Hardware Requirements of Digital Pulse Measurements Using DAQmx

Updated Jun 14, 2019

Reported In

Hardware

  • cDAQ-9189
  • NI-9361
  • CompactRIO Controller

Software

  • LabVIEW

Issue Details

I would like to measure the frequency and the duty-cycle of a PWM-Signal (Pulse Width Modulated Signal) using a single physical channel and a single counter. Reading the high time and low time measurements of the signal with a single physical channel and a single counter would also be suitable for this purpose.

I get the error message with the code -200431 in LabVIEW, if I try to use either of the CI-Pulse Freq, CI-Pulse Time or CI-Pulse Ticks variants of the DAQmx Create Virtual Channel vi together with the physical channel of the NI 9361 Counter Digital Input module in a CompactDAQ chassis.
 

 
My code implementation is similar to the one below:

Solution

There are two possible solutions to the problem, both require modification of the hardware configuration:
  1. Use the NI 9361 Counter Digital Input module together with a CompactRIO system. The NI 9361 supports pulse measurements only for CompactRIO systems.
  2. Alternatively replace the NI 9361 Counter Digital Input module with a parallel digital I/O module in the CompactDAQ chassis. The NI 9344, NI 9401, NI 9402, NI 9411, NI 9421, NI 9422, NI 9423, NI 9435, NI 9436, NI 9437, NI 9472, NI 9474, NI 9475, NI 9481, NI 9482, and NI 9485 are parallel digital I/O modules that can access the cDAQ's on board counter (s). 
With either of the above modules, it will be possible to measure duty cycle with a single counter using a single physical and virtual channel.

Additional Information

Each PWM measurement requires one counter at least. The number of parallel PWM readings you can perform will strictly depend on the number of counters available in your cDAQ. Please refer to the specific DAQ Series Manual for more detailed information about these types of readings. 

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