[RASMB] Lamp intensity fluctuations

[Titus M. Franzmann]

Good morning, 
FYI: This morning, I recorded the intensities on an empty holes (Hole#1 and
2) at 22°C at 3000 rpm. Both show the same phenomenon, however I just
plotted the results from Hole 1. 
FYI: Erby Perdue from Beckman suggested the following. 
> 1) Lamp
>
> 2) Lamp Power Supply
>
> 3) Flash Timing as set up by the pickup in the chamber and the magnets 
> in the overspeed disk
>
> 4) The PMT and PMT socket
>
> 5) The Data Acquisition Board
>
> 6) In theory, the PMT supply, but not
> very likely as the spec for voltage output is within 50V of what the 
> board asks for. It's a pretty wide margin.

We requested a service. I will post an update as soon as the service was
done.


Best and I thank all of you for your comments, suggestions and insight. Your
help is greatly appreciated.
Titus

-----Original Message-----
From: Leech, AP [mailto:apl3 at york.ac.uk] 
Sent: Tuesday, May 04, 2010 12:39 PM
To: Titus M. Franzmann
Cc: 'RASMB'
Subject: Re: [RASMB] Lamp intensity fluctuations

Hi Titus,

I notice the "peak" in your intensities is at different scan numbers
(#5 in the one plot, #25 in the other) - do these points correspond to
the same or different elapsed time (e.g. different number of cells in
the rotor making time between scans different)?

Also, you did not say how the PMT voltage varied - does it go up with
the lamp intensity, or down?

Does the same thing happen on scanning an empty hole?

Best regards,

Andrew


Titus M. Franzmann wrote:
> 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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