J. Oberling, J. Bartlett, P. King (via phone)
Following yesterday's initial investigation into the PSl diode chiller issues (see alogs here), we swapped the control panel for the diode chiller with the one from the chiller we recently removed from service (this is a known working unit, just installed last year). After installation the chiller restarted without issue and ran for several minutes, also without issue. The serial number of the control panel we installed in the diode chiller is 44806P605; the faulty unit we removed from the diode chiller had no SN on it.
We then took the time to restart the PSL Beckhoff PC to unstick the frozen diode chiller channels. According to Dave Barker these channels froze sometime on Saturday morning. Fortunately the PSL interlocks are not tied to these channels, otherwise we would not have the PSL shutting down when the diode chiller shuts down (as we did yesterday). Once restarted the channels appeared to be reading OK. It is possible that these channels freezing for no reason can be used as an early warning sign of imminent chiller failure. The chiller communicates with the PSL Beckhoff PC via a serial RS-232 interface and we have seen channels freeze when the cables are unplugged and plugged back in but the PC not restarted (which is expected behavior as RS-232 is not hot swappable), but this is the first time I've seen the chiller spontaneously loose communication with the PSL Beckhoff PC. Jeff Bartlett is setting up a temporary Strip Tool on the PSL monitor in the control room that will monitor these channels. If anyone sees that these are flatlined (there should always be some variation), please let someone on the PSL team (Peter King, Jeff Bartlett, Ed Merilh, Rick Savage, or myself) know immediately. Thank you.
We then turned on the HPO, which came up with no problems. We let it sit and run for a little while, then restarted the rest of the PSL. As of now, everything is up an running. We are going to continue to monitor over the next couple days to ensure that everything is working correctly. The removed control panel will go back to Termotek with the chiller we are sending back and will be replaced as part of the service being done on that chiller.
Completely forgot to mention that after performing the above front panel swap and restarting the laser, we adjusted the calibration of the vortex flow sensors in both chillers. Using the chiller we just recently removed from service, we hooked it up to an external flow meter and compared the 2 readings (1 from the chiller's internal flow meter and 1 from our external flow meter) and calculated a new pulses/liter calibration for the vortex flow sensors. According to that measurement the vortex flow sensors should be set to 494 pulses/liter (they were originally set to ~970 pulses/liter, a number we got from LZH). The flow information from both chillers is now accurate.