We tested a new scheme for IMC locking that is based on fast triggering on the IMC transmitted power. This allows discriminating against higher order modes, without lowering the feed-back gain. Our plan was to - acquire with the fast path (frequency feed-back) only - immediately engage the slow path (MC2 feed-back) once above the threshold - but avoid a large switching transient - and put some slow motion on the optic to make sure we see fringes. All that was achieved by - leaving the the slow path to MC2 on, but - have an additional 0.3Hz pole in the slow path. this puts some slow motion on MC2. - once triggered, this 0.3Hz pole is simply turned off, engaging the full feed-back without a transient. To implement this we had to make one minor change to the FILTBANK_TRIGGER.mdl library part: - our filter needed to be turned OFF on trigger (not the opposite) - we thus added an epics input named "_INVERT" (e.g. H1:LSC-MC_FM_TRIG_INVERT) to the library part - if "_INVERT" is 0 (the default), the behavior is unchanged from the previous model. - if "_INVERT" is ~0, the trigger fires if the input is below threshold. With this logic the IMC seems to grablock in less than 1 sec, reproducibly. The changes (both h1lsc and FILTBANK_TRIGGER.mdl were submitted to the svn (revision 5458).