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takafumi.ushiba - 16:33 Tuesday 19 October 2021 (18620) Print this report
Health check of GAS filter of ITMX

[Ikeda, Ushiba, R.Takahashi (remote)]

I checked the GAS filter behaviours for health check.
F2 seems to have strange behaviour when its position is close to higher mechanical limit (above -600um at VIS-ITMX_F2_LVDTINF_GAS_OUT).
Also BF actuators seems to be too weak, so we need to investigate.

To check the health of GAS filters of ITMX, I added offset signals to each GAS.
Added offset is from -30000cnts to 30000cnts, and F0, F1,F2, and BF seems to move smoothly (see fig1, 2, 3, and 4).
As a result, actuator ranges of F0, F1, F3, and BF are about +/-200um, 150um, 120um, and 8.5um.
After checking the actuator ranges, I chatted Takahashi-san and we concluded that BF actuator range of +/-8.5um seems too small.
So, we compared the mechanical transfer function of ITMX BF GAS with ITMY's (see fig5), and 3 times DC gain difference was observed.
So, we need to investigate the reason.

Also, F2 GAS doesn't move smoothly when GAS position moves from -about 900um to -100um as shown in fig6.
So, I checked the smoothness at oher GAS position (-1300um to -800um).
At this region, F2 GAS seems to move smoothly, so we need to avoid above -600um.
This situation reduces the movable range of F2 GAS about 0.8mm.

During the work, I and Ikeda-san moves fishing rod for GAS filters and checked the polarity and efficiency.
F0: +step -> keyston position up, +12800step = +60um at VIS-ITMX_F0_LVDTINF_GAS_OUT
F0: +step -> keyston position up, +12800step = +50um at VIS-ITMX_F1_LVDTINF_GAS_OUT
F0: +step -> keyston position up, +12800step = +90um at VIS-ITMX_F2_LVDTINF_GAS_OUT
F0: +step -> keyston position up, +12800step = +80um at VIS-ITMX_F3_LVDTINF_GAS_OUT
F0: +step -> keyston position down, +12800step = -20um at VIS-ITMX_BF_LVDTINF_GAS_OUT

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