I've been having a look at the CO2Y flow meter issue (aLOG 32230). If we look back at the flow rate through July of this year, we see several periods where the "flow" has dropped by up to 30% (see attached time series showing H1:TCS-ITMY_CO2_FLOWRATE). There is zero change in any of the corresponding temperature sensors (laser, manifold, beam dump - all of which are attached to things that are cooled by the water), neither do we see anything in the laser output power.

We know, from measurements at LLO, that we expect the temperature of the laser to change in response to a change in flow rate. For example, we saw a 0.4C decrease in temperature in the LLO laser in response to the flow rate increase of 0.6GPM. There is nothing remotely commensurate here at LHO when the "flow" drops from 3.1GPM to 2.6GPM in mid-July.

There is a single observed drop in temperature around July 18. However, close examination shows that this does not correspond to change in flow - the nearest change in flow rate is approximately 19 hours earlier.

This leads me to believe that the flow rate itself is unaffected and that the electronic interface to the flow meter (the CO2 laser interlock controller) is most likely the source of the problem.