1 KAGRA vibration isolation meeting (5th of September 2012) 2 3 Attendees: Takahashi, Majorana, DeSalvo, Sekiguchi, Uchiyama, Yamamoto 4 5 Ryutaro and Takanori: Yesterday, they tuned the pre-isolator in Kashiwa. 6 The output of the LVDT, the sensor signals of the 3 degrees of 7 freedom (x,y,yaw), the efficiencies of the actuators were checked. 8 Then, the displacement of each degree of freedom is measured 9 when the DC force is applied by each actuator. Then, 10 they tried the diagonization and measured the transfer functions. 11 The diagonazation looks so good if the force along x-axis or for yaw rotation 12 (In this case, the phase and coherence also look perfect). 13 However, if the force is along y-axis, the diagonization is not so good. 14 Probably, it is due to the asymmetry of the Inverted Pendulum 15 or the insufficient parameter adjustment. 16 Riccardo said that the repeat of the diagonalization and gain equalization process 17 could improve the diagonization. 18 This was observed also in Virgo, two or three iterations were necessary. 19 Takanori said that the resonant peak separation is not so easy. Riccardo 20 proposed that 21 the mass on the stage is moved to change the resonant frequnecies. 22 Riccardo also gave another idea; we remove the load on the top 23 and try the diagonization without any load. 24 And we check what happens when we put load again. 25 (Riccardo's comment after the meeting: this should be tested 26 only if the multiple diagonalization and gain equalization 27 iterations fail) 28 29 Riccardo: Nick and he measured a new LED and found that it is better for 30 OSEM. 31 (Riccardo's comment after this meeting: It is actually an older LED, not a new one, 32 already in use for LIGO; I attach here 33 curves measured by Nick and I, that convinced us to switch from OP 224 back to the 34 older OP 232. you will note how the 232 has a better and more symmetric response 35 uniformity. Even the 232 will need a software linearization table to convert the 36 voltage readout into position readout, but with less dynamic range. Additionally 37 the OP 232 gives more light, which will turn into less noise. 38 Please note how the OSEMs are not so linear.) 39 40 So, they changed the design. Ten OSEM's will delivered on the 41 beginning of the next week. 42 (Riccardo's comment after this meeting: the design will be finished at the beginning of next week, 43 then production starts.) 44 Probably, the ciruit boards can be printed in 45 NAOJ. 46 So, the mechanical parts will be made at Lucca. But the circuit boards 47 will be made at NAOJ (Riccardo's comment after this meeting: 48 details of the circuits to be discussed during my stay in Japan). 49 Some pieces of the OSEM can be used for the cryogenic test. 50 The production of the pre-isolator has already been started. 51 (Riccardo's comment after this meeting: therefore I suggested to order 2 additional units 52 for cryogenic tests 53 I also suggested that we should also order a replacement rotational unit with AML 54 motors to replace the not functional unit with picomotors presently installed in the 55 pre-isolator prototype.) 56 57 Riccardo is concerned about the safty structure. However, the budget is a 58 problem. 59 Nothing is decided yet. 60 61 Riccardo is prepapring slides for the LV meeting and has already put them 62 on JGW doc. 63 He will give this talk on Monday. 64 http://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=1259 65 66 On the next week, Riccardo will stay in Rome for the LV meeting and dicuss 67 the 68 cryogenic payload with Ettore. 69 And he will attend the meeting of the Italian physical society. 70 Two weeks later, he is going to Amsterdam and works for the cryogenics 71 suspension and 72 seismic isolation ... 73 74 There will be the meeting of the Physical society of Japan on the next 75 Tuesday.
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