Evan, Sheila
We have been slowly stepping up the input power tonight, and we see the power drop when we request increased power. Here is an example, from 4-24-15 9:35 UTC. The top left panel shows the power which Evan requested, the bottom left panel shows the actual cmd position, which approriately goes in the same direction consistently when the requested power increases. The right two panels show the problem, that the readback of the actual rotation stage position goes in the wrong direction briefly when a new comand is sent. This is a real decrease in power, the lower right panel shows that the power monitor PD sees these power decreases.
If you zoom in, you can see many things.
1. At the very beginning of the rotation, the cmd position (left bottom) doesn't ramp for about 2 seconds, and suddenly it jumps up (red circle), which coincides with the reversing motion of the rotator. This behavior is repeated in every power step in Sheila's data.
(Updated after reading Daniel's comment: 2 sec delay might be a non-issue, but the jump seems to be an issue.)
2. At the end of the rotation, the cmd position looks good but the rotator jumps up, causing another power jump (blue circle). This also is repeated in every power step in Sheila's data.
3. There's one instance where the rotator reversed direction in the middle of ramping in Sheila's data (green circle).
4. There's one instance where the power increase was requested, nothing happened for 11 seconds, another power was requested, and the rotator started moving (second attachment).
(Updated after reading Daniel's comment: This might be a non-issue.)
After the power request one also needs to press the go button to get it started. So, I guess the 2s delay is just that. For the request without moving, are we sure the button was pressed?
I requested a small power step (from 2W to 2.1W) and immediately back to the original power, and the measured power dropped from 2.25W to 1.9W.
I repeated again, and the power went further down to 1.5W.
All in all, the calculated angle got back to the original number, of course, but the measured angle is down by about 0.4 degrees or so.
Daniel hit the "Go To Power" button without changing the power request, and the driver still did its thing and the power dropped.
After repeating the routine 4 times, the encoder value happened to get back to the number before Daniel started, but the power is still down from 1.5-ish to 1.1-ish W.
