PXI-6704 Generates Negative Pulses When Two AO Tasks Are Running Simultaneously

Updated Oct 31, 2025

Reported In

Hardware

  • PXI-6704

Driver

  • NI-DAQmx

Issue Details

When I run two AO tasks simultaneously on the PXI-6704, my 1 V output shows spikes up to 2 V and drops to –9 V like in the image below. If I wire the DAQmx Write functions sequentially using the error wire, the glitches disappear. The issue only occurs when the tasks can execute at the same time.

Solution

The PXI-6704 module has only one DAC shared across all 32 analog output channels, meaning it supports only one analog output task at a time. Hence, only one task per device should be set up to avoid this behavior.

 

Some of the workarounds are:

  1. Calling the two DAQmx Write Analog VIs sequentially when connecting them through an error wire.

  2. Wrapping the DAQmx Write Analog VI inside a non-reentrant subVI, allowing only one instance to execute at a time.

Additional Information

This behavior wasn't observed in the following AO DAQ modules:

  • PXI-6733
  • PXI-6711
  • PXI-6723
  • PXI-6713

Related Links

Number of Parallel DAQmx Tasks on NI Multifunction Devices

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