KAGRA Logbook

VIS (EX)

takafumi.ushiba - 18:28 Tuesday 13 July 2021 (17496)

ETMX IM photosensor trouble shooting

[mTakahashi, Ushiba]

Since DC output of IMV1 photosensor is very small compaired to the others, we started to investigate.
First, I measured the spectra of all EX photosensors, checked the spectra
Attached figure shows the result in this morning and I found that IMV2 and IMV3 has some strange behaviour (though the first motivation is checking IMV1...).

Then, I checked DC current from satelite box to LED by connecting 1 ohm standard resistance.
Current for IMH3, IMV1, IMV2, and IMV3 photosensors are about 30mA and all channels have the same values.

Then, I checked the forward voltage of LEDs and PDs but no significant difference is observed.

Next time, we tried to measure the circuit noise to confirm that the circuit itself is healthy.

Images attached to this report

17496_1626153953_Screenshot from 2021-07-13 14-20-21.png

Comments to this report:

kouseki.miyo - 10:00 Thursday 15 July 2021 (17533)

As you can see in the attached image, the LVDT signal of the ETMX IP changed significantly, and we found that we could not request ETMX to the ISOLATED state. we found out that the timing of the IP shift was around noon on the 13th, but the workers, Ushiba and Tomaru, did not know what caused the shift. Ushiba and Tomaru said that they released Payload. I don't know what caused the IP shift. At any rate, it was decided to have them check again this afternoon to see if it had been released.

Images attached to this comment

17533_1626310821_Screenshot from 2021-07-15 09-54-55.png

takafumi.ushiba - 19:22 Thursday 15 July 2021 (17543)

[mTakahashi, Ushiba]

Abstract:
We measured the spectrum of several configuration to confirm where is the noise source.
We haven't yet obtained the conclete results, so further investigation is necessary.

Details:
We measured the spectra with several configurations and found the strange 4kHz peaks.
This peak can be seen even when coil driver is turned OFF, which means satellite box is also turned OFF because the power is supplied from coil driver.
Also, this peak doesn't disappear when corresponding photosensor cable is disconnected.
The peak will disappear only when we disconnect all photosensor cables from the satellite box.

Images attached to this comment