EXFO IQS-12004B DWDM Passive Component Test System for IQS-500 - Manual (Page 87)

Calibrating the DWDM Passive Component Test System
DWDM Passive Component Test System 75
Calibrating the System
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.
The IQS-12004B DWDM Passive Component Test System uses both external
optical power meters and internal optical power meters inside the
IQS-9401 WRM.
Protective caps should be placed on the external power meters. The WRM
can be blacked out by placing protective caps on both the input and output
or by placing a protective cap only on the output if the Turn Source Off
option is selected.
This operation ensures accuracy of the power readings by taking a
measurement while a protective cap is put on the power meter detector.
I
MPORTANT
Light must not reach the detector when nulling offsets.