Author Topic: Restoring a Mass Spectrometer - maybe  (Read 8946 times)

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Offline Alex Nikitin

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Re: Restoring a Mass Spectrometer - maybe
« Reply #25 on: February 08, 2017, 02:50:43 pm »
I use this book as the reference on Quadrupoles. If you want a very short version, a quadrupole mass filter combines RF AC and opposite polarity DC on the pairs of rods and works as a very narrow BPF. For a correct ratio of the RF AC and DC voltages only ions with a certain mass will make it through to the other end where the ion detector is placed, the lighter ions will be thrown out to a side in one direction, the heavier ions - also to a side but in another direction. The ratio between RF AC and DC is critical, as it defines the selectivity and thus the mass spectrum resolution. The required stability for the voltages is high and not that easy to achieve, especially for the RF AC part.

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Re: Restoring a Mass Spectrometer - maybe
« Reply #26 on: February 08, 2017, 11:30:27 pm »
Back in my days at National Semiconductor, we used powder free latex gloves for everything, including work inside the hivac systems.  Later, at SVG Lithography (formerly one of the Perkin Elmer divisions in CT), blue nitrile gloves were the norm.  I much preferred the nitrile to the latex, as they stretched and fit tightly, rather than being loose as the latex ones at National were.

For what it's worth.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline TerraHertz

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Re: Restoring a Mass Spectrometer - maybe
« Reply #27 on: March 05, 2017, 01:46:45 pm »
Just a mention, I've posted a writeup of progress so far. Still a long way to go with this one.

  http://everist.org/NobLog/20170224_summer_vacuum_odyssey.htm
  157KB of text, 40MB of images linked (275 of them). Only 6MB of image thumbnails in the initial page load.
  Longest NoBlog article ever, by a long shot.

The turbo pump and vacuum gauge on the mass spectrometer WORK!

Cubdriver, to my surprise it turns out that our major hardware chain, called Bunnings, has nitrile gloves. In packs of 100, for $10. Bought a pack recently. Will post how they seem, once I've used them.
« Last Edit: March 05, 2017, 01:50:22 pm by TerraHertz »
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Offline mikeselectricstuff

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Re: Restoring a Mass Spectrometer - maybe
« Reply #28 on: March 05, 2017, 02:35:18 pm »
SMD resistors over 1Gohm do exist. And if the resistors was suspended away from PCB it's likely that it is a very high value. Try to measure it with something that goes up to 10Gohm.

I don't have anything that can do that.  Oh wait... nanovoltmeter. Hmm.

Remember some DMMs ( e.g. Fluke 87) have conductance ranges that will measure very high resistances.
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Offline TiN

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Re: Restoring a Mass Spectrometer - maybe
« Reply #29 on: March 05, 2017, 03:59:11 pm »
TerraHertz
Vacuum stuff is unknown to me, but I had great pleasure reading thru your article. Keep it going, I've learned few things there already  :-+
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Offline evb149

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Re: Restoring a Mass Spectrometer - maybe
« Reply #30 on: March 05, 2017, 05:53:08 pm »
Nice equipment / project, good luck with it!
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Offline TerraHertz

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Re: Restoring a Mass Spectrometer - maybe
« Reply #31 on: March 21, 2017, 01:45:58 pm »
Progressing, mostly working on refurbishing the Helium Leak detector atm.
In going through the pile of vaccum related stuff I have, I came across these two Alcatel "PL1" vacuum sensors. Unfortunately Alcatel no longer exists as such, and I can't find any data on them at all.

Does anyone recognize these and have some technical data on them?
They seem quite interesting, in that the only wiring is a single mini 50-ohm coax. The black connector body contains only one component wired on the socket - what looks like a small MOV.

I *might* even have the driver circuits for these, since I have many of the cards from the machine these came from. But 100% certainty I will never find a schematic, and not much chance of figuring out which card/pins the coax from these attached to. Via the wiring looms, etc that I don't have.
Unless someone has service manuals for an ARL FISONS  8480+ XRF X-ray Flourescence crystalography machine.


Incidentally, a slightly vacuum-system related update here: http://everist.org/NobLog/20170321_machining_pool_noodle.htm
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Re: Restoring a Mass Spectrometer - maybe
« Reply #32 on: March 21, 2017, 02:28:55 pm »
They look to me to be Pirani gauge tubes, but a quick search online doesn't reveal anything further (as you've already found). 

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline TerraHertz

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Re: Restoring a Mass Spectrometer - maybe
« Reply #33 on: March 22, 2017, 03:00:31 am »
They look to me to be Pirani gauge tubes, but a quick search online doesn't reveal anything further (as you've already found). 

No I don't think they are. For one thing, can't do Pirani with 2-wire (unless there's a lot of intelligence inside the gauge and it's some kind of data plus power on the coax.)
Reading what I can find of Alcatel stuff, they came up with some kind of monolitic mechanical vibrating thing, that works over a very wide pressure range. But not much info on it.
Because these *might* be quite special, is why I'm trying to find out more. They were used in an extremely expensive machine.

The hole end is slightly too small to fit my endoscope camera, darnit. There's nothing in the tube, and some 'thing' right down in the body part. But I can't make it out enough to have any idea.
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Online Cubdriver

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Re: Restoring a Mass Spectrometer - maybe
« Reply #34 on: March 22, 2017, 03:41:38 am »
Hmm...  I'd never heard of that.  (Though I mainly worked with Balzers/Pfeiffer, Varian and Leybold stuff)

I wonder if it's some sort of crystal based thing (like a film thickness monitor), but somehow set up to have the pressure change the crystal's oscillation frequency.  Maybe if the crystal were either part of the wall between atmosphere and vacuum, or on a diaphragm that also acts as the wall?  High pressure on both sides would let it oscillate freely, and as the pressure on the vacuum side went down the loading caused by the pressure differential would slow it down?  I can't imagine that would be very accurate at lower pressures, though...  (Bear in mind that this is pure speculation on my part, and I'm pulling it out of my backside!)

And of COURSE the hole is too small for your camera.  You didn't seriously expect Mr. Murphy to exempt you from his law on this, did you?   :P

Good luck finding more info on it, and I'm curious what it turns out to be...

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline Alex Nikitin

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« Last Edit: March 22, 2017, 12:08:52 pm by Alex Nikitin »
 

Offline TerraHertz

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Re: Restoring a Mass Spectrometer - maybe
« Reply #36 on: March 22, 2017, 12:56:22 pm »
It looks like a Pirani. Here is what I've found:
http://copaseticflow.blogspot.com/2014/07/leak-detector-down-but-not-out-code.html

Thanks! That is the one. Just a different mounting - theirs is a KF. And the pic of the inside of theirs shows the little light bulb mounted on the same two pins as the wiring of mine. Pretty funny to use a nice case, with 9 vacuum sealed pins, then only use two.

There's an NTC thermistor mounted in series with the Pirani filament, in the connector case. It's using a spare pin as a mounting post.
At around 25 deg C, my two ones measure:
Filaments:  66.3,  63.8 ohms.
NTC:          7.7, 7.7

Oh well, they are quite ordinary. But now I really want to get a close look at the bulbs in mine. Bet they are just some standard mini-bulb, with a hole in the glass.

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Offline TerraHertz

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Re: Restoring a Mass Spectrometer - maybe
« Reply #37 on: March 28, 2017, 12:21:05 pm »
About those nitrile rubber gloves, that I'd found at Bunnings. I've been using them and find them excellent. They're very thin, stretchy, but amazingly tough. I've been wearing them while doing metalwork for whole days, and so far no rips. Despite being 'disposable' I've been reusing the same pair for working with greasy, dirty stuff. Because they are close fitting and so thin, there's almost no loss of touch sensitivity or dexterity. Wish I'd had these years ago.

Made by Ansel, about $10 for 100. It took a while to find them, since the word 'nitrile' only occurs once on the box, in the fine print on the bottom. Maybe Ansel's marketing department thinks the word sounds scary for consumers, or something. Idiots.

One note: They are not impervious to MEK.
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