EXFO FTB -5240S/5240BP Optical Spectrum Analyzer for FTB 500 (NS-1434) - Manual (Page 29)

Preparing Your Optical Spectrum Analyzer for a Test
Optical Spectrum Analyzer 21
Nulling Electrical Offsets
Nulling Electrical Offsets
The offset nulling process provides a zero-power reference measurement,
thus eliminating the effects of electronic offsets and dark current due to
detectors.
Temperature and humidity variations affect the performance of electronic
circuits and optical detectors. For this reason, EXFO recommends
performing a nulling of the electrical offsets whenever environmental
conditions change.
Nulling can be performed for all tests modes. In addition, a nulling is
performed automatically each time you start the OSA application, and at
regular intervals afterwards for WDM test mode.
To perform offset nulling:
1. From the main window, select the Acquisition tab.
2. Disconnect any incoming signal to obtain an optimal accuracy.