06-28-2008 04:34 PM
06-29-2008 01:23 AM
Hi Villalro,
The digital output shown in "Time Graph" seems to require a 120Hz signal coming out of the Butterworth filter - with the amplitude of leading and trailing portions falling below your "threshold limit" and being "clipped". The frequency-domain chart indicates a strong 120Hz component in the input (and practically nothing at 60Hz.)? If you're still working on this, it would be good to know the value of "high-cutoff freq." and "low-cutoff freq."
Cheers.
06-29-2008 07:47 AM
06-29-2008 11:41 AM
06-29-2008 01:22 PM
Offset is zero and multiplier is 1... Autoscale is off.
What is really unusual is the fact that the measured output signal seems to be made of 0.5 seconds of square wave (at twice the required frequency) and 0.5 seconds of either +4 or -4, as if the output got stuck or was filling out with the last requested condition.
Does it help if I upload the code?
06-29-2008 02:02 PM
villalro wrote:
Does it help if I upload the code?
06-29-2008 07:50 PM
06-29-2008 11:35 PM
Hey, I still can't reproduce any unexpected behaviour, though suspect that the threshold value of 2 may produce some unexpected - asymetric - behaviour.
Here's a VI I used to test your code - maybe it will help understand this behaviour.
Cheers!
06-30-2008 01:28 PM
07-01-2008 05:38 PM
Hi villalro,
I see the image you posted about only having a the square wave being generated for part of the time. What I don't see is the filter output that corresponds with that - the values that trigger the +/- 4 volt logic levels. Does the partial square wave correspond to the data you read that's over the Threshold Limit in your VI?
If what is coming out of the DAQmx write is different from the square wave image you posted, how are they different? Can you post an image of the DAQmx write output?
Kevin S.
Applications Engineer
National Instruments