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debounce filter for compactDAQ triggering

I have a compactDAQ system that I use for cylinder pressure data acquisition in engine applications.  I trigger the start of acquisition with a TTL pulse from a shaft encoder at a fixed engine crank angle.  Sometimes I get false trigger signals from noise on the line and I am trying to apply a debounce filter to the trigger (9401 unit in slot #5 of a 9172 chassis).  when I try and use a property node to turn on the debounce filter and set the filter constant, I get an error and the triggering doesn't work.  Its not clear to me if you can use the debounce filter for this device for the start trigger.  Any ideas?
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Hi hiltnerj,

       Have you tried to apply a digital filter?  To do this, You'll want to place a DAQmx Trigger Property Node, and then choose Start»Digital Edge»Digital Filter» Enable.  This should help- let me know how it works out for you!

 

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I have tried this, but when I try to add the digital filter property and the digital filter duration properties to the property node, I get an error that I can't find the defintion for when I try to run the VI.  I am not sure if the 9172 chassis supports digital filters on trigger lines.  I also tried adding a 'dummy' counter to allow the filter to be turned on and set up, and this runs without error but doesn't seem to have any impact on the triggering.  I'm running my engine right now so I can't get the error code (can't switch over the the VI with the filter) but I'll send the error number when I try again.

 

Thanks,

 

hiltnerj

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I tried again today to turn on the digital filter for my compactDAQ trigger problem.  When I try to add the Start.DigEdge.Enable property to my DAQmx Trigger property node I get error #-200452.  I get this error regardless of what value I have entered for MinPulseWidth property.  The error description says 'Specified Property is not supported by the device or is not applicable to the task'.
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Hi Hiltnerj,

       I appologize, I was wrong in my last post, and as you suspected, you cannot use a digital filter on cDAQ, as explained here in the cDAQ manual.  You should be able to set up a counter input (like an edge count) on the same trigger line and when you set up filtering for the counter it should filter the trigger line as well. Another option is to set up a retriggerable single pulse output, then trigger off of the single pulse. Since a retriggerable pulse will ignore triggers received while it is generating, you'll only get that first edge. Hope that helps, let me know if you have any questions about that!

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Hi All,

 

Just to clarify the solution to this forum thread, as of DAQmx 9.4 onwards support has been added for Digital Filtering on CompactDAQ, the readme file found here for 4.0 states under "New Features": Support for digital filtering on the NI cDAQ-9171, 9174, 9178, 9181, 9188, and 9191.

 

The solution to resolve this is to download 9.4 or above of DAQmx (ensuring the version supports your Operating System and NI Software Environment versions) from www.ni.com/drivers

 

 

Applications Engineer
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