Electronics > Projects, Designs, and Technical Stuff
2ch >1GHz PCIe (or similar) ADCs on a reasonable budget. Ideas?
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SiliconWizard:

--- Quote from: KaneTW on August 11, 2019, 04:06:06 pm ---There's only so much sample and a tiny bit of the sample is vaporized with each trigger, so you can't do too many captures.

--- End quote ---

I can understand the point. Just still not sure how it mixes with the need to average a bunch of runs...

Anyway, this certainly sounds like an interesting project. How much did you pay (or are you going to) for the spectrometer itself?
Will be interesting to see what you get out of it.
KaneTW:

--- Quote from: ogden on August 11, 2019, 05:25:02 pm ---Mass spectrometer is obscure for many. I know that there exist (existed) spectrometers that do not need high speed sampling:



Do you have pointers to info about instrument you are aiming at? Could be nice to learn something new along the path.

--- End quote ---

There's a used "for-parts" 1k EUR Applied Biosystems Voyager DE-PRO on eBay. I'm not sure if I want to buy it at all---I'd have to find compatible replacement parts for the PCI parallel I/O cards and I'm not sure if it was properly decommissioned. I posted a link to the manual further up (http://www.chem.cmu.edu/cma/DE-STR%20Manual.pdf)

It's a time-of-flight device with direct (amplified) detector outputs, from what I can tell.


In the end it's not quite an ideal device, because I'd like to be able to use it in conjunction with a LC system. But it's certainly a step up from nothing at all and looks like an interesting project.
ogden:
Page 88 of manual mentions oscilloscope as sampler option:

KaneTW:
Yeah, saw those. These would be ideal but hard to find or expensive.
KaneTW:
I've done some simulations and with a 350MHz/2.5GSPS scope I can actually get a pretty good resolution; around 0.015 Dalton on a 500 Dalton molecule, yielding a resolution of about 30000. Higher bandwidth doesn't seem to help much, and you can drop down to about 250MHz without compromising the signal.

Some further testing reveals that the resolution is proportional to the sample rate, with a bandwidth requirement of at least 1/10th. (I wonder if that's a theorem somewhere)

E: Bandwidth does seem to matter once you have close-by peaks where one peak is significantly larger (~10x) than the other.
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