[Ushiba, Kamiizumi, Tomura, Aoumi, YamaT]
 

Abstract

We measured DAC noise for MN, IM, and TM actuators on ITMY.
Noise level at AI output for TM actuators had been already measured in klog#24157 (ITMY) and klog#24249 (ITMX).
As an update from the previous works, we measured also for IM/MN actuators.
And also, noise level at outputs of the coil driver chassis for TM and and of the satellite box for IM/MN were measured.
All results are stored in /users/DGS/measurements/DAC/k1iy1

As in past measurements, frequency dependent structure was found on DAC noise.
But they can be removed by enabling two or three stages of de-whitening filters at the coil driver chassis.

Results of same measurement on ITMX will be reported in klog#24726
 

Details

Measurement setup for noise at AI output
Measurement was done by connecting the AI output of actuators to the universal whitening filter chassis which was connected to the AA chassis.
Because expected DAC noise is smaller than the AA and ADC noise level, DAC output must be amplified by whitening filters.
According to the previous works (klog#24157 and klog#24249), overall gain as 36dB is enough for this measurement.
For the measurement at AI output, all channels were measured with the 36dB whitening gain.

Whitening filter chassis were already installed in Type-A rack for the monitor of coil output (connected from Volt Mon port of the coil driver).
When we will do same thing for Type-B, -Bp, and -C suspensions, we will need to bring a new whitening filter chassis.

Measurement setup of noise level at coil driver/satellite box output
Because the signal path for TM coils doesn't have a satellite box, we measured noise level at the output of coil drivers.
On the other hand, satellite box output (in correctly, Drv. Mon port of the satellite box) was used for the IM and MN actuators.

For TM actuators, we measured all situation of the de-whitening filter in the coil driver chassis.
For IM and MN actuators, only nominal situation in OBSERVATION state was measured.

Measurement results
Measured spectra of four TM actuators were shown in Fig.1-4.
Broad peaks around 30Hz, 60Hz, ... can be seen on some of AI outputs and the coil driver outputs without de-whitening filters.
(These peaks seem to move in time...)

These peaks can be suppressed with one or two stages of dewhitening filters.
And also, the 3rd stage of the dewhitening filter makes slightly better noise floor.

Figure 5-10 show the spectra of IM actuators.
As the nominal dewhitening configuration, one and three stages were enabled for horizontal and vertical actuators, respectively.
For both actuators, broad peaks which can be seen on AI output are removed by dewhitening filters.

Spectra of MN actuators are shown in Fig.11-16.
Dewhitening filter of horizontal and vertical actuators are one and two stages, respectively.
Broad peaks remain on the satellite box output even with dewhitening filters.