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I need to measure the frequency of a signal on Pin 39 (PFI 15) of a PXIe-6361 module.

I need to measure the frequency of a signal on pin 39 (PFI 15) of a PXIe-6361 module.  All of the digital I/O pins are already assigned and in use.  The signal frequency range is 50KHz to 500KHz.  I have tried all of the sample programs for DAQmx Counter/Timer frequency measurement.  If I modify them to use my hardware, I get run-time errors with conflicts with resources already assigned.


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Hi wkesling,


What are the specific errors that you are getting? Feel free to post screenshots of these and to let us know which example program you are using.


In addition, you mentioned that the digital I/O pins are already assigned and in use. Are you by any chance already using the counter you are trying to perform this frequency measurement with? What other measurements are you performing at the same time?


The answers to these questions, along with any other information you can provide, will be helpful in troubleshooting these errors.

Julia P.
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Hi Julia,

Thanks for the response.  As I stated before, I have tried all of the examples available that apply.  There are only three and one of those uses two counters.  The two I have tried are:

  Examples/Hardware Input and Output/Counter Measurements/Digital Frequency/

      DigFreq-Buff-Cont-ExtClk-ArmStart.prj     and


These examples default to using what appears to be traditional DAQ hardware (Dev1/ctr0 and /Dev1/PFI0).  I changed the counter to mine (/PXI1Slot3/ctr3) and directed my signal source (PFI15 on pin 39) to the counter.  No matter what I tried would not run.  They would always compile but gave run-time errors ranging from resources already in use to “external trigger required”.  I have no external trigger source and, if I did, there is no indication of how to assign it to the counter.  NI has a very good X Series Users Manual that tells all of the great things you can do with the hardware, but there is NO CLUE how to do any of those things!!!!  I know that some NI DAQmx functions use hardware resources that they never tell you about.  I discovered that when trying to produce a single output pulse from a timer using counter #0.  (Which, by the way, no one at NI could tell me how to do it.)

Measuring frequency should be very simple.  The unknown signal is routed through a precise gate to a counter, and then the counter is read.  NI DAQmx uses the opposite approach of using my signal as the gate and counting their internal source.  However, the examples would not let me use the internal reference sources.

To answer your other questions, I am not performing any other measurements at the same time and the counter is not being used for anything else, period.

Any help would be greatly appreciated.  Thanks again.


Wayne K.


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You mentioned that you edited the examples to direct your signal source to the counter. Could you please post sample code of how you did this?

Julia P.
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