Digital Pattern Module Showing Nonzero with PPMU on Disconnected Channel

Updated Nov 15, 2019

Reported In

Hardware

  • PXI Digital Pattern Instrument
  • PXIe-6570

Driver

  • NI-Digital Pattern Driver

Issue Details

I have a PXIe-6570 Digital Pattern Instrument and am using the Pin Parametric Measurement Unit (PPMU) to measure the voltage level of a disconnected pin I am not using.  I am measuring a nonzero voltage, is this expected? 

Solution

This is expected behavior for an unused, disconnected pin. If the pin needs to be 0V, you can use the PPMU to force 0V on the pin as a solution, but this is unnecessary in most cases.

Additional Information

On pins that are disconnected and not being utilized by the device, the pins will float due to very small leakage currents and the high impedance seen at the disconnected output. If there is a path to ground, these pins will settle.