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Good PRECISION low frequency data acquistion ADC -> Ethernet or USB

Started by Spehro Pefhany August 18, 2014
Hi, all:- 

Any suggestions for a really good low frequency (up to a few hundred
Hz would be great) 24+ bit ADC box with very low low frequency noise
and drift? Preferably something like 20-30ppb RMS noise from 10uHz to
1Hz, with at least two-four channels input (that's roughly a true 20
bits at 1kHz).  

The usual NI boards and their clones have really high low frequency
noise and others have low drift but a bit too high a noise floor. 

I don't really want to build something here (that will come later).
Any suggestions would be most welcome. A few K$ would be fine. 

Best regards, 
Spehro Pefhany

On Mon, 18 Aug 2014 16:20:11 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>Hi, all:- > >Any suggestions for a really good low frequency (up to a few hundred >Hz would be great) 24+ bit ADC box with very low low frequency noise >and drift? Preferably something like 20-30ppb RMS noise from 10uHz to >1Hz, with at least two-four channels input (that's roughly a true 20 >bits at 1kHz). > >The usual NI boards and their clones have really high low frequency >noise and others have low drift but a bit too high a noise floor. > >I don't really want to build something here (that will come later). >Any suggestions would be most welcome. A few K$ would be fine. > >Best regards, >Spehro Pefhany
How about two to four good DVMs? -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Mon, 18 Aug 2014 13:42:18 -0700, the renowned John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Mon, 18 Aug 2014 16:20:11 -0400, Spehro Pefhany ><speffSNIP@interlogDOTyou.knowwhat> wrote: > >>Hi, all:- >> >>Any suggestions for a really good low frequency (up to a few hundred >>Hz would be great) 24+ bit ADC box with very low low frequency noise >>and drift? Preferably something like 20-30ppb RMS noise from 10uHz to >>1Hz, with at least two-four channels input (that's roughly a true 20 >>bits at 1kHz). >> >>The usual NI boards and their clones have really high low frequency >>noise and others have low drift but a bit too high a noise floor. >> >>I don't really want to build something here (that will come later). >>Any suggestions would be most welcome. A few K$ would be fine. >> >>Best regards, >>Spehro Pefhany > >How about two to four good DVMs?
Yes, I've suggested that (and lent an Agilent/Keyshite LXI 34401A to the cause). I was hoping to get a bit better, for less than the ~$7K that would cost. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I've got a labjack that sorta meets those specs.
(~$3-400)
I've not looked closely. 
The low end (10uHz.) sounds hard,
I mean what's a day? 3600x24 =~10^5 seconds

George H. 
On Mon, 18 Aug 2014 16:58:56 -0700 (PDT), the renowned George Herold
<gherold@teachspin.com> wrote:

>I've got a labjack that sorta meets those specs. >(~$3-400) >I've not looked closely. >The low end (10uHz.) sounds hard, > >I mean what's a day? 3600x24 =~10^5 seconds > >George H.
Specsmanship is a problem. For example, the PSD on one product looks almost good enough until you start actually measuring something that isn't almost zero, then the reference 1/f noise dominates. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
On Mon, 18 Aug 2014 17:42:43 -0700, Spehro Pefhany  
<speffSNIP@interlogdotyou.knowwhat> wrote:

> ....snip... > Specsmanship is a problem. For example, the PSD on one product looks > almost good enough until you start actually measuring something that > isn't almost zero, then the reference 1/f noise dominates. > > > > Best regards, > Spehro Pefhany
How about use a good soundcard? Or, a 24 bit soundcard like Creative Labs EMU1212 system. setup as 'professional' balanced to drive a cheap MC1496 analog multiplier-like for each channel and recive balanced, too, then knowing the frequency of the drive [sine wave], synchronously demod to recreate the DC to ?? spectrum, easily get two channels DC to 8kHz, and run at 44.1 kS/s which allows for 8 channel operation, could result in getting 8 channels DC to 4 kHz, and probably still get better than 20 bits. Haven't looked at resulting specs but awfully easy to try out. From memory the input noise is around 12nV/rtHz, which is pretty equal to the 10k input Z.
RobertMacy wrote:
> On Mon, 18 Aug 2014 17:42:43 -0700, Spehro Pefhany > <speffSNIP@interlogdotyou.knowwhat> wrote: > >> ....snip... >> Specsmanship is a problem. For example, the PSD on one product looks >> almost good enough until you start actually measuring something that >> isn't almost zero, then the reference 1/f noise dominates. >> >> >> >> Best regards, >> Spehro Pefhany > > How about use a good soundcard? Or, a 24 bit soundcard like Creative > Labs EMU1212 system. setup as 'professional' balanced to drive a cheap > MC1496 analog multiplier-like for each channel and recive balanced, too, > then knowing the frequency of the drive [sine wave], synchronously demod > to recreate the DC to ?? spectrum, easily get two channels DC to 8kHz, > and run at 44.1 kS/s which allows for 8 channel operation, could result > in getting 8 channels DC to 4 kHz, and probably still get better than 20 > bits. Haven't looked at resulting specs but awfully easy to try out. > From memory the input noise is around 12nV/rtHz, which is pretty equal > to the 10k input Z.
Sound cards are stunning and I am using a USB sound card for lab measurements here, a Behringer UCA202. But these will not go down to DC without a serious hack or an "inverse sampler" a.k.a. modulator up front. -- Regards, Joerg http://www.analogconsultants.com/
On 8/18/14, 3:20 PM, Spehro Pefhany wrote:
> Hi, all:- > > Any suggestions for a really good low frequency (up to a few hundred > Hz would be great) 24+ bit ADC box with very low low frequency noise > and drift? Preferably something like 20-30ppb RMS noise from 10uHz to > 1Hz, with at least two-four channels input (that's roughly a true 20 > bits at 1kHz). > > The usual NI boards and their clones have really high low frequency > noise and others have low drift but a bit too high a noise floor. > > I don't really want to build something here (that will come later). > Any suggestions would be most welcome. A few K$ would be fine. > > Best regards, > Spehro Pefhany >
HP3457A? I've been pining for one all day and would be willing to buy one when you're done. ChesterW
On 18/08/2014 21:20, Spehro Pefhany wrote:
> Hi, all:- > > Any suggestions for a really good low frequency (up to a few hundred > Hz would be great) 24+ bit ADC box with very low low frequency noise > and drift? Preferably something like 20-30ppb RMS noise from 10uHz to > 1Hz, with at least two-four channels input (that's roughly a true 20 > bits at 1kHz). > > The usual NI boards and their clones have really high low frequency > noise and others have low drift but a bit too high a noise floor. > > I don't really want to build something here (that will come later). > Any suggestions would be most welcome. A few K$ would be fine. > > Best regards, > Spehro Pefhany >
Can you tell us a bit about the application - a lot of my time now is spent designing high end data acquisition stuff (current emphasis on massively multichannel and quite high speed) but spreading out to to other things. It won't do you any short term good but we might eventually look at very low noise if we could see enough demand. As you are probably aware audio stuff is poor to dreadful at low frequency noise/stability (one of the reasonable trade-offs is to loosen up on stuff that can't be heard). From my (not exhaustive) experience I think that the DMMs (suggested earlier) might be the simplest off the shelf route to truly low noise at ultra low frequencies. Michael Kellett
On 20/08/14 02:48, Joerg wrote:
> Sound cards are stunning and I am using a USB sound card for lab > measurements here, a Behringer UCA202. But these will not go down to DC > without a serious hack or an "inverse sampler" a.k.a. modulator up front.
I think that might have been my suggestion, a year or two back. I've not used mine for anything but audio yet. Did you make any modifications to it? I must have a more extensive play with mine... Clifford Heath.