This morning we received an alarm because the water level of the main chiller was low. By better looking at the signal we realized that since the 30/09, the water level started to oscillates with a period of about 1 minute (figure 1)
We went in chiller to refill it and see if it has some effects. It did not. (figure 2)
This oscillation can not be seen in the main INJ PSL signals. (figure 3)
The flow sensor that senses the water going out of the chiller do not see that oscillation, the temperature sensor instead sees it (figure 4). And what we see is that when the level is increasing, the temperature of the water in the tank is decreasing. This may indicates that the flow between the cooling system and the tank is oscillating.... But, the oscillation on the temperature sensor was already present before the level sensor started to oscillates... (figure 5) This is not clear, we will monitor the situation in the coming days.
For recall this chiller is cooling the SL electronics and head as well as beam dumps for PMC REFL, IPC 1, IMC REFL.
Today we took the spare OMI chiller that was in the Optics Lab to the Chiller Room in CEB. The idea was to swap the chillers but the spare didn't work as expected (the chiller couldn't reach the setpoint temperature) and we decided to leave the current chiller running as it was.
We performed two tests:
- We put the level sensor in another water container in order to investigate the oscillation observed since 30/09 (Fig. 1). During the test period (red zone in the figure), we can see that the oscillation is not present, so our conclusion is that probably the sensor is mechanically interfering with the temperature sensor inside the water container of the OMI chiller and creates this oscillation.
The oscillation on the level signal is correlated to the oscillation on the temperature signal (Fig. 2)
- The second test was to verify the pH of the water inside the OMI chiller. The background measurement was a pH and chloride test on ultra pure water just poured from the filtering system: pH 5.5, no chloride detected (Cl- < 0.1 ppm). The water that has been running inside the OMI chiller and into the utilities had a pH of 6.7 and Cl- < 0.1 ppm. This is a further proof of chemical reactions happening (corrosion, for example). It could explain the debris we find in untreated ultra pure water cooling systems.
