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more noise than expected, excluding any occasional fluctuations, the cell may need cleaning.
Please contact the Viscotek Technical Service and Support department for further instructions.
D.3 PROBLEMS IN THE REFRACTOMETER BASELINE
D.3.a General Instrument Function
Noise in the Refractometer baseline can be characterized as either random, pulsation, or
drift type.
D.3.b Baseline Noise
Random white noise generated by the refractometer is generally the lowest level of the
triple detector configuration. It’s value is always less than 0.1 mv and often approaches that of
the individual bits. Pulsation noise is sometimes found in the refractive index detector signal,
however, when it occurs, generally the viscometer signal has already become unusable since it
is much more sensitive to solvent compressibility changes than even the RI. The most
frequently encountered form of baseline noise in the RI signal is that of drift. The RI is
extremely sensitive to compositional changes in the solvent and to thermal variation. Often
when mixed solvent systems are used it is necessary to continuously stir the mixture to
minimize the drift caused by the continuous change in composition (possibly caused by the
more rapid evaporation of one component over another). The Model 300TDA is temperature
controlled to minimize thermal effects encountered in the RI.
Note: Thermal equilibration is normally slow and will may require several hours to
accomplish. We recommend leaving the oven On for periods of time when the detectors are not
being used continuously, but are needed frequently, to minimize start-up time for analysis.