Filtering a counter timer signal.

[DieselPower]

I am measuring a signal that is roughly 50 kHz max.  I use a 10 Hz clock from another timer and count pulses in between those clock pulses.  When I apply a load (VFD) to the system, I get a high frequency noise on my primary signal which causes erroneous measurement.  I am trying to add filtering from a PXI-6602, but the two functions I need are not in the help files.  I am getting an error on the second to last line below saying that the channel is not in the task. 

1. If that is the case, what channel am I supposed to pass?  I thought filters were tied to all "PFI lines." 

2. Also, what boolean data do I pass as the third parameter in the second to last line? 

3. Can I pick any pulse width for the last line or does it have to be one of the four I've seen documented? 

4. Why aren't these function calls nicely documented in the help files?

		/***************************************************************************/
		/* Configure task To count rising edges from 1,024 pulses/rev torque meter */
		/***************************************************************************/				
		DAQmxErrChk (DAQmxCreateTask("HBKSpeedTask",&speedTaskHandle));
		DAQmxErrChk (DAQmxCreateCICountEdgesChan(speedTaskHandle,"PXI1Slot7/ctr0","CountEdges",DAQmx_Val_Rising,0,DAQmx_Val_CountUp));
		DAQmxErrChk (DAQmxSetChanAttribute(speedTaskHandle, "CountEdges", DAQmx_CI_CountEdges_Term, "/PXI1Slot7/PFI38"));   // 9
		DAQmxErrChk (DAQmxCfgSampClkTiming(speedTaskHandle,"/PXI1Slot7/PFI39",100,DAQmx_Val_Rising,DAQmx_Val_ContSamps,10));   // 8
		DAQmxErrChk (DAQmxSetCICountEdgesDigFltrEnable(speedTaskHandle, "/PXI1Slot7/PFI38", 1));
		DAQmxErrChk (DAQmxSetCICountEdgesDigFltrMinPulseWidth(speedTaskHandle,  "/PXI1Slot7/PFI38", 0.00002));

[Kevin_Price]

I don't know text language syntax for DAQmx, but I'll take a shot at these otherwise-unanswered questions.

you wrote:

1. If that is the case, what channel am I supposed to pass?  I thought filters were tied to all "PFI lines." 

2. Also, what boolean data do I pass as the third parameter in the second to last line? 

3. Can I pick any pulse width for the last line or does it have to be one of the four I've seen documented? 

4. Why aren't these function calls nicely documented in the help files?

1. Maybe no channel at all?   In LabVIEW, there's no input argument available for designating a channel or PFI line when setting up a digital filter for an Edge Counting task.  Apparently, DAQmx handles this internally, applying the filter to the PFI line that was configured to be the source of the edges to be counted.

2. Sorry, dunno the text language syntax.  In LabVIEW, one sets the Enable property to either True or False.  The numeric value 1 looks reasonable but I don't know if it's correct.

3. WIth the 6602, I think you're limited to one of the 4 documented pulse widths.  Not sure what happens if you request something different.  Could be ignored, could cause an error, could silently coerce to one of the 4 it supports (probably rounding up to the nearest supported width that's longer than you requested).  You may need to experiment.

4. Fair question.  I have no familiarity with those help files so I don't know where to point you or if there is such a place.

-Kevin P

[DieselPower]

The code is below, and should be fairly similar to LabVIEW in terms of parameters passed and functions called.

I cannot set the minimum pulse width AND turn the filter on.  If it do this it will throw an error.  I had to comment out the line that turns it on, so I can't be certain that it is actually on.  It also doesn't appear to be filtering enough, at least for my application.  You are correct in that I cannot pass a channel name to it.  I just leave it blank.  If it try to pass a channel name, it will say that channel is not in the task even though it is.

		/***************************************************************************/
		/* Configure task To count rising edges from 1,024 pulses/rev torque meter */
		/***************************************************************************/				
		DAQmxErrChk (DAQmxCreateTask("HBKSpeedTask",&speedTaskHandle));
		DAQmxErrChk (DAQmxCreateCICountEdgesChan(speedTaskHandle,"PXI1Slot7/ctr0","CountEdges",DAQmx_Val_Rising,0,DAQmx_Val_CountUp));
		DAQmxErrChk (DAQmxSetChanAttribute(speedTaskHandle, "CountEdges", DAQmx_CI_CountEdges_Term, "/PXI1Slot7/PFI38"));   // 9
		DAQmxErrChk (DAQmxCfgSampClkTiming(speedTaskHandle,"/PXI1Slot7/PFI39",10,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1));   // 8

		DAQmxErrChk (DAQmxSetCICountEdgesDigFltrMinPulseWidth(speedTaskHandle, "", 0.000005));
		//DAQmxErrChk (DAQmxSetCICountEdgesDigFltrEnable(speedTaskHandle, "", 1)); //"/PXI1Slot7/PFI38"

[Kevin_Price]

It isn't much to go on, but I found a *very* old thread using similarly-named function calls from ANSI C.  Using that as a hint, have you tried designating the string arguments in the filter function calls as "PXI1Slot7/ctr0"?

To test out functionality generally, I'd recommend you generate a pulse train with another counter, physically wire its output PFI pin to a different PFI pin you'll use as input, and attempt to apply digital filtering to that input PFI pin.  Then you can experiment with either the pulse train or the filter parameters to verify whether or not the filtering is functioning properly.

-Kevin P