Error -200019 When Increasing Sampling Rate of External Clock on Analog Input Task

Updated Jan 11, 2019

Reported In


  • LabVIEW Full


  • NI-DAQmx

Issue Details

I am using an external clock to sample an analog input. When I sample the data at a lower rate everything works as expected. When I increase the frequency of the external clock, I receive DAQmx Error -200019: ADC conversion attempted before the prior conversion was complete.


Even though the clock is external, the rate specified in the task configuration determines the buffer size and other task parameters. To keep from overwriting the data, the rate must be set to the greatest expected clocking frequency.

Follow one of the steps below:
  • Measurement & Automation Explorer (MAX)
Edit the rate located on the Configuration tab on the lower half of the Input Setup Window. Rate (Hz) is located in the lower right side of the pane. 
  • DAQmx: 
    Use the DAQmx Timing (Sample Clock).vi to set the sampling rate. 
  • Traditional DAQ: Configure the rate settings through the AI Acquire VIs' rate terminal 

Additional Information

Make sure to check the integrity of the external clock signal either by visualizing it on a scope or on an input on the DAQ device itself. If the edges of this external signal have glitches or noise, this can cause sampling to occur more often, as glitches in a single edge can be misidentified as being multiple edges. This will cause more samples to be read and more ADC conversions to take place, which can lead to this error.


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