This is a brief update on the recent calibration activity. It is still a working progress, but seemingly we are moving forward.

(Of course, I made a mistake)

• I had a wrong sign in the MICH open loop gain when undoing the MICH supression (see alog 16733).
  • => Fixing this mistake gave a ITM L2 stage response @13.05 Hz of 5.5x10^-18 m/cnts which is close to what the suspension model expects (5.8x10^-18m/cnts).

(Please discard the DIFF VCO-based calibration)

• With this bug fix in mind, the original ALS DIFF VCO-based calibration (alog 16701) have been underestimating the ESD response by a factor of 3.4 which was previously mistakenly thought as a factor of 5.3 (alog 16733).
  • Also, we now think that the DIFF VCO calibration coefficient we have is not trustable. So we will discard the DIFF VCO-based calibration hereafter unless we revisit the VCO calibration.

(New ETMX ESD calibration is stronger than the suspension model by a factor of 2-ish)

• Now, if we compare the measured ETMX response (alog 16733 with the mistake fixed) with the suspension model without linearization in the ESD, the measured response is stronger by a factor of 2.07.
  • This is the point which makes me think that something is still not right. We need to understand why there is such a large discrepancy.
  • Note that the suspension model uses the new updated alpha of 2x10^-10 N/V² (see for example G1500036-v1).
  • I am suspecting that the ESD linearization code in the digital system maybe a cause of the discrepancy. When I get a chance, I will study how the linearization function behaves in the actual system.

(ETMY was consistent with ETMX)

• I did the same measurement on ETMY in the Friday night (alog 16733), it gave me a very similar result to that of ETMX. The ETMY ESD response was only a few percent stronger than that of ETMX.
  • Note that the linearization was active on ETMY.