Following our discovery of the vacuum drift and temperature rise (Mini Update US) we decided to replicate these findings. Before we swept the vacuum range we would be operating in (1 to 14 mbar) there were a few things we wanted to take care of.
First, we noticed a pressure leak in the pressure tee of Cell B. Second, we wanted to test out the addition of thermal grease between the glass and copper bands of the exterior thermocouples on Cell B (also applied to Cell A if positive results on Cell B). Third, we wanted to employ Robert Ellefson's suggestion of using weather stripping to seal the bottom edges of the temperature control box.
Once these were taken care of, we turned on the cells and waited for an equilibrium. We then stepped down in pressure from 14 mbar to 0.38 mbar. Here are our results:
|Cell A||Cell B|
|Vac (mbar)||T_Ext1 Rise||Vac (mbar)||T_Ext1 Rise|
We can see that our temperature rise over ambient varied little within our range from 1 to 14 mbar. Also, there is no clear relationship between the temperature and a decreasing pressure in our range. However, if we go much below 1 mbar, we could have a problem.
For our operating range the standard deviation for Cell A is 0.23 C and for Cell B it is 0.17 C. The tightness of B compared to A is most likely the thermal grease present under Cell B's copper bands. So, we will apply thermal grease to Cell A as well.
Within our range of operating pressure(1 to 10 mbar), we can safely say that we won't see a pressure dependent temperature reading from our exterior thermocouples.
Our next steps in preparing the V 1.3 Cells for the V 2.0 protocols are to:
- Add thermal grease to Cell A underneath copper bands