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AdV-FLT (Pre-commissioning)
bertolini, capocasa, guo, montanari, paoletti - 13:02 Wednesday 05 May 2021 (51645) Print this report
FCIM coil drivers issue: oscillations and crate electric problem

While keeping the investigations on FCIM coil jumps we found out two major issues:

LARGE HIGH-FREQUENCY OSCILLATION AT THE COIL DRIVER OUTPUT 

We measured the FCIM coil driver output current monitor directly with an oscilloscope and we found large oscillation (tens of volts) at high frequency (hundreds of kHz)  for all the 16 coil drivers.

The oscillation is not present when we connect directly the dummy loads to the coil driver output but it is there when connecting the coil driver to the suspension and even when we put a dummy load at the end of the long cables that go into the chamber.

Oscillations are also present at the FCEM but quite smaller and higher frequency (~ Mhz) 

A recap of all the measurements can be found in the attached PDF.

We are investigating  the difference between IN and END (cabling, etc..) and check coil driver of other suspension. 

UNSTABLE CURRENT SUNK BY COIL DRIVER CRATE

We powered the coil driver crate with an external power supply. 

We noticed that in the same configuration the current required by the crate changed considerably. Yesterday afternoon it was highly non-symmetric between + and -  (~1.2 A vs ~0.6 A). Pic 1 By removing the modules one by one we found out that such asymmetry is due to the DDS module and LVDT demod.  In the evening the current was almost the same for + and - (pic 2)  and then this morning again it was antisymmetric and saturating for the +. (pic3) 

We also noticed that the DDS stops when we plug the coil driver cable (and we need to switch the power supply on and off to restart it). This is not expected as the two boards are not connected to each other except for the fact that they are powered by the same backplane. This made us suspect an issue at that level.

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