| [Cao]
After leaving the the chamber to bake at 120 deg C from Thursday 3:41 pm. Today I started to cool the chamber down to room temperature at 11:30 am (total bake duration: 91 hours 49 minutes). Ideally, this process should be ramped down slowly, approx. 6 degree per hour. However we had no ramping function with out controller. The only method to tune this cool/ heat rate is to tune the PID parameters, which are:
- Pb : Proportional band, this quantity is inversely proportional to the P-gain
- ti : Integral time. Increasing integral time makes the output response slower to error, thus the opposite effect of increasing integration gain
- td : Differential time
Since the differential term doesn't contribute to rise time significantly, we neglect it for now and first change Pb and ti . The factory default settings :
- Pb : 50
- ti : 100 s
- td : 25 s
Initially Ichanged Pb from 50 to 200 (max) and ti to 999 s (max) but there is a large offset error. Currently, Pb and ti are sitting on the following settings:
- Pb : 200
- ti : 800 s
At this setting it takes 25-30 mins to drop 6 degrees, which is not as slow as we want but we will have to tune our PID more carefully.
At the first stage, I dropped the temperature to 60 deg C. After 3 hours, we dropped the setpoint to 25 degrees and let the vacuum chamber to cool to room temperature. |