Debounce Digital Filtering With NI 62xx M Series and cDAQ

Updated Jul 30, 2018

Reported In

Hardware

  • Multifunction I/O Device

Software

  • LabVIEW
  • LabVIEW Base
  • LabVIEW Full
  • LabVIEW Professional

Driver

  • NI-DAQmx

Issue Details

I am seeing noise, unexpected, inaccurate, or incorrect counts on my counter tasks with sensors like my encoder. I have seen on the specification sheets of NI 62xx M Series and cDAQ devices that I can implement digital filters (digital debounce filters) on the device's PFI line(s). How do I implement this?

Solution

For M Series and cDAQ cards, NI-DAQmx currently supports digital line filtering on counter input tasks only, not DIO tasks. You can enable a programmable debouncing filter on each PFI, RTSI, or PXI_STAR signal. Enabling debounce filters when the PFI line is not a part of a counter task (e.g. AI Sample Clock or Digital Trigger) requires the use of a dummy counter as shown below.


This workaround sets up and commits a "dummy" counter task using the PFI line of interest as one of the counter inputs and enabling filtering on it through the counter options of the DAQmx Channel Property Node. Please see the below snippet for an example of using this workaround for the filtering of a digital start trigger.


For M Series devices the valid values for the minimum digital pulse width are 0s, 2.56ms, 6.425us and 125ns. Also, we can apply this workaround to both RTSI and the PXI Star filters.

 

Additional Information

This workaround is not required for X Series DAQ Devices under most cases since digital filtering is built into the DAQmx Driver for these devices for more subsystems. Refer to the X Series User Manual for more information on digital filtering with X Series devices.

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