Peter F, Evan, Kiwamu,

ETMY was not damping today. It sometimes damps OK and sometimes does not. When it does not damp, it grows an oscillation in pitch at 0.5 Hz. Also, steering the suspension often kicked the suspension for some reason. After many hours of investigation, we finaly found that the DAC outputs show some discrete steps in every ~ 2000 counts or so. This, of course, made the actuators highly nonlinear. This was very sneaky -- one would not notice until he or she crossed a discrete point because the actuators are locally linear. The attached is a screen shot of StripTool showing the nonlinearlity. The purple curve is the requested DAC counts and the yellow one is an actual analog voltage observed by VOLTMON. As seen in the screen shot, the analog signal has multiple discrete steps. This behavior was seen at all 6 coils on the M0 (top) stage of ETMY and very repeatable. We didn't have energy to check the lower stages and therefore we don't know if this is true at the lower stages.

We must fix this issue.