PerkinElmer 200 UV/VIS Series User Manual page 149

Troubleshooting Methods
Light Intensity Level
Light intensity levels are dependent only upon the monochromator's internal optics and the
lamp intensity (which will vary with lamp age). As the instrument is used, the reflective sur-
faces inside the monochromator will oxidize or deteriorate with time. Keep in mind that this
is a long term process and is usually seen only in aged monochromators.
Monochromator internal optics are not field replaceable. Realignment following repair or
replacement can only be done in an PerkinElmer service facility.
The detector performance required by the user determines the useful life of a lamp. Users
who run their detectors at the highest sensitivities (lamp intensities) may need to replace
their lamps more frequently than less demanding users. If a deuterium lamp is over 1,000
hours old, its output level must be suspect and the lamp should be replaced.
Optical Misalignment
This can be a cause of instrument drift. Due to the structure of the monochromator, lamp,
and other optical components, it is not expected that an alignment problem will occur during
routine use and handling. If the lamp and flowcell have been ruled out as the sources of
baseline noise and/or drift, and the detector has been installed in a location with a stable
ambient temperature and reliable power lines, alignment of the detector's monochromator
may be suspect. However, none of the optical alignments can be performed in the field by the
user. Contact your PerkinElmer service engineer for assistance.
Environmental
Whenever a material is warmed or cooled, its dimensions change. The monochromator of any
absorbance detector will follow the thermal changes of its environment with slight changes
in its physical size. This slight variation will cause changes in the wavelength passing
through the flowcell lightpath and may be seen as drift that goes in one direction upon heat-
ing and the opposite direction upon cooling. In addition, any temperature variation that can
affect the instrument can also affect the column. The column should therefore be held at a
constant temperature both to optimize the resolution of a given separation and to ensure the
thermal stability, and therefore absorbance characteristics, of the eluent.
The detector's monochromator has been specially constructed in a massive mechanically
rigid manner in order to minimize thermal effects. If temperature changes are affecting
operational stability, the following courses of action may be considered.
• The thermal environment can be stabilized by providing baffles or covers around nearby
ventilators, air ducts, etc. in order to keep drafts off the instrument and stabilize temper-
ature.
• In some cases (e.g., in cold rooms or when operating at wavelengths of 200 nm or lower),
it is recommended that purified dry nitrogen be metered into the monochromator during
use. The flow of gas will help reduce and/or minimize thermal expansion/contraction of
the monochromator, and in cold rooms, prevent moisture from condensing inside the
monochromator housing. A polypropylene fitting is provided for connection of the N
source. Use only connecting tubing that does not have softeners or plasticizers in its
chemical formulation. Set the nitrogen input pressure at approximately 1-2 psi. Allow
Maintenance
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