[RASMB] Lamp intensity fluctuations

[Leech, AP]

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
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