[RASMB] Lamp Assembly

[John Philo]

Tim,

If your noise value is really for a windowless cell, not just an empty cell
with windows, then indeed that sounds 3-4X higher than is typical, and I
believe that value may be outside specifications.

But as Jeff said, you must not do this test through dry windows---they will
always appear quite noisy. That is why I said to scan an empty hole in the
rotor, or as Jeff says, you can use an aluminum centerpiece without the
windows. (There is no weight for the counterbalance that will balance an
epon centerpiece without windows).

John Philo

-----Original Message-----
From: rasmb-admin at rasmb-email.bbri.org
[mailto:rasmb-admin at rasmb-email.bbri.org] On Behalf Of Timothy R. Mack
Sent: Monday, September 22, 2003 2:22 PM
To: jphilo at mailway.com
Cc: mack at cabm.rutgers.edu; rasmb at rasmb-email.bbri.org
Subject: RE: [RASMB] Lamp Assembly


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The standard deviation for our instrument using an empty double sector
centerpiece taken at 280nm is 0.0117AU (after the slit assembly and lamp
were cleaned). Is this a value I should be satisfied with?

With regards to my question about the gouge in the lamp assembly, I should
have been more clear. My thinking was that if the fan gate rubbed up against
the lamp assembly enough to cause a gouge in it than it could cause the lamp
to vibrate thus introducing noise. I was just curious if any one else has
seen this before. It seems to me if the gate is modified such that it no
longer contacts the assembly then the problem should be solved however I
just wanted to ask to see if anyone thought that this could be a symptom of
a more systemic problem. Thank you for your responses.

Regards,
Tim
> Tim,
>
> I tend to doubt that scratches on the outside of the housing are any 
> big issue and very unlikely related to a noise issue. Certainly too it 
> sounds like your lamp was quite dirty. But you have given us no 
> information about the actual noise level of the instrument, so we have 
> no idea what to you is a level that causes concern.
>
> The noise is measured by scanning an empty hole in the rotor and 
> measuring the r.m.s. deviation around the mean value (the mean should 
> of course be very close to zero). Your service tech should have done 
> this. For most instruments that r.m.s. is 0.003-0.004 at 280 nm, 
> although the official Beckman specification is much higher than that 
> (and I think perhaps they spec it at 400 nm).
>
> Since your lamp intensity now sounds fine, if the noise is indeed 
> abnormally high I would suspect that your slit assembly is dirty.
>
> John Philo
> Alliance Protein Laboratories
>
> -----Original Message-----
> From: rasmb-admin at rasmb-email.bbri.org 
> [mailto:rasmb-admin at rasmb-email.bbri.org] On Behalf Of Timothy R. Mack
> Sent: Thursday, September 18, 2003 11:28 AM
> To: rasmb at rasmb-email.bbri.org
> Subject: [RASMB] Lamp Assembly
>
>
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> The older archived RASMB emails can be found at:
> http://rasmb-email.bbri.org/rasmb_archives
> and current archives at http://rasmb-email.bbri.org/pipermail/rasmb/
> Search All the Archives at:
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>
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>
> Hello,
> My question concerns the absorbance optics of the XL-I. I was 
> initially concerned with the level of noise in my data. A wavelength 
> scan was carried out using an empty double-sector centerpiece (without 
> windows) and the intensity was low (maximum intensity was 6500 units 
> at 440 nm). The lamp was subsequently cleaned and the intensity 
> increased dramatically (maximum intensity is 25000 units at 240nm). 
> However, when the lamp assembly (the black cylinder that houses the 
> lamp) was visually inspected there was a very deep (about 2mm deep and 
> about 0.75 cm long) gouge in it. It was immediately apparent that this 
> was caused by the gate that covers the front fan that sits just behind 
> the lamp assembly. Has anyone ever seen this before? Is it normal to 
> permanently remove the gate that covers the fan? The Beckman service 
> person cut off the portion of the gate that contacts the assembly but 
> the level of noise in the data did not seem to decrease. Could there 
> be a more systemic problem present? Any advice would be greatly 
> appreciated.
>
> Regards,
> Tim
>
>
> Timothy R. Mack
> UMDNJ-Robert Wood Johnson Medical School
> Center for Advanced Biotechnology and Medicine
> 679 Hoes Lane
> Piscataway, New Jersey 08854-5627
>
> Phone: (732) 235-4206
> Fax: (732) 235-5289
> Email: mack at cabm.rutgers.edu
>
>
>
>
> _______________________________________________
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Timothy R. Mack
UMDNJ-Robert Wood Johnson Medical School
Center for Advanced Biotechnology and Medicine
679 Hoes Lane
Piscataway, New Jersey 08854-5627

Phone: (732) 235-4206
Fax: (732) 235-5289
Email: mack at cabm.rutgers.edu




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