He shoots, he scores! Mass spec under $300

[Doug Coulter]

Bill's been at it again. The other day this pretty nifty thing showed up, and it actually works. Not only that, the manual was written by a person with English as their native language, and is for a change -- complete. Full schematics, and the thing is made out of stuff I can still get easily, but old enough to fix should it break. But, it's not broken! Needs some calibration, but that's a snap with a good manual, so I'll be doing that this afternoon. Here it is looking at my smaller system, which has been up to STP for a couple of weeks, so there's plenty of trash in it. Some of those "echos" will probably go away with calibration and of course, the system getting cleaner. It's baking now.

Mass spec in it's new home, Dycor/Ametek M100

I'll try for a better picture later, when what's on the screen is more impressive (and agrees with my gages). The previous owner had set the sensitivity way high.

Anyone know where I can get filaments for this thing? Probably cost 1/3 of the price we paid for the entire thing, but hey -- still worth it. They claim two types, thoriated irridium (!) and thoriated tungsten. They call them part number M102 and M102(t). Ametek is such a large company, I doubt I'll be able to get much out of them (they seem to own many other companies, of which Dycor was one). It'd be like calling up 3M and trying to buy tape!

[johnf]

doug
before you blow the filament measure its cold resistance.

I'll find out from work where they get their filaments for our real mass specs -the ones that go to 1000's of AMU and cost what people would pay for a large farm.


Way back we used to make our own thoriated tungsten ones on a jig on the side of one of the mass specs

[Doug Coulter]

Right on, John. This model measures the filament volts and current in-place and all the time, kind of cool, and calculates the resistance for display -- it has an ion gage that shuts down filament power too if the pressure gets high (but they warn it's not really quick enough to save it always). This filament is good, but with this old gear, I find it wise to start looking for the obvious maintenance parts right off before they really disappear from the face of the earth -- sometimes you get lucky on old stock re pricing too. BillF found this place: http://www.sisweb.com/ms/replacement-rga-filament.htm which has one, at a higher cost than we paid for the whole thing! This does look like something I could reasonably make here if I had some thoriated tungsten wire the right gage. I've already build a capacitive discharge spot welder to do type C thermocouples (tungsten/rhenium) which are a bear to do almost any other way.

Anybody know why you'd even want irridium for a filament? Longer life? Better emission? They warn it's really brittle (would be hard to be more so than tungsten is) and this one's a bit warped, but it works anyway, seemingly.

In some other testing here for something else, we found that using plain tungsten with yttria coating has pretty decent emission, and isn't trashed by the odd bit of gas either. Can't use the classic barium/strontium/calcium stuff if it's ever going to see air -- we kind of proved that too. But the yttria is about 1/3 as good emission at the same temp, and doesn't mind air one bit.

[Joe Jarski]

Anybody know why you'd even want irridium for a filament? Longer life? Better emission?

My ion gauge uses iridium filaments (they also have tungsten), but they're supposed to be more resistant to oxidation at higher pressures and have a lower vapor pressure than tungsten at low pressures.

[Doug Coulter]

Gotcha, saw the same thing looking myself. Tungsten doesn't like air (either main gas) but it really doesn't like water when hot. Takes the stuff apart, makes hydrogen, the oxide evaporates off the filament, condenses on the walls, gets reduced by the hydrogen there, which then makes water -- rinse and repeat. But, "it's not that bad" if you're reasonably careful and don't try to run this at high pressures.

If Edison had had tungsten wire, he couldn't have used the stuff -- vacuum not good enough (dry) then for things like that. I got a record here of about 20 hours with 1 mil wire as a yellow hot filament with a really good 2 stage vane pump and tight bell jar chamber.

It's worse at higher heats than lower, hence thoria, which reduces the work function a bunch. From what I can tell, yttria (we apply it catephorically, it's easy) does about as well, reducing the temps needed to get emission; the one in there gets low-yellow hot, and at similar temperatures, we got 10 ma off a nominal 6.3v, 2a bulb filament with the coating, but running it at 3v and about half an amp. Hmmm. The one in there, which is a wire in a circle about an 3/4 inch diameter, is running at 2.6v and 3.3 amps now -- and the calculated resistance is going down, as it's regulated for a certain emission (1 ma) and things are cleaning up over the last few hours. It's not having to get as hot as it and the rest clean up. Still a lot more power in than we got off the bulb we used as a test filament -- but it's less compact, so probably radiates more heat per degree above ambient.

Tungsten/rhenium is mentioned in Kohl as being more resistant to the nasty water cycle, and...I've got some, I got at Nanmac. The rhenium raises the electrical resistance of the tungsten too. They aren't the easiest to deal with -- large minimums, but are nice people -- their gift "calibrated hot sauce" is really good, no kidding.

Type C thermocouples are W/5%Re, and W/26%Re wire. It is very %$&#$% hard to weld, but good stuff once you do. Joe, did I show you my jig for the TIG welder for that? Really works great.
Better than the spot welder I built (the normal one from Harbor freight doesn't work on this stuff unless you want to just weld it to the welder).

Scratches head. No way I'm going to invest 3 bills in a stock filament for this at the moment. That would kinda ruin the gloat -- this thing cost about the same as shipping and paperwork on the new one I got from Pfeiffer -- and seems about as good, besides. It's not like the Pfeiffer doesn't eat some power -- has a fast computer in it, and needs another for display. Makes a goodly amount of warm air out the vent itself. I kinda dig the green screen...I used to design and build stuff like this when it was the hottest tech there was. It was certainly a great leap forward from the ASR-33 teletypes we were stuck with just before that.

Here's what it looks like now.

After some running and baking, in analog and 4 decade span mode

I can make it dwell longer and see deeper into the noise if I reduce the scan range. It will go to 15 divs per amu if you want. I think the downward spikes to the baseline are basically some magic nulls you get in this type gear, and that some of the mass one is "zero blast" you also get with quadrupoles. This is just good old gear telling the truth (no faking out the hardware limitations), or so it looks to me.

I haven't calibrated the gains on this yet. My other gage is reading half this thing's total pressure (couple e-6) and they had jacked up the gain to make the peaks read in torr instead of amps, or something like that. But, this stuff tends to be a bit relative, but I'll work on making it hard numbers for fun and giggles anyway. At least I got water on-scale after some hard baking. This is an all viton (many linear inches) sealed system with a tiny (60lps) turbo/drag on it - about the same as the turbo-only I'm also working up a good controller for. Not so bad, considering.

[Bill Fain]

Hi, This is so cool! I'm really impressed it came through shipping and fired up so easily. I emailed the seller and asked him some questions before I bought it. He was real honest about it. This looks like something we can really play with and and not be afraid to. I'm trying to decipher what I see. I know water's there, nitrogen, maybe CO and CO2, what are 57, 68, and 80 likely to be? I believe there is some open source software that can tell you what you see here, but I guess that's like driving an automatic and we really need to drive it as a manual. -bill

[Doug Coulter]

I believe the heavy stuff is hydrocarbons, probably from the "sekrit sauce" grease I gently wiped the O rings with when I put this together.

Unlike say, a gamma spectrometer, in a mass spec there is more than one way to get a particular line, and one substance can make many lines. All sorts of things can exist at this level of vacuum that can't in normal conditions - they'd be too unstable. An H can (and does) grab onto anything, and so can most hydrocarbon radicals, which themselves get split off what's really there, then join up in dimers, trimers, with and without various hangers-on. It's no small trick to correctly interpret one of these, and it helps I've had this system all along, and had another mass spec on it as well, earlier on. Kind of like, you do this, and these new lines appear, or other ones go away, you get a "feel" for what's really going on.

In this particular case, when heated to about 75 C (more in places) the heavy stuff comes up, absolutely as well as relative to the other stuff, which helps with the interpretation. This hydrocarbon stuff is also the likely source of the unusually large hydrogen lines, as hitting that yellow hot filament tends to break the stuff up -- to recombine as it happens to encounter other fragments. I doubt I used 10 milligrams of my grease (forepump oil and beeswax, about 1::3 volumetrically) altogether, and it's been showing for about 2 years now. Fingerprints show through several baking cycles too -- but in this case there weren't many.

If I run a hot discharge in there, some of that might finally get out of the system. I will try it and see. The electrode I have in there now is all wrong for fusion, but opening the door and fooling around right now gives up all the gains of today, so it might be worthwhile to play with it some as is. Maybe I can get the horizontal scale setup with Ar and Ne, then play with new things in the tank.

[Joe Jarski]

Doug, I think you did show me your setup for TIG welding - as I recall it was essentially an argon purged box that you used, though not quite that simple.

BTW, That's a pretty nice find one on the mass spec. I'm constantly amazed at the stuff Bill comes up with - that guy is worth his weight in gold.

[Jerry]

Neat-o.

My newer RGA is a Ametek Dycor. I have called them before and they were helpful. They sent me the control software when I called. I also have a power up issue and they helped me try to figure out what it may be. And even told me ebay would probably be the best place to find the $1200 board!

You should be able to get info from them if you really need it.

[Doug Coulter]

That's nice to know Jerry - did you call Ametek or find a special number for Dycor? I found the Ametek website and contact info, but nothing on Dycor yet. But as well as they wrote that manual, I likely won't want anything from them -- it's really outstanding. Only thing missing would be the firmware listings...and no one publishes that.

I forgot where I posted this before (I think it was on my website, rather than the forums) here is the TIG furnace for welding W wires together. Probably has other uses, perhaps with some mods. If you have a TIG welder, try making one of these to get yet another use out of it. It also melts quartz real quick.