[Kamiizumi, Tomura, YamaT]
 

Abstract

We checked current situations of ADC glitches on K1LSC0, K1PR2, K1PR3, K1PRM, and K1BS.
ADC glitches are absence on CH8 and CH24 of ADC1 on K1LSC0 which are assigned for GrPDH signals.
So a cause of glitches on GrPDH doesn't seem to be ADC glitches.
 

Details

In order to check presence or absence of ADC glitches, we measured spectra of 65kHz TestPoints of each ADC channel with unplugging DB9 cables at the inputs of AA chassis.

Spectra of all channels on K1LSC are shown in Fig.1~Fig.8.
Note that 1Hz peak and its harmonics on 31CH of ADC0 is coming from the timing signal. So it's no problem.

Floor noise is slightly worse than the nominal ADC noise level (~3e-3ct/rHz) which was measured in circuit room when only AA and AI are installed.
We doubt ADC glitches as a cause of glitches on GrPDH signals but glitches cannot be seen on CH8 and CH24 of ADC1 which are assigned for ALS-{X,Y}_PDH_MIXER_DAQ.
On some channels e.g. CH20 of ADC1, ADC glitches are presence. Fortunately(?), these channels are unused now.

It's not related to glitches, but we can see strange peak its harmonics.
Their frequency is 65Hz, 130Hz, ... So they doesn't seem to be a power line noise.


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We also measured ADC noise on K1PR2 (Fig.9~Fig.12), K1PR3 (Fig.13~Fig.16), K1PRM (Fig.17~Fig.20), and K1BS (Fig.21~Fig.24).
All measurement data is stored in /users/DGS/measurements/ADC/`hostname`/*.xml
Channel list on which noise excess is presence is as follows.
- CH8 on PR2 (PR2_IM_OSEMINF_H2)
- CH19 on PR2 (blank)
- CH8 on PR3 (PR3_IM_OSEMINF_H2)
- CH17 on PR3 (PR3_BF_LVDTINF_V2)
- CH3 on PRM (PRM_TM_OPLEV_SEG3)
- CH15 on PRM (blank)
- CH20 on PRM (PRM_BF_LVDTINF_H1)
- CH21 on PRM (PRM_BF_LVDTINF_H2)
- CH24 on PRM (PRM_TM_OPLEV_TILT_SEG1)
- CH2 on BS (BS_TM_OPLEV_LEN_SEG2)
- CH29 on BS (blank)
I haven't checked that how much larger the signal level in nominal situation e.g. ALIGNED is compared to the ADC noise level yet.