menzel
778b508023
CI for csaxs_bec / test (push) Successful in 1m53s
The first point of every line is under-exposed. Four commissioning scans
put a number on it, against the 2e-3 head start that was in place:
scan exp_time first/near lost
324 15 ms 0.655 5.18 ms
254 20 ms 0.732 5.36 ms
411 50 ms 0.881 5.93 ms
450 50 ms 0.879 6.04 ms
A fixed time, not a fixed fraction: it varies by 17% across a 3.3x range
of exposure while the fraction varies by 2.9x. The same deficit appears
on the integrated scattering, a different detector behind a different
gate, so the cause is upstream of both readout chains rather than in
either of them. 2e-3 allowed and ~5.6e-3 still lost means the shutter
needs about 7.6 ms.
The trigger scheme was already right -- the shutter fires on cd at t0
and the acquisition on ab is held back by _shutter_to_open_delay, with
the widths, burst_period and cont_grid's acc_time and premove all
derived from it. Only the value was wrong, and it was a literal in two
places, so setting one and not the other would have been silently undone
by keep_shutter_open_during_scan.
Lifts it to DEFAULT_SHUTTER_TO_OPEN_DELAY next to the other defaults,
with the measurement recorded, and adds set_shutter_to_open_delay to
USER_ACCESS so the value can be converged from the client instead of by
redeploying the device server. It is bounded, because a delay is paid on
every line and a fat-fingered value would stretch the scan rather than
fail.
Cost at the new value is 5.6 ms per line -- 0.25 s over scan 450 -- and
0.8 um of extra premove.
The existing stage test asserted the 2e-3 literal and now asserts the
constant. New tests cover the default, the bound, the USER_ACCESS entry,
that a set value actually reaches the ab channel while cd still fires at
t0, and that keep_shutter_open_during_scan discards a tuned value, which
is a sharp edge worth pinning rather than leaving to be rediscovered.