From: JOHN PHILO <JOHN_PHILO@amgengate.amgen.com>
  To  : rasmb <rasmb@bbri.eri.harvard.edu>
  Date: 18 May 1994 07:56:39 U

autogain & differential sed

                          autogain & differential sedimentation
In the discussion about differential sedimentation 
Geoff Howlett and Tom Laue have both mentioned 
the desirability of disabling the adjustment of the 
photomultiplier voltage to maintain a constant 
signal in the reference channel (the "autogain").  

My understanding is that this feature is already 
disabled (mostly) when you run the XL-A in 
"continuous" scan mode, which is normal for 
velocity runs anyway.  That is, for continuous 
scans the photomultiplier is adjusted only for the 
first data point for each scan, and not thereafter.  
Therefore, in a differential sedimentation run there 
would be no problem as long as the first point is 
above the meniscus.