HP 83481A, User Manual, Page: 66 / 98

Calibration Overview
User Calibrations|Optical and Electrical
Dark Calibration
The dark calibration is for optical measurements , or electrical measurements
if an external O/E is being used. This calibration measures the optical
channel oset signal when there isn't any light present and then uses this
information in performing extinction ratio measurements . Dark calibrations
should be done for the following conditions:
Before any critical extinction ratio measurements are made
After a plug-in vertical calibration
If a module has been removed
If the mainframe power has been cycled
If extinction ratio measurements are being made after the vertical scale or
the oset has changed.
If the line power has been cycled, the dark calibration invokes either the
oset zero calibration or plug-in vertical calibration as needed. This increases
the time required for the dark calibration to complete . The
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Dark cal
softkey is located within the Extinction ratio menu.
T o initiate a dark
calibration
1. Press the 4 Displa y 5 key . Press the
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Color grade softkey , and set its setting
to
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on .
Color grade must be enabled to perform an extinction ratio
measurement and a Dark calibration. In addition, the dark level
(amplitude when there is no signal present) must be on the screen to
perform a Dark calibration.
2.
Press the blue shift key , and then the
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Meas eye softkey which is located
beneath the display .
3.
Press
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Extinction ratio ... and then
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Dark cal .
Disconnect all inputs from the module , including the trigger signal, and block
any ambient light to the photodetector with a connector plug. F ollow the
instructions on the screen.
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