Max frequency of quadrature input for NI-9401

[beck0644]

I am using a cRIO-9057 and NI-9401 in its quadrature encoder specialty mode.  I am losing encoder ticks somewhere in the path between my motor and the cRIO (motor > encoder > motor controller > IC transceiver > NI-9401 > cRIO).  During diagnosis, I found that the signal was good at 3.6 MHz (272ns) and then I lost ticks at 3.8 MHz (260ns).  When I look at the datasheet (attached), there isn't specific information about the quadrature encoder specialty mode.  In the section marked 'Maximum signal switching frequency, per channel' it has values of 9MHz for 8 inputs, 16MHz for 4 inputs, and 30MHz for 2 inputs.  I'm not sure which set of data pertains to me, or if there is an additional conversion needed for the quadrature encoder specialty mode.  Does anyone know the maximum frequency of quadrature inputs for the NI-9401 card?

Thank you in advance for your help.

Best,

Travis

[RIObotics · Accepted solution]

Hi there,

Have a look at this document:  https://www.ni.com/docs/en-US/bundle/ni-compactrio/page/configuring-a-counter-to-measure-frequency.h...

It doesn't look like your digital signal can exceed 4Mhz for the NI-9401 quad encoder, as "pulses shorter than 250 ns may be rejected."  If you need to count higher frequencies, you might need a dedicated counter card like the PCI-6602, which can measure up to 80Mhz.  

BR

John

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[beck0644]

Thank you for pointing me to that documentation, it was very informative.  Have a great day!

Best,

Travis