The cylinder at 7:42 is a getter container. It's just a stub inside that contains a material activated by heat(hence why it's so discolored, it was induction heated) that absorbs the remaining gases from the reference side after pumpdown, which is evacuated to an ultrahigh vacuum through the cold weld pinchoff(which you may have popped by prying through the hole, they are exceptionally fragile) - typically as high as possible, but the pressure is still recorded and calibrated for. These gauges operate around RF frequencies, the diaphragm/dual capacitor set being part of the coupling circuit, or the resonant circuit(varies by manufacturer). There's not much to it, but the physical design does get tricky. That's why the matched diodes are there. The heating bands are most likely to keep the physical structure, membranes, and the diode/opamp package at a constant temperature, since material properties change with temp. That's why the RF part sits in a clean desiccant can. There's basically nothing to see inside the gauge - it's assembled through welding, so you won't find anything besides a set of three rings welded together with a membrane between the two and the endcap on the end. This is however an advantage - capacitance gauges are extremely robust, and are very nice to clean. Just fill the vacuum side with acetone, swirl it around, rinse with DI water, then dry with ethanol and bake to ~50C(or just place under a vacuum immediately and evaporate).
Great info! Thanks. To your point about the getter container- what is the mechanism for induction heating of the activated material? I didn't see any coils on the PCB that came off of it.
ua-cam.com/video/mmsBT3Fuggk/v-deo.html i think a lot of that is all about getting a clean reference so that you get that nice solid signal out. Here's a video by a self proclaimed volt-nut which you'll probably enjoy pretty well. Cheers!
Yes, I love Marco Reps' channel! I haven't watched that video, I'll have to give it a look. I agree with you, I think that's what all of the layers of shielding are about. The digital board is on top and the analog board is buried deeper in the onion.
The cylinder at 7:42 is a getter container. It's just a stub inside that contains a material activated by heat(hence why it's so discolored, it was induction heated) that absorbs the remaining gases from the reference side after pumpdown, which is evacuated to an ultrahigh vacuum through the cold weld pinchoff(which you may have popped by prying through the hole, they are exceptionally fragile) - typically as high as possible, but the pressure is still recorded and calibrated for.
These gauges operate around RF frequencies, the diaphragm/dual capacitor set being part of the coupling circuit, or the resonant circuit(varies by manufacturer). There's not much to it, but the physical design does get tricky. That's why the matched diodes are there.
The heating bands are most likely to keep the physical structure, membranes, and the diode/opamp package at a constant temperature, since material properties change with temp. That's why the RF part sits in a clean desiccant can.
There's basically nothing to see inside the gauge - it's assembled through welding, so you won't find anything besides a set of three rings welded together with a membrane between the two and the endcap on the end. This is however an advantage - capacitance gauges are extremely robust, and are very nice to clean. Just fill the vacuum side with acetone, swirl it around, rinse with DI water, then dry with ethanol and bake to ~50C(or just place under a vacuum immediately and evaporate).
Great info! Thanks.
To your point about the getter container- what is the mechanism for induction heating of the activated material? I didn't see any coils on the PCB that came off of it.
@@reedpetersen It's only heated once to activate it, during production.
Nice work
When will part2 be uploaded?
ua-cam.com/video/mmsBT3Fuggk/v-deo.html i think a lot of that is all about getting a clean reference so that you get that nice solid signal out. Here's a video by a self proclaimed volt-nut which you'll probably enjoy pretty well. Cheers!
Yes, I love Marco Reps' channel! I haven't watched that video, I'll have to give it a look. I agree with you, I think that's what all of the layers of shielding are about. The digital board is on top and the analog board is buried deeper in the onion.