DAQmx Create Timing Source (Digital Change Detetion) using Digital Filter?

[ScottUAF]

Hello,

I have a PXI-6509 DIO card that I am using to control the flow of a labview program.  I am using the DAQmx Create Timing Source VI with the Digital Change Detection option to provide the timing source to a Timed Loop.  This works fine when using a low-noise digital signal produced from a function generator.  However, I need to use a signal from a sensor that contains noise.  If I run my VI with the noisy signal the Timed Loop is incremented too often due to noise spikes being detected as a digital change.

Is there a way to apply a digital filter to the signal so changes are only detected for pulses greater than a certain width?  I know this is possible using a property node for a DAQmx channel, but the DAQmx Create Time Source VI does not have a DAQmx channel.

-Scott

[EricS.]

Hi Scott,

That is an excellent question.  Unfortunately there's not a way to enable digital filtering on the DAQmx Create Timing Source terminal.  The same question came in on the phones to me several months ago and I spent a significant amount of time looking into it and trying different things.  I could not come up with a solution.

The customer just ended up creating an external circuit to do the filtering before it came in to the DAQ card.

Maybe someone else on the forums has been successful at this, but from my experience I don't know how to do it.

[ScottUAF]

If I open the DAQmx Create Timing Source VI there is the DAQmx channel wire connecting various sub-VIs.  If i could place a property node on this wire I think I should be able to add the digitial filter, however, the VI is locked and I cannot edit it.  Is there a way to edit this VI and save it as under a different name?

I considered recreating the DAQmx Create Timing Source VI as a new VI, but there is a proplem with this as well.  The DAQmx Create Timing Source VI uses DAQmx VIs that I cannot locate in labview to place them into a new VI.  Since the Create Time Source VI is locked I cannot copy any of the sub-VIs from it.  Is there a way to use those sub-VIs in a new program so I can create a new Create Timing Source VI that can use a digital filter?

thanks for your thoughts.

[EricS.]

I think by 'Locked' you actually mean that it is currently in run mode, a read-only mode where you only have the hand-grabber tool and can't edit the VI.  To get back to edit mode simply go to Operate» Change to Edit Mode.  This will allow you to modify the VI, and save a new copy.  It will also allow you to  copy and paste the subVIs if you want to use them, too.  This is contrary to "Locked" which is literally if the block diagram of the VI is password protected.

In my attempts I did try to add that digital filtering property node into the create timing source VI, but somehow it was always being re-set back to no filter, or returning an error.

Let me know if you have different luck and are able to get this to work.  Thanks,