Limit switches and reed switches for use in vacuum - Page 1
Forum section: electronics / projects

author: GasperSB
author_rank: Newbie
timestamp: January 16, 2020, 04:07:05 pm
content: Hello everyone!I'm designing a test setup based on requirements from our physics department. The major part of the test setup is a linear rail with a slide. In order to safely perform required tests I need to add a limit switch at each end of the rail. Tests are going to be performed inside a vacuum chamber.I'm interested if anyone here knows any suppliers or manufacturers that provide limit or reed switches for vacuum environment. Preferably in small form factor.Best regards,GasperEDIT: Vacuum level: ~ 10^-7 Pa (10^-9 Torr)

author: Kleinstein
author_rank: Super Contributor
timestamp: January 16, 2020, 04:27:14 pm
content: The glass encapsulated reed contacts should be no problem with vacuum. For other type is depends on the vacuum grade - down to some mPa should be OK with most types, better vacuum could be tricky, especially if a bake out is used.Beside reed switches hall sensors could be an option too, as they can be smaller. It just need the power part outside.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 16, 2020, 04:35:00 pm
content: If the vacuum chamber is just a glass bell, or of it has a visiting window, maybe an optical switch can be put in place, where both the emitter and the receiver of the light ray(s) can stay outside.

author: richard.cs
author_rank: Super Contributor
timestamp: January 16, 2020, 05:16:02 pm
content: Is the vacuum sufficiently good that you need to worry about out-gassing from components? Operating in vacuum is quite different from not messing up an experiment that requires a very high vacuum.

author: grifftech
author_rank: Frequent Contributor
timestamp: January 16, 2020, 06:10:25 pm
content: to simplify: how strong is the suck

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 16, 2020, 08:03:06 pm
content: https://shop.allectra.com/products/363-SWITCH-2They do a UHV and bakeout rated switch. Pricey though.Other option is peek block with spring plungers crimped on.As others say, depend on levels.

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 16, 2020, 08:04:38 pm
content: Would it be an option to use a mechanical feedthrough? Brings switches out of vacuum.

author: GasperSB
author_rank: Newbie
timestamp: January 16, 2020, 08:07:44 pm
content: Science experiments will be done in a high vacuum, close to ultra-high vacuum. ~ 10^-7 Pa (10^-9 Torr). So, yes I need to consider outgassing.

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 16, 2020, 08:10:40 pm
content: And bake out to hit those in any reasonable time. Just be aware of your material selection (PEEK, PTFE, ceramics and many common metals).Do you have UHV design experience?

author: GasperSB
author_rank: Newbie
timestamp: January 16, 2020, 08:25:00 pm
content: Unfortunately, there is no space for a mechanical feedthrough.Not much, pretty new on the job... Though, I knew I need to be careful with material selection. The vacuum chamber design is on the mechanical department, they just asked me to help them select limit switches and electrical feedthroughs.Thought to ask on this forum to see if anybody has a goto manufacturer for vacuum compatible electrical components.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 16, 2020, 08:37:32 pm
content: If you are on a very tight budget, auto spark-plugs can be used as electrical feed-through.

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 16, 2020, 08:46:02 pm
content: Allectra & hositrad for the UK and europe. but pretty much that switch I linked was all I found when I was looking for my application. Most vac specialists sell the same one.Couple of gold plated spring terminals is cheaper option. Take care with handling, gloves are a must to keep clean.Not tried reed switches, but glass with compatible leads should be fine. Crimp or screw, don't solder.Sorted the feedthroughs already?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 16, 2020, 08:54:35 pm
content: If you're thinking reed switches, then you're thinking magnetics.Which opens up the road to HALL sensors.If you want them small, they can be bought in SOT23 packages.

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 16, 2020, 09:02:05 pm
content: Be wary of any conventional chips. PCBs become a huge issue with solder, silicone, out gassing... EtcYou can get hal effect transducers for UHV, but they are crazy expensive and need external drivers.

author: GasperSB
author_rank: Newbie
timestamp: January 16, 2020, 09:33:45 pm
content: No, I haven't selected feedthroughs yet. I first want to define all electrical components and then based on that decide what is needed and what is the most suitable.Yeah, I thought about reed switches because some already have a vacuum inside the glass tube, therefore, the leads could already be vacuum compatible.We have a moderate budget for this project. But I would definitely like to stay away from super expensive components.

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 16, 2020, 09:59:23 pm
content: Are stray magnetic fields an issue? Is this electron / ion beam based experiment?

author: TimFox
author_rank: Super Contributor
timestamp: January 16, 2020, 10:17:31 pm
content: Also, for 10-9Torr, you will need bakeout. The solid-state Hall effect switch and permanent magnets may limit the bake out temperature.

author: GasperSB
author_rank: Newbie
timestamp: January 17, 2020, 02:29:50 pm
content: @i_am_fubar nop, stray magnetic fields shouldn't be a problem...

author: Kleinstein
author_rank: Super Contributor
timestamp: January 17, 2020, 04:11:11 pm
content: There is still the option to use a direct mechanical contract - kind of build your own switch, especially if the switch is for low power only.A mechanical feed through is difficult at that vacuum level anyway.

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 17, 2020, 05:25:51 pm
content: Bellow feedthroughs are good down to -10. But pretty costly.And stray magnetics kill spot size on low energy charges, even if fat away. Magents in the chamber could magnetise lower grade stainless and be a problem in the future. Just be mindful and if you do go down the reed switch route, use lowest strength you can get away with.Seconded the DIY route. Will try and get some sneaky pics of our solution on Monday.