Yup. Or piezo balances. (Spehro and Co. are using SQUIDs for measuring gravity, but they're wild men.) We're doing the measurement interferometrically, which has a lot of advantages, including small size.
That's 10**-8 m/s**2, not m/s. It's the acceleration accuracy we need--a tiny fraction of a fringe, at DC. (Hence the plaque.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
How about doppler-shifting your laser reference (retroreflector on a moving disk... like a phonograph turntable) to raise the base frequency of the fringes?
AKA: 'We all have our bears to cross'.
-- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
Hi Phil,
Like ADS1278 ?
-- John Devereux
That might work fine, thanks. It's a bit of a tight squeeze on the 0.8 inch diameter board, but we'd be able to save some parts on the other side by not having to deal with the truly awful mux charge injection.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Adding any sort of motion makes the detection problem much, much harder. Bearing noise, lubricant thinning, creep in flexures, temperature coefficient of Young's modulus.... One of the guys I'm working with on this is a mechanical genius, but he does need to be able to sleep at night. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Chopping generally increases noise floor but in the 1/F area. I don't know how to estimate chopping noise, however the typical figures for choppers are ~20nV/root(Hz). The 5nV/root(Hz) of ADS1282 is outstanding; don't know how hard it would be to achieve that with a home made circuit.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
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