[RASMB] Lamp intensity fluctuations

[John Philo]

Titus, it might help narrow possibilities if you told us (1) what Beckman
has done to try to fix this (components swapped or tested) and (2) what is
the age of this instrument?

John 

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of Titus M. Franzmann
Sent: Tuesday, May 04, 2010 7:11 AM
To: 'RASMB'
Subject: Re: [RASMB] Lamp intensity fluctuations

Hi,
I should have been a little bit more precise about my sample.
I loaded a cell with water (dH20) in the reference channel and a sample of
0.5 Abs in the sample channel. I recorded intensities instead of OD values.
Thereafter I plotted the lamp intensities from the reference channel (water)
as a function of the scan number using Ultrascan. The same graph can be
produced using Origin, plotting the raw intensities at any given radial
position, or the average of it, as a function of the scan number. Basically
the same profile. 
Titus

-----Original Message-----
From: Leech, AP [mailto:apl3 at york.ac.uk]
Sent: Tuesday, May 04, 2010 9:52 AM
To: RASMB
Cc: Tom.Laue at unh.edu; Titus M. Franzmann
Subject: Re: [RASMB] Lamp intensity fluctuations

Hi Tom, Titus, all

I thought the "incident" readings come from the reference detector:
these can be seen using the menu Scan -> Request Data -> Incident from the
GUI, but they are only available from the last scan and do not seem to be
collected during a run. The incident data should be flat across the scan,
slightly noisy and slightly higher than the maximum reference sector data
(at least, that is how they are on our XL/I). We once had a problem with the
reference detector which resulted in this data being a perfect flat line,
solved by replacing the monochromator assembly.

Best regards,

Andrew


Tom Laue wrote:
> Hi Titus, et al.-
> I am not sure what the intensity reading is you are presenting- is it 
> the average value across the radial scan? Is it the reading at a 
> particular radial position? In any case, it is worthwhile getting some 
> idea of the complexity that is behind the XLA intensity readings.
> There are two intensity readings taken with each lamp flash- 1) 5 or 
> 10% (can't recall which) of the lamp flash intensity itself is 
> monitored using light bounced off of a semi-reflecting mirror and a 
> photodiode sensor. This signal is used to correct for the inherent ~3% 
> variation in flash intensity characteristic of the lamp. 2) The light 
> intensity at the photomultiplier (PMT) after it has passed through the 
> cell and slit/lens assembly. I do not believe the photodiode intensity 
> readings are accessible to the outside world, so your readings are from
the PMT.
[...]

-- 
Dr Andrew Leech                   *  Laboratory Head
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


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