Agilent Technologies 8163B, Manual, Page: 216 / 466

Setting Attenuation and/or Power Levels How to Use a Variable Optical Attenuator module
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Agilent 8163A/B, 8164A/B & 8166A/B Mainframes, Sixth Edition
How to Use the Power Control Feature
81576A/77A Attenuator modules incorporate Power Control functionality that
automatically corrects for power changes at its input to maintain your desired
output power.
This feature is designed to compensate, for example, for output power drift by the
source.
When Power Control is On:
• If P
actual
deviates by more than 0.1 dB from your desired P
SET
value, the
Attenuator module automatically restores P
SET
at the maximum possible filter
transition speed of 12 dB/s.
• Input power is measured using your set Averaging Time.
• To avoid ‘hunting’, and consequent wear on the filter motor mechanism in
response to an unstable source, for differences between P
SET
and P
actual
greater than 0.01 dB, but less than 0.1 dB, P
SET
is updated approximately every
30 s.
• The Attenuator module does not respond to a power difference of 0.01dB or
less. Such a change is regarded as noise.
• If the attenuation is driven beyond 0 dB, Exp (“Excessive Power”) is displayed.
There is now insufficient input power for the Attenuator to maintain your
desired P
SET
.
Power Control On/Off
To enable or disable Power Control, select the [Pwr Ctrl] parameter.
When Power Control is On the Attenuator’s status display includes ‘PC’.
The Menu item <Pwr Control> is functionally equivalent to the
[Pwr Control] parameter.