From: Greg Ralston <gregr@atp.biochem.usyd.edu.au>
  To  : RASMB@bbri.harvard.edu
  Date: Tue, 12 Nov 1996 10:14:08 +1100

Overspeed rings

Thanks to everyone who contributed to my query about the overspeed disk problem.
To summarise the replies:

There are two types of disk in circulation. The ones we used earlier were not so
shiny; the later ones are much shinier. I understand that the original 
manufacturer was unable to continue making the disks (for reasons we don't need 
to go into), and that there was some problem about what the specs were supposed 
to be, but Beckman is getting this under control. The consensus of advice was 
that dropping the pick-off voltage to 1.25 volts would allow the system to cope 
with either type of disk.

It turned out that our problem was the height of the detector below the rotor. 
The height setting was too low, so a sharp transition from light to dark could 
not be made at high speed. Resetting the height fixed the problem (which also 
occurred with a brand new disk of the old type).

Nevertheless, our experience has shown that it is important  not just to keep 
the black sectors black, but also to maintain the shiny sectors shiny and free 
from scratches. Given the cost of the replacement disks, it is worth taking care
of them.


Greg Ralston
(Associate Professor)

Phone (61 2) 9351 3906
Fax   (61 2) 9351 4726

e-mail: G.Ralston@biochem.usyd.edu.au 

Department of Biochemistry
University of Sydney
Sydney, NSW, 2006
Australia