I've been trying for a while to get feedforward running on HAM's 4&5, but not having much luck. Originally, I just tried copying the filter we are using on the BSC's, only because it was there, and the test was quick and easy. And not the right answer, as (kind of) expected. In order to design a proper filter, I've taken measurements as outlined in Brian Lantz's SEI log 682. Two measurments are needed, 1. a driven tf from the FF path to the ISI GS-13's and 2. a passive tf between the St0 (or HEPI) L4C's and the St1 GS-13's. First attachment is the driven tf for Y on HAM4, second picture is of 2 passive tf's between the ISI GS-13s and St0 L4C's (in blue) and between the ISI GS-13s and the HPI L4C's (in red). The filter should be a fit of the ratio between the passive tf and the driven tf (so green / blue (OR red), depending on the path you choose). Third attachment is plot of these ratios, blue is St0 FF, red is for HPI FF. I've tried a number of filters and so far the best I've gotten is a small improvement between 20 and 25 hz, and at best, no worse any where else. Fourth attachments is of my fits to the St0 feedforward. I've tried closer fits and they didn't work either.
Just to make sure I wasn't totally missing something I tried doing the same for the BSC's and was at least able to get something that worked (fifth plot is the performance, last plot is the design). A work in progress.
There was an error on the phase part of the last plot, I grabbed the wrong data. That's fixed now.
It came up in the seismic call that there may be a sign error in either HEPI or the St0 L4C's. I think that's probably the case. I looked at the transfer function between HEPI and HAM4's St0 L4C's to the HAM5 STS. HAM4's St0 L4C's are 180 degrees out of phase from HEPI's. I checked T1000388, our design document, and it looks like our installed cartesian matrices are "right", but according to my measurements, they ain't right. This probably doesn't explain my difficulties with feedforward(maybe?), but it came up. First 2 images are are the Y direction tf from the HAM4 sensors (HEPI (red) and ISI(blue)) to the STS. X and Z were the same. I will need to repeat this sometime when I can put the ISI into a damped state so I can get the ISI's GS-13's for comparison.
The next 2 images are of the passive measurement from the previous post, but a longer, finer measurement with the phase this time. Same color scheme, red is the GS13/HEPI measurment, blue is GS13/St0 measurement.
