counter output noisy at different freqencies

[Brian G]

I am having some issues generating a gated pulse train.  I am using the Peg.vi to perform this task (LV 7.0, hardware - PCI-6221, SCC-2345).  The vi works well for some frequencies but not for all.  An example of a good signal output would be a pulse frequency of 20000hz and a gate pulse of 100hz.    At 20000hz and 90hz, the signal begins to shift high to low.  At many frequencies the output will generate extraneous pulses that should not be there as measured on an oscilloscope.  I have checked the issue out on the Generate Pulse Train - Continuous.vi, and at higher frequencies, I am seeing instability in the output pulse train as well.  How can I get a stable output at all frequencies?  Am I encountering some limitation in the hardware or software?

Thanks,
Brian

[Yardov]

Hello Brian,

Welcome to the forums and thank you for including the code which work correctly with no modifications.
I think your connections can be causing this issue since your counter should be able to do this. I have run your program and externally connect the output signals to the AIs of your DAQ card. I have included some screenshoots to show the results not only with the values you mention but 5 times more than that.
I have also seen the signal correctly on an external scope. Perhaps you could include some screenshoots of your measurements to better describe the issue and possible cause.

To simplify your code, you might want to use the finite pulse generation (not sure if this is an option for your application).
Hope this information helps.

[Brian G]

Thanks for the feedback.  Sorry it took so long.  I have tried to replicate what you have done, but I run into a problem where I can not run both Vi's at once to replicate.  Any suggestions?

Thanks,

[Yardov]

Hi Brian,

Use the shipped example "Cont Acq&Graph Voltage-Int Clk.vi". You should not have problems running both VIs at the same time. If for some reason you do, use test panels for the analog input. If you still do, use two shipped examples: the one we mention before and the one named "Gen Dig Pulse Train-Finite.vi".
Make sure, you connect externally the outputs of both counters to your analog inputs.

Best of luck,