EXFO PM-1100 Optical Power Meter - Manual (Page 24)

Operating the Optical Power Meter
14 PM-1100
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.
EXFO recommends performing a nulling before every test session. Since
temperature and humidity variations affect the performance of electronic
circuits and optical detectors, EXFO also recommends performing a
nulling of the electrical offsets whenever environmental conditions
change.
To perform a nulling:
1. Place protective cap over detector port.
2. Push Null. The offset nulling process takes approximately 90 seconds.
Once done, the unit returns to the previously active operation state.
If you are trying to perform an offset nulling with the protective cap
improperly tightened on the detector port, the message PUT CAP will flash
on the display. When PUT CAP is displayed, ensure the protective cap is
properly tightened and press Null to resume the offset nulling process or
press ENTER to cancel the offset nulling.
Note: Offset nulling constants are retained until a new offset nulling is performed.
I
MPORTANT
Light must not reach the detector when nulling offsets.