This morning at 6:42 UTC I have disabled the power supply of the Right Down DAQ box in SDB2. This is the DAQ box with the least power consumption, but it is still 50W, a bit more than the 30W we wanted to check the suspension response to a change in dissipated power on SDB2. We will keep this DAQ box off for 1 or 2 days to see the thermal transient in the suspension.
of SDB2_F0_V (act3) reached again -4 V so I will repeat the procedure: modify the fishing rod of filter-1 to compensate for the lower temperature of the GAS filter. I will include trend plots later
-4.1 V (code yellow) to -0.9 V, but the thermal transient is still in operation. The GAS springs of filter-1 are still getting stiffer, the keystone in filter1 moves up and in filter-0 down.
The trend plots of the actuator voltage, the vertical positions of filter-0, lvdt-filter-1 and the bench, and a PD temperature are included. I switched the stepper motor power off again at 16:46.
Yesterday, at around 18:00 UTC +/-2 hours the temperature in the detection lab started dropping by almost 1 degree as visible on the thermometer on EDB. So the transient in the SDB2 suspension due to change in thermal load on the SDB2 bench cannot be studied further. I have switched back on the DAQbox in SDB2 this morning around 8:10 UTC.
Figure 2 shows a summary of the temperatures over the past few days, and the voltage on the vertical actuator of the SDB2 suspension (act3), with two adjustments of the stepper motors clearly visible. Before the external temperature change in total the voltage increased by 3+2 = 5 volts, and it was getting close to finding a new steady state. So probably the step of 52W in power consumption on SDB2 correspond to 6V on the actuators, so moving from saturation at -3V to +3V.
For the ~30W dumped on SDB2 during the CARM offset reduction during O4 lock acqusition commissiong this should not be a problem, as this should last a week or two, during which daily adjustments of the SDB2 mSAS stepper motors might be needed. But after the CARM offset reduction is commissioned the 30W power dump on SDB2 will last only a a few minutes, and won't have a large impact, as the time scale of the thermal response is ~1 day.
For the ~40W dumped on SIB2 when PR is misaligned, it will be a larger issue once SIB2 is suspended in vacuum. The power will be dumped when PR misaligned, but there will be no power dumped on the bench when the interferometer is locked. This means that the SIB2 suspension will need to be adjusted whenever the ITF is unlocked for more than 1 day, or whenever the ITF is locked for more than 1 day after being unlocked for more than 1 day. It might be cumbersome for operations. This could be reduced if the power reflected by the ITF is also dumped on SIB2 when the ITF is locked, instead of a beam dump in air outside SIB2. That beam dump in air is expect to receive 10W when the ITF is locked. So having these 10W dumped on SIB2 would reduce the power variation by 25%, from 40W to 30W. And as a bonus it could reduce acoustic coupling through scattered light of the beam dump that is presently in air attached to SIB2.
In retrospect this was thus not necessary, since the GAS blades will heat up in the course of the next two days. The steep change in the actuator voltage from UTC 8:15 till UTC 9:10 is due to actions with the motor. trend plots included.
