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It depends a bit on the insulator on the ribbon cable. Most flexible plasti c cables depend a "plasticiser" in the plastic to stay flexible. If you pum p them for long enough, the plasticiser evaporates off (degrading your vacu um in the process) and the plastic insulation gets brittle.

PTFE (Teflon) insulation doesn't have this problem, nor does Kel-F.

For a half millimetre slot width he might have to go to flexible printed ci rcuit rather than a cable.

You can buy D-type connector vacuum feed-throughs. For high vacuum work the y can incorporate glass to metal seals. They weren't cheap in the late 1980 s.

Ribbon cable and vacuum seal.. Threre's the question of gas leaking along the cable. Good vacuum seals are mostly metal to epoxy/ insulator. plastic leaks.

George H.

What are theses negative numbers? torr is an absolute scale.

People tend to talk about pressures of 2x10^-7 torr, and that can get truncated to -7 by people who weren't influenced hard enough by their instructors early on.

Pirani gauges are essentially a hot filament in a bridge that gets a whole lot hotter in a good vacuum. No high voltages involved. They run coolish at atmospheric pressure and can stand a fair bit of abuse.

Typically they are used to determine when it is safe to switch the hard vacuum pumps and power to the more sensitive hard vacuum Penning gauge.

One other thing to be aware of in high vacuum stuff with high voltages is that every now and then a flashover can occur when an unfortunate emission of ions shorts out the bit at HT to ground. All bets are off when that happens - you tend to hear it go crack if near enough.

OK. That is a fair bit more in line with the gauge capability.

Worth talking to the manufacturer. I wouldn't expect having any flexible plastic in a hard vacuum enclosure to be a good idea. The plasticiser has a non-trivial vapour pressure and will coat everything internally.

Probably not. Especially not when you bake the enclosure.

Almost certainly. I thought from a quick scan that they offered a connector to allow the sensor to be connected to a feed through.

I'm not up to date with modern hard vacuum practice. But ISTR the only plastic we would ever use in hard vacuum was PEEK and even then we rejected some batches as too gassy.

Implicit prefix of "10^"

People tend to talk about hard vacuum as -N or even N (since the vacuum bit is already implied by the kit)

Its a bit like pH but with the log10 bit unstated.

Well, in a vacuum environment, sure. However, liquids have tensile strength (at least transiently, before cavitation occurs) so you can actually get negative absolute pressure in some instances.

Cheers

Phil Hobbs

the failures may be due to moisture inside plastic parts, boiling out.

snipped-for-privacy@yahoo.com wrote in news: snipped-for-privacy@googlegroups.com:

a half hour.

That should happen before any PCB sealant treatment or encapsulant application.