Hi It's not at all uncommon for the seismic guys to go a bit uber-nuts on clean supplies and references.
Bob On Dec 10, 2012, at 7:54 PM, David <[email protected]> wrote: > On Mon, 10 Dec 2012 23:01:49 +0000, "Poul-Henning Kamp" > <[email protected]> wrote: > >> In message <[email protected]>, David writes: >> >>> The gain drift is specified at 2ppm per degree C. There are >>> provisions for a calibration cycle but that requires external >>> multiplexing. >> >> That's the really smart thing about this particular chip: You can >> drive the geophone calibration signal in through the second input >> and out onto the first, which eliminates the external calibration >> mux and the errors that usually cause. > > I see now from the data sheet that the 3000 ppm typical gain mismatch > applies between the PGA gain settings and not between the multiplexor > input channels so you can use the internal multiplexor for external > calibration. The other instrumentation delta-sigma ADCs I am familiar > with do a gain and offset calibration for every conversion which > knocks the drift down by an order of magnitude unless you disable that > feature. > >> And yes, in seismology you do care about frequencies from 0.1Hz and up >> (0.01Hz if you're involved with the CTBT) and most voltage references >> will be stable enough for that. > > Voltage reference 1/f noise will be a problem but only because the > ADS1282 input stage is already chopped allowing that kind of > sensitivity at low frequencies. Competing instrumentation > delta-signal converters have the same problem if you consider that a > problem. > >> For longer term you calibrate your entire system, starting with the >> geophone, so the voltage reference is caught that way. > > What they need is a ratiometric geophone . . . :) > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
