Don Stanley wrote: > Hi All; > I am attempting to configure EMC2 10.04.06 to control RPM > on a 60 HZ AC generator. > > The basic approach is: > -Set the steps per inch to the number of AC cycles per day. > -Monitor the AC frequency into phase A of a HAL encoder. > -Feed the encoder output into the axis and PID feedback. > -Feed the axis motor-pos-cmd to stepgen position-cmd. > -Feed the stepgen out through the paraport to a stepper motor driver. > > This seems to work in general but there are two problems I > have not been able to pin down. > 1- The PID error is a sawtooth shape causing the throttle > stepper motor to quiver at 60 HZ. > A HAL Scope image is available at > http://imagebin.org/135986 > > The sawtooth appears to be happening at 16.6 ms, which is one 60 Hz cycle. Perhaps that is significant. What is the velocity coming out of the encoder counter component? Does it waver at all? If all these calculations are performed in arithmetic scaled to days, you may be looking at the limits of binary precision. I notice your sawtooth is fluctuating by much less than 1 millionth of a unit, roughly 2 x 10 ^ -7.
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