Filtering Noise - Waters ACQUITY Refractive Index Detector Overview And Maintenance Manual

1 The ACQUITY Refractive Index Detector

Filtering noise

The detector's digital, finite-impulse-response Hamming filter minimizes
noise by degrading peak height and enhancing the filtering of high frequency
noise.
The filter's performance depends on the filter time-constant you select. You
can program a filter time to be fast, slow, normal, or other. If you select Fast,
Slow, or Normal, you need not enter a value; the filter constant is determined
by the sampling rate. If you select Other, you can enter a value. Note,
however, that the value you enter is rounded up or down to a value based on
the sampling rate.
The filter time-constant adjusts the filter response time to achieve an optimal
signal-to-noise ratio. Selecting Other and entering a value of 0.0 disables all
filtering.
Lower time-constant settings produce these effects:
• Remove less baseline noise
• Produce narrow peaks, with minimal peak distortion and time delay
• Make very small peaks harder to discern from baseline noise
Higher time-constant settings produce these effects:
• Greatly decrease baseline noise
• Shorten and broaden peaks
The software includes fast or normal filtering constants at each sampling rate
that are appropriate for high speed or high sensitivity applications,
respectively.
34 October 13, 2014, 715003547 Rev. C