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2475 message, triggered during peak detection: Sample signal is saturated. Gain set too high - WKB17612

Article number: 17612

SYMPTOMS

  • At 0.9 minutes, the baseline straight drops to negative 10,000 (-9999) emission units and spikes back up to positive 1000 emission units
    • After peak detection finishes, the signal drops back down to zero; stable baseline
    • Baseline at injection is stable
  • 2475 passed both normalization and calibration

Sample signal is saturated_Gain set too high.png

ENVIRONMENT

  • 2475 Multi-Wavelength Fluorescence Detector

CAUSE

  • When the gain setting for the peak of interest is set to high, the photomultiplier tube (PMT) shuts down momentarily to protect itself.
  • This results in a -9999 negative peak as the voltage shuts off.

This is normal behavior, documented in the 2475 Operators and Maintenance Guide, section 3.4.10, "Setting Gain and EUFS".

Fluoresence signal pinned negative_gain set too high alarm message .png

FIX or WORKAROUND

  1. Incrementally reduce the excitation gain setting by a factor of 2 to 10 until the error clears.
    • It's best to reduce the gain setting via programming within the instrument method.
  2. The auto-optimize gain function tests the correct settings to use in the instrument method.
    • See section 3.4.10 in the screen capture below
    • Auto optimizing gain and EUFS.png
    • Note: The gain settings for one 2475 may not transfer to another because the light is generated in the flow cell and is dependent on lamp age, quality of the mirrors/windows, and variations in the flow cell.
  3. If the gain setting is already at it lowest, you can set the PMT to a low sensitivity mode via the diagnostics menu.

ADDITIONAL INFORMATION

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