Setting Digital Inputs to Sinking/Sourcing on my NI 651x Device

Updated Nov 17, 2017

Reported In

Hardware

  • PXI-6515

Software

  • LabVIEW Base

Driver

  • NI-DAQmx

Issue Details

  • I am using an NI 651x device, and the specifications say that I can configure the digital inputs to sink/source current.
  • There is a property in LabVIEW to set digital outputs to sinking or sourcing, but I cannot find a similar property for the inputs.
  • How do I configure the digital inputs?

Solution

  • To sink input, you'll just need to wire your digital signal as you normally would. This means that the negative reference goes into COM and the positive reference goes into the AIN pin.
  • To source input, just reverse the polarity of the input. This means the negative reference goes into the AIN pin and the positive reference goes into COM.
    • Note: Do not connect two different voltages¬†to the COM at once!

 

Additional Information

  • The digital input hardware is made to handle sinking and sourcing without any additional configuration.
The following picture is an excerpt from the NI 651x User Manual that shows the controlling circuit:
  • The inputs to the DI pins consist of input photocouplers. These react to any voltage differential instead of just a voltage increase, so it is safe to reverse the polarity of the digital input
  • Note: In the sourcing input configuration, the positive reference will be connected to the COM of the bank, so it is important to avoid connecting two different voltages at once

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