NI 9472 is not generating a pulse train correctly with 500Hz

[tlandim]

Hello,

I have a NI-9472 inserted in the slot 6 of a cDAQ-9189 chassi. I am trying to generate a PWM, however I am facing some difficulties. When in frequencies around 150 Hz, I obtain correctly the pulse train, but as I increase the frequency it looks like the signal takes longer to go to low level.

I tryed to get the waveform with an oscilloscope connected directly to the output of the NI-9472, and the attached images show the situation I have described.

I looked at the manuals but couldn't find any clue. I think the module should be able to generate higher frequencies but I couldn't do it. Does anyone had this issue before or what should be done?

Thanks in advance.

Best regards.

[lferreira]

Hello,

How are you generating the PWM Signals? Can you post your code for analyzing?

The following whitepaper is a good example how to create a PWM signal using the DAQmx Counter Output. 

Pulse Width Modulation (PWM) Using NI-DAQmx and LabVIEW

Thanks,

[TimH_647]

My guess is this has been resolved already, but I just ran into a similar issue. The issue is likely the a result of not driving any load with your signal output. Put a 1kohm across your signal and that should discharge any capacitance in the circuit.