EXFO IQS-12004B DWDM Passive Component Test System for IQS-500 - Manual (Page 167)

Using the Power Meter Linearity Verification Tool
DWDM Passive Component Test System 155
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.
This operation allows to perform an electrical zero measurement on both
external (IQS-1643/1643T) and internal (IQS-9401 WRM) power meters.
Null measurement ensures accuracy of the power readings by taking a
measurement while protective caps are put on all power meters’
detectors. A correction factor is determined and applied to any future
measurement.
Note: You don’t have to disconnect any patchcord except the DUT when
performing a null measurement. Once the nulling is started, the source will
automatically stop emitting.
I
MPORTANT
Light must not reach the detector when nulling offsets.