Configuring a quadrature encoder frequency divider with digital filtering with PCI6602, DAQmx, LabView8.0

[E-Rock]

I´m using labview 8.0 and the PCI6602 counter-board. I want to configure two counter as frequency-dividers with variable division-rate to divide down the pulses from a quadrature encoder.

I have the A phase connected to CTR 0 SRC and B phase connected to CTR 0 AUX.  The A phase division is output on CTR 0 OUT using "CO Pulse Ticks" and setting the high and low ticks inputs.  The B phase division is actually the A phase delayed by 90 degrees output on CTR 1 OUT using a retriggerable digital trigger.  This seems to work better than dividing A and B phases separately.  So far just dumb division of the A and B signals works fine.

However vibration on my encoder caused by the servos locking in on a position causes a bunch of state changes on the A line even though the encoder is not actually moving very much.  The PCI6602 interprets this as movement and increments the count used to divide down the frequency.  Since the vibration pulses are much shorter than normal movement pulses I was thinking there might be a way to filter out the short pulses.  Any thoughts would be appreciated.

P.S.  The A phase frequency division is done much like this example i found:

http://forums.ni.com/attachments/ni/40/2582/1/Divider_Config_mw.vi

Thanks,

Eric Hoffman

[Jesse_O]

Hello Eric,

If you application is working basically how you need, and simply requires some filtering you maybe able to do this with the built in filter circuitry of the 6602.  There is a KB here that talks about this more.  You can access the filter for a counter output task under Counter Output >>  General Properties >> Counter Timebase >> Digital Filter.  You can read more about the digital filters in the TIO help file starting on page 3-1.

I hope this helps.  If not please let us know.

Regards,

Jesse O.
Applications Engineering
National Instruments