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takafumi.ushiba - 19:51 Friday 01 October 2021 (18421) Print this report
Strange behaviour of ACCBLEND_ACC{L,T,Y}_OUT of ITMX after the work of LVDT driver exchange.

[YamaT, Ushiba]

We found the strange behaviour (drift) of ITMX_IP_ACCBLEND_ACC{L,T,Y}_OUT, geophone signals, today.
As it can be seen in fig1, the drift started two days ago, which is the date of LVDT driver exchange (klog18398).

After we found the problem, we checked the spectra of each geophone but no significant difference can be found (fig2).
So, we once clear the histroy of filter banks and see what happens during the weekend.

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takahiro.yamamoto - 21:04 Friday 01 October 2021 (18423) Print this report
I attached the plot of all related signals between ADC to ACCBLEND as Fig.1

From the left column are
ACCINF_IN1 (ADC counts in sensor basis),
ACCINF_OUT (calibrated as velocity in sensor basis),
ACCBLEND_IN1 (calibrated as velocity in Euler basis),
and ACCBLEND_OUT (calibrated as displacement in Euler basis).

Around t=-2.3d is the timing when the LVDT driver work reported in klog#18398.
Though filters at ACCINF contains DC cut, slow drift can be seen around t=-2.3d.

Filters applied on ACCINF are shown in Fig.2
Measured transfer function from ACCINF_IN1 to ACCINF_OUT shown in Fig.3 seem to be consistent with Fig.2
Reference plots shows TF before the LVDT driver work (around t=-4d in Fig.1)
So implemented filters seem to work well and there is no change before and after the LVDT driver work.

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takafumi.ushiba - 11:49 Saturday 02 October 2021 (18425) Print this report

After clearing the histroy of filter banks, signals seem to be fine.
I'm not sure the reason but one possibility is that large signals once injected the digital system during the LVDT driver replacement  and triggered the calculation errors inside the digital system.

Anyway, we can now use the geophone signals.

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