We are trying to measure the position of Top Dead Center (TDC) of a cam shaft. We have an encoder connected to the crank shaft so there is a 2:1 speed ratio between crank and cam shafts. Alternately, for every 360 degrees rotation of the cam, the crank rotates 720 degrees.
With our 1800 ppr encoder on the crank shaft, we are able to measure the number of A pulses between the Z-index marker pulse and TDC. The problem is, our current counter resets every 1800 pulses. Since the crank rotates twice for every cam rotation, we don't know whether the TDC occured in the first rotation (0-1800 pulses) or in the second rotation (1800-3600).
One idea is to try to generate a pulse, call it G, that is:
1. Triggered off the Z-index
2. Has the same pulse width as the Z-index
3. Has half the frequency of the Z-index pulse
So we would then have a counter that goes from 0-3600 instead of 0-1800. We haven't been successful at this. We can generate the G pulse with half the frequency of the Z-index pulse, but we weren't able to modify the pulse width, which alsos change as the speed changes. Does anyone have any suggestions on how to accomplish this, or any other thoughts on measuring TDC?
Edit: We are using DAQmx boards and a Desktop ETS for hardware.
Thanks.
Message Edited by Sima on 05-17-2009 09:56 AM
