[RASMB] XL/I absorbance problem

[John Philo]

Andrew,

First, I think the dip in intensity around 6.3 cm could be a photomultiplier
issue rather than a slit issue (and might be as simple as the face being
dirty). 

Your current incident data are very strange. The fact that it no2 seems to
bounce between only two possible values suggests to me that this is actually
an electronic problem with the data acquisition board (DAB) rather than the
optical components.

If your old XL-A still has the older type of lamp housing then I believe it
also has the older style of mounting socket for the monochromator and
therefore you can't swap monochromators or lamp housings. I would certainly
consult your field service engineer before attempting a swap that might
damage a $20K+ component. I see nothing here that clearly indicates a
monochromator problem. A dirty monochromator could drop the overall
intensities and perhaps produce the dip near 6.3 cm but I don't think it
would make the incident data look so odd.

If the r.m.s. noise on your empty hole scan is above 0.01 OD then you are
out of spec and you should have no trouble getting Beckman to address the
issue.

John

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of Leech, AP
Sent: Wednesday, June 13, 2007 10:46 AM
To: rasmb at server1.bbri.org
Subject: Re: [RASMB] XL/I absorbance problem


Hello again,

Many thanks to Virgil, John, Borries and Tom for such timely and informative
replies.

I have now attached two plots showing actual data: the first
(IncidentIntensityComp.gif) shows the data from 00001.RN2 scan 280 nm
velocity scan on an empty hole. The top trace is the incident and the bottom
the intensity as seen through the empty hole. The second graph shows two
incident (.RNx) plots. These were both at 280 nm; the top one from an old
scan long before this problem arose and the bottom one from a recent scan.
Note the different scales.

I agree with Virgil that we may have a slit problem, but I think this is
causing the broad dip in the intensity profile. The marked difference
between the old and new incident light profiles makes me think the problem
is with the lamp and/or reference detector.

I've tried re-aligning the lamp (no difference) but I hadn't thought of
swapping between machines. I'm not sure we can do this as the lamp housing
is rather different on the old XL/A and I don't think it would fit.

What I did wonder is whether it is permissible/advisable to try the XL/A
monochromator in the XL/I? It would appear to fit, though it has less pins.
But I don't know if this would do something nasty e.g. short out the laser
power supply at the socket!

Any further comments are appreciated - I will let you know the resolution
(if any) of the problem.

Best to all,

Andrew

-- 
Dr Andrew Leech                   *  Laboratory Manager
Technology Facility               *  Molecular Interactions Laboratory
Department of Biology (Area 15)   *  Tel   : +44 (0)1904 328723
University of York                *  Fax   : +44 (0)1904 328804
PO Box 373,  York  YO10 5YW       *  Email : apl3 at york.ac.uk