| [Shane, Cao]
With the new change in wiring configuration described in elog 136, we tried to power up the heaters for baking the vacuum chamber again.
Given that we were worried about the turbo pump overheats, we set the setpoints of of bother high temperature controller and PID controller to be 120 deg C before turning the heaters on
1. Evidence of smoke originating from CoolSkin insulation
We then removed most of the CoolSkin insulation on the Pump and RGA lines ( apart from the one around the flexible bypass line connecting the two ) (see image Pumpline_afterRemoveInsul and RGAline_afterRemoeInsul) .
Upon removal of the insulation, we noticed that the insulating foam melted onto the heating tape (see image MeltedInsulation1 and MeltedInsulation2). This is the first indication that the smoke had most likely coming from the insulating foam itself
Once we started baking, upon reaching 80 degree range. We observed no smoke at the location that we removed the insulation. However, We observed smoked coming from underneath the insulation around the flexible pipe, and not from the velcro areas.
What could be causing this, given that the maximum operating temperature of the insulation is 200 deg C? Most likely, the heating tape is much hotter than we think it is. But given that the temperature sensor readout is much lower than 200 deg C, it's likely that this is due to poor thermal contact and it takes a while for sensor to reach a thermal equilibrium with the heating tape. Here, I suggest we should implement the following:
- We should look into usingsome form of thermal tape (if possible to secure the temperature sensors)
- Unfortunately or controller does not allow programming process, we will have to implement manual temperature stepping, emulating ramping process over the first hour, until slowly reach 120 deg C
- OR Tune the PID controller coeffs, especially P and I for longer rise time and settling time
2. The heaters still trip our power
Upon reaching 80 deg C,our main power trip. Unfortunately I don't know how to reset this. Do we need to contact facility on this? Reading elog 136, I noticed that both controllers are connected to the same circuit LP3B 6, which is the same circuit the some of the fan-filters and LED light panels of the cleanroom connected to. From the elog, the circuit has a 20 A limit . An max operation, the 2 heater controllers draw 30 Amps, approx 7 Amps for the fan-filters, and another 1.5 A for LED panel. The combination of these equipment must have overload the circuit and tripped it . Currently half the fans + lights are off in the cleanroom are off due to power trip. Here, I would make a suggestion that each heater controller should be connected to a separate circuit . Currently we LP3B 7 (same side next to LB3B 6) and LB3B 4 (opposite side of the rail) having no equipemts connected to them, but will require cable extensions. |