Log entry time 17:43:51 on June10,2004

Entry number 125258

Yesterday and today Darcy and Kirsten calibrated scanner positions in ADC channels versus LabVIEW position values (cm) measured in local frame of reference (relative to platform on which scanner movers are mounted). Signals sent to ADCs are voltages generated in attached to the movers linear potentiometers supplied by 8.5 DCV (this voltage corresponds to channel number ~62000). 
Linear fit to the data yielded the following slopes:
Right Arm: short axis 139.10 channels/mm
           long axis 85.87 channels/mm
Left Arm: short axis 85.39 channels/mm
          long axis -84.85 channels/mm
Potentiometer in short axis of the Right Arm is different (shorter range); it explains the higher slope for this axis. 

Unfortunately both potentiometers in the Left Arm are noisy and unstable. It can be seen in the figure below showing variation of the position ADC signals over 100000 events collected in full run. Both scanners were placed at (x,y) (17cm,34cm) in local frame of reference (close to the middle of the scan area).       
Correlation between X and Y readings for the Right Arm shows fluctuations of the reference voltage, which with range of 25 channels is negligible. However, the same plot for the Left Arm shows erratic behavior covering about 300 channels (3mm). These potentiometers will be replaced in the near future.