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Injection system (General activities)
derossi, pillant, gosselin, sposito, coulon, chiummo, paoletti - 20:33 Monday 18 February 2019 (44912) Print this report
videodriver swapped again

This morning we swapped again the videodriver and we installed a modified one with a new filter, whose zero is at 3 kHz (it was at 14 Hz before), in order to reduce the rms by avoiding to send EOM corrections at 50, 100 and 150 Hz. Its trasfer function is shown in the first plot.

The IMC is currently locking with an attenuation from 5 to 14 dB (until 7 dB it shows a loop oscillation @ 270 kHz), and we left it with 15 dB. Since by increasing the attenuation from 7 to 15 dB we lowered the general gain of the rampeauto, we then increased the EOM corrections thanks to the videodriver gain. The overall effect should be to release the piezo corrections.

With this videodriver saturation is now occurring at 0.5 V rather than 0.4 V (an example is given in the 2nd plot), so that we gained a little bit in the actuation range.

We finally remeasured the IMC trasfer function, which is shown on the 3rd plot in blue, compared with the previous one in pink.

 

Images attached to this report
Comments to this report:
Cleva, Coulon - 22:05 Monday 18 February 2019 (44918) Print this report

Unless wrong, removing the 50 ohms attached to the amplifier which follows the Videodriver increases the gain after the videodriver by a factor 2 while keeping the dynamic of that amplifier compliant.

Hence 0.5V at videodriver output becomes 1V once the 50 ohm is removed, and then 100 V at the following amplifier output, with no saturation at those levels. This would release the pressure on the videodriver by a factor 2. The bandwidth should not be affected.

 

Simple to check since the 50 ohm is a BNC one attached to the input of the amplifier on the LB close to the crystal

 

 

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