[RASMB] Lamp intensity fluctuations

[Tom Laue]

Hi-
Weird! Erby knows his stuff. I'd be interested in knowing which 
component is causing the trouble.
Best wishes,
Tom

Titus M. Franzmann wrote:
> 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.
>>>       
>> [...]
>>
>>     
>
>   
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-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
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E-mail: Tom.Laue at unh.edu
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