After a series of tests performed during yesterday maintenance (a swap between PSDi and PSDm DSP boards SCSI cables followed by a reset of the PSDi board), this afternoon we decided to replace the PSDi board (serial #41071) with a new one (serial #45271). Unfortunately, after the crate reboot required for the intervention, the board connected to F7 LVDTs (serial #43144) stopped to be reachable on the network and had to be replaced as well with a spare (serial #41038). The payload and F7 signals have been checked, the various control loops have been closed successfully and the configuration files of the relative TANGO servers have been updated. Even though the system is now working properly, this event highlights the risk involved in doing any kind of intervention involving reboots on the DSP crates.

Today the WE DSP code has been modified in order to perform the control of DIFFp in a different board. This change had obviously no impact on the communication problem related to PSDI board, but removed the problems of angular disturbance at CARM NULL. A few modification of the code have to be done in order to replicate all the functions currently performed by PSDI, but in principle a control code free from troubles can be implemented.

As shown in a previous entry, a strange event detected by the channel Sc_WE_MIR_Z (and the others generated by MIR_PSDI) is coincident with a loss of dark fringe alignment, mainly due to a rotation of WE in TY. As we can see in fig 1, the coincidence is not perfect: the aligment problem occurs a few secons erlier than the noise.

In fig 2 we can see that the channels generated by PSDI are not the only affected by the noise: Sc_WE_tyAA is a channel generated in the same board (ScWEPSDi), sent to the master board and then to the DAQ. It makes the same path of the channels form PSDI, but has no correlation with that device.

In fig 3 we have a zoom of a noisy event: both signals goes quickly towards zero. Considering that DSPs run at 40kHz and DAQ shows the signals at 10 kHz, this is compatible with the loss of one sample at 40 kHz.

Observing the same event when the ITF is not locked and MIR_Z is used in loop to damp the mirror, we can notice that the noise dose not enter the loop correction (fig 4, fig 5). This means that the same channel, sent to a different board (MIR coil driver), is not noisy. It looks like a problem of communication between PSDi board and master board.

Anyway, the problem is no more there since a couple of days: the debugging is a bit difficult.

The response of the two vertical accelerometers has been measured by a noise injection. For ACC_V2 it has not changed significantly from the latest measurement, while for ACC_V1 it is a factor of five lower. It would be possible to restore the vertical ID updating the calibration curve of ACC_V1, but maybe it would be better to investigate a bit the origin of the problem.

NE vertical control is not working well in Inertial Damping mode. Untill the problem will be investigated and fixed, it is necessary to stay in position control mode. This is compatible with locking operation.

After unplugging and re-connecting the primary and secondary coils LEMO cables of the affected LVDT, the sensor is now back to previous state with correct sign and phase. Previous controller gain has been restored. Further investigation will be done in future maintenance breaks.

Yesterday afternoon the lock of the north arm became unstable, due to the common oscillation of the payload pendulum mode at 415 mHz. This is a known problem of the arm lock, likely induced by the radiation pressure,  and stabilized by the use of local dampers of that mode, acting on both F7_TX.

Yesterday the NE_F7 damper stopped working, due to something happened on F7 vertical LVDT #3 (fig 1). Looking better at the signal, one can notice that its response to the vertical motion changed sign and amplitude (fig 2), as the modulation/demodulation phase was rotated by 180+-45 deg.

This morning the problem has been 'fixed' adjusting the gain of that sensor before the d.o.f.'s reconstruction. The origin of the problem has not been understood, which means that it could happen again.

With reference to the logbook entries n. 33973 and n. 33970, the repairing activity and test of the fishing rods installed on the mechanical filters of the WE suspension is concluded.

All the systems have been changed and tested to check their functionalities.

The full dynamic range (number of steps to go from a closed micro-switch to the other) of each fishing-rod has been re-verified and reported here below:

MV  F0  fishing-rod                                 about  8450 steps

MV  F1  fishing-rod                                 about  11200 steps

MV  F2  fishing-rod                                 about  10200 steps 

MV  F3  fishing-rod                                  about  10850 steps

MV  F4  fishing-rod                                 about  10560 steps

Following the scheduled working activity of the entry 33959 and concerning the problem detected on the fishing rod system installed on Filter0 of the WE Superattenuator, this morning all threaded shafts mounted on the stepping motor of all fishing roads have been changed together with their threaded bushing. 

A general check on the functionalities of all the fishing rod systems is needed before starting the usual protocol to close the tower vacuum vessel.

Note: A general check has been suggested just to prevent possible problems as reported in log-entry n.  33970.

Since it was found that the motor reaches a quite worrying temperature of about 60C, the follow up was the following:

- with the aim to reduce this working temperature, the proposal was to reduce the amplitude of the driving current  (the value set in the delivered cfg is of 2A), as also suggested by  our  Trento  colleagues (C.Salomon and M.Gennara, that realized teh motor driver);

- we checked the feasibility of this, by acting on the motor at BS  (#33601)  (meanwhile the installation  of  motor and the vertical hoist at WE in their final position was in progress);

- last week  the  motor was operated at WE (motor in its final position and nominal load) , performing long runs and measuring the temperature (only WE is equipped with a setup -temporary- to monitor the temperature);

It was performed a single run per day, each one of 500000 steps (~11 hours long), at different currents  (the current was set thanks to a SW command prepared by G.Ballardin), in detail:

- run #1,   driver HP,  I=1A   potentiometer value:  385-->659 ohms

- run #2,   driver HP,  I=0.5A   potentiometer value:  659-->385 ohms

- run #3,   driver LP,  I=1A   potentiometer value:  386-->659 ohms  (since this driver is set at a speed 4 times higher with respect the HP driver, the duration of the run was 4 times shorter);

- run #4,   driver HP,  I=2A   potentiometer value:  659-->385 ohms

In fig1 is reported the temperature behavior during these runs.

It appears that a current of 1A might be a safe and acceptable value.

Not clear why, with 1A, the T is lower using the LP driver, with respect to the HP driver.

Activity performed this week:

-          Installation of the in-vacuum cables along the filter chain, from F#4 bottom to the TopStage  (Gheradini, Sposito)

-          Installation of the in-vacuum cables from  to the TopStage down to the bottom ring, along the IP legs (Gheradini, Sposito)

-          Installation of the  protective metallic frame around the 2 CF250 flanges with the electrical feedthroughs (Gherardini, Sposito)

-          length selection and labeling of those air-side cables whose path is already confirmed.

-          Installation on the tower lower part of the CF150 flange with the electrical feedthroughs  (Gherardini)

The activity will be continued once some work on the IP (positioning,checking, blocking, etc) will be completed.

Remaining cabling tasks:

-          Connection of the in-vacuum cables to the feedtroughs;  at that point will be fully clear the path of the air-side cables and therefore their lenght and labeling can be finalized and these cable installed.

-          Unpacking of the cables special&fragile bundle between F#4 and F#7, and their connection to the F#4 and F#7 panel connectors

-          Installation of the in-vacuum cables (cables T and W)  in the tower lower part (once the ring of the F#7 monitoring system will be put and blocked in its final angular position)

-          Connection of the air-side cables to the distribution frames

-          Checks and  tuning

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After the fine tuning of the seismic filters for the WE Superattenuator performed a few weeks ago (see logbook entry n. 33490), the preparation activity of the suspension chain has been concluded today. All the filters have been put on the shelves of the Safety Structure and then connected each other to form the multi-stages pendulum chain.

The vertical hoist (“chioccilone”), previously tested with different driver boards, was installed on the Filter0 crossbar after a vacuum test (see logbook entry n. 33577 for details). The vacuum test of the metallic box, containing the stepping motor and the gear of the system, has been passed with a Leak Rate < 4E-7 mbar.l/s.

The integration of the Vertical Hoist (“chiocciolone”) on the Filter0 has been completed by fixing the vertical dynamic range of the suspension (mirror). This has been done through the positioning of the micro-switches connected to the stepping motor. The complete dynamic range has been fixed at about 65 mm, corresponding at 20 Ohm on the variable resistor when TOP Micro-Switch is closed and 735 Ohm on the variable resistor when BOTTOM Micro-Switch is closed. The mechanical contact has been positioned at half range corresponding at about 389 Ohm on the variable resistor.   

Finally, a complete set of NEW accelerometers (3 horizontal + 2 vertical) has been installed on the top stage in accordance with the geometrical distribution reported here below.

Horizontal Accelerometers:

O1N       in front of the IP leg at NORTH-WEST side

O2N       in front of the IP leg at EAST side

O3N       in front of the IP leg at SOUTH-WEST side

Vertical Accelerometers:

V1N       on Filter0 crossbar at NORTH side

V2N       on Filter0 crossbar at SOUTH side

In the last days, some test was performed on the motor of the WE F#0 vertical hoist ("chioccolone"), with the aim to measure the motor heating under running conditions.

Motor and mounting described in elog #33290.

This motor is quite particular with respect to the other ones installed on each SA, because it has to move  a large load (about 1 ton) and because the duration of the movement can last up to tens of hours.

Therefore, it is important to check the thermal behaviour of the motor when running with the usage of the new motor driver. 

To perform this measurement:

-  a temperature sensor (a 3-wire PT100)  was attached on the motor body;

- the chiocciolone was installed in its final position inside the Filter #0

- the Filter #0 was loaded with a dummy load equivalent to the nominal weight (around 1 ton).

In the first  run  the old motor driver was used, performing 600000 steps (400 steps to perform one  motor revolution, speed equals to 1 rev every 16 seconds);

In the second  run  the new motor driver was used, performing 900000 steps (200 steps to perform one  motor revolution, speed equals to 1 rev every 16 seconds,  current set at 2A/phase via SW by G.Ballardin),

The attached  fig show the comparison between the temperature behaviour during the two runs:

- the 1st plot is the T sensor on the motor body, the 2nd plot is a T sensor on one end of the crossbar (ie about 0.5m far from the motor),

-black curves denote the 1st run, purple curves denote the 2nd run (the noise on the purple curve, 1st plot is due to an elecrtical  contact problem)

A few considerations:

- with the new driver, the steady state temperature is 65C, instead with the old one is not higher than 40C.  --> ie the heating produced by the new driver is at least twice the old one.

- the test was performed in air, so once under real conditions (ie in vacuum), the T increase is expected to be higher.

Further investigation will follow.

In the past weeks different activities have been performed around the mechanical seismic filters of the WE suspension. The filters have been assembled at the Pisa INFN laboratory fixing the magnetic anti-spring in a preliminary position. The fine tuning (vertical mode) of all filters has been done in accordance with the parameters here below:

Filter4 tuned with load L= 4240 N + Crossbar Damper + Accelerometer; fv = 320 mHz (March 11, 2016)

Filter3 tuned with load L= 5247 N + Crossbar Damper + Accelerometer; fv = 375 mHz (March 11, 2016)

Filter2 tuned with load L= 6695 N + Crossbar Damper + Accelerometer; fv = 320 mHz (March 17, 2016)

Filter1 tuned with load L= 7908 N + Crossbar Damper + Accelerometer; fv = 320 mHz (March 17, 2016)

Filter0 tuned with load L= 9615 N including Vertical Hoist, 2 Vertical Accelerometers and Ballast (14 kg); fv = 190 mHz (March 31, 2016).

The piezoelectric actuators have been mounted within the feet of the IP legs in accordance with the table here reported.

Bottom Ring IP:

PZT_1    under IP leg at NORTH side                         (PZT n. 216k033, s.n. 113010495)

PZT_2    under IP leg at EAST side                             (PZT n. 216k033, s.n. 113010500)

PZT_3    under IP leg at SOUTH side                         (PZT n. 216k033, s.n. 113010493)

• The disk with the laser diode was mounted on the SNEB flange, with the position of the departing beam adjusted to y = -1.6 mm (towards west), z = -2.4 mm (down) with respect to the center of the disk.
  
• This beam was aligned to a point on the NE flange at coordinates y = +2.7 mm (towards east), z = +4.0 mm (up) with respect to the center of the disk.
  
• After removing the screen on the NE flange, the beam was reflected off the NE mirror back towards the SNEB flange. The NE mirror should be in its nominal position when the reflected spot falls 20.15 mm below its departing point, so at y = -1.6 mm (towards west), z = -22.55 mm (down).

• Initially, the reflected spot was off by about 20 cm towards west, see fig 1. This corresponds to a mis-alignment of a bit more than 10 mrad in ty, which is similar to what was seen for previous payloads. This has already been corrected by making adjustments to the payload.
  
• Increasing the laser power a bit, two additional ghost beams can be seen above and below the main reflection. The lower one is a bit brighter, this is probably the direct reflection of the AR coating, while the weaker upper one is likely a triple reflection (HR-AR-HR), see fig 2. The fact that the stronger one is below suggests that the wedge has it thinnest part pointing down. The spots are separated by about 22 mm, which is consistent with the wedge of the mirror substrate of 1070 urad. The reflections from the AR coating are not perfectly above and below the main reflection of the HR coating, suggesting that the wedge might be rotated by about 7 degrees around tz. Note that these measurements were not very accurate, since the payload was still uncontrolled at the moment the picture was taken.
  
• Two overlapping spots can be seen about 75 cm to the east of the SNEB flange, see fig 1 and 3. These are not moving with the mirror, so they should be the reflections of the viewport. This is consistent with an intended tilt of about 4 degrees and no wedge.