We need some bias to the PZT out.
> 5. I found that if the PZT output goes to negative on the oscilloscope,
> the gyro signal have larger noise than usual. I put an offset to the slow servo
> such that it does not go into the negative side.
I noticed that there was a (slow) error signal offset of about 4000 cts. Koji had recently put in a manual offset of the same amount to counteract what was an offset in the other direction before. I turned this off and was able to get the error signal back to around 0 by clearing the servo memory (i.e. just turning the filter block off and on and then reengaging the output).