Sept 21:
We pulled a hard vacuum with a turbomolecular pump to test for tightness. The cell pumped down after tightening down the nuts to squeeze the glass against the o-ring a little more.
We heated it under a vacuum to almost 200C in the center. Then we noticed a small amount of condensation on the inside of the glass. Our best guess is that is a silicone of some type coming out of the mica and condensing on the relatively cooler glass (80C). We are undecided if we should try to bake it out or assume it won't be a problem at higher pressures. The mica is rated to 700C.
Here is a picture of the vacuum gauge showing where the off gassing was holding the pressure at. We can usually achieve 10^-7 torr readily with this vacuum pump.
Sept 24:
We have some prelimary calibration done using Helium, which has a thermal conductivity much closer to Hydrogen than Argon does. So far we have only been up to 90Cand 40 psi.
The resistance of the two filaments are just a little different, so, the same voltage delivers different power when switched between them.
The cell was very tight under vacuum, but seems to show a slow leak at pressure. We will continue to investigate that.
We are also trying to figure out why the GFCI protector on the outlet keeps tripping every once in a while.
Meanwhile we are working on the software display to make it more usable and useful. It archives the data fine, but the real time display needs improvements in the graphing.
Sept 25:
We have found some internal temperature variation at the measurements points depending on which wire was heated. We have re-wound the second apparatus to be alternating wires (red/blue/red/blue) That copy is currently waiting for some plumbing fittings. We have had to order some different pressure sensors because of the way we are powering it and to make it easier for other people to put their data collection systems on it. The new pressure sensors will output 0 to 5 volts, instead of millivolts.
I ordered up the gas supply bottles of Argon and Hydrogen and regulators.
The initial calibration in helium is going on. We are up to 40 watts and about 160C. I would like to run it up to 300 C or so, depending on where the flange temperatures get to. With the silicone o-rings, I do not want to get too hot. After we get done with this initial test we will re-wrap the wires on the first apparatus to be alternating and terminate at each end of the apparatus instead of wrapping back, again.