[RASMB] Lamp Assembly

[John Philo]

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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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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