The reason for the NCal phase unlocking is a decrease of the LED signal used to capture rotor rotation as can be seen on top plot of LED_Alim_rotor_phase.png
The bottom plot of this image shows that about 1 minute later, the rotor phase begins to diverge from 0. When LED signal gets back to its normal value, the phase lock back after few cycles.
The second image shows how the phase unlock result in the bad subtraction of calibration line at about 36Hz
The problem is under investigation.
