This afternoon at 15:50 UTC we received an alert because the temperature of the neovan head was increasing.
We went there and found that, as saturday night, the chiller had a failure. Since the situation was not critical yet, we took time to analyze what was happening.
The water was still flowing into the tube (as it can be also seen on the flow monitor) but was not cooled down anymore. The failure seems to come from the electronics control of the chiller.
We switched it on and off and it came back to a normal situation (see plot 1).
We took advantage of being there and having the interferometer in troubleshooting to bring the power at the input of the interferometer back to 26 W. The power was indeed slowly increasing since the intervention of Friday. It comes from the PMC that, for once, is getting a better transmission (see plot 2).
Yesterday, we also noticed a leak of water. We took advantage of the maintenance this morning to had a better look at it.
It seems that it comes from an excess of pressure in the outgoing pipe of the chiller that makes the pump leaking.
There is indeed a huge difference of pressure between the outgoing and incoming pipe. This pressure difference suggests that the water is somehow not flowing well into the neovan head.
In any case, because of this, and the failures that we noticed these last days we decided to swap this chiller with a similar one that we had in optics lab and had never shown any failures up to now (see picture 1).
We did the swap without switching off the amplifier. It went well, and the temperature is again stabilized around 23 degrees (see picture 2).
The pressure of the water outing the chiller was 2.2Bar, coming back was almost 0Bar.
Unfortunately, in order to speed up the replacement without switching off the neoVAN, it was not possible to move manometers on the new chillers.
- the water flux is essentially the same. Fig1 shows the flow signal around the time of the swap ( ~10 UTC ), the flow passed from 4.8*60/80=3.60L/min to 3.67L/min)
- the temperature glitches are no more present (Fig2)
