Ed,
True quadrature conversion is a built-in feature of the M-series boards so there should be no need for an LS7083 or similar interface circuit.
Personal testimonial: I've been using an M-series counter connected directly to a quadrature device for several months with no miscount issues. The device is a non-contact laser interferometer that resolves at the sub-micron level, and we're getting very repeatable measurements. This in an environment where the otherwise unnoticeable air currents from normal operation of the HVAC system cause a vibration-like fluctuation in counts.
-Kevin P.
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