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

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

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".

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
   • 
   • 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