JeffK, JimW

I spent the afternoon trying to get feedforward working at ETMX, but I've had little luck so far. Currently, we are using a high blend on the St1, per Sebastiens posts  last week. This costs us at low frequency, so we wanted to see if we could gain some of that back by getting extra performance out of HEPI. We would like to try feed forward, versus ground to st1 sensor correction, because this lets us partially get around the Z-RZ T240 coupling the seismic has been dealing with for a while, by reducing the amount we are driving on St1.

When I looked at EX initially, the HEPI platform had none of the Hua sensor correction/feedforward filters installed, so I copied the IIR from the EX ISI foton, and the FIR from the EY HEPI .fir file. When I tried turning on the HEPI STS Z feedforward loop, with a gain of .1 the ISI vertical drives started ringing up. After a few calls to Fabrice, I realized that, per JeffK's alog 13560, the EX HEPI had never had it's STS cal filter adjusted for the T240 we are temporarily using. I fixed that, and Jeff helped check that the ISI, HEPI and PEM sensors were all seeing the same ground. We then looked at the coherence between the St1 T240s and the ground. Currently the St1 sensor correction is working at EX, which affects that measurement. The attached 1st picture shows the coherence between the STS Z and the St1 Z, the black dashed line is with St1 senscor running, the green is without. The high green coherence is encouraging, it means we can do a lot of good with FF if we can get it running.

We then tried turning on the HEPI FF with a gain of .1 again, with the St1 senscor turned off. Pretty much immediately we saw a bunch of higher frequency stuff in the BLRMS and in a rolling DTT plot, my second attachment. After a bit, while we were distracted by HAM2, EX tripped in spectacular fashion (last two pics, first is zoomed on when I think we pushed the button, second is of the trip), so we've given up for the moment. EY might be easier, with it's more nominal configuration, but the filters installed in foton down there are not the Hua standard filters, so I'm not sure what has been done there.  We also have a filter designed by RyanD that I can try, but that will require more foton copy/paste.