J. Kissel, K. Venkateswara

We installed and tested the damping turn-table for the BRS. While the basic scheme seemed to be working, we turned it off as we experienced some grounding issues which need to be sorted out.

The turn-table has two 1-kg masses located diametrically opposite. It's angular position between 0 and 90 degrees is controlled by a stepper motor/controller which is in turn controlled by an analog signal between 0-5V.

The control signal is currently being written out by the BRS DAQ program to the USB DAC card. The stepper controller is kept floating so that the control-signal ground defines the ground for it. This was apparently causing the controller to restart irregularly. So I tried grounding one end of the control-signal to the platform (which is grounded through the ion pump). This may have been slightly better but unfortunately there seemed to be a big voltage drop (~2 V) across the DAC card's ground and the platform ground which was corrupting the control signal. Better grounding of the platform and controller may help.