DAQ Assistant Edge Counting Error for N Samples or Continuous Samples

Updated Jan 11, 2019

Reported In


  • NI-DAQmx



Issue Details

I am using the DAQ Assistant and configuring a counter input, edge count acquire operation from a quadrature encoder. When I select the Acquisition Mode as N Samples or Continuous Samples, and try to run the task (or hit OK on DAQ Assistant), I receive a DAQ Assistant Error. The error states an external sample clock source must be specified for this application. How can I fix this?


When setting the Acquisition Mode to N Samples or Continuous Samples, you must specify an external sample clock source for the counter to run.  This is because there are no internal timing engines for the counters.  To resolve this, you can use a separate counter to generate a clock signal on a PFI line, you can connect an external clock signal to a PFI line, or you can use the analog input or output sample clock as the clock source for your counter.  More information on these three methods can be found in this article about the Options for Hardware-Timed Digital I/O on M Series DAQ Device

Once you have decided on an external clock source, specify the clock source under the Advanced Timing tab as shown below:

If you have chosen to use a second counter as the external source, or the analog input or output sample clock, make sure that the counter or analog task is started and running, otherwise there will not be a sample clock running for the N Sample or Continuous Samples counter task when you attempt to run it. 

If you do not want to specify an external clock source, you must choose the 1 Sample (On Demand) option for Acquisition Mode.


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