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Acquiring instantaneous of quad encoder with NI USB-6212

Hello all,


I have an encoder mounted on a one cylinder diesel engine. I'm trying to obtain a speed profile of the engine over a single cycle, as it speeds up and slows down because of friction and the combustion event. I have a USB-6212 card and a USD incremental encoder.

Based on the examples there are two ways to do this; time sample a digital input and record the period or semi-period of the counter input. The issue with the first is my DAQ card doesn't seem to support it. The second basically counts up the number of elapsed pulses on a set time interval. So every .001 seconds it calculates how many pulses have ticked. This creates a number of issues for me, both in accuracy and data processing and I can't use this method.


Some potentially relevant math: my encoder pulses 1250 times per revolution on each line. The engine spins at about 3600 RPM so it takes 16.6 ms per revolution. That's about 0.01328 ms per pulse or about 75 kHz, if my math holds up.


Can anyone tell me another way to calculate instantaneous speed of an encoder?

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