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CAL (XPcal)
dan.chen - 16:07 Tuesday 02 June 2026 (37003) Print this report
Check of QPD readout circuit for Pcal-X

With Jiahui Xiong

Today, we checked the circuit and cabling for the QPD readout at Pcal-X.

First, we checked the circuit diagram: DocDB 9608 . From the diagram, this circuit seems to provide the 15 V power supply to the PDQ80A and to convert the QPD signals, X, Y, and Sum, from single-ended signals to differential signals.

Then we checked the setup at the Pcal-X area, and found the cable connecting the PDQ80A and the D-sub 9-pin connector.
We also tried to check the actual circuit, but it was difficult to remove the cables, so we could not directly inspect the inside of the circuit box.

However, after connecting the PDQ80A, we could confirm that the QPD signals were visible in the Pcal real-time model. Therefore, the basic signal readout seems to be working.

Although the alignment was not available today, we fixed one PDQ80A behind the mirror inside the Rx module as a temporary setup.

If possible, we would like to align the ETMX suspension tomorrow morning and adjust the position of QPDs.

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dan.chen - 6:18 Wednesday 03 June 2026 (37011) Print this report

Quick checks on the QPD signals at Pcal-X Rx module.

I checked the signals from a QPD that had been temporarily placed in the Pcal-X Rx module yesterday.
At that time, the Pcal beam had not yet reached the Rx module, so the QPD had not been properly aligned.

I requested ETMX to go to the LOCK_ACQUISITION state and switched Pcal-X to high-power mode.
A clear signal was observed in the QPD sum channel (Fig. 1).

I also moved the setpoints of ETMX TM pitch and yaw.
Although small responses were seen in the QPD X and Y signals, no clear position response was observed (Fig. 2).

After the above checks, the ETMX TM pitch and yaw setpoints were returned to their original values.

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