 | NI Input photocouplers

The input lines on the NI 6514/6515 consist of input photocouplers, which react to a voltage differential rather than only to a voltage increase. If the voltage connected to a digital input is either greater than or less than the voltage connected to PX.COM by at least the logic threshold, the reading on the digital line will be logic high, even though in one instance the digital line has a lower voltage level than PX.COM.The output lines on the NI 6515 consist of photocouplers and Darlington arrays. To connect to these signals, connect a 5 V to 30 V power supply to COM, connect GND to ground, and cross a load between digital output and COM.