The error signal of PLL X suddenly changed around 18:50 UTC (3:50 JST) though other signals such as LO RF power or beat RF power from RFPD, and the input gain of servo did not change.
Did anyone modify the parameters?
This is a followup on report 17113.
Given the recent finding that the AA filter had been busted for the X PLL phase error (17188), the jump that Tanioka kun reported can be explained by a voltage jump in the AA unit and not by the phase error.
Looking back into the trend, the relevant channels stayed as normal while the X_BEAT_ERR channel showed the jump.
The channels I have checked are:
- ALS-X_BEAT_ERR_OUT (the busted readout channel)
- GRD-ALS_PLLX_STATE_N
- ALS-X_PLL_IN1GAIN
- ALS-X_PLL_OFS_COM_CALI_OUT
- ALS-X_PLL_IN2EN (to make sure that input 2 was disconnected)
- ALS-X_LASER_TEMP_BIAS_OUT
- ALS-X_PLL_SUM_MON_OUT (equivalent to BEAT_ERR_OUT but a factor of 100 worse in SNR )
The attached is a screenshot of the trend data generated by dataviewer for recording purpose.
